Preface

Presently, graphene is widely researched worldwide because of its unique properties, which have led to a wide range of applications. This book provides a brief overview of recent developments in the synthesis methods of graphene and its derivatives as well as its applications.

The review in the first part of the book covers the recent synthesis methods of graphene and its modified derivatives that include graphene oxide (GO), graphene (rGO), graphene-metal nanoparticle composites, graphene-polymer hybrids, and graphene/organic structures for a variety of applications such as catalysts, energy storage/conversion, anti-microbial agents, and as a water decontaminant. Also presented in this section is a unique and advanced technique that is the liquid phase exfoliation method for the synthesis and concentration enhancement of graphene with the addition of certain additives and salts. This method is suitable for the enhancement of the concentration of graphene. This process can be easily scaled up for better performance and efficiency to be used for the fabrication of modern electronic devices.

The final section of this book addresses the most important applications of graphene and its derivatives. Discussed in detail in this book are photocatalytic applications, electronic applications, and the latest graphene-based heterogeneous electrodes for energy storage. In addition, sound devices based on graphene are also presented in this book.

The authors are very thankful and want to acknowledge all those who contributed to this book: Prof. Dr. Seema Humaira, Prof. Dr. Randhir Singh, Prof. Dr. Ning Wang, Prof. Dr. Haixu Wang, Prof. Dr. Guang Yang, Prof. Dr. Rong Sun, Prof. Dr. Ching-Ping Wong, Prof. Dr. He Tian, Prof. Dr. Guang-yang Gou, Prof. Dr. Fan Wu, Prof. Dr. Lu-Qi Tao, Prof. Dr. Yi Yang, Prof. Dr. Tian-Ling Ren, Dr. R . M. Obodo, and Ms. Manuela Gabric, Author Service Manager.

**Ishaq Ahmad** NPU-NCP Joint International Research Center on Advanced Nanomaterials and Defects Engineering, National Centre for Physics, Islamabad, Pakistan

> **Fabian I. Ezema**  Department of Physics and Astronomy, University of Nigeria, Nsukka, Nigeria

> > Coal City University, Enugu State, Nigeria

**1**

Section 1

Synthesis of Graphene and

Its Derivatives

Section 1

## Synthesis of Graphene and Its Derivatives

**3**

**Chapter 1**

**1. Introduction**

tance, and rate capability.

**2. Synthesis of graphene**

Introductory Chapter: Graphene

Presently, graphene is widely researched worldwide because of its unique properties such as zero bandgap, remarkable electron mobility at room temperature, high thermal conductivity and stiffness, large surface area, impermeability to gases, etc. Graphene charge carrier exhibits core mobility, is massless, and moves a few micrometers distance maintaining its structure at room temperature. Recently, graphene-based materials have gained intense awareness on energy storage systems, electronics, chemical sensors, optoelectronics, nanocomposites, and health such as osteogenic. Graphene is among the allotropes of carbon; its carbon atoms are arranged in a single layer. These carbon atoms are organized in a honeycomb lattice with a two-dimensional arrangement. The carbon–carbon bond distance in a single graphene sheet approximates 0.142 nm [1]. One of the unique and major properties of graphene is that increased researcher's interest is its constituent's electrons that seem to be massless relativistic particles, hence, anomalous quantum Hall effect and the absence of localization [2, 3]. Graphene has been used in many applications, which include energy storage devices like supercapacitors and lithium-ion batteries [4], gas detection [5], and conducting electrodes [6]. Recently, the rate at which graphene awareness is rising is highly remarkable and suggests that it is a good route of the scientists' search for new materials for advancement in science, engineering, health, and composite industries. This brief introduction of graphene narrates its brief history, synthesis method, derivatives, and applications. Addition of graphene in a composite inhibits the fabrications of active material in a nanosize, enhances non-faradaic capacitive behavior, increases conductivity, and prevents disintegration. Graphene also induces a physical barrier in between the electrolyte and active material, hence increasing cycling stability, specific capaci-

Graphene synthesis means any process of fabricating or extracting graphene from

graphite. The method to be chosen is governed by the desired size, quantity, and purity. Synthesis technique contributes to the structure and properties of graphene produced. There are variations of graphene layers from different techniques such as a single layer, double layer, or multiple layers, and they have different applications in various fields of science and technology like energy storage devices, biotechnology, memory, electronics, sensors, etc. Researchers employ different techniques especially

and Its Applications

*and Fabian Ifeanyichukwu Ezema*

*Raphael Mmaduka Obodo, Ishaq Ahmad*

#### **Chapter 1**

## Introductory Chapter: Graphene and Its Applications

*Raphael Mmaduka Obodo, Ishaq Ahmad and Fabian Ifeanyichukwu Ezema*

#### **1. Introduction**

Presently, graphene is widely researched worldwide because of its unique properties such as zero bandgap, remarkable electron mobility at room temperature, high thermal conductivity and stiffness, large surface area, impermeability to gases, etc. Graphene charge carrier exhibits core mobility, is massless, and moves a few micrometers distance maintaining its structure at room temperature. Recently, graphene-based materials have gained intense awareness on energy storage systems, electronics, chemical sensors, optoelectronics, nanocomposites, and health such as osteogenic. Graphene is among the allotropes of carbon; its carbon atoms are arranged in a single layer. These carbon atoms are organized in a honeycomb lattice with a two-dimensional arrangement. The carbon–carbon bond distance in a single graphene sheet approximates 0.142 nm [1]. One of the unique and major properties of graphene is that increased researcher's interest is its constituent's electrons that seem to be massless relativistic particles, hence, anomalous quantum Hall effect and the absence of localization [2, 3]. Graphene has been used in many applications, which include energy storage devices like supercapacitors and lithium-ion batteries [4], gas detection [5], and conducting electrodes [6]. Recently, the rate at which graphene awareness is rising is highly remarkable and suggests that it is a good route of the scientists' search for new materials for advancement in science, engineering, health, and composite industries. This brief introduction of graphene narrates its brief history, synthesis method, derivatives, and applications. Addition of graphene in a composite inhibits the fabrications of active material in a nanosize, enhances non-faradaic capacitive behavior, increases conductivity, and prevents disintegration. Graphene also induces a physical barrier in between the electrolyte and active material, hence increasing cycling stability, specific capacitance, and rate capability.

#### **2. Synthesis of graphene**

Graphene synthesis means any process of fabricating or extracting graphene from graphite. The method to be chosen is governed by the desired size, quantity, and purity. Synthesis technique contributes to the structure and properties of graphene produced. There are variations of graphene layers from different techniques such as a single layer, double layer, or multiple layers, and they have different applications in various fields of science and technology like energy storage devices, biotechnology, memory, electronics, sensors, etc. Researchers employ different techniques especially

when a large quantity is required. Subsequently, we will discuss various synthesis techniques, applications, its status now, progress so far, and future prospects.

In the synthesis of graphene-based materials, ball milling and hydrothermal methods show to be cheaper, the electrospinning method exhibits the benefits in the nanowire composite assembly, and the microwave-assisted method is easier and superfast in fabrication. We also explained methods of graphene synthesis while its derivatives are discussed in the second chapter of this book. The third chapter explained the new technique such as liquid phase exfoliation method for the synthesis and concentration enhancement of graphene which is suitable for the fabrication of the highly efficient modern electronic devices (**Figure 1**).

#### **2.1 Cleavage and exfoliation technique**

This method is divided into two: (1) mechanical exfoliation and (2) chemical exfoliation. Mechanical exfoliation is the distortion of weak van der Waals force holding carbon–carbon atom together. The chemical method is the production of colloidal suspension which produces graphene from graphite compounds. Graphite is several densely packed layers of graphene sheets, hence, fixed together by weak van der Waals force. High-purity graphene sheets can be produced from graphite sheet by breaking the bonds that held them together. Therefore, exfoliation and cleavage are the use of mechanical or chemical energy to break down these weak bonds and separate distinctive graphene sheets. Viculis et al. [4] were the first to apply this principle by using potassium metal to separate pure graphite sheet and then exfoliate them using ethanol to form a dispersion of graphene sheets.

**5**

*Introductory Chapter: Graphene and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.86023*

regular graphite sheets.

**2.3 Pyrolysis of graphene**

**2.4 Other techniques**

*2.4.1 Unzipping CNTs*

chemical vapor deposition method.

process detaches graphene from graphite [10].

ment, which induces exfoliation immediately [11].

*2.4.2 Thermal decomposition of ruthenium crystal*

*2.4.3 Thermal decomposition of SiC*

**3. Graphene oxide**

**2.2 Chemical vapor deposition (CVD) methods**

Chemical vapor techniques use steam phase exfoliation. This method chemically extracts graphene sheets from graphite without passing through exfoliation stage. Horiuchi et al. [9] were the first people to produce graphene sheets using this method. They engaged the method to fabricate carbon nanofilms (CNF) using

There are many types of CVD, depending on the precursors available, the structure needed, quality of material, and dimension, and there are many applicable CVD processes such as thermal, plasma-enhanced (PECVD), cold wall, reactive, hot wall [9], etc. Graphene thin films are formed on copper or nickel mostly by a

The pyrolysis uses solvothermal technique to synthesize graphene from graphite

One of the most recent techniques of fabricating graphene is a type of synthesis that uses multiwall carbon nanotubes (MWNT) as initial material. This method is commonly known as "**CNTs' un-zipping."** MWNTs can be unzipped longitudinally using lithium and ammonia intercalation, followed by intense acid and heat treat-

Graphene single layers can be grown on single crystal ruthenium (Ru 0001) surface at ultra-high vacuum (4.0 × 10<sup>−</sup>11 Torr) [11]. It was discovered that graphene could form on the crystal surface. This can be achieved by heat breakdown of ethylene (pre-adsorbed on the crystal surface at room temperature) at 1000 K or by

Thermal disintegration of silicon on the surface plane of a single crystal of 6H-SiC to produce graphene recently gained researchers' awareness. It takes less time to achieve and become popular techniques of graphene growth recently [13].

Graphene oxide (GO) is a product of graphene obtained by oxidizing graphene.

It has a single monomolecular layer containing oxygen functionalities such as carboxyl, carbonyl, epoxide, or hydroxyl groups [14]. These added functionalities expand the separation between the layers and make the material hydrophilic (meaning that they can be dispersed in water). Layers of graphene stacked on top of each other form graphite, with an interplanar spacing of 0.335 nm. The separate

controlled segregation of carbon from the bulk of the substrate [12].

by a bottom-up approach. Sodium ethoxide and ethanol were mixed in a molar mass ratio of 1:1 in a closed vessel with intense heat treatment and sonication; this

#### **2.2 Chemical vapor deposition (CVD) methods**

Chemical vapor techniques use steam phase exfoliation. This method chemically extracts graphene sheets from graphite without passing through exfoliation stage. Horiuchi et al. [9] were the first people to produce graphene sheets using this method. They engaged the method to fabricate carbon nanofilms (CNF) using regular graphite sheets.

There are many types of CVD, depending on the precursors available, the structure needed, quality of material, and dimension, and there are many applicable CVD processes such as thermal, plasma-enhanced (PECVD), cold wall, reactive, hot wall [9], etc. Graphene thin films are formed on copper or nickel mostly by a chemical vapor deposition method.

#### **2.3 Pyrolysis of graphene**

*Graphene and Its Derivatives - Synthesis and Applications*

**2.1 Cleavage and exfoliation technique**

form a dispersion of graphene sheets.

when a large quantity is required. Subsequently, we will discuss various synthesis techniques, applications, its status now, progress so far, and future prospects.

fabrication of the highly efficient modern electronic devices (**Figure 1**).

In the synthesis of graphene-based materials, ball milling and hydrothermal methods show to be cheaper, the electrospinning method exhibits the benefits in the nanowire composite assembly, and the microwave-assisted method is easier and superfast in fabrication. We also explained methods of graphene synthesis while its derivatives are discussed in the second chapter of this book. The third chapter explained the new technique such as liquid phase exfoliation method for the synthesis and concentration enhancement of graphene which is suitable for the

This method is divided into two: (1) mechanical exfoliation and (2) chemical exfoliation. Mechanical exfoliation is the distortion of weak van der Waals force holding carbon–carbon atom together. The chemical method is the production of colloidal suspension which produces graphene from graphite compounds. Graphite is several densely packed layers of graphene sheets, hence, fixed together by weak van der Waals force. High-purity graphene sheets can be produced from graphite sheet by breaking the bonds that held them together. Therefore, exfoliation and cleavage are the use of mechanical or chemical energy to break down these weak bonds and separate distinctive graphene sheets. Viculis et al. [4] were the first to apply this principle by using potassium metal to separate pure graphite sheet and then exfoliate them using ethanol to

*Structure of graphene sheet, stacked graphene, wrapped graphene, and rolled graphene. Reproduced from Ref. [7].*

**4**

**Figure 1.**

The pyrolysis uses solvothermal technique to synthesize graphene from graphite by a bottom-up approach. Sodium ethoxide and ethanol were mixed in a molar mass ratio of 1:1 in a closed vessel with intense heat treatment and sonication; this process detaches graphene from graphite [10].

#### **2.4 Other techniques**

#### *2.4.1 Unzipping CNTs*

One of the most recent techniques of fabricating graphene is a type of synthesis that uses multiwall carbon nanotubes (MWNT) as initial material. This method is commonly known as "**CNTs' un-zipping."** MWNTs can be unzipped longitudinally using lithium and ammonia intercalation, followed by intense acid and heat treatment, which induces exfoliation immediately [11].

#### *2.4.2 Thermal decomposition of ruthenium crystal*

Graphene single layers can be grown on single crystal ruthenium (Ru 0001) surface at ultra-high vacuum (4.0 × 10<sup>−</sup>11 Torr) [11]. It was discovered that graphene could form on the crystal surface. This can be achieved by heat breakdown of ethylene (pre-adsorbed on the crystal surface at room temperature) at 1000 K or by controlled segregation of carbon from the bulk of the substrate [12].

#### *2.4.3 Thermal decomposition of SiC*

Thermal disintegration of silicon on the surface plane of a single crystal of 6H-SiC to produce graphene recently gained researchers' awareness. It takes less time to achieve and become popular techniques of graphene growth recently [13].

#### **3. Graphene oxide**

Graphene oxide (GO) is a product of graphene obtained by oxidizing graphene. It has a single monomolecular layer containing oxygen functionalities such as carboxyl, carbonyl, epoxide, or hydroxyl groups [14]. These added functionalities expand the separation between the layers and make the material hydrophilic (meaning that they can be dispersed in water). Layers of graphene stacked on top of each other form graphite, with an interplanar spacing of 0.335 nm. The separate

layers of graphene in graphite are held together by van der Waals forces. GO are synthesized mostly based on widely reported Hummers method in which graphite is oxidized by a solution of potassium permanganate in hydrogen tetraoxosulfate (IV) acid [15].

The diagram in **Figure 2** illustrates the processes and stages involved in moving from graphite to graphene, graphene to graphene oxide, and graphene oxide to reduced graphene oxide [14, 16]. Many scientists are confused about the difference between carbon derivatives (**Figure 3**).

Graphene oxide is dispersible in water and other organic solvents like ethanol, 1-propanol, acetone, methanol, ethylene glycol, pyridine, etc. as well as in different matrixes. This property of GO was due to the presence of the oxygen functionalities.

**Figure 2.**

*Stages of synthesis of GO and rGO. Reproduced from Ref. [8].*

**7**

**4.1 Electronics**

electrode like FTO and ITO [20].

**4.2 Energy storage**

*Introductory Chapter: Graphene and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.86023*

**3.1 Reduced graphene oxide (rGO)**

*Diagram of reduced graphene oxide (rGO). Reproduced from Ref. [34].*

**Figure 4.**

tendency to create aggregates (**Figure 4**).

**4. Applications of graphene/GO/rGO**

Reduced graphene oxide (rGO) is a graphene oxide (GO) in which its oxygen content is reduced either by thermal, chemical, or any other methods. Graphene oxide is reduced to improve the honeycomb hexagonal lattice distorted during oxidation from graphene to graphene oxide and also enhance its electrical conductivity [14, 34]. It is also observed that once most of the oxygen groups are removed, the reduced graphene oxide obtained becomes indispersible in a solvent due to its

Graphite and its derivate recently gained science and engineering awareness due to its numerous applications. The discovery of graphene is rightly regarded as a milestone in the world of material science; as can be seen in the worldwide attention, the material has received in the fields of electronics, photonics, capacitors/supercapacitors, biosensing, etc. They are used in numerous applications as illustrated below. In this book, applications of graphene and its derivatives are discussed in detail. These applications include photocatalysis, electronics, gas sensing, graphene-based heterogeneous electrodes for energy storage devices, etc. In

GO are used in electronic fabrications as initial materials. Electronic devices such as graphene effect transistors (GFETs) and field effect transistors (FETs) are graphene-based [17]. Reduced graphene oxides (rGO) are used as chemical sensors [18]. Functionalized graphene oxide in conjunction with glucose oxidase deposited on electrode material is used as an electrochemical glucose sensor [19]. They are widely used in the manufacturing of electronic devices like light-emitting diodes (LEDs) and solar cells. Reduced graphene oxide dispersed in a solvent can be used in the production of the transparent electrode, which is an alternative transparent

Reduced graphene oxide nanocomposites have a high surface area and good conductivity, which suited them for use in supercapacitors and lithium-ion batteries

addition, sound devices based on graphene is also explained in this book.

**Figure 3.** *Cycle synthesis of graphene/GO/rGO. Reproduced from Ref. [33].*

*Introductory Chapter: Graphene and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.86023*

**Figure 4.**

*Graphene and Its Derivatives - Synthesis and Applications*

between carbon derivatives (**Figure 3**).

(IV) acid [15].

functionalities.

layers of graphene in graphite are held together by van der Waals forces. GO are synthesized mostly based on widely reported Hummers method in which graphite is oxidized by a solution of potassium permanganate in hydrogen tetraoxosulfate

The diagram in **Figure 2** illustrates the processes and stages involved in moving from graphite to graphene, graphene to graphene oxide, and graphene oxide to reduced graphene oxide [14, 16]. Many scientists are confused about the difference

Graphene oxide is dispersible in water and other organic solvents like ethanol, 1-propanol, acetone, methanol, ethylene glycol, pyridine, etc. as well as in different matrixes. This property of GO was due to the presence of the oxygen

**6**

**Figure 3.**

**Figure 2.**

*Cycle synthesis of graphene/GO/rGO. Reproduced from Ref. [33].*

*Stages of synthesis of GO and rGO. Reproduced from Ref. [8].*

*Diagram of reduced graphene oxide (rGO). Reproduced from Ref. [34].*

#### **3.1 Reduced graphene oxide (rGO)**

Reduced graphene oxide (rGO) is a graphene oxide (GO) in which its oxygen content is reduced either by thermal, chemical, or any other methods. Graphene oxide is reduced to improve the honeycomb hexagonal lattice distorted during oxidation from graphene to graphene oxide and also enhance its electrical conductivity [14, 34]. It is also observed that once most of the oxygen groups are removed, the reduced graphene oxide obtained becomes indispersible in a solvent due to its tendency to create aggregates (**Figure 4**).

#### **4. Applications of graphene/GO/rGO**

Graphite and its derivate recently gained science and engineering awareness due to its numerous applications. The discovery of graphene is rightly regarded as a milestone in the world of material science; as can be seen in the worldwide attention, the material has received in the fields of electronics, photonics, capacitors/supercapacitors, biosensing, etc. They are used in numerous applications as illustrated below. In this book, applications of graphene and its derivatives are discussed in detail. These applications include photocatalysis, electronics, gas sensing, graphene-based heterogeneous electrodes for energy storage devices, etc. In addition, sound devices based on graphene is also explained in this book.

#### **4.1 Electronics**

GO are used in electronic fabrications as initial materials. Electronic devices such as graphene effect transistors (GFETs) and field effect transistors (FETs) are graphene-based [17]. Reduced graphene oxides (rGO) are used as chemical sensors [18]. Functionalized graphene oxide in conjunction with glucose oxidase deposited on electrode material is used as an electrochemical glucose sensor [19]. They are widely used in the manufacturing of electronic devices like light-emitting diodes (LEDs) and solar cells. Reduced graphene oxide dispersed in a solvent can be used in the production of the transparent electrode, which is an alternative transparent electrode like FTO and ITO [20].

#### **4.2 Energy storage**

Reduced graphene oxide nanocomposites have a high surface area and good conductivity, which suited them for use in supercapacitors and lithium-ion batteries

with good energy storage capacity. GO-based supercapacitors and lithium-ion batteries possess high-energy storage capacity, long life span, and good cycle stability.

#### **4.3 Water purification**

As far, back as the 1960s [21], scientists have started studying graphite oxide usage in desalination of water. In 2011, some group of researchers employed the principle of reverse osmosis using GO to achieve the same goal [22]. It was discovered that graphite allows water to pass through but retain some larger ions [23]. Its narrow mono- or bilayer capillaries allow water but restrain heavy ions.

Moreover, in the year 2015, a group of scientists also purified water using graphene tea by removing 95% of heavy metal ions in water solution [24].

It was reported that in 2006, engineers fabricated graphene-based thin film powered by solar energy that possesses the quality of filtering dirty and salty water. These films are non-heavy and can be easily produced on a large scale [24].

#### **4.4 Biomedical applications**

Graphite and its derivative like GO are widely used in the biomedical field as a constituent in the drug delivery system. Magnetite stacked with GO and doxorubicin hydrochloride (DXR) drug adsorbed onto the system is used as anticancer treatment by targeting it to a specific site to kill cancer cells.

#### **4.5 Biosensors**

Graphene oxide and reduced graphene oxide have been incorporated into many gadgets. These GO-/rGO-based gadgets are fabricated with the quality to identify biologically significant molecules. GO/rGO uses fluorescence resonance energy transfer (FRET) characteristics to work effectively as a biosensor.

#### **4.6 Elemental storage**

All elements that form part of GO or rGO functional groups can be effectively stored in their sheets and extracted later for use and are also being explored for their applications in hydrogen storage.

#### **4.7 Plasmonics**

Recently, the science of plasmonics discovered that near field infrared optical microscopy [25] and infrared spectroscopy [26] of graphene provide accommodations for plasmonic surface mode [27].

#### **4.8 Lubricant**

Scientists recently found out that graphene lubricants perform better than regularly used graphite lubricants. A graphene lubricant applied to a ball and bearing roller or steel ball and steel disc lasted for 6500 cycles, while our usually used graphite lubricants lasted only for 1000 cycles [24].

#### **4.9 Radio wave absorption**

A heavenly crammed graphene layer deposited on glass substrates absorbs radio waves of the wavelength range of 125–165 GHz bandwidth by 90% [24]. In our

**9**

**Author details**

Nsukka, Enugu, Nigeria

provided the original work is properly cited.

Raphael Mmaduka Obodo1,2, Ishaq Ahmad2

1 Department of Physics and Astronomy, University of Nigeria,

uniform frequency output throughout the audible range [32].

\*Address all correspondence to: fabian.ezema@unn.edu.ng

Defects Engineering, National Center for Physics, Islamabad, Pakistan

*Introductory Chapter: Graphene and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.86023*

houses from radio wave interference [28].

**4.10 Nanoantennas**

**4.11 Sound transducers**

modern houses, graphene serves as roof, door, and window coatings to safeguard

A nanoantenna called graphene-based plasmonic nanoantenna (GPN) operates on a wavelength of millimeter within the radio wavelength range. This nanoantenna is better than our conventional antennas because its operational surface plasmon polaritons wavelength is much smaller compared to the wavelength of electromagnetic waves propagating at the same frequency. Our conventional antenna operational frequencies range from 100 to 1000, which is very huge compared to GPNs [29].

Graphene has been predicted as a good candidate for the manufacturing of electrostatic audio microphones and speakers due to their lightweight, which provides moderately good frequency response [30]. In 2015 an A model audio ultrasonic microphone and the speaker was fabricated; it operates at a frequency range of 20–500 kHz [31]. Its performance operation was up to 99% efficiency, good and

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 NPU-NCP Joint International Research Center on Advance Nanomaterials and

and Fabian Ifeanyichukwu Ezema1

\*

modern houses, graphene serves as roof, door, and window coatings to safeguard houses from radio wave interference [28].

#### **4.10 Nanoantennas**

*Graphene and Its Derivatives - Synthesis and Applications*

**4.3 Water purification**

**4.4 Biomedical applications**

**4.5 Biosensors**

**4.6 Elemental storage**

**4.7 Plasmonics**

**4.8 Lubricant**

their applications in hydrogen storage.

tions for plasmonic surface mode [27].

**4.9 Radio wave absorption**

graphite lubricants lasted only for 1000 cycles [24].

with good energy storage capacity. GO-based supercapacitors and lithium-ion batteries possess high-energy storage capacity, long life span, and good cycle stability.

As far, back as the 1960s [21], scientists have started studying graphite oxide usage in desalination of water. In 2011, some group of researchers employed the principle of reverse osmosis using GO to achieve the same goal [22]. It was discovered that graphite allows water to pass through but retain some larger ions [23]. Its

Moreover, in the year 2015, a group of scientists also purified water using graphene tea by removing 95% of heavy metal ions in water solution [24].

It was reported that in 2006, engineers fabricated graphene-based thin film powered by solar energy that possesses the quality of filtering dirty and salty water.

Graphite and its derivative like GO are widely used in the biomedical field as a constituent in the drug delivery system. Magnetite stacked with GO and doxorubicin hydrochloride (DXR) drug adsorbed onto the system is used as anticancer

Graphene oxide and reduced graphene oxide have been incorporated into many gadgets. These GO-/rGO-based gadgets are fabricated with the quality to identify biologically significant molecules. GO/rGO uses fluorescence resonance energy

All elements that form part of GO or rGO functional groups can be effectively stored in their sheets and extracted later for use and are also being explored for

Recently, the science of plasmonics discovered that near field infrared optical microscopy [25] and infrared spectroscopy [26] of graphene provide accommoda-

Scientists recently found out that graphene lubricants perform better than regularly used graphite lubricants. A graphene lubricant applied to a ball and bearing roller or steel ball and steel disc lasted for 6500 cycles, while our usually used

A heavenly crammed graphene layer deposited on glass substrates absorbs radio

waves of the wavelength range of 125–165 GHz bandwidth by 90% [24]. In our

narrow mono- or bilayer capillaries allow water but restrain heavy ions.

These films are non-heavy and can be easily produced on a large scale [24].

treatment by targeting it to a specific site to kill cancer cells.

transfer (FRET) characteristics to work effectively as a biosensor.

**8**

A nanoantenna called graphene-based plasmonic nanoantenna (GPN) operates on a wavelength of millimeter within the radio wavelength range. This nanoantenna is better than our conventional antennas because its operational surface plasmon polaritons wavelength is much smaller compared to the wavelength of electromagnetic waves propagating at the same frequency. Our conventional antenna operational frequencies range from 100 to 1000, which is very huge compared to GPNs [29].

#### **4.11 Sound transducers**

Graphene has been predicted as a good candidate for the manufacturing of electrostatic audio microphones and speakers due to their lightweight, which provides moderately good frequency response [30]. In 2015 an A model audio ultrasonic microphone and the speaker was fabricated; it operates at a frequency range of 20–500 kHz [31]. Its performance operation was up to 99% efficiency, good and uniform frequency output throughout the audible range [32].

### **Author details**

Raphael Mmaduka Obodo1,2, Ishaq Ahmad2 and Fabian Ifeanyichukwu Ezema1 \*

1 Department of Physics and Astronomy, University of Nigeria, Nsukka, Enugu, Nigeria

2 NPU-NCP Joint International Research Center on Advance Nanomaterials and Defects Engineering, National Center for Physics, Islamabad, Pakistan

\*Address all correspondence to: fabian.ezema@unn.edu.ng

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **References**

[1] Mallard LM, Pimenta MA, Dresselhaus G, Dresselhaus MS. Raman spectroscopy in graphene. Physics Reports. 2009;**473**:51-87

[2] Geim AK, Kim P. Carbon wonderland. Scientific American. 2008;**298**:90

[3] Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, et al. Electric field effect in atomically thin carbon films. Science. 2004;**306**:666

[4] Viculis LM, Mack JJ, Kaner RB. A chemical route to carbon nanoscrolls. Science. 2003;**299**:1361

[5] Berger C, Song Z, Li T, Li X, Ogbazghi AY, Feng R, et al. Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics. The Journal of Physical Chemistry. 2004;**108**:19912

[6] Land TA, Michely T, Behm RJ, Hemminger JC, Comsa G. STM investigation of single layer graphite structures produced on Pt(111) by hydrocarbon decomposition. Surface Science. 1992;**264**:261

[7] Castro Neto AH, Guinea F, Peres NMR. Drawing conclusions from graphene. Physics World. 2006;**19**:33

[8] Swain SS, Unnikrishnan L, Mohanty S, Nayak SK. Hybridization of MWCNTs and reduced graphene oxide on random and electrically aligned nanocomposite membrane for selective separation of O2/N2 gas pair. Nayak Journal of Materials Science. 2018;**53**(22):15442-15464

[9] Horiuchi S, Gotou T, Fujiwara M, Asaka T, Yokosawa T, Matsui Y. Single graphene sheet detected in a carbon nanofilm. Applied Physics Letters. 2004;**84**:2403

[10] Obraztsov AN, Zolotukhin AA, Ustinov AO, Volkov AP, Svirko Y, Jefimovs K. DC discharge plasma studies for nanostructured carbon CVD. Diamond and Related Materials. 2003;**12**:917

[11] Bhuyan MSA, Uddin MN, Islam MM, Bipasha FA, Hossain SS. Synthesis of graphene. International Nano Letters. 2016;**6**:65-83

[12] Cano-Márquez AG, Rodríguez-Macías FJ, Campos-Delgado J, Espinosa-González CG, Tristán-López F, Ramíre-González D, et al. Ex-MWNTs: Graphene sheets and ribbons produced by lithium intercalation and exfoliation of carbon nanotubes. Nano Letters. 2009;**9**:1527

[13] Vázquez de Parga AL, Calleja F, Borca B, Passeggi MCG Jr, Hinarejos JJ, Guinea F, et al. Periodically rippled graphene: Growth and spatially resolved electronic structure. Physical Review Letters. 2008;**100**:056807

[14] Mao S, Pu H, Chen J. Graphene oxide and its reduction: Modeling and experimental progress. RSC Advances. 2012;**2**:2643-2662

[15] Hummers WS, Offeman RE. Preparation of graphitic oxide. Journal of the American Chemical Society. 1958;**80**:1339

[16] Raccichini R, Varzi A, Passerini S, Scrosati B. Nature Materials. Boosting the power performance of multilayer graphene as lithium-ion battery anode via unconventional doping with in-situ formed Fe nanoparticles. 2015;**14**:271-279

[17] Wang S, Ang PK, Wang Z, Tang ALL, Thong JTL, Loh KP. High mobility, printable, and solution-processed graphene electronics. Nano Letters. 2010;**10**:92

**11**

*Introductory Chapter: Graphene and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.86023*

> [27] Low T, Avouris P. Graphene plasmonics for terahertz to midinfrared applications. ACS Nano.

[28] Wu B, Tuncer HM, Naeem M, Yang B, Cole MT, Milne WI, et al. Experimental demonstration of a transparent graphene millimetre wave absorber with 28% fractional bandwidth at 140 GHz. Scientific

[29] https://en.wikipedia.org/wiki/ Graphite\_oxide#lubricants [Accessed:

[30] https://en.wikipedia.org/wiki/ Graphite\_oxide#micriphones [Accessed:

[31] http://research.physics.berkeley. edu/zettl/pdf/471 [Accessed: February

[32] Yu W, Xie H, Wang X, Wang X. Significant thermal conductivity enhancement for nanofluids containing graphene nanosheets. Physics Letters A.

2011;**375**(10):1323-1328

[33] Vinoth R, Ganesh Babu S, Bharti V, Gupta V, Navaneethan M, Venkataprasad Bhat S, et al. Ruthenium based metallopolymer grafted reduced graphene oxide as a new hybrid solar light harvester in polymer solar cells. Scientific Reports. 2017;**7**:43133

[34] Priyadarsini S, Mohanty S, Mukherjee S, Basu S, Mishra M. Graphene and graphene oxide as nanomaterials for medicine and biology application. Journal of Nanostructure in

Chemistry. 2018;**8**:123-137

2014;**8**(2):1086-1101

Reports. 2014;**4**:4130

February 22, 2019]

February 22, 2019]

22, 2019]

[18] Chen K, Lu G, Chang J, Mao S, Yu K, Cui S, et al. Hg(II) ion detection using thermally reduced graphene oxide decorated with functionalized gold nanoparticles. Analytical Chemistry.

[19] Liu Y, Yu D, Zeng C, Miao Z, Dai L. Biocompatible graphene oxidebased glucose biosensors. Langmuir.

[20] Matyba P, Yamaguchi H, Eda G, Chhowalla M, Edman L, Robinson ND. Graphene and mobile ions: The key to all-plastic, solution-processed light-emitting devices. ACS Nano.

[21] Bober ES. Final Report on Reverse Osmosis Membranes Containing Graphitic Oxide. U.S. Dept. Of the

[22] Gao W, Majumder M, Alemany LB, Narayanan TN, Ibarra MA, Pradhan BK, et al. Engineered graphite oxide materials for application in water purification. ACS Applied Materials and

Interfaces. 2011;**3**(6):1821-1826

[23] Joshi RK, Carbone P, Wang FC, Kravets VG, Su Y, Grigorieva IV, et al. Precise and ultrafast molecular sieving through graphene

oxide membranes. Science. 2014;**343**(6172):752-754

2012;**487**(7405):82-85

2013;**7**(5):394-399

[24] https://en.wikipedia.org/wiki/ Graphite\_oxide#Water\_purification [Accessed: February 22, 2019]

[25] Fei Z, Rodin AS, Andreev GO, Bao W, McLeod AS, Wagner M, et al. Gatetuning of graphene plasmons revealed by infrared nano-imaging. Nature.

[26] Yan H, Low T, Zhu W, Wu Y, Freitag M, Li X, et al. Damping pathways of mid-infrared plasmons in graphene nanostructures. Nature Photonics.

2012;**84**:4057

2010;**26**:6158

2010;**4**:637

Interior; 1970. 116p

*Introductory Chapter: Graphene and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.86023*

[18] Chen K, Lu G, Chang J, Mao S, Yu K, Cui S, et al. Hg(II) ion detection using thermally reduced graphene oxide decorated with functionalized gold nanoparticles. Analytical Chemistry. 2012;**84**:4057

[19] Liu Y, Yu D, Zeng C, Miao Z, Dai L. Biocompatible graphene oxidebased glucose biosensors. Langmuir. 2010;**26**:6158

[20] Matyba P, Yamaguchi H, Eda G, Chhowalla M, Edman L, Robinson ND. Graphene and mobile ions: The key to all-plastic, solution-processed light-emitting devices. ACS Nano. 2010;**4**:637

[21] Bober ES. Final Report on Reverse Osmosis Membranes Containing Graphitic Oxide. U.S. Dept. Of the Interior; 1970. 116p

[22] Gao W, Majumder M, Alemany LB, Narayanan TN, Ibarra MA, Pradhan BK, et al. Engineered graphite oxide materials for application in water purification. ACS Applied Materials and Interfaces. 2011;**3**(6):1821-1826

[23] Joshi RK, Carbone P, Wang FC, Kravets VG, Su Y, Grigorieva IV, et al. Precise and ultrafast molecular sieving through graphene oxide membranes. Science. 2014;**343**(6172):752-754

[24] https://en.wikipedia.org/wiki/ Graphite\_oxide#Water\_purification [Accessed: February 22, 2019]

[25] Fei Z, Rodin AS, Andreev GO, Bao W, McLeod AS, Wagner M, et al. Gatetuning of graphene plasmons revealed by infrared nano-imaging. Nature. 2012;**487**(7405):82-85

[26] Yan H, Low T, Zhu W, Wu Y, Freitag M, Li X, et al. Damping pathways of mid-infrared plasmons in graphene nanostructures. Nature Photonics. 2013;**7**(5):394-399

[27] Low T, Avouris P. Graphene plasmonics for terahertz to midinfrared applications. ACS Nano. 2014;**8**(2):1086-1101

[28] Wu B, Tuncer HM, Naeem M, Yang B, Cole MT, Milne WI, et al. Experimental demonstration of a transparent graphene millimetre wave absorber with 28% fractional bandwidth at 140 GHz. Scientific Reports. 2014;**4**:4130

[29] https://en.wikipedia.org/wiki/ Graphite\_oxide#lubricants [Accessed: February 22, 2019]

[30] https://en.wikipedia.org/wiki/ Graphite\_oxide#micriphones [Accessed: February 22, 2019]

[31] http://research.physics.berkeley. edu/zettl/pdf/471 [Accessed: February 22, 2019]

[32] Yu W, Xie H, Wang X, Wang X. Significant thermal conductivity enhancement for nanofluids containing graphene nanosheets. Physics Letters A. 2011;**375**(10):1323-1328

[33] Vinoth R, Ganesh Babu S, Bharti V, Gupta V, Navaneethan M, Venkataprasad Bhat S, et al. Ruthenium based metallopolymer grafted reduced graphene oxide as a new hybrid solar light harvester in polymer solar cells. Scientific Reports. 2017;**7**:43133

[34] Priyadarsini S, Mohanty S, Mukherjee S, Basu S, Mishra M. Graphene and graphene oxide as nanomaterials for medicine and biology application. Journal of Nanostructure in Chemistry. 2018;**8**:123-137

**10**

2004;**84**:2403

*Graphene and Its Derivatives - Synthesis and Applications*

[10] Obraztsov AN, Zolotukhin AA, Ustinov AO, Volkov AP, Svirko Y, Jefimovs K. DC discharge plasma studies for nanostructured carbon CVD. Diamond and Related Materials.

[11] Bhuyan MSA, Uddin MN, Islam MM, Bipasha FA, Hossain SS. Synthesis of graphene. International Nano Letters.

[12] Cano-Márquez AG, Rodríguez-Macías FJ, Campos-Delgado J, Espinosa-

Ramíre-González D, et al. Ex-MWNTs: Graphene sheets and ribbons produced by lithium intercalation and exfoliation of carbon nanotubes. Nano Letters.

[13] Vázquez de Parga AL, Calleja F, Borca B, Passeggi MCG Jr, Hinarejos JJ, Guinea F, et al. Periodically rippled graphene: Growth and spatially resolved electronic structure. Physical Review

[14] Mao S, Pu H, Chen J. Graphene oxide and its reduction: Modeling and experimental progress. RSC Advances.

[16] Raccichini R, Varzi A, Passerini S, Scrosati B. Nature Materials. Boosting the power performance of multilayer graphene as lithium-ion battery anode via unconventional doping with in-situ formed Fe nanoparticles.

[17] Wang S, Ang PK, Wang Z, Tang ALL, Thong JTL, Loh KP. High mobility, printable, and solution-processed graphene electronics. Nano Letters.

Letters. 2008;**100**:056807

[15] Hummers WS, Offeman RE. Preparation of graphitic oxide. Journal of the American Chemical

2012;**2**:2643-2662

Society. 1958;**80**:1339

2015;**14**:271-279

2010;**10**:92

González CG, Tristán-López F,

2003;**12**:917

2016;**6**:65-83

2009;**9**:1527

**References**

2008;**298**:90

[1] Mallard LM, Pimenta MA,

Reports. 2009;**473**:51-87

Science. 2003;**299**:1361

2004;**108**:19912

Science. 1992;**264**:261

[2] Geim AK, Kim P. Carbon wonderland. Scientific American.

Dresselhaus G, Dresselhaus MS. Raman spectroscopy in graphene. Physics

[3] Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, et al. Electric field effect in atomically thin carbon films. Science. 2004;**306**:666

[4] Viculis LM, Mack JJ, Kaner RB. A chemical route to carbon nanoscrolls.

[5] Berger C, Song Z, Li T, Li X, Ogbazghi AY, Feng R, et al. Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics. The Journal of Physical Chemistry.

[6] Land TA, Michely T, Behm RJ, Hemminger JC, Comsa G. STM investigation of single layer graphite structures produced on Pt(111) by hydrocarbon decomposition. Surface

[7] Castro Neto AH, Guinea F, Peres NMR. Drawing conclusions from graphene. Physics World. 2006;**19**:33

[8] Swain SS, Unnikrishnan L, Mohanty S, Nayak SK. Hybridization of MWCNTs and reduced graphene oxide on random and electrically aligned nanocomposite membrane for selective separation of O2/N2 gas pair. Nayak Journal of Materials Science.

2018;**53**(22):15442-15464

[9] Horiuchi S, Gotou T, Fujiwara M, Asaka T, Yokosawa T, Matsui Y. Single graphene sheet detected in a carbon nanofilm. Applied Physics Letters.

**13**

**Chapter 2**

**Abstract**

*Humaira Seema*

organic chemicals to degrade.

**1. Introduction**

Water Remediation by

Graphene, a two-dimensional sheet of sp2

G-/GO-Based Photocatalysts

to be the most fascinating and promising option among nanomaterials for a variety of applications, because of its unique structure and tunable physiochemical properties. It can be either in the pure form or in its modified derivatives that include graphene oxide (GO), reduced graphene oxide (rGO), graphene-metal nanoparticle composites, graphene-polymer hybrids, and graphene/organic structures that showed improved results while maintaining inherent properties of the material. These modified nanostructures have a variety of applications as catalysts, energy storage/conversion, antimicrobial, and water decontaminant. In the field of environmental science, graphene has been widely used for molecular sieving involving gas phase separation and organic waste removal from water, due to its biocompatibility, various functional groups, and accessible surface area. Modified graphene can also serve as a semiconductor that can increase the efficiency of the photocatalytic ecosystems that results in the inactivation of the microorganisms causing the

**Keywords:** graphene, environmental, remediation, photocatalyst, water

photoconversion efficiency of the photocatalytic materials [1–74].

**1.1 Graphene (rGO)-based photocatalysts**

Recently photocatalysis by using semiconductors has fascinated universal consideration for its energy-related and environmental applications. Nevertheless, the decrease in the efficiency of the photocatalysis restricted its practical applications because of the prompt reunion of photogenerated electrons and holes. Thus, to decrease the reunion of charge carriers is significant for improvement of semiconductor photocatalysis. Among numerous approaches, water remediation has been done by rGO-/GO-based materials which are the most favorable candidates due to their high capacity of dye adsorption, prolonged light absorption range, improved separation of charge carriers, and transportation properties leading to improved

Various numbers of graphene-based photocatalysts have been prepared with its derivatives which mainly comprise metal oxides (e.g., P25 [1, 8], TiO2 [9–34, 36, 37], ZnO [17, 39–43], CuO [44], SnO2 [13, 45], WO3 [46]), metals (e.g., Cu [51], Au [52]), metal-metal oxides (e.g., Ag-TiO2 [35]), upconversion material—P25 (e.g., YF3:Yb3+,Tm3+—TiO2 [38]), salts (e.g., CdS [47–49], ZnS [50], ZnFe2O4 [53],

hybridized carbon atoms, has shown

#### **Chapter 2**

## Water Remediation by G-/GO-Based Photocatalysts

*Humaira Seema*

#### **Abstract**

Graphene, a two-dimensional sheet of sp2 hybridized carbon atoms, has shown to be the most fascinating and promising option among nanomaterials for a variety of applications, because of its unique structure and tunable physiochemical properties. It can be either in the pure form or in its modified derivatives that include graphene oxide (GO), reduced graphene oxide (rGO), graphene-metal nanoparticle composites, graphene-polymer hybrids, and graphene/organic structures that showed improved results while maintaining inherent properties of the material. These modified nanostructures have a variety of applications as catalysts, energy storage/conversion, antimicrobial, and water decontaminant. In the field of environmental science, graphene has been widely used for molecular sieving involving gas phase separation and organic waste removal from water, due to its biocompatibility, various functional groups, and accessible surface area. Modified graphene can also serve as a semiconductor that can increase the efficiency of the photocatalytic ecosystems that results in the inactivation of the microorganisms causing the organic chemicals to degrade.

**Keywords:** graphene, environmental, remediation, photocatalyst, water

#### **1. Introduction**

Recently photocatalysis by using semiconductors has fascinated universal consideration for its energy-related and environmental applications. Nevertheless, the decrease in the efficiency of the photocatalysis restricted its practical applications because of the prompt reunion of photogenerated electrons and holes. Thus, to decrease the reunion of charge carriers is significant for improvement of semiconductor photocatalysis. Among numerous approaches, water remediation has been done by rGO-/GO-based materials which are the most favorable candidates due to their high capacity of dye adsorption, prolonged light absorption range, improved separation of charge carriers, and transportation properties leading to improved photoconversion efficiency of the photocatalytic materials [1–74].

#### **1.1 Graphene (rGO)-based photocatalysts**

Various numbers of graphene-based photocatalysts have been prepared with its derivatives which mainly comprise metal oxides (e.g., P25 [1, 8], TiO2 [9–34, 36, 37], ZnO [17, 39–43], CuO [44], SnO2 [13, 45], WO3 [46]), metals (e.g., Cu [51], Au [52]), metal-metal oxides (e.g., Ag-TiO2 [35]), upconversion material—P25 (e.g., YF3:Yb3+,Tm3+—TiO2 [38]), salts (e.g., CdS [47–49], ZnS [50], ZnFe2O4 [53],

MnFe2O4 [54], NiFe2O4 [55], CoFe2O4 [56], Bi2WO6 [57–59], Bi2MoO6 [60], InNbO4 [61], ZnSe [63]), Ag/AgCl [62]), and other carbon material (e.g., CNT [64]).

#### **1.2 Graphene oxide (GO)-based photocatalysts**

Graphene oxide (GO) has recently received considerable attention due to oxygen-containing functional groups which increase its solubility in solvents for the preparation of GO-based nanocomposites required for photodegradation of pollutants [65–74]. GO-based nanocomposites mainly include metal oxides (TiO2) [66–72], metal-free polymers [73], and silver/silver halides [74].

#### **2. Preparation of rGO-/GO-based composite photocatalysts**

Some of the commonly used synthesis techniques include in situ growth strategy, solution mixing, hydrothermal/ solvothermal, and microwave-assisted process.

#### **2.1 In situ growth strategy**

This method is usually used to prepare reduced graphene oxide-/graphene oxide-based metal composites. Zhang et al. reported that TiO2/graphene composite photocatalyst [14] is synthesized by a simple liquid-phase deposition technique. Moreover, adopting a similar approach, Wang et al. prepared nanocarbon/TiO2 nanocomposites where titania nanoparticles were decorated by thermal reaction on the surfaces of three different dimensional nanocarbons [9]. While in thermal reduction method, TiO2/graphene composite [12] with a remarkable visible light photocatalytic activity was prepared by Zhang et al. using a heat treatment method of GO, where GO changed to reduced graphene oxide. Uniform ZnO nanoparticles were found on functionalized graphene sheets evenly via thermal decay of mixture of zinc salt, graphene oxide, and poly(vinyl pyrrolidone) [39].

Furthermore, Sn2+ or Ti3+ ions were converted to oxides at low temperatures, while GO was reduced to reduced graphene oxide by tin or titanium salts in redox method [13–45]. In our recent work, we prepared SnO2-G nanocomposite which displayed higher photocatalytic activity in sunlight as compared to bare metal oxide nanoparticles as shown in **Figure 1** [45]. Similarly reduced graphene oxide-zinc oxide composite was prepared where zinc ions were decorated on GO sheets and transformed to metal oxide nanoparticles by using chemical reagents at 150°C. Reduced graphene oxide-ZnO photocatalyst is formed by reducing the graphene oxide [43].

Li et al. prepared uniform mesoporous titania nanospheres on reduced graphene oxide layers via a process of a template-free self-assembly [20]. Du et al. [21] also developed the macro-mesoporous titania-reduced graphene oxide composite film by a confinement of a self-assembly process as shown in **Figure 2**.

Moreover Kim et al. synthesized strongly coupled nanocomposites of layered titanate and graphene by electrostatically derived self-assembly between negatively charged G nanosheets and positively charged TiO2 nanosols, followed by a phase transition of the anatase TiO2 component into layered titanate [37]. Chen et al. prepared graphene oxide/titania composites by using the self-assembly technique [72].

While Cu ion-modified reduced graphene oxide [51] prepared by an immersion technique displayed a high photocatalytic activity, gold nanoparticles were decorated on the surface of the reduced graphene oxide through spontaneous chemical reduction of HAuCl4 by GOR [52] as shown in **Figure 3**.

**15**

**Figure 1.**

**Figure 2.**

Bi2WO6/reduced graphene oxide photocatalysts were successfully prepared via in situ refluxing method in the presence of GO [57]. Zhang et al. presented reduced graphene oxide sheet grafted Ag@AgCl plasmonic photocatalyst with high activity via a precipitation reaction followed by reduction [62]. TiO2-GO was well prepared

*Schematic view for the preparation of a macro-mesoporous TiO2-reduced graphene oxide composite film.* 

*Time-dependent absorption spectra of MB solution during UV light irradiation in the presence of (a) SnO2 and (b) reduced graphene oxide-SnO2 and during sunlight irradiation in the presence of (c) SnO2 and (d)* 

*reduced graphene oxide-SnO2. Reprinted with permission of the publisher [45].*

Liu et al. have established a process of water/toluene two-phase for self-assembling TiO2 nanorods on graphene oxide [69, 70]. Jiang et al. prepared GO/titania

at 80°C by using GO and titanium sulfate as precursors [66].

*Reprinted with permission of the publisher [21].*

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

#### **Figure 1.**

*Graphene and Its Derivatives - Synthesis and Applications*

**1.2 Graphene oxide (GO)-based photocatalysts**

**2.1 In situ growth strategy**

graphene oxide [43].

technique [72].

MnFe2O4 [54], NiFe2O4 [55], CoFe2O4 [56], Bi2WO6 [57–59], Bi2MoO6 [60], InNbO4 [61], ZnSe [63]), Ag/AgCl [62]), and other carbon material (e.g., CNT [64]).

Graphene oxide (GO) has recently received considerable attention due to oxygen-containing functional groups which increase its solubility in solvents for the preparation of GO-based nanocomposites required for photodegradation of pollutants [65–74]. GO-based nanocomposites mainly include metal oxides (TiO2)

Some of the commonly used synthesis techniques include in situ growth strategy, solution mixing, hydrothermal/ solvothermal, and microwave-assisted process.

This method is usually used to prepare reduced graphene oxide-/graphene oxide-based metal composites. Zhang et al. reported that TiO2/graphene composite photocatalyst [14] is synthesized by a simple liquid-phase deposition technique. Moreover, adopting a similar approach, Wang et al. prepared nanocarbon/TiO2 nanocomposites where titania nanoparticles were decorated by thermal reaction on the surfaces of three different dimensional nanocarbons [9]. While in thermal reduction method, TiO2/graphene composite [12] with a remarkable visible light photocatalytic activity was prepared by Zhang et al. using a heat treatment method of GO, where GO changed to reduced graphene oxide. Uniform ZnO nanoparticles were found on functionalized graphene sheets evenly via thermal decay of mixture

Furthermore, Sn2+ or Ti3+ ions were converted to oxides at low temperatures,

Li et al. prepared uniform mesoporous titania nanospheres on reduced graphene oxide layers via a process of a template-free self-assembly [20]. Du et al. [21] also developed the macro-mesoporous titania-reduced graphene oxide composite film

Moreover Kim et al. synthesized strongly coupled nanocomposites of layered titanate and graphene by electrostatically derived self-assembly between negatively charged G nanosheets and positively charged TiO2 nanosols, followed by a phase transition of the anatase TiO2 component into layered titanate [37]. Chen et al. prepared graphene oxide/titania composites by using the self-assembly

While Cu ion-modified reduced graphene oxide [51] prepared by an immersion technique displayed a high photocatalytic activity, gold nanoparticles were decorated on the surface of the reduced graphene oxide through spontaneous chemical

while GO was reduced to reduced graphene oxide by tin or titanium salts in redox method [13–45]. In our recent work, we prepared SnO2-G nanocomposite which displayed higher photocatalytic activity in sunlight as compared to bare metal oxide nanoparticles as shown in **Figure 1** [45]. Similarly reduced graphene oxide-zinc oxide composite was prepared where zinc ions were decorated on GO sheets and transformed to metal oxide nanoparticles by using chemical reagents at 150°C. Reduced graphene oxide-ZnO photocatalyst is formed by reducing the

[66–72], metal-free polymers [73], and silver/silver halides [74].

of zinc salt, graphene oxide, and poly(vinyl pyrrolidone) [39].

by a confinement of a self-assembly process as shown in **Figure 2**.

reduction of HAuCl4 by GOR [52] as shown in **Figure 3**.

**2. Preparation of rGO-/GO-based composite photocatalysts**

**14**

*Time-dependent absorption spectra of MB solution during UV light irradiation in the presence of (a) SnO2 and (b) reduced graphene oxide-SnO2 and during sunlight irradiation in the presence of (c) SnO2 and (d) reduced graphene oxide-SnO2. Reprinted with permission of the publisher [45].*

#### **Figure 2.**

*Schematic view for the preparation of a macro-mesoporous TiO2-reduced graphene oxide composite film. Reprinted with permission of the publisher [21].*

Bi2WO6/reduced graphene oxide photocatalysts were successfully prepared via in situ refluxing method in the presence of GO [57]. Zhang et al. presented reduced graphene oxide sheet grafted Ag@AgCl plasmonic photocatalyst with high activity via a precipitation reaction followed by reduction [62]. TiO2-GO was well prepared at 80°C by using GO and titanium sulfate as precursors [66].

Liu et al. have established a process of water/toluene two-phase for self-assembling TiO2 nanorods on graphene oxide [69, 70]. Jiang et al. prepared GO/titania

**Figure 3.**

*Possible mechanism of photosensitized degradation of dyes over a rGO Cu composite under visible light irradiation. Reprinted with permission of the publisher [52].*

composite by in situ depositing titania on GO through liquid-phase deposition, followed by a calcination at 200°C [71].

GO nanostructures are prepared by modified Hummer's method, which has promising applications in photocatalysis [65].

#### **2.2 Solution mixing method**

It has been widely used to prepare graphene-based photocatalysts. Previously, titania nanoparticles and GO colloids have been mixed by ultrasonication followed by ultraviolet (UV)-assisted photocatalytic reduction of GO to yield graphenetitania nanocomposites [18, 23, 31].

Akhavan and Ghaderi used a similar strategy to prepare the titania/reduced graphene oxide composite thin film [25].

Guo et al. [28] prepared TiO2/graphene composite via sonochemical method. GO/g-C3N4 with efficient photocatalytic capability was also fabricated by the same sonochemical approach [73].

ZnO and GO mixture was dispersed by ultrasonication followed by chemical reduction of GO to graphene ultimately leading to synthesize ZnO/graphene composite [40]. The G-hierarchical ZnO hollow sphere composites are synthesized by Luo et al. by using a simple ultrasonic treatment of the solution [43].

Cheng et al. [40] presented a new facile ultrasonic approach to prepare graphene quantum dots (GQDs), which exhibited photoluminescent in a water solution. The water/oil system is used by Zhu et al. [74] to produce graphene oxide enwrapped Ag/AgX (X = Br, Cl) composites. Graphene oxide and silver nitrate solution were added to chloroform solution of surfactants stirring condition at room temperature to produce hybrid composites which displayed high photocatalytic activity under visible light irradiation as shown in **Figure 4**. Titania/graphene oxide composites were synthesized using one-step colloidal blending method [68].

#### **2.3 Hydrothermal/solvothermal method**

This one-pot process can lead to highly crystalline nanostructures, which operates at elevated temperatures in an autoclave to generate high pressure, without calcination, and at the same time GO reduced to rGO. Typically, graphene-based composites, e.g., P25 [1, 8], TiO2 [15, 16, 24, 29, 30, 32–34], Ag-TiO2 [35], UC-P25 [38], WO3 [46], CdS [49], ZnFe2O4 [53], MnFe2O4 [54], NiFe2O4 [55], Bi2WO6 [58, 59], Bi2MoO6 [60], InNbO4 [61], and ZnSe [63], have been prepared by the

**17**

**Figure 5.**

**Figure 4.**

of methylene blue (MB).

hydrothermal process, while others such as TiO2 [11, 22, 26, 27], CuO [44], CdS

*Photodegradation of MB under (a) UV light (λ = 365 nm) and (b) visible light (λ > 400 nm) over (1) P25, (2) P25-CNTs, and (3) P25-GR photocatalysts, respectively. (c) Schematic structure of P25-GR and process of the photodegradation of MB over P25-GR. (d) Bar plot showing the remaining MB in solution: (1) initial and equilibrated with (2) P25, (3) P25-CNTs, and (4) P25-GR in the dark after 10-min stirring. Pictures of the corresponding dye solutions are on the top for each sample. Reprinted with permission of the publisher [8].*

*(A) Photocatalytic activities of silver/silver bromide (a) and silver/silver bromide/GO (b) nanospecies for photodegradation of MO molecules under visible light irradiation and (B) those of the Ag/AgCl (a) and Ag/*

*AgCl/GO (b) nanospecies. Reprinted with permission of the publisher [74].*

Li et al. have prepared P25-G nanocomposite using GO and P25 as raw materials via hydrothermal technique [8]. As illustrated in **Figure 5**, the photocatalysis determines that composite showed improved activity toward the photodegradation

[48], and CoFe2O4 [56] are prepared by the solvothermal process.

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

#### **Figure 4.**

*Graphene and Its Derivatives - Synthesis and Applications*

followed by a calcination at 200°C [71].

**2.2 Solution mixing method**

**Figure 3.**

sonochemical approach [73].

titania nanocomposites [18, 23, 31].

graphene oxide composite thin film [25].

**2.3 Hydrothermal/solvothermal method**

promising applications in photocatalysis [65].

*irradiation. Reprinted with permission of the publisher [52].*

composite by in situ depositing titania on GO through liquid-phase deposition,

*Possible mechanism of photosensitized degradation of dyes over a rGO Cu composite under visible light* 

GO nanostructures are prepared by modified Hummer's method, which has

It has been widely used to prepare graphene-based photocatalysts. Previously, titania nanoparticles and GO colloids have been mixed by ultrasonication followed by ultraviolet (UV)-assisted photocatalytic reduction of GO to yield graphene-

Akhavan and Ghaderi used a similar strategy to prepare the titania/reduced

Guo et al. [28] prepared TiO2/graphene composite via sonochemical method. GO/g-C3N4 with efficient photocatalytic capability was also fabricated by the same

ZnO and GO mixture was dispersed by ultrasonication followed by chemical reduction of GO to graphene ultimately leading to synthesize ZnO/graphene composite [40]. The G-hierarchical ZnO hollow sphere composites are synthesized

This one-pot process can lead to highly crystalline nanostructures, which operates at elevated temperatures in an autoclave to generate high pressure, without calcination, and at the same time GO reduced to rGO. Typically, graphene-based composites, e.g., P25 [1, 8], TiO2 [15, 16, 24, 29, 30, 32–34], Ag-TiO2 [35], UC-P25 [38], WO3 [46], CdS [49], ZnFe2O4 [53], MnFe2O4 [54], NiFe2O4 [55], Bi2WO6 [58, 59], Bi2MoO6 [60], InNbO4 [61], and ZnSe [63], have been prepared by the

Cheng et al. [40] presented a new facile ultrasonic approach to prepare graphene quantum dots (GQDs), which exhibited photoluminescent in a water solution. The water/oil system is used by Zhu et al. [74] to produce graphene oxide enwrapped Ag/AgX (X = Br, Cl) composites. Graphene oxide and silver nitrate solution were added to chloroform solution of surfactants stirring condition at room temperature to produce hybrid composites which displayed high photocatalytic activity under visible light irradiation as shown in **Figure 4**. Titania/graphene oxide composites

by Luo et al. by using a simple ultrasonic treatment of the solution [43].

were synthesized using one-step colloidal blending method [68].

**16**

*(A) Photocatalytic activities of silver/silver bromide (a) and silver/silver bromide/GO (b) nanospecies for photodegradation of MO molecules under visible light irradiation and (B) those of the Ag/AgCl (a) and Ag/ AgCl/GO (b) nanospecies. Reprinted with permission of the publisher [74].*

#### **Figure 5.**

*Photodegradation of MB under (a) UV light (λ = 365 nm) and (b) visible light (λ > 400 nm) over (1) P25, (2) P25-CNTs, and (3) P25-GR photocatalysts, respectively. (c) Schematic structure of P25-GR and process of the photodegradation of MB over P25-GR. (d) Bar plot showing the remaining MB in solution: (1) initial and equilibrated with (2) P25, (3) P25-CNTs, and (4) P25-GR in the dark after 10-min stirring. Pictures of the corresponding dye solutions are on the top for each sample. Reprinted with permission of the publisher [8].*

hydrothermal process, while others such as TiO2 [11, 22, 26, 27], CuO [44], CdS [48], and CoFe2O4 [56] are prepared by the solvothermal process.

Li et al. have prepared P25-G nanocomposite using GO and P25 as raw materials via hydrothermal technique [8]. As illustrated in **Figure 5**, the photocatalysis determines that composite showed improved activity toward the photodegradation of methylene blue (MB).

**Figure 6.**

*(A) Schematic illustration of synthesis steps for graphene-wrapped anatase TiO2 nanoparticles (NPs) and corresponding SEM images of (B) bare amorphous TiO2 NPs, (C) GO-wrapped amorphous TiO2 NPs, and (D) graphene-wrapped anatase TiO2 NPs (scale bar: 200 nm); (E) the suggested mechanism for the photocatalytic degradation of MB by graphene-wrapped anatase TiO2 NPs under visible light irradiation. Reprinted with permission of the publisher [8].*

Lee et al. synthesized graphene oxide (GO)-wrapped TiO2 nanoparticles by combining positively charged TiO2 nanoparticles with negatively charged GO nanosheets, as shown in SEM images in **Figure 6**. Furthermore, it demonstrates the reduction of graphene oxide to reduced graphene oxide and the crystallization of amorphous titania nanoparticles which occurred after a hydrothermal treatment.

#### **2.4 Microwave-assisted method**

In situ microwave irradiation is a facile method which has been used for the simultaneous formation of metal oxide (e.g., TiO2 [17], ZnO [17, 41], CdS [47],

#### **Figure 7.**

*(A) Photocatalytic degradation for RhB under different experimental conditions with catalysts GOCNT-15-4 and P25. (B) Photocatalytic properties of different samples in degrading RhB. (C) Experimental steps of pillaring GO and RGO platelets with CNTs while energy diagram showing the proposed mechanism of photosensitized degradation of RhB under visible light irradiation. Reprinted with permission of the publisher [64].*

**19**

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

chemical vapor deposition (CVD) [64].

ticles as the catalysts as shown in **Figure 7**.

ticles on G surfaces.

**2.5 Other methods**

cyclic voltammetry [19].

briefly summarized in **Table 1**.

**fraction**

P25-rGO 0.2% G Hydrothermal

P25-rGO 1.0% G Hydrothermal

**Preparation strategy**

method

method

**Photocatalysts Mass** 

(1) rGO-based

**3. Photocatalysis**

ZnS [50]) and reduction of GO. The drawback of this process is that it did not show its fine control over the uniform size and surface distribution of nanopar-

In addition to the abovementioned examples, graphene-based photocatalysts are synthesized by developing new synthetic strategies, e.g., electrospinning [10] and

Zhao et al. pillared reduced graphene oxide platelets with carbon nanotubes using the CVD method with acetonitrile as the carbon source and nickel nanopar-

Photocatalytic TiO2 films were prepared by Yoo et al. using RF magnetron sputtering and GO solutions with different concentrations of GO in ethanol which were coated on TiO2 films [67]. Graphene film was formed on the surface of TiO2 nanotube arrays through in situ electrochemical reduction of GO dispersion by

Due to widespread environmental applications, photocatalysis has fascinated an increasing consideration. The graphene-/graphene oxide-based photocatalyst revealed a significant improvement of photocatalytic degradation of methylene blue (MB) [1, 8, 11, 12, 15, 18, 21, 22, 26, 28, 30–33, 35, 36, 40, 41, 43, 45, 48, 50, 52–56, 60, 61, 67–69], rhodamine B (RhB) [13, 20, 24, 27, 32, 42, 44, 51, 52, 56–59, 62, 64, 73], methyl orange (MO) [9, 10, 14, 37, 38, 49, 63, 66, 71, 72, 74], anthracene-9 carboxylic acid (9-AnCOOH) [19], phenol [22, 54], 2,4-dichlorophenoxyacetic acid (2,4-D) [23], 2,4-dichlorophenol [61, 73], malachite green (MG) [29], 2-propanol [34], rhodamine 6G (Rh 6G) [39], rhodamine B 6G (RhB 6G) [46], orange ll [52], 2,4-dichlorophenol (2,4-DCP) [61], acid orange 7(AO 7) [64], and resazurin (RZ) [65], as well as photocatalytic reduction of Cr(VI) [17, 47, 71], along with photocatalytic antibacterial activity for killing *E. coli* bacteria [25] by UV [1, 8–10, 13, 14, 16–24, 26, 28–34, 37, 39–45, 50, 54, 65–71], as well as visible irradiation [1, 8–13, 15, 16, 20, 22, 25, 27, 30–33, 35–38, 42, 45–49, 51–64, 67, 68, 72–74], in water which are

> **Photocatalytic experiments**

Photodegradation of MB

5% 1.50 times 30% 0.97 times 0.2% 1.42 times higher than

5% 2.32 times 30% 0.75 times

> Photodegradation of MB

**Performances as compared to reference photocatalyst**

1.17 times higher than P25; DP of 60%

P25; DP of 28%

3.40 or 1.21 times higher than P25 or P25-CNTs; DP of 25% or 70%, respectively (2% = 90 min)

**Type of irradiation**

Visible

UV 1

UV 2

**References**

ZnS [50]) and reduction of GO. The drawback of this process is that it did not show its fine control over the uniform size and surface distribution of nanoparticles on G surfaces.

#### **2.5 Other methods**

*Graphene and Its Derivatives - Synthesis and Applications*

Lee et al. synthesized graphene oxide (GO)-wrapped TiO2 nanoparticles by combining positively charged TiO2 nanoparticles with negatively charged GO nanosheets, as shown in SEM images in **Figure 6**. Furthermore, it demonstrates the reduction of graphene oxide to reduced graphene oxide and the crystallization of amorphous titania nanoparticles which occurred after a hydrothermal

*(A) Schematic illustration of synthesis steps for graphene-wrapped anatase TiO2 nanoparticles (NPs) and corresponding SEM images of (B) bare amorphous TiO2 NPs, (C) GO-wrapped amorphous TiO2 NPs, and (D) graphene-wrapped anatase TiO2 NPs (scale bar: 200 nm); (E) the suggested mechanism for the photocatalytic degradation of MB by graphene-wrapped anatase TiO2 NPs under visible light irradiation.* 

In situ microwave irradiation is a facile method which has been used for the simultaneous formation of metal oxide (e.g., TiO2 [17], ZnO [17, 41], CdS [47],

*(A) Photocatalytic degradation for RhB under different experimental conditions with catalysts GOCNT-15-4 and P25. (B) Photocatalytic properties of different samples in degrading RhB. (C) Experimental steps of pillaring GO and RGO platelets with CNTs while energy diagram showing the proposed mechanism of photosensitized degradation of RhB under visible light irradiation. Reprinted with permission of the publisher [64].*

**18**

**Figure 7.**

treatment.

**Figure 6.**

**2.4 Microwave-assisted method**

*Reprinted with permission of the publisher [8].*

In addition to the abovementioned examples, graphene-based photocatalysts are synthesized by developing new synthetic strategies, e.g., electrospinning [10] and chemical vapor deposition (CVD) [64].

Zhao et al. pillared reduced graphene oxide platelets with carbon nanotubes using the CVD method with acetonitrile as the carbon source and nickel nanoparticles as the catalysts as shown in **Figure 7**.

Photocatalytic TiO2 films were prepared by Yoo et al. using RF magnetron sputtering and GO solutions with different concentrations of GO in ethanol which were coated on TiO2 films [67]. Graphene film was formed on the surface of TiO2 nanotube arrays through in situ electrochemical reduction of GO dispersion by cyclic voltammetry [19].

### **3. Photocatalysis**

Due to widespread environmental applications, photocatalysis has fascinated an increasing consideration. The graphene-/graphene oxide-based photocatalyst revealed a significant improvement of photocatalytic degradation of methylene blue (MB) [1, 8, 11, 12, 15, 18, 21, 22, 26, 28, 30–33, 35, 36, 40, 41, 43, 45, 48, 50, 52–56, 60, 61, 67–69], rhodamine B (RhB) [13, 20, 24, 27, 32, 42, 44, 51, 52, 56–59, 62, 64, 73], methyl orange (MO) [9, 10, 14, 37, 38, 49, 63, 66, 71, 72, 74], anthracene-9 carboxylic acid (9-AnCOOH) [19], phenol [22, 54], 2,4-dichlorophenoxyacetic acid (2,4-D) [23], 2,4-dichlorophenol [61, 73], malachite green (MG) [29], 2-propanol [34], rhodamine 6G (Rh 6G) [39], rhodamine B 6G (RhB 6G) [46], orange ll [52], 2,4-dichlorophenol (2,4-DCP) [61], acid orange 7(AO 7) [64], and resazurin (RZ) [65], as well as photocatalytic reduction of Cr(VI) [17, 47, 71], along with photocatalytic antibacterial activity for killing *E. coli* bacteria [25] by UV [1, 8–10, 13, 14, 16–24, 26, 28–34, 37, 39–45, 50, 54, 65–71], as well as visible irradiation [1, 8–13, 15, 16, 20, 22, 25, 27, 30–33, 35–38, 42, 45–49, 51–64, 67, 68, 72–74], in water which are briefly summarized in **Table 1**.



**21**

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

> **Preparation strategy**

> > assisted method

mixing method

voltammetric reduction method

strategy (self-assembly synthesis)

strategy (self-assembly method)

method

mixing method

method

mixing method

method

method

method

method

**Photocatalytic experiments**

Photocatalytic reduction of Cr(VI)

Photodegradation of MB

Photodegradation of anthracene-9 carboxylic acid (9-AnCOOH)

Photodegradation of RhB

Photodegradation of MB

Photodegradation of phenol

Photodegradation of MB

Photodegradation of 2,4-dichlorophen-oxyacetic acid (2,4-D)

Photodegradation of RhB

Photocatalytic antibacterial activity for killing *E. coli* bacteria

Photodegradation of MB

Photodegradation of RhB

Photodegradation of MB

Photodegradation of Malachite green

**Performances as compared to reference photocatalyst**

3.33 times higher than P25; DP of 15%

1.09 or 1.30 times higher than pure TiO2 or commercial P25 = removal rate of 83% or 70%, respectively

1.25 times higher than P25; DP of 80%

2.13 times higher than bare TiO2 nanotubes; DP of 46%

3.92 times higher than TiO2; DP of 25%

1.57 times higher than TiO2; reaction rate constant = 0.045 min<sup>−</sup><sup>1</sup>

1.68 times higher than P25; DP of 48%

3.10 times higher than P25; DP of 20%

3.5 times higher than P25; DP of 20%

4.0 times higher than TiO2 film; reaction rate constant = 0.002 min<sup>−</sup><sup>1</sup>

4.0 or 2.94 times higher than pure TiO2 or P25; reaction rate constant = 0.05 or 0.068 min<sup>−</sup><sup>1</sup>

7.55 times higher than TiO2; reaction rate constant = 0.0086 min<sup>−</sup><sup>1</sup>

2.08 times higher than P25; DP of 40.8%

2.79 times higher than P25; reaction rate constant = 0.0162 min<sup>−</sup><sup>1</sup>

2.57 times higher than P25; reaction rate constant = 0.0054 min<sup>−</sup><sup>1</sup>

3.09 times higher than TiO2 nanotubes; reaction rate constant = 0.0218 min<sup>−</sup><sup>1</sup>

**Type of irradiation**

Visible

UV 11

UV 12

UV 13

UV-vis 14

UV 15

UV 16

UV 17

UV 18

Visible 19

UV 20

Visible 21

UV 22

UV 23

Visible

Visible

**References**

**fraction**

TiO2-rGO 0.8% G Microwave-

rGO-w-TiO2 1:10 Solution

TiO2-rGO film No data Cyclic

TiO2-rGO 6.5% G In situ growth

TiO2-rGO 0.6% G In situ growth

TiO2-rGO No data Solvothermal

TiO2-rGO film No data Solution

TiO2-rGO 10% GO Hydrothermal

TiO2-rGO No data Solution

TiO2-rGO 0.3 mg GO Solvothermal

TiO2-rGO No data Solvothermal

TiO2-rGO 75% G Sonochemical

TiO2-rGO 10% G Hydrothermal

**Photocatalysts Mass** 

*Graphene and Its Derivatives - Synthesis and Applications*

**Preparation strategy**

strategy (thermal treatment)

ning method

method

strategy (thermal reduction method)

strategy (redox method)

strategy (simple liquid-phase deposition method)

method

method

SnO2-rGO 2.24 times higher

**Photocatalytic experiments**

Degradation of MO

Degradation of MO

Photodegradation of MB

Photodegradation of MB

Photodegradation of RhB

Photodegradation of MO

Photodegradation of MB

Photodegradation of RhB

30 mg 3.0 or 1.92 times 50 mg 2.88 or 1.84 times

**Performances as compared to reference photocatalyst**

4.33 or 1.18 times higher than P25 or P25-CNTs; DP of 15% or 55%, respectively (2% = 90 min)

2.05 times higher than P25; DP of 40%

5.46 times higher than P25; 15%

1.51 times higher than TiO2; DP of 54%

2.04 times higher than TiO2; DP of approx. 22%

2.32 or 1.50 times higher than pure TiO2 or P25; DP of 25% or 39%, respectively

7.0 times higher than pure P25; DP of 10%

1.16 times higher than P25 reaction rate constant = 0.0049 min<sup>−</sup><sup>1</sup>

0.53 times higher than P25 reaction rate constant = 0.043 min<sup>−</sup><sup>1</sup>

than P25 reaction rate constant = 0.0049 min<sup>−</sup><sup>1</sup>

0.62 times higher than P25 reaction rate constant = 0.043 min<sup>−</sup><sup>1</sup>

1.89 times higher than P25 and graphene; DP of 45%

13.04 or 10.62 times higher than P25 or anatase TiO2; reaction rate constant = 0.0026 min<sup>−</sup><sup>1</sup>

1.63 times higher than P25; DP of 52%

0.0032 min-1

or

, respectively

**Type of irradiation**

Visible

Visible

Visible

UV 3

UV 4

Visible 5

Visible 6

Visible 7

UV

Visible

UV

UV 8

Visible 9

UV 10

**References**

**Photocatalysts Mass** 

**fraction**

TiO2-rGO 10 mg G In situ growth

TiO2-rGO 0.75% G Electrospin-

TiO2-rGO 10 mg G Solvothermal

TiO2-rGO 10 mg G In situ growth

TiO2-rGO No data In situ growth

TiO2-rGO 20 mg G In situ growth

TiO2-rGO No data Hydrothermal

TiO2-rGO 20: 1 Hydrothermal

**20**



**23**

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

> **Preparation strategy**

> > strategy (thermal method)

mixing method (sonochemical)

> assisted method

strategy (chemical deposition method)

mixing method (ultrasonic method)

method

strategy (redox method)

method

assisted method

method

method

**Photocatalytic experiments**

Photodegradation of Rh 6G

Photodegradation of MB

Photodegradation of MB

Photodegradation of RhB

Photodegradation of MB

Photodegradation of RhB in the presence of H2O2

Photodegradation of MB

Photodegradation of RhB 6G

Photocatalytic reduction of Cr(VI)

Photodegradation of MB

Photodegradation of MO

0.5% 2.54 times 1.0% 3.13 times 2.0% 4.45 times 3.0% 4.13 times 5.0% 3.27 times

0.8% G 1.46 or 1.21 times 1.0% G 1.68 or 1.40 times

**Performances as compared to reference photocatalyst**

2.13 times higher than ZnO; reaction rate constant = 0.022 min<sup>−</sup><sup>1</sup>

1.29 times higher than ZnO; DP of 68%

1.05 times higher than ZnO; DP of 95%

1.02 times higher than ZnO; DP of 98%

2.25 times higher than ZnO; DP of 40%

2.50 times higher than ZnO; DP of 40%

0.40 or times higher than SnO2; DP of 100%

24.86 times higher than SnO2; DP of 4%

2.2 or 53 times higher than WO3 nanorods or WO3 particles; reaction rate constant = 0.00167or 0.000069 min<sup>−</sup><sup>1</sup>

respectively

1.16 times higher than CdS = removal rate of 79%

2.5 times higher than CdS; DP of 37.6%

7.86 times higher than CdS; reaction rate constant = 0.0075 min<sup>−</sup><sup>1</sup>

,

**Type of irradiation**

UV 35

UV 36

UV 37

UV 38

UV 39

UV 40

Visible 41

Visible 42

Visible 43

Visible 44

Visible

Visible

Enhancement UV 34

**References**

**fraction**

ZnO-FGS 0.1 g GO In situ growth

ZnO-rGO 0.1% G Solution

ZnO-rGO 1.1% G Microwave-

ZnO@ rGO In situ growth

ZnO-rGO 3.56% G Solution

CuO-rGO No data Solvothermal

SnO2-rGO 5% G In situ growth

WO3-rGO 3.5% G Hydrothermal

CdS-rGO 1.5% G Microwave-

CdS-rGO 5% G Solvothermal

CdS-rGO 0.01:1 Hydrothermal

**Photocatalysts Mass** 

#### *Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

*Graphene and Its Derivatives - Synthesis and Applications*

**Preparation strategy**

method

mixing method

method

method

method and Thermal method

and solution mixing method

mixing method

strategy (self-assembly method)

method

assisted method

0.05% G Hydrothermal

0.05 g G Solution

No data In situ growth

4 mg GO Hydrothermal

2 mg G Hydrothermal

**Photocatalytic experiments**

Photodegradation of MB

Photodegradation of MB

Photodegradation of MB

Photodegradation of MB

Photodegradation of RhB

Photodegradation of MB

Photodegradation of RhB

Photodegradation of MB

Photodegradation of 2-propanol

Photodegradation of MB

Photodegradation of MO

Photodegradation of MO

Photocatalytic reduction of Cr(VI)

Degradation of MB Enhancement for rutile

0.15% 1.7 times 0.4% 1.27 times 0.6% 0.96 times

**Performances as compared to reference photocatalyst**

1.46 times higher than P25; DP of 65%

2.41 times higher than P25; DP of 29%

4.0 or 1.73 times higher than P25 or physical mixture of G-P25 (1:3); DP of 13% or 30%, respectively

2.93–2.20 times higher than P25 or physical mixture of G-P25 (1:3); DP of 30–40%

4.30 times higher than TiO2; reaction rate constant = 0.010 min<sup>−</sup><sup>1</sup>

1.6 times higher than TiO2; reaction rate constant = 0.005 min<sup>−</sup><sup>1</sup>

2.4 times higher than TiO2; reaction rate constant = 0.010 min<sup>−</sup><sup>1</sup>

3.2 times higher than TiO2; reaction rate constant = 0.005 min<sup>−</sup><sup>1</sup>

1.4 times higher than TiO2/MCM-41; conversion rate of 26%

TiO2/GQD than anatase TiO2/GQD

Enhancement as compared to bulklayered titanates or nanocrystalline-layered titanate

2.88 or times higher than P25 or P25-G or UC-P25; DP of 27% or 53% or 46%, respectively

1.12 or 0.92 times higher than pure ZnO or P25; removal rate of 58 or 70%, respectively

4 times higher than TiO2 UV-vis 27

Enhancement Visible 29

**Type of irradiation**

Visible

UV

UV 24

Visible 25

UV-vis 26

UV 28

Visible 30

UV-vis 31

Visible 32

UV 33

**References**

**Photocatalysts Mass** 

TiO2-B-doped rGO

TiO2-N-doped rGO

TiO2-rGO/ MCM-41

RutileTiO2- GQD/anatase TiO2-GQD

Layered titanate rGO

UC-P25-rGO UC = YF3:Yb3+,Tm3+ **fraction**

TiO2-rGO No data Hydrothermal

rGO @TiO2 1:3 Solution

TiO2-rGO-TiO2 0.01 g G Hydrothermal

Ag-TiO2-rGO No data Hydrothermal

ZnO-rGO 0.6% G Microwave-

**22**



**25**

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

> **Preparation strategy**

> > method

mixing method

method

vapor deposition (CVD) method

> mixing method (modified Hummers' method)

> > strategy

sputtering followed by coating

method (simple colloidal blending method)

strategy

strategy (two phase assembling method)

18 mg G Hydrothermal

**Photocatalytic experiments**

Photodegradation of MB

Photodegra-dation of 2,4-dichlorophenol

Photodegradation of RhB

Photodegradation of MO

Photodegradation of RhB

Photocatalytic reduction of resazurin (RZ)

Photodegradation of MO

Photodegradation of MB

Photodegradation of MB

4.3% 4.98 times 8.2% 8.59 times 1.2% 1.36 times higher

4.3% 3.03 times 8.2% 7.15 times

> Photodegradation of MB

> Photodegradation of acid orange 7 (AO 7)

0.44% 4.55 times 1.56% 5.1 times

**Performances as compared to reference photocatalyst**

1.87 times higher than InNbO4; reaction rate constant = 0.0185 min<sup>−</sup><sup>1</sup>

2.10 times higher than InNbO4 reaction rate constant = 0.0256 min<sup>−</sup><sup>1</sup>

3.88 times higher than Ag@AgCl reaction rate constant = 0.060 min<sup>−</sup><sup>1</sup>

Enhancement as compared to ZnSe; (no photocatalytic activity)

4.28 times higher than P25; reaction rate constant = 0.0049 min<sup>−</sup><sup>1</sup>

2.27 times higher than pure P25; DP of 38.4%

2.5 times higher than TiO2; DP of 20%

4.51 times higher than P25 reaction rate constant = 0.0084 min<sup>−</sup><sup>1</sup>

than P25 reaction rate constant = 0.0033 min<sup>−</sup><sup>1</sup>

1.41 times higher than P25; DP of 70%

11.59 times higher than P25 reaction rate constant = 0.0182 min<sup>−</sup><sup>1</sup>

1.75 times Visible

**Type of irradiation**

Visible 56

Visible 57

Visible 58

Visible 59

UV 61

UV 62

UV 63

UV 64

UV 65

Visible

No data UV 60

**References**

**fraction**

InNbO4-rGO No data Hydrothermal

Ag@AgCl-rGO 0.22% G Solution

CNT-rGO No data Chemical

GO 1 mg GO Solution

TiO2-GO No data In situ growth

TiO2-GO 0.03 mg GO RF magnetron

TiO2-GO 1.2% GO Solution mixing

TiO2-GO 50 mg GO In situ growth

TiO2-GO 500 mg GO In situ growth

**Photocatalysts Mass** 

ZnSe-N-doped rGO

(2) GO-based

*Graphene and Its Derivatives - Synthesis and Applications*

**Preparation strategy**

> assisted method

strategy (immersion method)

strategy (chemical reduction)

method

method

method

method

strategy (refluxing method)

method

method

method

**Photocatalytic experiments**

Photodegradation of MB

Photodegradation of RhB

Photodegradation of RhB

Photodegradation of MB

Photodegradation of orange II

Photodegradation of MB in the presence of H2O2

Photodegradation of MB

Photodegradation of MB

Photodegradation of phenol

Photodegradation of MB

Photodegradation of RhB and MB

Photodegradation of RhB

Photodegradation of RhB

Photodegradation of RhB

Photodegradation of MB

1% 3.67 times

2.5% 1.40 times 5% 1.80 times 10% 1.10 times 15% 0.80 times

**Performances as compared to reference photocatalyst**

4 times higher than P25; DP of 25%

2.94 or 30.61 times higher than P25 or graphene; reaction rate constant = 0.0051 min<sup>−</sup><sup>1</sup> or 0.00049 min<sup>−</sup><sup>1</sup>

respectively

1.77 times higher than P25; reaction rate constant = 0.0049 min<sup>−</sup><sup>1</sup>

8.36 times

0.19 times

4.50 times higher than ZnFe2O4 (DP of 22% = 90 min)

9.62 times higher than MnFe2O4; DP of 10%

1.33 times higher than MnFe2O4; DP of 75%

1.13 times higher than MnFe2O4; DP of 75%

Enhancement as compared to NiFe2O4; reaction rate constant almost zero (no photocatalytic activity)

1.30 times higher than Bi2WO6; DP of 50%

Enhancement as compared to Bi2WO6

2.04 times higher than Bi2WO6; DP of 44% in 4 min

2.45 times higher than pure Bi2MoO6; reaction rate constant 0.0037 min<sup>−</sup><sup>1</sup>

,

**Type of irradiation**

UV 45

Visible 46

Visible 47

Visible 48

Visible 49

Visible 50

Visible 52

Visible 53

Visible 54

Visible 55

UV

UV

Enhancement Visible 51

**References**

**Photocatalysts Mass** 

**fraction**

ZnS-rGO No data Microwave-

Cu-rGO No data In situ growth

Au-rGO No data In situ growth

ZnFe2O4-rGO 20% G Hydrothermal

MnFe2O4-rGO 30% G Hydrothermal

NiFe2O4-rGO 25% G Hydrothermal

CoFe2O4-rGO No data Solvothermal

Bi2WO6-rGO 1% G In situ growth

Bi2WO6-rGO 1% G Hydrothermal

Bi2WO6-rGO No data Hydrothermal

Bi2MoO6-rGO 0.5% G Hydrothermal

**24**



#### **Table 1.**

*Photocatalytic degradation of pollutants.*

#### **Author details**

Humaira Seema Institute of Chemical Sciences, University of Peshawer, Pakistan

\*Address all correspondence to: hawkkhan2@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**27**

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

[1] Zhang Y, Tang ZR, Fu X, Xu YJ. TiO2 graphene nanocomposites for gas-phase photocatalytic degradation of volatile aromatic pollutant: Is TiO2-graphene truly different from other TiO2-carbon composite materials? ACS Nano.

self-assembling TiO2 nanoparticles on nanocarbons surface. Current Applied

composite with enhanced photovoltaic and photocatalytic properties by electrospinning. ACS Applied Materials

[11] Zhou K, Zhu Y, Yang X, Jiang X, Li C. Preparation of graphene-TiO2

photocatalytic activity. New Journal of

[12] Zhang Y, Pan C. TiO2/graphene composite from thermal reaction of graphene oxide and its photocatalytic activity in visible light. Journal of Materials Science. 2011;**46**:2622-2626

[13] Zhang J, Xiong Z, Zhao XS. Graphene-metal-oxide composites for the degradation of dyes under visible light irradiation. Journal of Materials Chemistry. 2011;**21**:3634-3640

[14] Zhang H, Xu P, Du G, Chen Z, Oh K, Pan D, et al. A facile one-step synthesis of TiO2/graphene composites for photodegradation of methyl orange.

Nano Research. 2011;**4**:274-283

[16] Wang F, Zhang K. Reduced graphene oxide-TiO2 nanocomposite with high photocatalystic activity for the degradation of rhodamine B. Journal of Molecular Catalysis A: Chemical.

[17] Liu X, Pan L, Lv T, Zhu G,

Lu T, Sun Z, et al. Microwave-assisted synthesis of TiO2-reduced graphene

2011;**345**:101-107

[15] Lee JS, You KH, Park CB. Highly photoactive, low bandgap TiO2 nanoparticles wrapped by graphene. Advanced Materials. 2012;**24**:1084-1088

Physics. 2012;**12**:346-352

[10] Zhu P, Nair AS, Shengjie P, Shengyuan Y, Ramakrishna S. Facile fabrication of TiO2-graphene

& Interfaces. 2012;**4**:581-585

composites with enhanced

Chemistry. 2011;**35**:353-359

[2] Huang X, Qi X, Boey F, Zhang H. Graphene-based composites. Chemical Society Reviews. 2012;**41**:666-686

[3] Han L, Wang P, Dong S. Progress in graphene-based photoactive nanocomposites as a promising class of photocatalyst. Nanoscale.

[4] Xiang Q, Yu J, Jaroniec M. Graphenebased semiconductor photocatalysts.

2010;**4**:7303-7314

**References**

2012;**4**:5814-5825

2012;**41**:782-796

Chemical Society Reviews.

[5] Zhang N, Zhang Y, Xu YJ. Recent progress on graphene-based

[6] Le NH, Seema H, Kemp KC, Ahmed N, Tiwari JN, Park S, et al. Solution-processable conductive microhydrogels of nanoparticle/graphene platelets produced by reversible selfassembly and aqueous exfoliation. Journal of Materials Chemistry A.

[7] Kemp KC, Seema H, Saleh M, Le NH, Mahesh K, Chandra V, et al. Environmental applications using graphene composites: Water remediation and gas adsorption. Nanoscale. 2013;**5**:3149-3171

[8] Zhang H, Lv X, Li Y, Wang Y, Li J. P25-graphene composite as a high performance photocatalyst. ACS Nano.

[9] Wang F, Zhang K. Physicochemical and photocatalytic activities of

2013;**1**:12900-12908

2009;**4**:380-386

photocatalysts: Current status and future perspectives. Nanoscale. 2012;**4**:5792-5813 *Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

#### **References**

*Graphene and Its Derivatives - Synthesis and Applications*

**Preparation strategy**

> strategy (thermal treatment method)

In situ growth strategy (self-assembly method)

mixing method (sonochemical method)

mixing method (surfactantassisted assembly protocol via an oil/water microemulsion)

Institute of Chemical Sciences, University of Peshawer, Pakistan

\*Address all correspondence to: hawkkhan2@gmail.com

provided the original work is properly cited.

Ag/AgBr/GO Photodegradation

**Photocatalytic experiments**

Photodegradation of MO

Photocatalytic reduction of Cr(VI)

Photodegradation of MO

Photodegradation of RhB and 2,4-dichlorophenol

Photodegradation of MO

of MO

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

0.14% 1.59 times 0.25% 1.0 times 0.51% 0.82 times

**Performances as compared to reference photocatalyst**

7.44 times higher than P25; reaction rate constant = 0.0426 min<sup>−</sup><sup>1</sup>

5.44 times higher than P25; conversion rate = 0.0127 min<sup>−</sup><sup>1</sup>

1.18 times higher than pure P25; DP of 22%

1.90 times higher than g-C3N4; DP of 49.5%

2.84 times higher than Ag/AgCl; DP of 25%

3.40 times higher than Ag/AgBr; DP of 25%

**Type of irradiation**

UV 66

Visible 67

Visible 68

Visible 69

Visible

**References**

**Photocatalysts Mass** 

TiO2-GO 0.13% C

**fraction**

TiO2-GO No data In situ growth

element

g-C3N4-GO 1 g GO Solution

Ag/AgCl/GO No data Solution

*Photocatalytic degradation of pollutants.*

**26**

**Table 1.**

**Author details**

Humaira Seema

[1] Zhang Y, Tang ZR, Fu X, Xu YJ. TiO2 graphene nanocomposites for gas-phase photocatalytic degradation of volatile aromatic pollutant: Is TiO2-graphene truly different from other TiO2-carbon composite materials? ACS Nano. 2010;**4**:7303-7314

[2] Huang X, Qi X, Boey F, Zhang H. Graphene-based composites. Chemical Society Reviews. 2012;**41**:666-686

[3] Han L, Wang P, Dong S. Progress in graphene-based photoactive nanocomposites as a promising class of photocatalyst. Nanoscale. 2012;**4**:5814-5825

[4] Xiang Q, Yu J, Jaroniec M. Graphenebased semiconductor photocatalysts. Chemical Society Reviews. 2012;**41**:782-796

[5] Zhang N, Zhang Y, Xu YJ. Recent progress on graphene-based photocatalysts: Current status and future perspectives. Nanoscale. 2012;**4**:5792-5813

[6] Le NH, Seema H, Kemp KC, Ahmed N, Tiwari JN, Park S, et al. Solution-processable conductive microhydrogels of nanoparticle/graphene platelets produced by reversible selfassembly and aqueous exfoliation. Journal of Materials Chemistry A. 2013;**1**:12900-12908

[7] Kemp KC, Seema H, Saleh M, Le NH, Mahesh K, Chandra V, et al. Environmental applications using graphene composites: Water remediation and gas adsorption. Nanoscale. 2013;**5**:3149-3171

[8] Zhang H, Lv X, Li Y, Wang Y, Li J. P25-graphene composite as a high performance photocatalyst. ACS Nano. 2009;**4**:380-386

[9] Wang F, Zhang K. Physicochemical and photocatalytic activities of

self-assembling TiO2 nanoparticles on nanocarbons surface. Current Applied Physics. 2012;**12**:346-352

[10] Zhu P, Nair AS, Shengjie P, Shengyuan Y, Ramakrishna S. Facile fabrication of TiO2-graphene composite with enhanced photovoltaic and photocatalytic properties by electrospinning. ACS Applied Materials & Interfaces. 2012;**4**:581-585

[11] Zhou K, Zhu Y, Yang X, Jiang X, Li C. Preparation of graphene-TiO2 composites with enhanced photocatalytic activity. New Journal of Chemistry. 2011;**35**:353-359

[12] Zhang Y, Pan C. TiO2/graphene composite from thermal reaction of graphene oxide and its photocatalytic activity in visible light. Journal of Materials Science. 2011;**46**:2622-2626

[13] Zhang J, Xiong Z, Zhao XS. Graphene-metal-oxide composites for the degradation of dyes under visible light irradiation. Journal of Materials Chemistry. 2011;**21**:3634-3640

[14] Zhang H, Xu P, Du G, Chen Z, Oh K, Pan D, et al. A facile one-step synthesis of TiO2/graphene composites for photodegradation of methyl orange. Nano Research. 2011;**4**:274-283

[15] Lee JS, You KH, Park CB. Highly photoactive, low bandgap TiO2 nanoparticles wrapped by graphene. Advanced Materials. 2012;**24**:1084-1088

[16] Wang F, Zhang K. Reduced graphene oxide-TiO2 nanocomposite with high photocatalystic activity for the degradation of rhodamine B. Journal of Molecular Catalysis A: Chemical. 2011;**345**:101-107

[17] Liu X, Pan L, Lv T, Zhu G, Lu T, Sun Z, et al. Microwave-assisted synthesis of TiO2-reduced graphene

oxide composites for the photocatalytic reduction of Cr (VI). RSC Advances. 2011;**1**:1245-1249

[18] Seema H, Shirinfar B, Shi G, Youn IS, Ahmed N. Facile synthesis of a selective biomolecule chemosensor and fabrication of its highly fluorescent graphene complex. The Journal of Physical Chemistry B. 2017;**121**:5007-5016

[19] Liu C, Teng Y, Liu R, Luo S, Tang Y, Chen L, et al. Fabrication of graphene films on TiO2 nanotube arrays for photocatalytic application. Carbon. 2011;**49**:5312-5320

[20] Li N, Liu G, Zhen C, Li F, Zhang L, Cheng HM. Battery performance and photocatalytic activity of mesoporous anatase TiO2 nanospheres/graphene composites by template-free selfassembly. Advanced Functional Materials. 2011;**21**:1717-1722

[21] Du J, Lai X, Yang N, Zhai J, Kisailus D, Su F, et al. Hierarchically ordered macromesoporous TiO2-graphene composite films: Improved mass transfer, reduced charge recombination, and their enhanced photocatalytic activities. ACS Nano. 2010;**5**:590-596

[22] Jiang B, Tian C, Zhou W, Wang J, Xie Y, Pan Q, et al. In situ growth of TiO2 in interlayers of expanded graphite for the fabrication of TiO2-graphene with enhanced photocatalytic activity. Chemistry–A European Journal. 2011;**17**:8379-8387

[23] Shirinfar B, Seema H, Ahmed N. Charged probes: Turn-on selective fluorescence for RNA. Organic & Biomolecular Chemistry. 2018;**16**:164-168

[24] Liang Y, Wang H, Casalongue HS, Chen Z, Dai H. TiO2 nanocrystals grown on graphene as advanced photocatalytic hybrid materials. Nano Research. 2010;**3**:701-705

[25] Akhavan O, Ghaderi E. Photocatalytic reduction of graphene oxide nanosheets on TiO2 thin film for photoinactivation of bacteria in solar light irradiation. The Journal of Physical Chemistry C. 2009;**113**:20214-20220

[26] Jiang B, Tian C, Pan Q, Jiang Z, Wang JQ, Yan W, et al. Enhanced photocatalytic activity and electron transfer mechanisms of graphene/TiO2 with exposed {001} facets. The Journal of Physical Chemistry C. 2011;**115**:23718-23725

[27] Sun L, Zhao Z, Zhou Y, Liu L. Anatase TiO2 nanocrystals with exposed {001} facets on graphene sheets via molecular grafting for enhanced photocatalytic activity. Nanoscale. 2012;**4**:613-620

[28] Guo J, Zhu S, Chen Z, Li Y, Yu Z, Liu Q, et al. Sonochemical synthesis of TiO2 nanoparticles on graphene for use as photocatalyst. Ultrasonics Sonochemistry. 2011;**18**:1082-1090

[29] Perera SD, Mariano RG, Vu K, Nour N, Seitz O, Chabal Y, et al. Hydrothermal synthesis of graphene-TiO2 nanotube composites with enhanced photocatalytic activity. ACS Catalysis. 2012;**2**:949-956

[30] Liu B, Huang Y, Wen Y, Du L, Zeng W, Shi Y, et al. Highly dispersive {001} facets-exposed nanocrystalline TiO2 on high quality graphene as a high performance photocatalyst. Journal of Materials Chemistry. 2012;**22**:7484-7491

[31] Zhao D, Sheng G, Chen C, Wang X. Enhanced photocatalytic degradation of methylene blue under visible irradiation on graphene@ TiO2 dyade structure. Applied Catalysis B: Environmental. 2012;**111**:303-308

[32] Gopalakrishnan K, Joshi HM, Kumar P, Panchakarla LS, Rao CN. Selectivity in the photocatalytic properties of the composites of TiO2

**29**

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

> performance of ZnO via graphene hybridization and the mechanism study. Applied Catalysis B: Environmental.

> Zhu G, Sun Z. Enhanced photocatalytic degradation of methylene blue by ZnO-reduced graphene oxide composite synthesized via microwave-assisted reaction. Journal of Alloys and Compounds. 2011;**509**:10086-10091

[42] Li B, Cao H. ZnO@ graphene composite with enhanced performance for the removal of dye from water. Journal of Materials Chemistry.

[43] Luo QP, Yu XY, Lei BX, Chen HY, Kuang DB, Su CY. Reduced graphene oxide-hierarchical ZnO hollow sphere composites with enhanced photocurrent

[44] Liu S, Tian J, Wang L, Luo Y, Sun X. One-pot synthesis of CuO nanoflowerdecorated reduced graphene oxide and its application to photocatalytic degradation of dyes. Catalysis Science &

and photocatalytic activity. The Journal of Physical Chemistry C.

Technology. 2012;**2**:339-344

[46] An X, Jimmy CY, Wang Y, Hu Y, Yu X, Zhang G. WO3 nanorods/ graphene nanocomposites for high-efficiency visible-light-driven photocatalysis and NO2 gas sensing. Journal of Materials Chemistry.

[47] Liu X, Pan L, Lv T, Zhu G, Sun Z, Sun C. Microwave-assisted synthesis of CdS-reduced graphene oxide

composites for photocatalytic reduction

[45] Seema H, Kemp KC, Chandra V, Kim KS. Graphene-SnO2 composites for highly efficient photocatalytic degradation of methylene blue under sunlight. Nanotechnology.

[41] Lv T, Pan L, Liu X, Lu T,

2011;**101**:382-387

2011;**21**:3346-3349

2012;**116**:8111-8117

2012;**23**:355705

2012;**22**:8525-8531

nanoparticles with B-and N-doped graphenes. Chemical Physics Letters.

[33] Seema H, Kemp KC, Le NH, Park SW, Chandra V, Lee JW, et al. Highly selective CO2 capture by S-doped microporous carbon materials. Carbon.

[34] Kamegawa T, Yamahana D,

activity. The Journal of Physical Chemistry C. 2010;**114**:15049-15053

Nanoscale. 2011;**3**:4411-4417

[36] Zhuo S, Shao M, Lee ST. Upconversion and downconversion fluorescent graphene quantum dots: Ultrasonic preparation and photocatalysis.

ACS Nano. 2012;**6**:1059-1064

[37] Kim IY, Lee JM, Kim TW, Kim HN, Kim HI, Choi W, et al. A strong electronic coupling between graphene nanosheets and layered titanate nanoplates: A soft-chemical route to highly porous nanocomposites with improved photocatalytic activity.

Small. 2012;**8**:1038-1048

2012;**22**:11765-11771

[39] Yang Y, Ren L, Zhang C,

Huang S, Liu T. Facile fabrication of functionalized graphene sheets (FGS)/ZnO nanocomposites with photocatalytic property. ACS Applied Materials & Interfaces. 2011;**3**:2779-2785

[40] Xu T, Zhang L, Cheng H, Zhu Y. Significantly enhanced photocatalytic

[38] Ren L, Qi X, Liu Y, Huang Z, Wei X, Li J, et al. Upconversion-P25-graphene composite as an advanced sunlight driven photocatalytic hybrid material. Journal of Materials Chemistry.

Yamashita H. Graphene coating of TiO2 nanoparticles loaded on mesoporous silica for enhancement of photocatalytic

[35] Wen Y, Ding H, Shan Y. Preparation and visible light photocatalytic activity of Ag/TiO2/graphene nanocomposite.

2011;**511**:304-308

2014;**66**:320-326

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

nanoparticles with B-and N-doped graphenes. Chemical Physics Letters. 2011;**511**:304-308

*Graphene and Its Derivatives - Synthesis and Applications*

[25] Akhavan O, Ghaderi E.

[26] Jiang B, Tian C, Pan Q, Jiang Z, Wang JQ, Yan W, et al. Enhanced photocatalytic activity and electron transfer mechanisms of graphene/TiO2 with exposed {001} facets. The Journal of Physical Chemistry C. 2011;**115**:23718-23725

[27] Sun L, Zhao Z, Zhou Y, Liu L. Anatase TiO2 nanocrystals with exposed {001} facets on graphene sheets via molecular grafting for enhanced photocatalytic activity. Nanoscale.

[28] Guo J, Zhu S, Chen Z, Li Y, Yu Z, Liu Q, et al. Sonochemical synthesis of TiO2 nanoparticles on graphene for use as photocatalyst. Ultrasonics Sonochemistry. 2011;**18**:1082-1090

[29] Perera SD, Mariano RG, Vu K, Nour N, Seitz O, Chabal Y, et al. Hydrothermal synthesis of graphene-TiO2 nanotube composites with enhanced photocatalytic activity. ACS

[30] Liu B, Huang Y, Wen Y, Du L, Zeng W, Shi Y, et al. Highly dispersive {001} facets-exposed nanocrystalline TiO2 on high quality graphene as a high performance photocatalyst. Journal of Materials Chemistry. 2012;**22**:7484-7491

[31] Zhao D, Sheng G, Chen C, Wang X. Enhanced photocatalytic degradation of methylene blue under visible irradiation on graphene@ TiO2 dyade structure. Applied Catalysis B: Environmental. 2012;**111**:303-308

[32] Gopalakrishnan K, Joshi HM, Kumar P, Panchakarla LS, Rao CN. Selectivity in the photocatalytic properties of the composites of TiO2

Catalysis. 2012;**2**:949-956

2012;**4**:613-620

Photocatalytic reduction of graphene oxide nanosheets on TiO2 thin film for photoinactivation of bacteria in solar light irradiation. The Journal of Physical Chemistry C. 2009;**113**:20214-20220

oxide composites for the photocatalytic reduction of Cr (VI). RSC Advances.

[19] Liu C, Teng Y, Liu R, Luo S, Tang Y, Chen L, et al. Fabrication of graphene films on TiO2 nanotube arrays for photocatalytic application. Carbon.

[20] Li N, Liu G, Zhen C, Li F, Zhang L, Cheng HM. Battery performance and photocatalytic activity of mesoporous anatase TiO2 nanospheres/graphene composites by template-free selfassembly. Advanced Functional Materials. 2011;**21**:1717-1722

[21] Du J, Lai X, Yang N, Zhai J, Kisailus D, Su F, et al. Hierarchically ordered macromesoporous TiO2-graphene composite films: Improved mass transfer, reduced charge recombination, and their enhanced photocatalytic activities. ACS

[22] Jiang B, Tian C, Zhou W, Wang J, Xie Y, Pan Q, et al. In situ growth of TiO2 in interlayers of expanded graphite for the fabrication of TiO2-graphene with enhanced photocatalytic activity. Chemistry–A European Journal.

[23] Shirinfar B, Seema H, Ahmed N. Charged probes: Turn-on selective fluorescence for RNA. Organic & Biomolecular Chemistry.

[24] Liang Y, Wang H, Casalongue HS, Chen Z, Dai H. TiO2 nanocrystals grown on graphene as advanced photocatalytic hybrid materials. Nano Research.

[18] Seema H, Shirinfar B, Shi G, Youn IS, Ahmed N. Facile synthesis of a selective biomolecule chemosensor

and fabrication of its highly fluorescent graphene complex. The Journal of Physical Chemistry B.

2011;**1**:1245-1249

2017;**121**:5007-5016

2011;**49**:5312-5320

Nano. 2010;**5**:590-596

2011;**17**:8379-8387

2018;**16**:164-168

2010;**3**:701-705

**28**

[33] Seema H, Kemp KC, Le NH, Park SW, Chandra V, Lee JW, et al. Highly selective CO2 capture by S-doped microporous carbon materials. Carbon. 2014;**66**:320-326

[34] Kamegawa T, Yamahana D, Yamashita H. Graphene coating of TiO2 nanoparticles loaded on mesoporous silica for enhancement of photocatalytic activity. The Journal of Physical Chemistry C. 2010;**114**:15049-15053

[35] Wen Y, Ding H, Shan Y. Preparation and visible light photocatalytic activity of Ag/TiO2/graphene nanocomposite. Nanoscale. 2011;**3**:4411-4417

[36] Zhuo S, Shao M, Lee ST. Upconversion and downconversion fluorescent graphene quantum dots: Ultrasonic preparation and photocatalysis. ACS Nano. 2012;**6**:1059-1064

[37] Kim IY, Lee JM, Kim TW, Kim HN, Kim HI, Choi W, et al. A strong electronic coupling between graphene nanosheets and layered titanate nanoplates: A soft-chemical route to highly porous nanocomposites with improved photocatalytic activity. Small. 2012;**8**:1038-1048

[38] Ren L, Qi X, Liu Y, Huang Z, Wei X, Li J, et al. Upconversion-P25-graphene composite as an advanced sunlight driven photocatalytic hybrid material. Journal of Materials Chemistry. 2012;**22**:11765-11771

[39] Yang Y, Ren L, Zhang C, Huang S, Liu T. Facile fabrication of functionalized graphene sheets (FGS)/ZnO nanocomposites with photocatalytic property. ACS Applied Materials & Interfaces. 2011;**3**:2779-2785

[40] Xu T, Zhang L, Cheng H, Zhu Y. Significantly enhanced photocatalytic performance of ZnO via graphene hybridization and the mechanism study. Applied Catalysis B: Environmental. 2011;**101**:382-387

[41] Lv T, Pan L, Liu X, Lu T, Zhu G, Sun Z. Enhanced photocatalytic degradation of methylene blue by ZnO-reduced graphene oxide composite synthesized via microwave-assisted reaction. Journal of Alloys and Compounds. 2011;**509**:10086-10091

[42] Li B, Cao H. ZnO@ graphene composite with enhanced performance for the removal of dye from water. Journal of Materials Chemistry. 2011;**21**:3346-3349

[43] Luo QP, Yu XY, Lei BX, Chen HY, Kuang DB, Su CY. Reduced graphene oxide-hierarchical ZnO hollow sphere composites with enhanced photocurrent and photocatalytic activity. The Journal of Physical Chemistry C. 2012;**116**:8111-8117

[44] Liu S, Tian J, Wang L, Luo Y, Sun X. One-pot synthesis of CuO nanoflowerdecorated reduced graphene oxide and its application to photocatalytic degradation of dyes. Catalysis Science & Technology. 2012;**2**:339-344

[45] Seema H, Kemp KC, Chandra V, Kim KS. Graphene-SnO2 composites for highly efficient photocatalytic degradation of methylene blue under sunlight. Nanotechnology. 2012;**23**:355705

[46] An X, Jimmy CY, Wang Y, Hu Y, Yu X, Zhang G. WO3 nanorods/ graphene nanocomposites for high-efficiency visible-light-driven photocatalysis and NO2 gas sensing. Journal of Materials Chemistry. 2012;**22**:8525-8531

[47] Liu X, Pan L, Lv T, Zhu G, Sun Z, Sun C. Microwave-assisted synthesis of CdS-reduced graphene oxide composites for photocatalytic reduction of Cr (vi). Chemical Communications. 2011;**47**:11984-11986

[48] Wang X, Tian H, Yang Y, Wang H, Wang S, Zheng W, et al. Reduced graphene oxide/CdS for efficiently photocatalytic degradation of methylene blue. Journal of Alloys and Compounds. 2012;**524**:5-12

[49] Ye A, Fan W, Zhang Q, Deng W, Wang Y. CdS–graphene and CdS– CNT nanocomposites as visible-light photocatalysts for hydrogen evolution and organic dye degradation. Catalysis Science & Technology. 2012;**2**:969-978

[50] Hu H, Wang X, Liu F, Wang J, Xu C. Rapid microwave-assisted synthesis of graphene nanosheets–zinc sulfide nanocomposites: Optical and photocatalytic properties. Synthetic Metals. 2011;**161**:404-410

[51] Xiong Z, Zhang LL, Zhao XS. Visible-light-induced dye degradation over copper-modified reduced graphene oxide. Chemistry–A European Journal. 2011;**17**:2428-2434

[52] Xiong Z, Zhang LL, Ma J, Zhao XS. Photocatalytic degradation of dyes over graphene-gold nanocomposites under visible light irradiation. Chemical Communications. 2010;**46**:6099-6101

[53] Fu Y, Wang X. Magnetically separable ZnFe2O4-graphene catalyst and its high photocatalytic performance under visible light irradiation. Industrial & Engineering Chemistry Research. 2011;**50**:7210-7218

[54] Fu Y, Xiong P, Chen H, Sun X, Wang X. High photocatalytic activity of magnetically separable manganese ferrite-graphene heteroarchitectures. Industrial & Engineering Chemistry Research. 2012;**51**:725-731

[55] Fu Y, Chen H, Sun X, Wang X. Graphene-supported nickel ferrite: A magnetically separable photocatalyst

with high activity under visible light. AIChE Journal. 2012;**58**:3298-3305

[56] Min YL, Zhang K, Chen YC, Zhang YG. Enhanced photocatalytic performance of Bi2WO6 by graphene supporter as charge transfer channel. Separation and Purification Technology. 2012;**86**:98-105

[57] Zhou F, Shi R, Zhu Y. Significant enhancement of the visible photocatalytic degradation performances of γ-Bi2MoO6 nanoplate by graphene hybridization. Journal of Molecular Catalysis A: Chemical. 2011;**340**:77-82

[58] Zhang X, Quan X, Chen S, Yu H. Constructing graphene/InNbO4 composite with excellent adsorptivity and charge separation performance for enhanced visible-light-driven photocatalytic ability. Applied Catalysis B: Environmental. 2011;**105**:237-422

[59] Ying H, Wang ZY, Guo ZD, Shi ZJ, YANG SF. Reduced graphene oxide-modified Bi2WO6 as an improved photocatalyst under visible light. Acta Physico-Chimica Sinica. 2011;**27**:1482-1486

[60] Bai S, Shen X, Zhong X, Liu Y, Zhu G, Xu X, et al. One-pot solvothermal preparation of magnetic reduced graphene oxide-ferrite hybrids for organic dye removal. Carbon. 2012;**50**:2337-2346

[61] Gao E, Wang W, Shang M, Xu J. Synthesis and enhanced photocatalytic performance of graphene-Bi2WO6 composite. Physical Chemistry Chemical Physics. 2011;**13**:2887-2893

[62] Zhang H, Fan X, Quan X, Chen S, Yu H. Graphene sheets grafted Ag@ AgCl hybrid with enhanced plasmonic photocatalytic activity under visible light. Environmental Science & Technology. 2011;**45**:5731-5736

**31**

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

> composites: Towards high-activity photocatalytic materials. Applied Catalysis B: Environmental.

> [71] Jiang G, Lin Z, Chen C, Zhu L, Chang Q, Wang N, et al. TiO2 nanoparticles assembled on

graphene oxide nanosheets with high photocatalytic activity for removal of pollutants. Carbon. 2011;**49**:2693-2701

[72] Chen C, Cai W, Long M, Zhou B, Wu Y, Wu D, et al. Synthesis of visiblelight responsive graphene oxide/TiO2 composites with p/n heterojunction.

ACS Nano. 2010;**4**:6425-6432

[73] Liao G, Chen S, Quan X, Yu H, Zhao H. Graphene oxide modified gC3N4 hybrid with enhanced photocatalytic capability under visible light irradiation.

Journal of Materials Chemistry.

ACS Nano. 2011;**5**:4529-4536

[74] Zhu M, Chen P, Liu M. Graphene oxide enwrapped Ag/AgX (X = Br, Cl) nanocomposite as a highly efficient visible-light plasmonic photocatalyst.

2012;**22**:2721-2726

2011;**106**:76-82

[63] Chen P, Xiao TY, Li HH, Yang JJ, Wang Z, Yao HB, et al. Nitrogen-doped graphene/ZnSe nanocomposites: Hydrothermal synthesis and their enhanced electrochemical and photocatalytic activities. ACS Nano.

[64] Zhang LL, Xiong Z, Zhao XS. Pillaring chemically exfoliated graphene

oxide with carbon nanotubes for photocatalytic degradation of dyes under visible light irradiation. ACS

[65] Krishnamoorthy K, Mohan R, Kim SJ. Graphene oxide as a

photocatalytic material. Applied Physics

[66] Zhang Q, He Y, Chen X, Hu D, Li L, Yin T, et al. Structure and photocatalytic properties of TiO2-graphene oxide intercalated composite. Chinese Science

Nano. 2010;**4**:7030-7036

Letters. 2011;**98**:244101

Bulletin. 2011;**56**:331-339

[67] Yoo DH, Cuong TV, Pham VH, Chung JS, Khoa NT, Kim EJ, et al. Enhanced photocatalytic activity of graphene oxide decorated on TiO2 films under UV and visible irradiation. Current

Applied Physics. 2011;**11**:805-808

[68] Nguyen-Phan TD, Pham VH, Shin EW, Pham HD, Kim S,

[69] Liu J, Bai H, Wang Y, Liu Z, Zhang X, Sun DD. Self-assembling TiO2 nanorods on large graphene oxide sheets at a two-phase interface and their anti-recombination in photocatalytic applications. Advanced Functional Materials. 2010;**20**:4175-4181

[70] Liu J, Liu L, Bai H, Wang Y, Sun DD. Gram-scale production of graphene oxide-TiO2 nanorod

2011;**170**:226-232

Chung JS, et al. The role of graphene oxide content on the adsorptionenhanced photocatalysis of titanium dioxide/graphene oxide composites. Chemical Engineering Journal.

2011;**6**:712-719

*Water Remediation by G-/GO-Based Photocatalysts DOI: http://dx.doi.org/10.5772/intechopen.85144*

*Graphene and Its Derivatives - Synthesis and Applications*

with high activity under visible light. AIChE Journal. 2012;**58**:3298-3305

[56] Min YL, Zhang K, Chen YC, Zhang YG. Enhanced photocatalytic performance of Bi2WO6 by graphene supporter as charge transfer channel. Separation and Purification Technology.

2012;**86**:98-105

2011;**340**:77-82

2011;**105**:237-422

2011;**27**:1482-1486

2012;**50**:2337-2346

[57] Zhou F, Shi R, Zhu Y. Significant enhancement of the visible photocatalytic degradation performances of γ-Bi2MoO6 nanoplate by graphene hybridization. Journal of Molecular Catalysis A: Chemical.

[58] Zhang X, Quan X, Chen S, Yu H. Constructing graphene/InNbO4 composite with excellent adsorptivity and charge separation performance for enhanced visible-light-driven photocatalytic ability. Applied Catalysis B: Environmental.

[59] Ying H, Wang ZY, Guo ZD, Shi ZJ, YANG SF. Reduced graphene oxide-modified Bi2WO6 as an

improved photocatalyst under visible light. Acta Physico-Chimica Sinica.

[60] Bai S, Shen X, Zhong X, Liu Y, Zhu G, Xu X, et al. One-pot

solvothermal preparation of magnetic reduced graphene oxide-ferrite hybrids for organic dye removal. Carbon.

[61] Gao E, Wang W, Shang M, Xu J. Synthesis and enhanced photocatalytic performance of graphene-Bi2WO6 composite. Physical Chemistry Chemical Physics. 2011;**13**:2887-2893

[62] Zhang H, Fan X, Quan X, Chen S, Yu H. Graphene sheets grafted Ag@ AgCl hybrid with enhanced plasmonic photocatalytic activity under visible light. Environmental Science & Technology. 2011;**45**:5731-5736

of Cr (vi). Chemical Communications.

2011;**47**:11984-11986

[48] Wang X, Tian H, Yang Y, Wang H, Wang S, Zheng W, et al. Reduced graphene oxide/CdS for efficiently photocatalytic degradation of methylene blue. Journal of Alloys and

Compounds. 2012;**524**:5-12

Metals. 2011;**161**:404-410

2011;**17**:2428-2434

2011;**50**:7210-7218

[51] Xiong Z, Zhang LL, Zhao XS. Visible-light-induced dye degradation over copper-modified reduced graphene oxide. Chemistry–A European Journal.

[52] Xiong Z, Zhang LL, Ma J, Zhao XS. Photocatalytic degradation of dyes over graphene-gold nanocomposites under visible light irradiation. Chemical Communications. 2010;**46**:6099-6101

[53] Fu Y, Wang X. Magnetically separable ZnFe2O4-graphene catalyst and its high photocatalytic performance under visible light irradiation. Industrial & Engineering Chemistry Research.

[54] Fu Y, Xiong P, Chen H, Sun X, Wang X. High photocatalytic activity of magnetically separable manganese ferrite-graphene heteroarchitectures. Industrial & Engineering Chemistry

[55] Fu Y, Chen H, Sun X, Wang X. Graphene-supported nickel ferrite: A magnetically separable photocatalyst

Research. 2012;**51**:725-731

[49] Ye A, Fan W, Zhang Q, Deng W, Wang Y. CdS–graphene and CdS– CNT nanocomposites as visible-light photocatalysts for hydrogen evolution and organic dye degradation. Catalysis Science & Technology. 2012;**2**:969-978

[50] Hu H, Wang X, Liu F, Wang J, Xu C. Rapid microwave-assisted synthesis of graphene nanosheets–zinc sulfide nanocomposites: Optical and photocatalytic properties. Synthetic

**30**

[63] Chen P, Xiao TY, Li HH, Yang JJ, Wang Z, Yao HB, et al. Nitrogen-doped graphene/ZnSe nanocomposites: Hydrothermal synthesis and their enhanced electrochemical and photocatalytic activities. ACS Nano. 2011;**6**:712-719

[64] Zhang LL, Xiong Z, Zhao XS. Pillaring chemically exfoliated graphene oxide with carbon nanotubes for photocatalytic degradation of dyes under visible light irradiation. ACS Nano. 2010;**4**:7030-7036

[65] Krishnamoorthy K, Mohan R, Kim SJ. Graphene oxide as a photocatalytic material. Applied Physics Letters. 2011;**98**:244101

[66] Zhang Q, He Y, Chen X, Hu D, Li L, Yin T, et al. Structure and photocatalytic properties of TiO2-graphene oxide intercalated composite. Chinese Science Bulletin. 2011;**56**:331-339

[67] Yoo DH, Cuong TV, Pham VH, Chung JS, Khoa NT, Kim EJ, et al. Enhanced photocatalytic activity of graphene oxide decorated on TiO2 films under UV and visible irradiation. Current Applied Physics. 2011;**11**:805-808

[68] Nguyen-Phan TD, Pham VH, Shin EW, Pham HD, Kim S, Chung JS, et al. The role of graphene oxide content on the adsorptionenhanced photocatalysis of titanium dioxide/graphene oxide composites. Chemical Engineering Journal. 2011;**170**:226-232

[69] Liu J, Bai H, Wang Y, Liu Z, Zhang X, Sun DD. Self-assembling TiO2 nanorods on large graphene oxide sheets at a two-phase interface and their anti-recombination in photocatalytic applications. Advanced Functional Materials. 2010;**20**:4175-4181

[70] Liu J, Liu L, Bai H, Wang Y, Sun DD. Gram-scale production of graphene oxide-TiO2 nanorod

composites: Towards high-activity photocatalytic materials. Applied Catalysis B: Environmental. 2011;**106**:76-82

[71] Jiang G, Lin Z, Chen C, Zhu L, Chang Q, Wang N, et al. TiO2 nanoparticles assembled on graphene oxide nanosheets with high photocatalytic activity for removal of pollutants. Carbon. 2011;**49**:2693-2701

[72] Chen C, Cai W, Long M, Zhou B, Wu Y, Wu D, et al. Synthesis of visiblelight responsive graphene oxide/TiO2 composites with p/n heterojunction. ACS Nano. 2010;**4**:6425-6432

[73] Liao G, Chen S, Quan X, Yu H, Zhao H. Graphene oxide modified gC3N4 hybrid with enhanced photocatalytic capability under visible light irradiation. Journal of Materials Chemistry. 2012;**22**:2721-2726

[74] Zhu M, Chen P, Liu M. Graphene oxide enwrapped Ag/AgX (X = Br, Cl) nanocomposite as a highly efficient visible-light plasmonic photocatalyst. ACS Nano. 2011;**5**:4529-4536

**33**

**Chapter 3**

**Abstract**

*Randhir Singh Bhoria*

the efficient modern electronics devices.

enhancement, organic solvents

**1. Introduction**

Enhancing Liquid Phase

Exfoliation of Graphene in

Organic Solvents with Additives

Graphene is the wonder carbon nanomaterial with excellent electrical, mechanical, chemical and optical properties suitable for the fabrication of modern electronics devices such as supercapacitors, sensors, FET etc. Liquid phase exfoliation is the economical, safe, facile method of graphene synthesis without the requirement of harmful chemicals, toxic gases. However, the low concentration of graphene (<0.01 mg/ml) obtained by this method limits its application in various fields. Various techniques have been employed for enhancing the graphene concentration in certain organic solvents. Addition of additives and salts can enhance the graphene concentration in organic solvents to some extent. In this chapter, the earlier work done in enhancing graphene concentration is explained. Further, this technique is employed for graphene concentration enhancement in solvents by using new salts and additives. The results obtained with various additives are compared and it was found that by adding anthracene in NMP solvent graphene concentration increases upto 0.04 mg/ml. This process can be easily scaled up for better performance, and resulting high concentration graphene can be used for the fabrication of

**Keywords:** graphene synthesis, liquid phase exfoliation, additives, concentration

Graphene is the most studied and explored nanomaterial with exceptional mechanical, electrical, optical and chemical properties. Graphene was discovered by Kostya Novoselov and Andre Geim via mechanical exfoliation method. Graphene has 2D hexagonal honeycomb structure made up of carbon atoms. Graphene is highly transparent as it reflects 2.3% and transmits 97.7% of light falling on it which makes it highly useful for making transparent conducting electrodes. Other exotic

modulus of 1.0 TPa. Graphene is approximately 200 times more conductive than copper and 100 times stronger than steel. In addition to this it is very flexible in

Because of its very high electrical conductivity, high transparency and flexibility it is being used for the fabrication of wide variety of devices such as flexible transparent displays, energy storage devices etc. Graphene can be prepared by various methods such as mechanical exfoliation, electrochemical, liquid phase exfoliation

 v<sup>−</sup><sup>1</sup> s<sup>−</sup><sup>1</sup>

), Young's

properties of graphene are high carrier mobility (200,000 cm2

nature as it can be stretched to 20% of its original length.

#### **Chapter 3**

## Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives

*Randhir Singh Bhoria*

#### **Abstract**

Graphene is the wonder carbon nanomaterial with excellent electrical, mechanical, chemical and optical properties suitable for the fabrication of modern electronics devices such as supercapacitors, sensors, FET etc. Liquid phase exfoliation is the economical, safe, facile method of graphene synthesis without the requirement of harmful chemicals, toxic gases. However, the low concentration of graphene (<0.01 mg/ml) obtained by this method limits its application in various fields. Various techniques have been employed for enhancing the graphene concentration in certain organic solvents. Addition of additives and salts can enhance the graphene concentration in organic solvents to some extent. In this chapter, the earlier work done in enhancing graphene concentration is explained. Further, this technique is employed for graphene concentration enhancement in solvents by using new salts and additives. The results obtained with various additives are compared and it was found that by adding anthracene in NMP solvent graphene concentration increases upto 0.04 mg/ml. This process can be easily scaled up for better performance, and resulting high concentration graphene can be used for the fabrication of the efficient modern electronics devices.

**Keywords:** graphene synthesis, liquid phase exfoliation, additives, concentration enhancement, organic solvents

#### **1. Introduction**

Graphene is the most studied and explored nanomaterial with exceptional mechanical, electrical, optical and chemical properties. Graphene was discovered by Kostya Novoselov and Andre Geim via mechanical exfoliation method. Graphene has 2D hexagonal honeycomb structure made up of carbon atoms. Graphene is highly transparent as it reflects 2.3% and transmits 97.7% of light falling on it which makes it highly useful for making transparent conducting electrodes. Other exotic properties of graphene are high carrier mobility (200,000 cm2 v<sup>−</sup><sup>1</sup> s<sup>−</sup><sup>1</sup> ), Young's modulus of 1.0 TPa. Graphene is approximately 200 times more conductive than copper and 100 times stronger than steel. In addition to this it is very flexible in nature as it can be stretched to 20% of its original length.

Because of its very high electrical conductivity, high transparency and flexibility it is being used for the fabrication of wide variety of devices such as flexible transparent displays, energy storage devices etc. Graphene can be prepared by various methods such as mechanical exfoliation, electrochemical, liquid phase exfoliation

and CVD method. This chapter uses liquid phase exfoliation method for the synthesis and concentration enhancement of graphene, after discussing its relative advantages over other techniques.

### **2. Graphene synthesis methods**

After the discovery of graphene a lot of research has been done for finding a suitable technique of graphene synthesis. Graphene synthesis method should be facile, economical and can be performed easily in the laboratory and should not require sophisticated equipment. Some of the most prominent graphene synthesis methods are described here (**Figure 1**).

#### **2.1 Mechanical exfoliation method**

Mechanical exfoliation method is the oldest and the simplest method, can be easily used in the college lab to prepare graphene of few micrometer length. It is called scotch tape method because here, a scotch tape repeatedly peels off various layers of graphene from the graphite source [1]. The disadvantage of this method is that it is time consuming and does not give graphene sheets of uniform thickness. Moreover, it is not a scalable method to produce high quality graphene sheets.

#### **2.2 Chemical exfoliation method**

Chemical exfoliation method uses harmful acids for the exfoliation of graphene sheets from graphite source. When graphite powder is mixed in solution of sulfuric acid and nitric acid, the inter-planar distance between individual graphene sheets

**35**

**Figure 2.**

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives*

treatment [5] are used for synthesis of graphene nanoribbons.

**2.3 Chemical vapor deposition (CVD) method**

temperature of 750–1200°C (**Figure 2**).

carrier density changes accordingly [26].

reducing agents such as hydrazine hydrate (**Figure 4**).

*Schematic illustration of CVD method of graphene synthesis.*

carbon source [22].

**2.4 Epitaxial growth on SiC**

**2.5 Hummer's method**

increases and hence exfoliation occurs [2]. The technique of increasing the interplanar distance between graphene sheets is called as intercalation [3]. The advantage of the intercalation is that after intercalation, the intercalated graphite can be easily exfoliated via sonication. Other processes such as ultrasonic heating [4], acid

CVD technique is used to produce good quality graphene on various substrates such as copper, nickel, cobalt etc. Here, the substrate is placed inside a furnace and hydrocarbon gas is passed at high temperatures. The carbon present in the hydrocarbon gas gets deposited on the substrate to form a graphene layer. Usually a mixture of hydrogen, argon and methane gas is passed through the furnace at

The CVD method is useful for scalable synthesis of high quality graphene. Using this method graphene has been successfully deposited upon various substrates such as Ni [6], Rh [7], Pt [8–11], Ir [12], Ru [13–16], Pd [17], Cu [18–21] using methane and ethylene. Graphene has also been prepared by using table sugar as a solid

Graphene layer can be grown on the silicon carbide substrate by heating at high temperature greater than 1100°C (**Figure 3**). The thickness of the graphene film which is prepared on SiC substrate depends upon size of the silicon carbide substrate because Si atoms are desorbed from surface during this process [23–25].

Whether SiC face is silicon or carbon terminated, graphene layer thickness and

Hummer's method is a well-known method to prepare high yield graphene. Here, graphite powder is first converted to graphite oxide with potassium permanganate, which is further converted into graphene oxide (GO) via sonication process. Graphene oxide is later reduced to reduced graphene oxide (rGO) using various

*DOI: http://dx.doi.org/10.5772/intechopen.81462*

**Figure 1.** *Various synthesis methods of graphene.*

increases and hence exfoliation occurs [2]. The technique of increasing the interplanar distance between graphene sheets is called as intercalation [3]. The advantage of the intercalation is that after intercalation, the intercalated graphite can be easily exfoliated via sonication. Other processes such as ultrasonic heating [4], acid treatment [5] are used for synthesis of graphene nanoribbons.

#### **2.3 Chemical vapor deposition (CVD) method**

CVD technique is used to produce good quality graphene on various substrates such as copper, nickel, cobalt etc. Here, the substrate is placed inside a furnace and hydrocarbon gas is passed at high temperatures. The carbon present in the hydrocarbon gas gets deposited on the substrate to form a graphene layer. Usually a mixture of hydrogen, argon and methane gas is passed through the furnace at temperature of 750–1200°C (**Figure 2**).

The CVD method is useful for scalable synthesis of high quality graphene. Using this method graphene has been successfully deposited upon various substrates such as Ni [6], Rh [7], Pt [8–11], Ir [12], Ru [13–16], Pd [17], Cu [18–21] using methane and ethylene. Graphene has also been prepared by using table sugar as a solid carbon source [22].

#### **2.4 Epitaxial growth on SiC**

*Graphene and Its Derivatives - Synthesis and Applications*

advantages over other techniques.

**2. Graphene synthesis methods**

methods are described here (**Figure 1**).

**2.1 Mechanical exfoliation method**

**2.2 Chemical exfoliation method**

sheets.

and CVD method. This chapter uses liquid phase exfoliation method for the synthesis and concentration enhancement of graphene, after discussing its relative

After the discovery of graphene a lot of research has been done for finding a suitable technique of graphene synthesis. Graphene synthesis method should be facile, economical and can be performed easily in the laboratory and should not require sophisticated equipment. Some of the most prominent graphene synthesis

Mechanical exfoliation method is the oldest and the simplest method, can be easily used in the college lab to prepare graphene of few micrometer length. It is called scotch tape method because here, a scotch tape repeatedly peels off various layers of graphene from the graphite source [1]. The disadvantage of this method is that it is time consuming and does not give graphene sheets of uniform thickness. Moreover, it is not a scalable method to produce high quality graphene

Chemical exfoliation method uses harmful acids for the exfoliation of graphene sheets from graphite source. When graphite powder is mixed in solution of sulfuric acid and nitric acid, the inter-planar distance between individual graphene sheets

**34**

**Figure 1.**

*Various synthesis methods of graphene.*

Graphene layer can be grown on the silicon carbide substrate by heating at high temperature greater than 1100°C (**Figure 3**). The thickness of the graphene film which is prepared on SiC substrate depends upon size of the silicon carbide substrate because Si atoms are desorbed from surface during this process [23–25].

Whether SiC face is silicon or carbon terminated, graphene layer thickness and carrier density changes accordingly [26].

#### **2.5 Hummer's method**

Hummer's method is a well-known method to prepare high yield graphene. Here, graphite powder is first converted to graphite oxide with potassium permanganate, which is further converted into graphene oxide (GO) via sonication process. Graphene oxide is later reduced to reduced graphene oxide (rGO) using various reducing agents such as hydrazine hydrate (**Figure 4**).

**Figure 2.** *Schematic illustration of CVD method of graphene synthesis.*

**Figure 3.**

*Process of epitaxial growth of graphene on SiC surface.*

#### **Figure 4.**

*Synthesis of reduced graphene oxide using Hummer's method.*

Most of rGO properties match with graphene, but due to structural defects in rGO, it does not produce high quality graphene. Moreover, because of the use of harmful and toxic chemicals, it is also not safe method.

#### **2.6 Electrochemical exfoliation method**

Electrochemical exfoliation method is another method for producing graphene from graphite rod in much shorter time as compared to CVD and Hummer's methods.

Typically, a platinum wire acts as cathode and graphite rod acts as anode (**Figure 5**).

Both anode and cathode are dipped in an electrolyte solution which is usually an acid solution such as sulfuric acid, phosphoric acid etc. After applying 10 V DC between anode and cathode, graphene exfoliation starts [27]. After 2 h graphene nanosheets accumulated in electrolyte are filtered, washed and dried for characterization using SEM, TEM etc. In this method of graphene synthesis also uses various toxic and harmful acids and chemicals.

**37**

**Figure 6.**

**Figure 5.**

*Electrochemical exfoliation of graphene.*

*Various steps involved in liquid phase exfoliation of graphene.*

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives*

Liquid phase exfoliation of graphene uses sonication process to exfoliate graphene from graphite in solvents. Graphite has various layers of graphene attached by Van der Waals forces which is overcome if the solvent used has surface tension

Dimethylformamide) and ODCB (ortho-dichlorobenzene). Typically, 2 g graphite powder is added to 300 ml of ODCB. This mixture is sonicated for 3 h. Then it is centrifuged for 30 min at 4000 rpm. (**Figure 6**) Finally supernatants are used for

**Table 1** shows that various synthesis methods have been explored by the researchers for graphene synthesis each having some disadvantages [29–34]. Hummer's method usually gives high-yield graphene but suffers from defects and impurities in graphene structure. So, rGO prepared by Hummer's method is not useful for the fabrication of electronics devices [35, 36]. Electronics devices fabrication requires good-quality defect-free graphene which can be easily prepared by

range. Some of the commonly used solvents are DMF (N,N-

*DOI: http://dx.doi.org/10.5772/intechopen.81462*

characterization using SEM and TEM [28].

**2.7 Liquid phase exfoliation**

near 40–50 mJ/m2

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives DOI: http://dx.doi.org/10.5772/intechopen.81462*

#### **2.7 Liquid phase exfoliation**

*Graphene and Its Derivatives - Synthesis and Applications*

*Process of epitaxial growth of graphene on SiC surface.*

Most of rGO properties match with graphene, but due to structural defects in rGO, it does not produce high quality graphene. Moreover, because of the use of

Electrochemical exfoliation method is another method for producing graphene from graphite rod in much shorter time as compared to CVD and Hummer's methods. Typically, a platinum wire acts as cathode and graphite rod acts as anode

Both anode and cathode are dipped in an electrolyte solution which is usually an acid solution such as sulfuric acid, phosphoric acid etc. After applying 10 V DC between anode and cathode, graphene exfoliation starts [27]. After 2 h graphene nanosheets accumulated in electrolyte are filtered, washed and dried for characterization using SEM, TEM etc. In this method of graphene synthesis also uses various

harmful and toxic chemicals, it is also not safe method.

**2.6 Electrochemical exfoliation method**

*Synthesis of reduced graphene oxide using Hummer's method.*

toxic and harmful acids and chemicals.

**36**

(**Figure 5**).

**Figure 4.**

**Figure 3.**

Liquid phase exfoliation of graphene uses sonication process to exfoliate graphene from graphite in solvents. Graphite has various layers of graphene attached by Van der Waals forces which is overcome if the solvent used has surface tension near 40–50 mJ/m2 range. Some of the commonly used solvents are DMF (N,N-Dimethylformamide) and ODCB (ortho-dichlorobenzene). Typically, 2 g graphite powder is added to 300 ml of ODCB. This mixture is sonicated for 3 h. Then it is centrifuged for 30 min at 4000 rpm. (**Figure 6**) Finally supernatants are used for characterization using SEM and TEM [28].

**Table 1** shows that various synthesis methods have been explored by the researchers for graphene synthesis each having some disadvantages [29–34]. Hummer's method usually gives high-yield graphene but suffers from defects and impurities in graphene structure. So, rGO prepared by Hummer's method is not useful for the fabrication of electronics devices [35, 36]. Electronics devices fabrication requires good-quality defect-free graphene which can be easily prepared by

**Figure 5.** *Electrochemical exfoliation of graphene.*

**Figure 6.** *Various steps involved in liquid phase exfoliation of graphene.*


*Note: The text is in italics to indicate that in this chapter liquid phase exfoliation method is used for the concentration enhancement of graphene.*

#### **Table 1.**

*Various graphene synthesis methods with advantages and disadvantages.*

liquid-phase exfoliation, and cannot be produced by Hummer's method [37–41]. The high quality graphene prepared by liquid-phase exfoliation is suitable for modern electronics device applications [42–47]. Graphene has high quantum capacitance [48], electrochemical properties [49] which can help to detect various explosives such as 2,4,6-trinitrotoluene [50], and generate chemiluminescence [51].

Although liquid phase exfoliation technique is the safe and environment friendly technique as compared to other graphene synthesis method, but its disadvantage is lower concentration of graphene obtained (usually less than 0.01 mg/ml). Therefore, there is a need of concentration enhancement of graphene for the fabrication of better and more efficient electronic devices.

#### **3. Process of concentration enhancement**

It has been experimentally found that graphene concentration can be enhanced by increasing sonication process time upto many weeks instead of hours which create defects in the graphene nanosheets [52]. Other approaches which have been utilized are mixed solvents [53–55], solvent exchange [56], solvothermal exfoliation [57, 58], intercalants [59–64]. It has been observed that Sodium hydroxide and naphthalene can enhance the graphene concentration in organic solvent [65, 66]. It has been experimentally found that solvents having surface tension near 40–50 mJ/ m2 are highly useful for graphene synthesis via sonication process. Some of the solvents satisfying this criterion such as 1-methyl-2-pyrrolidinone (NMP), benzyl benzoate (BB), 1,2-dichlorobenzene (ODCB), acetophenone (ACP), benzonitrile (BZN), dimethyl sulfoxide (DMSO) and 1,4-dioxane are used in concentration enhancement. It has been found that addition of organic salts can enhance the grapheme concentration in various organic solvents [67]. In addition to various salts, some additives such as phenolphthalein and anthracene have been explored for enhancing graphene concentration in solvents.

Initially, graphite powder is added to NMP, DMSO and CYN solvents (100 ml) with a concentration of 10 mg/ml. Then 100 mg of the additive or salt is added and sonicated for 3 h and centrifuged at 3000 rpm for 30 min (**Figure 7**). After centrifugation, supernatants are used for characterization using UV-Vis spectrum for finding graphene concentration by applying Lambert Beer's law.

**39**

**Figure 8.**

*UV-Vis spectrum of graphene.*

**Figure 7.**

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives*

UV-Vis spectrum plots the variation of absorbance with wavelength. This technique is based on the principle that the absorption in a particular wavelength range is directly proportional to the color of the sample used for characterization. From the UV-Vis spectrum it is observed that at a particular wavelength the absorbance is maximum. For pure graphene sample the peak absorbance is obtained near 270 nm (**Figure 8**). As the impurities and functional groups are introduced in graphene the

After plotting the UV-Vis spectrum curves we calculated the absorbance value at 660 nm wavelength. This absorbance A can be used to find the concentration of the graphene by applying Lambert Beer's law. So, according to the **Lambert Beer's law**

**A = C l**. (1)

*DOI: http://dx.doi.org/10.5772/intechopen.81462*

absorbance peak is shifted from 270 nm.

the absorbance in terms of concentration is given by:

where **A** is the absorbance measured at **660 nm**, **l** is the sample path length which is **1 cm**,

*Schematic diagram of liquid phase exfoliation of graphene with addition of additive.*

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives DOI: http://dx.doi.org/10.5772/intechopen.81462*

UV-Vis spectrum plots the variation of absorbance with wavelength. This technique is based on the principle that the absorption in a particular wavelength range is directly proportional to the color of the sample used for characterization. From the UV-Vis spectrum it is observed that at a particular wavelength the absorbance is maximum. For pure graphene sample the peak absorbance is obtained near 270 nm (**Figure 8**). As the impurities and functional groups are introduced in graphene the absorbance peak is shifted from 270 nm.

After plotting the UV-Vis spectrum curves we calculated the absorbance value at 660 nm wavelength. This absorbance A can be used to find the concentration of the graphene by applying Lambert Beer's law. So, according to the **Lambert Beer's law** the absorbance in terms of concentration is given by:

$$\mathbf{A} = \text{ or } \mathbf{C} \text{ l.} \tag{1}$$

where **A** is the absorbance measured at **660 nm**, **l** is the sample path length which is **1 cm**,

**Figure 7.**

*Graphene and Its Derivatives - Synthesis and Applications*

Chemical vapor deposition High quality, large area

Epitaxial growth on SiC Large continuous film,

Electrochemical exfoliation Lesser time, facile,

*Liquid phase exfoliation Easy, safe, high quality,* 

*Various graphene synthesis methods with advantages and disadvantages.*

Mechanical exfoliation

*enhancement of graphene.*

**Table 1.**

method

**Synthesis method Advantages Disadvantages**

graphene

good quality

economical

*economical*

Good quality, low yield Not a scalable process, low yield

conditions

conditions Not transferable

chemicals used

*graphene concentration*

High temperature and low vacuum

High temperature and low vacuum

DC voltage and electrolytes requirements

*Long sonication time requirement, low* 

better and more efficient electronic devices.

**3. Process of concentration enhancement**

for enhancing graphene concentration in solvents.

finding graphene concentration by applying Lambert Beer's law.

liquid-phase exfoliation, and cannot be produced by Hummer's method [37–41]. The high quality graphene prepared by liquid-phase exfoliation is suitable for modern electronics device applications [42–47]. Graphene has high quantum capacitance [48], electrochemical properties [49] which can help to detect various explosives such as 2,4,6-trinitrotoluene [50], and generate chemiluminescence [51]. Although liquid phase exfoliation technique is the safe and environment friendly technique as compared to other graphene synthesis method, but its disadvantage is lower concentration of graphene obtained (usually less than 0.01 mg/ml). Therefore, there is a need of concentration enhancement of graphene for the fabrication of

*Note: The text is in italics to indicate that in this chapter liquid phase exfoliation method is used for the concentration* 

Hummer's method High yield High defects in graphene, harmful

It has been experimentally found that graphene concentration can be enhanced by increasing sonication process time upto many weeks instead of hours which create defects in the graphene nanosheets [52]. Other approaches which have been utilized are mixed solvents [53–55], solvent exchange [56], solvothermal exfoliation [57, 58], intercalants [59–64]. It has been observed that Sodium hydroxide and naphthalene can enhance the graphene concentration in organic solvent [65, 66]. It has been experimentally found that solvents having surface tension near 40–50 mJ/

 are highly useful for graphene synthesis via sonication process. Some of the solvents satisfying this criterion such as 1-methyl-2-pyrrolidinone (NMP), benzyl benzoate (BB), 1,2-dichlorobenzene (ODCB), acetophenone (ACP), benzonitrile (BZN), dimethyl sulfoxide (DMSO) and 1,4-dioxane are used in concentration enhancement. It has been found that addition of organic salts can enhance the grapheme concentration in various organic solvents [67]. In addition to various salts, some additives such as phenolphthalein and anthracene have been explored

Initially, graphite powder is added to NMP, DMSO and CYN solvents (100 ml) with a concentration of 10 mg/ml. Then 100 mg of the additive or salt is added and sonicated for 3 h and centrifuged at 3000 rpm for 30 min (**Figure 7**). After centrifugation, supernatants are used for characterization using UV-Vis spectrum for

**38**

m2

*Schematic diagram of liquid phase exfoliation of graphene with addition of additive.*

**Figure 8.** *UV-Vis spectrum of graphene.*

#### **Figure 9.** *Representation of Lambert-Beer's law.*

**Figure 10.** *(a) TEM images, (b) SEM images of graphene exfoliated in NMP solvent.*

**C** is the graphene concentration in the sample,

**α** is the extinction coefficient.

This process of UV-Vis spectroscopy is shown in **Figure 9** below.

The absorbance value at 660 nm in the UV spectrum of graphene is used to calculate the graphene concentration with absorption coefficient value **α = 2460 ml/mg/m**.

It is observed that additives intercalate onto the graphitic layers which enhances graphene concentration by helping in the exfoliation process. The grapheme nanosheets produced by this process are used for the characterization using SEM and TEM. The TEM results of the grapheme nanosheets shows that single and fewlayered, overlapped nanosheets have been produce (**Figure 10**).

**Figure 10** shows the SEM results of the graphene nanosheets produced in NMP organic solvent which indicates that graphene sheets size varies from 5 μm to 20 μm.

#### **4. Concentration enhancement with salts and additives**

DMSO solvent is used for grapheme concentration enhancement by adding sodium tartrate (ST), sodium chloride (NaCl), potassium chloride (KCl), edetate

**41**

**Figure 11.**

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives*

observed that SC and ST produces maximum concentration in DMSO.

such as NMP, ODCB, BB, ACP, BZN etc. from their UV-Vis spectra.

low concentration may be again due to the aggregation effect.

*Concentration variation of graphene in DMSO solvent with addition of salts and additives.*

disodium (ED), sodium citrate (SC), naphthalene (N) and phenolphthalein (P) in it and analyzing their UV spectrum. The absorbance at 660 nm in UV spectrum is used for finding graphene concentration via Lambert Beer's law. By using this law graphene concentration is calculated and plotted in **Figure 11**. From **Figure 11** it is

The main reason of the concentration enhancement is that additives intercalates onto graphene layers and helps in exfoliation process. It is also observed that lesser time is required for exfoliation after adding additives. Further, in contrast to organic salts, the inorganic salt KCl does not enhances the graphene concentration in DMSO. One reason for low concentration may be the aggregation of graphene

Firstly, the UV-Vis spectrum of the various graphene samples (with and without

After repeating this procedure with the CYN solvents it is observed that in CYN maximum concentration is achieved by adding phenolphthalein additive. By adding phenolphthalein additive graphene concentration is increased upto nine times. But, as expected the inorganic salts such as CaCl, KCl does not enhance the graphene concentration. As compared to inorganic salts, organic salts are more useful for concentration enhancement with maximum concentration given by sodium citrate salt. **Figure 12** shows the UV spectra of NMP with and without adding salts and additives. There is a great change in graphene concentration in NMP solvent after adding salts and additives in it with maximum graphene concentration of 0.08 mg/ml in NMP was observed by adding anthracene additive in it. In comparison to organic salts, inorganic salt KCl does not increase the graphene concentration in NMP. This

**Figure 13** shows the effect of adding three additives anthracene, phenolphthalein, naphthalene in NMP, ODCB, BB, ACP, BZN, DMSO and 1,4-dioxane organic solvents. It has been observed that highest concentration is obtained by adding

addition of additives in DMSO) is used to find the absorbance value at 660 nm. This absorbance value A, with α the absorption coefficient is used to find graphene concentration as given by Beer's law, A = α C l. Here, A is the absorbance at 660 nm, l is sample path length (1 cm), C is concentration and constant α = 2460 ml/mg/m. This procedure is repeated to calculate the graphene concentration in other solvents

*DOI: http://dx.doi.org/10.5772/intechopen.81462*

nanosheets upon addition of KCl.

#### *Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives DOI: http://dx.doi.org/10.5772/intechopen.81462*

disodium (ED), sodium citrate (SC), naphthalene (N) and phenolphthalein (P) in it and analyzing their UV spectrum. The absorbance at 660 nm in UV spectrum is used for finding graphene concentration via Lambert Beer's law. By using this law graphene concentration is calculated and plotted in **Figure 11**. From **Figure 11** it is observed that SC and ST produces maximum concentration in DMSO.

The main reason of the concentration enhancement is that additives intercalates onto graphene layers and helps in exfoliation process. It is also observed that lesser time is required for exfoliation after adding additives. Further, in contrast to organic salts, the inorganic salt KCl does not enhances the graphene concentration in DMSO. One reason for low concentration may be the aggregation of graphene nanosheets upon addition of KCl.

Firstly, the UV-Vis spectrum of the various graphene samples (with and without addition of additives in DMSO) is used to find the absorbance value at 660 nm. This absorbance value A, with α the absorption coefficient is used to find graphene concentration as given by Beer's law, A = α C l. Here, A is the absorbance at 660 nm, l is sample path length (1 cm), C is concentration and constant α = 2460 ml/mg/m. This procedure is repeated to calculate the graphene concentration in other solvents such as NMP, ODCB, BB, ACP, BZN etc. from their UV-Vis spectra.

After repeating this procedure with the CYN solvents it is observed that in CYN maximum concentration is achieved by adding phenolphthalein additive. By adding phenolphthalein additive graphene concentration is increased upto nine times. But, as expected the inorganic salts such as CaCl, KCl does not enhance the graphene concentration. As compared to inorganic salts, organic salts are more useful for concentration enhancement with maximum concentration given by sodium citrate salt.

**Figure 12** shows the UV spectra of NMP with and without adding salts and additives. There is a great change in graphene concentration in NMP solvent after adding salts and additives in it with maximum graphene concentration of 0.08 mg/ml in NMP was observed by adding anthracene additive in it. In comparison to organic salts, inorganic salt KCl does not increase the graphene concentration in NMP. This low concentration may be again due to the aggregation effect.

**Figure 13** shows the effect of adding three additives anthracene, phenolphthalein, naphthalene in NMP, ODCB, BB, ACP, BZN, DMSO and 1,4-dioxane organic solvents. It has been observed that highest concentration is obtained by adding

**Figure 11.** *Concentration variation of graphene in DMSO solvent with addition of salts and additives.*

*Graphene and Its Derivatives - Synthesis and Applications*

*(a) TEM images, (b) SEM images of graphene exfoliated in NMP solvent.*

This process of UV-Vis spectroscopy is shown in **Figure 9** below.

layered, overlapped nanosheets have been produce (**Figure 10**).

**4. Concentration enhancement with salts and additives**

graphene concentration by helping in the exfoliation process. The grapheme nanosheets produced by this process are used for the characterization using SEM and TEM. The TEM results of the grapheme nanosheets shows that single and few-

The absorbance value at 660 nm in the UV spectrum of graphene is used to calculate the graphene concentration with absorption coefficient value **α = 2460 ml/mg/m**. It is observed that additives intercalate onto the graphitic layers which enhances

**Figure 10** shows the SEM results of the graphene nanosheets produced in NMP organic solvent which indicates that graphene sheets size varies from 5 μm to 20 μm.

DMSO solvent is used for grapheme concentration enhancement by adding sodium tartrate (ST), sodium chloride (NaCl), potassium chloride (KCl), edetate

**C** is the graphene concentration in the sample,

**α** is the extinction coefficient.

**40**

**Figure 10.**

**Figure 9.**

*Representation of Lambert-Beer's law.*

#### **Figure 12.**

*UV-Vis spectra of graphene in NMP solvent with and without addition of various salts and additives.*

anthracene in NMP solvent, with 0.04 mg/ml concentration. Anthracene additive acts as molecular wedge between the individual edges of graphite and results in higher concentration. Anthracene when intercalates between the graphene layers, it increases the interplanar spacing between adjacent nanosheets and enhances the exfoliation process. It is also observed that by adding larger amount of anthracene additive (>100 mg) in the solvents, much lower concentration is obtained due to f the aggregation effect. But as the additive amount decreases towards 100 mg, molecules are easily adsorbed onto graphene nanosheets which results in higher graphene concentration.

The structure of the additive and solvents also affects the concentration. Anthracene has structure of three benzene rings. Hence, those solvents which have benzene ring in its structure provides highest graphene concentration enhancement. It is found that solvents such as 1,4-dioxane and DMSO produces minimum graphene concentration as there is an absence of benzene ring structure in them [68]. NMP, BZN and ODCB exhibited maximum concentration of graphene

**43**

**Figure 14.**

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives*

because of benzene ring structures. Two organic solvents BB and ACP have side chains in addition to benzene ring which restricts their intercalation between the individual graphitic layers and hence provides least graphene concentration as

Various additives and salts have been explored for graphene concentration enhancement in NMP, ODCB, DMF, CYN, DMSO solvents. It has been observed that addition of phenolphthalein in CYN increases graphene concentration from 0.005 to 0.045 mg/ml. With addition of SC salt in DMSO solvent, graphene concentration increased from 0.002 to 0.015 mg/ml which is comparable to earlier

The effect of adding Anthracene additive in solvents NMP, DMSO, ODCB, BZN,ACP, BB and 1,4-dioxane have been explored and it has been observed that the concentration depends upon additive-solvent structures and interactions. Because the molecular structure of anthracene has three benzene rings, hence solvents with benzene ring structure produced maximum concentration such as NMP, BZN, ODCB solvents. The results obtained with various additives are compared and it was found that by adding anthracene in NMP solvent graphene concentration increases

This result is in agreement with earlier published work on naphthalene additive [26]. Here, it is found that anthracene is more useful in BZN solvent (three times concentration) than naphthalene in NMP solvent (two times concentration) [26]. The effect of anthracene in concentration enhancement is most prominent in 1-methyl-2-pyrrolidone (NMP), orthodichlorobenzene (ODCB) and BZN solvents as compared to others. With addition of anthracene, the graphene concentration in

From **Figure 13** it is observed that benzyl benzoate (BB) solvent is not very effective in concentration enhancement with anthracene. The least concentration is exhibited by the organic solvents acetophenone, benzyl benzoate, 1,4-dioxane and DMSO. With addition of anthracene, the graphene concentration in NMP and ODCB solvents is increased to 0.04 mg/ml [28]. From **Figure 14** a comparison of

NMP and ODCB solvents is increased to 0.04 mg/ml.

*Comparison of the enhanced concentration in this work with earlier published works.*

*DOI: http://dx.doi.org/10.5772/intechopen.81462*

compared to other solvents [68].

**5. Results and discussions**

published works [27].

upto 0.04 mg/ml.

because of benzene ring structures. Two organic solvents BB and ACP have side chains in addition to benzene ring which restricts their intercalation between the individual graphitic layers and hence provides least graphene concentration as compared to other solvents [68].

#### **5. Results and discussions**

*Graphene and Its Derivatives - Synthesis and Applications*

anthracene in NMP solvent, with 0.04 mg/ml concentration. Anthracene additive acts as molecular wedge between the individual edges of graphite and results in higher concentration. Anthracene when intercalates between the graphene layers, it increases the interplanar spacing between adjacent nanosheets and enhances the exfoliation process. It is also observed that by adding larger amount of anthracene additive (>100 mg) in the solvents, much lower concentration is obtained due to f the aggregation effect. But as the additive amount decreases towards 100 mg, molecules are easily adsorbed onto graphene nanosheets which results in higher

*Graphene concentration variation in seven organic solvents with and without addition of additives.*

*UV-Vis spectra of graphene in NMP solvent with and without addition of various salts and additives.*

The structure of the additive and solvents also affects the concentration. Anthracene has structure of three benzene rings. Hence, those solvents which have benzene ring in its structure provides highest graphene concentration enhancement. It is found that solvents such as 1,4-dioxane and DMSO produces minimum graphene concentration as there is an absence of benzene ring structure in them [68]. NMP, BZN and ODCB exhibited maximum concentration of graphene

**42**

**Figure 12.**

**Figure 13.**

graphene concentration.

Various additives and salts have been explored for graphene concentration enhancement in NMP, ODCB, DMF, CYN, DMSO solvents. It has been observed that addition of phenolphthalein in CYN increases graphene concentration from 0.005 to 0.045 mg/ml. With addition of SC salt in DMSO solvent, graphene concentration increased from 0.002 to 0.015 mg/ml which is comparable to earlier published works [27].

The effect of adding Anthracene additive in solvents NMP, DMSO, ODCB, BZN,ACP, BB and 1,4-dioxane have been explored and it has been observed that the concentration depends upon additive-solvent structures and interactions. Because the molecular structure of anthracene has three benzene rings, hence solvents with benzene ring structure produced maximum concentration such as NMP, BZN, ODCB solvents. The results obtained with various additives are compared and it was found that by adding anthracene in NMP solvent graphene concentration increases upto 0.04 mg/ml.

This result is in agreement with earlier published work on naphthalene additive [26]. Here, it is found that anthracene is more useful in BZN solvent (three times concentration) than naphthalene in NMP solvent (two times concentration) [26]. The effect of anthracene in concentration enhancement is most prominent in 1-methyl-2-pyrrolidone (NMP), orthodichlorobenzene (ODCB) and BZN solvents as compared to others. With addition of anthracene, the graphene concentration in NMP and ODCB solvents is increased to 0.04 mg/ml.

From **Figure 13** it is observed that benzyl benzoate (BB) solvent is not very effective in concentration enhancement with anthracene. The least concentration is exhibited by the organic solvents acetophenone, benzyl benzoate, 1,4-dioxane and DMSO. With addition of anthracene, the graphene concentration in NMP and ODCB solvents is increased to 0.04 mg/ml [28]. From **Figure 14** a comparison of

**Figure 14.** *Comparison of the enhanced concentration in this work with earlier published works.*

the graphene concentration enhancement in this work with the earlier published results has been made. The criterion of comparison is the how many times the concentration is increased with additives in various solvents such as CYN, BZN, DMSO, ODCB, NMP etc. From **Figure 14** it is observed that by adding additives graphene concentration is increased to approx. nine times in CYN solvent, approx. three times in BZN solvent, approx. seven times in DMSO solvents after experimental verification. On the other hand by observing earlier published results, graphene concentration was increased from 2.5 to 4.5 only in NMP solvent [69–71].

#### **6. Conclusion**

Generally liquid phase exfoliation produces graphene in low concentration (<0.01 mg/ml) which is not suitable for electronics device fabrication. Various additives and salts have been explored for enhancing graphene concentration in organic solvents such as DMSO, CYN, NMP, ODCB, DMF etc. In this study new additives such as phenolphthalein and anthracene have been found to enhance the graphene concentration in solvents such as NMP, ODCB, DMSO and BZN etc. By adding phenolphthalein in cyclohexanone (CYN) solvent the graphene concentration was increased from 0.005 to 0.045 mg/ml and by adding sodium citrate (SC) organic salt, the graphene concentration in dimethyl sulfoxide (DMSO) was increased from 0.002 to 0.015 mg/ml. Further, the effect of addition of anthracene additive in seven organic solvents NMP, DMSO, ODCB, BZN, ACP, BB and 1,4-dioxane have been studied. It was observed that the additive-solvent interactions affect the graphene production yield. Since, the molecular structure of additive anthracene having three benzene rings matches with structure of the solvents such as NMP, BZN, hence causes enhancement in the graphene concentration. The results obtained with various additives are compared and it was found that by adding anthracene in NMP solvent graphene concentration increases upto 0.04 mg/ml. A significant concentration enhancement (three times) was observed with addition of anthracene additive in BZN solvent as compared to two times enhancement with addition of naphthalene in NMP solvent.

#### **Author details**

Randhir Singh Bhoria University Institute of Engineering and Technology, Kurukshetra University, Kurukshetra, India

\*Address all correspondence to: mr\_randhir\_singh@yahoo.co.in

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**45**

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives*

Guinea F, et al. Physical Review Letters.

[17] Kwon SY, Ciobanu CV, Petrova V, Shenoy VB, Bareño J, Gambin V, et al.

[18] Kim KS, Zhao Y, Jang H, Lee SY, Kim JM, Kim KS, et al. Nature. 2009;**457**:706

[19] Jian X et al. Science. 2009;**323**:1701

[20] Reina A, Jia X, Ho J, Nezich D, Son H, Bulovic V, et al. Nano Letters.

[21] Li X et al. Science. 2009;**324**:1312

Tour JM. Nature. 2010;**468**:549

[22] Sun Z, Yan Z, Yao J, Beitler E, Zhu Y,

[23] Van Bommel AJ, Crombeen JE, van Tooren A. Surface Science. 1975;**48**:463

[24] Forbeaux I, Themlin J-M, Debever J-M. Physics Review B. 1998;**58**:16396

[26] Emtsev KV, Seyller T, Ley L, Tadich A, Broekman L, Riley JD, et al. Surface

[25] Charrier A, Coati A, Argunova TJ, Thibaudau F, Garreau Y, Pinchaux R, et al. Journal of Applied Physics.

2008;**100**:056807

2009;**9**:30

2002;**92**:2479

Science. 2006;**600**:3845

2013;**7**:3598-3606

2009;**10**:3460-3462

2012;**12**:2871

[27] Parvez K et al. ACS Nano.

[30] Park S, Ruoff RS. Nature Nanotechnology. 2009;**4**:217

[28] Hamilton CE et al. Nano Letters.

[29] Pham VH, Pham HD, Dang TT, Hur SH, Kim EJ, Kong BS, et al. Journal of Materials Chemistry. 2012;**22**:10530

[31] Park KH, Kim BH, Song SH, Kwon J, Kong BS, Kang K, et al. Nano Letters.

Nano Letters. 2009;**9**:395

*DOI: http://dx.doi.org/10.5772/intechopen.81462*

[1] Geim A, Novoselov K. Nature Materials. 2007;**6**:183-191

[2] Hernandez Y, Nicolosi V, Lotya M, Blighe F, Sun Z, De S, et al. Nature Nanotechnology. 2008;**3**:563-568

[3] Viculis L, Mack J, Kaner R. Science.

[4] Chen G, Weng W, Wu D, Wu C, Lu J, Wang P, et al. Carbon. 2004;**42**:753-759

[5] Li X, Wang X, Zhang L, Lee S, Dai

[6] Mattevi C, Kim H, Chhowalla M. Journal of Materials Chemistry.

[7] Eizenberg M, Blakely JM. Surface

[8] Castner DG, Sexton BA, Somorjai GA. Surface Science. 1978;**71**:519

[9] Lang B. Surface Science. 1975;**53**:317

[10] Land TA, Michely T, Behm RJ, Hemminger JC, Comsa G. Surface

[11] Sasaki M, Yamada Y, Ogiwara Y, Yagyu S, Yamamoto S. Physical Review

[12] N'Diaye A, Coraux J, Plasa T, Busse C, Michely T. New Journal of Physics.

DW. The Journal of Physical Chemistry.

[15] Marchini S, Günther S, Wintterlin J. Physical Review B. 2007;**76**:075429

[16] Vazquez de Parga AL, Calleja F, Borca B, Passeggi MCG Jr, Hinarejos JJ,

[13] Sutter PW, Flege JI, Sutter EA. Nature Materials. 2008;**7**:406

[14] Wu M-C, Xu Q, Goodman

H. Science. 2008;**319**:1229

2003;**299**:1361

**References**

2011;**21**:3324

Science. 1970;**82**:228

Science. 1992;**264**:261

B. 2000;**61**:15653

2008;**10**:043033

1994;**98**:5104

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives DOI: http://dx.doi.org/10.5772/intechopen.81462*

#### **References**

*Graphene and Its Derivatives - Synthesis and Applications*

the graphene concentration enhancement in this work with the earlier published results has been made. The criterion of comparison is the how many times the concentration is increased with additives in various solvents such as CYN, BZN, DMSO, ODCB, NMP etc. From **Figure 14** it is observed that by adding additives graphene concentration is increased to approx. nine times in CYN solvent, approx. three times in BZN solvent, approx. seven times in DMSO solvents after experimental verification. On the other hand by observing earlier published results, graphene

Generally liquid phase exfoliation produces graphene in low concentration (<0.01 mg/ml) which is not suitable for electronics device fabrication. Various additives and salts have been explored for enhancing graphene concentration in organic solvents such as DMSO, CYN, NMP, ODCB, DMF etc. In this study new additives such as phenolphthalein and anthracene have been found to enhance the graphene concentration in solvents such as NMP, ODCB, DMSO and BZN etc. By adding phenolphthalein in cyclohexanone (CYN) solvent the graphene concentration was increased from 0.005 to 0.045 mg/ml and by adding sodium citrate (SC) organic salt, the graphene concentration in dimethyl sulfoxide (DMSO) was increased from 0.002 to 0.015 mg/ml. Further, the effect of addition of anthracene additive in seven organic solvents NMP, DMSO, ODCB, BZN, ACP, BB and 1,4-dioxane have been studied. It was observed that the additive-solvent interactions affect the graphene production yield. Since, the molecular structure of additive anthracene having three benzene rings matches with structure of the solvents such as NMP, BZN, hence causes enhancement in the graphene concentration. The results obtained with various additives are compared and it was found that by adding anthracene in NMP solvent graphene concentration increases upto 0.04 mg/ml. A significant concentration enhancement (three times) was observed with addition of anthracene additive in BZN solvent as compared to two times enhancement with

concentration was increased from 2.5 to 4.5 only in NMP solvent [69–71].

**44**

**Author details**

**6. Conclusion**

Randhir Singh Bhoria

Kurukshetra, India

provided the original work is properly cited.

addition of naphthalene in NMP solvent.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

University Institute of Engineering and Technology, Kurukshetra University,

\*Address all correspondence to: mr\_randhir\_singh@yahoo.co.in

[1] Geim A, Novoselov K. Nature Materials. 2007;**6**:183-191

[2] Hernandez Y, Nicolosi V, Lotya M, Blighe F, Sun Z, De S, et al. Nature Nanotechnology. 2008;**3**:563-568

[3] Viculis L, Mack J, Kaner R. Science. 2003;**299**:1361

[4] Chen G, Weng W, Wu D, Wu C, Lu J, Wang P, et al. Carbon. 2004;**42**:753-759

[5] Li X, Wang X, Zhang L, Lee S, Dai H. Science. 2008;**319**:1229

[6] Mattevi C, Kim H, Chhowalla M. Journal of Materials Chemistry. 2011;**21**:3324

[7] Eizenberg M, Blakely JM. Surface Science. 1970;**82**:228

[8] Castner DG, Sexton BA, Somorjai GA. Surface Science. 1978;**71**:519

[9] Lang B. Surface Science. 1975;**53**:317

[10] Land TA, Michely T, Behm RJ, Hemminger JC, Comsa G. Surface Science. 1992;**264**:261

[11] Sasaki M, Yamada Y, Ogiwara Y, Yagyu S, Yamamoto S. Physical Review B. 2000;**61**:15653

[12] N'Diaye A, Coraux J, Plasa T, Busse C, Michely T. New Journal of Physics. 2008;**10**:043033

[13] Sutter PW, Flege JI, Sutter EA. Nature Materials. 2008;**7**:406

[14] Wu M-C, Xu Q, Goodman DW. The Journal of Physical Chemistry. 1994;**98**:5104

[15] Marchini S, Günther S, Wintterlin J. Physical Review B. 2007;**76**:075429

[16] Vazquez de Parga AL, Calleja F, Borca B, Passeggi MCG Jr, Hinarejos JJ, Guinea F, et al. Physical Review Letters. 2008;**100**:056807

[17] Kwon SY, Ciobanu CV, Petrova V, Shenoy VB, Bareño J, Gambin V, et al. Nano Letters. 2009;**9**:395

[18] Kim KS, Zhao Y, Jang H, Lee SY, Kim JM, Kim KS, et al. Nature. 2009;**457**:706

[19] Jian X et al. Science. 2009;**323**:1701

[20] Reina A, Jia X, Ho J, Nezich D, Son H, Bulovic V, et al. Nano Letters. 2009;**9**:30

[21] Li X et al. Science. 2009;**324**:1312

[22] Sun Z, Yan Z, Yao J, Beitler E, Zhu Y, Tour JM. Nature. 2010;**468**:549

[23] Van Bommel AJ, Crombeen JE, van Tooren A. Surface Science. 1975;**48**:463

[24] Forbeaux I, Themlin J-M, Debever J-M. Physics Review B. 1998;**58**:16396

[25] Charrier A, Coati A, Argunova TJ, Thibaudau F, Garreau Y, Pinchaux R, et al. Journal of Applied Physics. 2002;**92**:2479

[26] Emtsev KV, Seyller T, Ley L, Tadich A, Broekman L, Riley JD, et al. Surface Science. 2006;**600**:3845

[27] Parvez K et al. ACS Nano. 2013;**7**:3598-3606

[28] Hamilton CE et al. Nano Letters. 2009;**10**:3460-3462

[29] Pham VH, Pham HD, Dang TT, Hur SH, Kim EJ, Kong BS, et al. Journal of Materials Chemistry. 2012;**22**:10530

[30] Park S, Ruoff RS. Nature Nanotechnology. 2009;**4**:217

[31] Park KH, Kim BH, Song SH, Kwon J, Kong BS, Kang K, et al. Nano Letters. 2012;**12**:2871

[32] Lu WB, Liu S, Qin XY, Wang L, Tian JQ, Luo YL, et al. Journal of Materials Chemistry. 2012;**22**:8775

[33] Tien HN, Luan VH, Lee TK, Kong BS, Chung JS, Kim EJ, et al. Chemical Engineering Journal. 2012;**211**:97

[34] Nguyen-Phan TD, Pham VH, Shin EW, Pham HD, Kim S, Chung JS, et al. Chemical Engineering Journal. 2011;**170**:226

[35] Cai M, Thorpe D, Adamson DH, Schniepp HC. Journal of Materials Chemistry. 2012;**22**:24992

[36] Viet HP, Tran VC, Hur SH, Oh E, Kim EJ, Shin EW, et al. Journal of Materials Chemistry. 2011;**21**:3371

[37] Hirsch A, Englert JM, Hauke F. Accounts of Chemical Research. 2013;**46:87**

[38] Loh KP, Bao Q, Ang PK, Yang J. Materials Chemistry. 2010;**20**:2277

[39] Ou EC, Xie YY, Peng C, Song YW, Peng H, Xiong YQ, et al. RSC Advances. 2013;**3**:9490

[40] Barwich S, Khan U, Coleman JN. Journal of Physical Chemistry C. 2013;**117**:19212

[41] Feng L, Liu Y-W, Tang X-Y, Piao Y, Chen S-F, Deng S-L, et al. Chemistry of Materials. 2013;**25**:4487

[42] Lotya M, Hernandez Y, King PJ, Smith RJ, Nicolosi V, Karlsson LS, et al. American Chemical Society. 2009;**131**:3611

[43] De S, Coleman JN. ACS Nano. 2010;**4**:2713

[44] De S, King PJ, Lotya M, OÕNeill A, Doherty EM, Hernandez Y, Duesberg GS, Coleman JN. Small. 2010;**6**:458

[45] Hernandez Y, Nicolosi V, Lotya M, Blighe FM, Sun Z, De S, et al. Nature Nanotechnology. 2008;**3**:563

[46] Du W, Lu J, Sun P, Zhu Y, Jiang X. Chemical Physics Letters. 2013;**198**:568-569

[47] Lin Y, Jin J, Kusmartsevab O, Song M. Journal of Physical Chemistry C. 2013;**117**:17237

[48] Jilin X, Fang C, Jinghong L, Nongjian T. Nature Nanotechnology. 2009;**4**:505-509

[49] Tang L, Wang Y, Li Y, Feng H, Jin L, Li J. Advanced Functional Materials. 2009;**19**:2782-2789

[50] Tang L, Feng H, Cheng J, Li J. Chemical Communications. 2010;**46**:5882

[51] Chen D, Feng H, Li J. Chemical Reviews. 2012;**112**:6027-6053

[52] Coleman JN. Accounts of Chemical Research. 2013;**46**:14

[53] Oyer AJ, Carrillo J-MY, Hire CC, Schniepp HC, Asandei AD, Dobrynin AV, et al. American Chemical Society. 2012;**134**:5018

[54] Yi M, Shen ZG, Ma SL, Zhang XJ. Journal of Nanoparticle Research. 2012;**1003**:14

[55] Yi M, Shen Z, Zhang X, Ma. Journal of Physics D: Applied Physics. 2013;**46**:025301

[56] Li JT, Ye F, Vaziri S, Muhammed M, Lemme MC, Ostling M. Carbon. 2012;**50**:3113

[57] Qian W, Hao R, Hou Y, Tian Y, Shen C, Gao H, et al. Nano Research. 2009;**2**:706

[58] Tang ZH, Zhuang J, Wang X. Langmuir. 2010;**26**:9045

[59] Yang H, Hernandez Y, Schlierf A, Felten A, Eckmann A, Johal S, et al. Carbon. 2013;**53**:357

**47**

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives*

[71] Wencheng D, Lu J, Sun P, Zhu Y, Jiang X. Organic salt-assisted liquidphase exfoliation of graphite to produce high-quality graphene. Chemical Physics Letters. 2013;**568-569**:198-201

*DOI: http://dx.doi.org/10.5772/intechopen.81462*

[60] An X, Simmons T, Shah R, Wolfe C, Lewis KM, Washing-ton M, et al. Nano

[62] Parviz D, Das S, Ahmed HST, Irin F, Bhattacharia S, Green MJ. ACS Nano.

[63] Xu L, McGraw J-W, Gao F, Grundy M, Ye Z, Gu Z, et al. Journal of Physical Chemistry C. 2013;**117**:10730

[61] Liu WW, Wang JN. Chemical Communications. 2011;**47**:6888

Letters. 2010;**10**:4295

[64] Pykal M, Šafarova K, MachalovaŠiškova K, Jureÿcka P, Bourlinos AB, Zboÿril R, et al. Journal of Physical Chemistry C. 2013;**117**:11800

[65] Wei Liu W, Nong Wang J. The royal society of chemistry. Chemical Communications. 2011;**47**:6888

[66] Xu J, Dang DK, Tran VT, Liu X, Chung JS, et al. Journal of Colloid and Interface Science. 2014;**418**:37-42

[68] Singh R, Tripathi CC. Enhancing Liquid-Phase Exfoliation of Graphene with Addition of Anthracene in Organic Solvents. Arabian Journal for Science and Engineering. 2017;**42**(6):2417-2424

[69] Haar S, El Gemayel M, Shin Y, Melinte G, Squillaci MA, Ersen O, et al. Enhancing the liquid-phase exfoliation of graphene in organic solvents upon addition of n-octylbenzene. Nature, Scientific Reports. 2015;**5** (Article

[70] Liua WW, Wang JN. Direct exfoliation of graphene in organic solvents with addition of NaOH. Chemical Communications.

[67] Du W, Lu J, Sun P, Zhu Y, Jiang X. Chemical Physics Letters.

2013;**568**:198-201

number: 16684)

2011;**47**:6888-6890

2012;**6**:8857

*Enhancing Liquid Phase Exfoliation of Graphene in Organic Solvents with Additives DOI: http://dx.doi.org/10.5772/intechopen.81462*

[60] An X, Simmons T, Shah R, Wolfe C, Lewis KM, Washing-ton M, et al. Nano Letters. 2010;**10**:4295

[61] Liu WW, Wang JN. Chemical Communications. 2011;**47**:6888

[62] Parviz D, Das S, Ahmed HST, Irin F, Bhattacharia S, Green MJ. ACS Nano. 2012;**6**:8857

[63] Xu L, McGraw J-W, Gao F, Grundy M, Ye Z, Gu Z, et al. Journal of Physical Chemistry C. 2013;**117**:10730

[64] Pykal M, Šafarova K, MachalovaŠiškova K, Jureÿcka P, Bourlinos AB, Zboÿril R, et al. Journal of Physical Chemistry C. 2013;**117**:11800

[65] Wei Liu W, Nong Wang J. The royal society of chemistry. Chemical Communications. 2011;**47**:6888

[66] Xu J, Dang DK, Tran VT, Liu X, Chung JS, et al. Journal of Colloid and Interface Science. 2014;**418**:37-42

[67] Du W, Lu J, Sun P, Zhu Y, Jiang X. Chemical Physics Letters. 2013;**568**:198-201

[68] Singh R, Tripathi CC. Enhancing Liquid-Phase Exfoliation of Graphene with Addition of Anthracene in Organic Solvents. Arabian Journal for Science and Engineering. 2017;**42**(6):2417-2424

[69] Haar S, El Gemayel M, Shin Y, Melinte G, Squillaci MA, Ersen O, et al. Enhancing the liquid-phase exfoliation of graphene in organic solvents upon addition of n-octylbenzene. Nature, Scientific Reports. 2015;**5** (Article number: 16684)

[70] Liua WW, Wang JN. Direct exfoliation of graphene in organic solvents with addition of NaOH. Chemical Communications. 2011;**47**:6888-6890

[71] Wencheng D, Lu J, Sun P, Zhu Y, Jiang X. Organic salt-assisted liquidphase exfoliation of graphite to produce high-quality graphene. Chemical Physics Letters. 2013;**568-569**:198-201

**46**

*Graphene and Its Derivatives - Synthesis and Applications*

[46] Du W, Lu J, Sun P, Zhu Y, Jiang X. Chemical Physics Letters.

[47] Lin Y, Jin J, Kusmartsevab O, Song M. Journal of Physical Chemistry C.

[49] Tang L, Wang Y, Li Y, Feng H, Jin L, Li J. Advanced Functional Materials.

[50] Tang L, Feng H, Cheng J, Li J. Chemical Communications.

[51] Chen D, Feng H, Li J. Chemical Reviews. 2012;**112**:6027-6053

[52] Coleman JN. Accounts of Chemical

[53] Oyer AJ, Carrillo J-MY, Hire CC, Schniepp HC, Asandei AD, Dobrynin AV, et al. American Chemical Society.

[54] Yi M, Shen ZG, Ma SL, Zhang XJ. Journal of Nanoparticle Research.

[56] Li JT, Ye F, Vaziri S, Muhammed M, Lemme MC, Ostling M. Carbon.

[57] Qian W, Hao R, Hou Y, Tian Y, Shen C, Gao H, et al. Nano Research.

[58] Tang ZH, Zhuang J, Wang X.

[59] Yang H, Hernandez Y, Schlierf A, Felten A, Eckmann A, Johal S, et al.

Langmuir. 2010;**26**:9045

Carbon. 2013;**53**:357

[55] Yi M, Shen Z, Zhang X, Ma. Journal of Physics D: Applied Physics.

[48] Jilin X, Fang C, Jinghong L, Nongjian T. Nature Nanotechnology.

2013;**198**:568-569

2013;**117**:17237

2009;**4**:505-509

2009;**19**:2782-2789

Research. 2013;**46**:14

2012;**134**:5018

2012;**1003**:14

2013;**46**:025301

2012;**50**:3113

2009;**2**:706

2010;**46**:5882

[32] Lu WB, Liu S, Qin XY, Wang L, Tian JQ, Luo YL, et al. Journal of Materials Chemistry. 2012;**22**:8775

Chung JS, Kim EJ, et al. Chemical Engineering Journal. 2012;**211**:97

[34] Nguyen-Phan TD, Pham VH, Shin EW, Pham HD, Kim S, Chung JS, et al. Chemical Engineering Journal.

[35] Cai M, Thorpe D, Adamson DH, Schniepp HC. Journal of Materials

[36] Viet HP, Tran VC, Hur SH, Oh E, Kim EJ, Shin EW, et al. Journal of Materials Chemistry. 2011;**21**:3371

[37] Hirsch A, Englert JM, Hauke F. Accounts of Chemical Research.

[38] Loh KP, Bao Q, Ang PK, Yang J. Materials Chemistry. 2010;**20**:2277

[39] Ou EC, Xie YY, Peng C, Song YW, Peng H, Xiong YQ, et al. RSC Advances.

[40] Barwich S, Khan U, Coleman JN. Journal of Physical Chemistry C.

[41] Feng L, Liu Y-W, Tang X-Y, Piao Y, Chen S-F, Deng S-L, et al. Chemistry of

[42] Lotya M, Hernandez Y, King PJ, Smith RJ, Nicolosi V, Karlsson LS, et al. American Chemical Society.

[43] De S, Coleman JN. ACS Nano.

[44] De S, King PJ, Lotya M, OÕNeill A, Doherty EM, Hernandez Y, Duesberg GS, Coleman JN. Small. 2010;**6**:458

[45] Hernandez Y, Nicolosi V, Lotya M, Blighe FM, Sun Z, De S, et al. Nature

Nanotechnology. 2008;**3**:563

Chemistry. 2012;**22**:24992

2011;**170**:226

2013;**46:87**

2013;**3**:9490

2013;**117**:19212

2009;**131**:3611

2010;**4**:2713

Materials. 2013;**25**:4487

[33] Tien HN, Luan VH, Lee TK, Kong BS,

**49**

Section 2

Graphene Applications

Section 2
