**3. Heterogeneous GO-based photocatalytic materials**

of photo-activated catalysts have been limited by the relatively low-efficiency resulting in a

The abundance of functional epoxide and hydroxyl groups on graphene oxide (GO) surfaces with the edges and rim sites around vacancies being decorated with pendant carboxylic acid, quinoidal, ketone, and lactone groups enables binding of active sites. Fortunately, the oxygenated groups can largely expand the structural/chemical diversity of GO by further chemical modification or functionalization, which offer an effective way to tailor the physical and chemical properties of GO to expected extents. Besides, GO also displays excellent optical and mechanical properties for a wide landscape of applications. Furthermore, the residual defects and holes arise through the reduction process of GO degrade the electronic quality of r-GO. As a consequence, GO, and GO-based composites have shown great potentials in the

The properties of GO such as readily dispersible in water at the molecular level, biocompatibility, and tunable band gap motivated researchers to explore its potential as photocatalytic material. Furthermore, GO combines two complementary qualities, electrons imbibition, and consumption. The electrons imbibition property stimulates the interfacial electron-transfer

promoting of the photocatalytic response. Simultaneously, the consumption of the received electrons occurs during the partial reduction of GO to reconstruct the conjugated network of the graphene under ultraviolet (UV) assistance. This sensation leads to efficient charge separation and the possibility of more interactions between the composite and targeted organic

Supported photocatalysts are a properly evolved concept in imparting progressed exposure of the catalysts to reactants and is common in industrial catalytic technologies. In this type of configuration, however, the nature of the photocatalyst-support interactions is important. For durable overall performance, a strong chemical bond is necessary, however, the influences of

lar surface area within the range from 50 to 300 m2 g−1, which in turn helps in keeping off mass

a very low photocatalytic activity because of the rapid recombination of conduction band (CB) electrons and valence band (VB) holes. However, a light transport limitation appears

the water after the remedy. To overcome this, the catalyst particles can be immobilized on a surface. In addition, this may lower the oxidation capacity in keeping with volume of water as compared to the suspension of solid particles system, due to the mass transfer difficulty and

, actively limiting the chance of charge carriers recombination with a striking

/GO composites extend the absorbable light range from the UV

in suspension

alone showed

particles from

powders have a high particu-

growing research activity to improve this technique.

108 Graphene Oxide - Applications and Opportunities

process from TiO2

compounds. In addition, TiO2

into the visible region.

applications of energy storage/conversion and environment protection.

**2. Supported photocatalysts onto graphene oxide (GO)**

is effective in capturing sunlight due to the fact suspended TiO<sup>2</sup>

bonding on photocatalytic mechanisms are considered. The application of TiO2

transfer limitation, ensuing in a high photocatalytic activity. Moreover, TiO<sup>2</sup>

with excessive catalyst loading. Besides, it is difficult to separate the small TiO<sup>2</sup>

Research series conducted by Fujishima and Honda pull the trigger of scientific research of photocatalysis stimulation. Their initial demonstration was based on the activation of a semiconductor particulate material by the action of radiation with an appropriate wavelength to catalyze the dissociation of water. Since this time, several photocatalysts have been subject to extensive studies. In general, when a semiconductor photocatalyst material undergoes irradiation with a light of suitable wavelength, an electron gain a quantum of energy sufficient to its promotion to the CB. This electron transmission causes a positive hole in the VB. The electron in the CB and the hole in the VB are responsible for reduction or oxidation of any substrate, respectively, as shown in **Figure 1**. The role of graphene-metal oxide composites as photocatalysts, adsorbents, and disinfectants in water treatment was previously reviewed [1].

**Figure 1.** Simplification of photocatalysis mechanism.

#### **3.1. Binary metal oxides**

Titanium oxide (TiO2 ) is the first and most important binary transition metal oxides that have been studied in the field of photocatalysis. TiO<sup>2</sup> is characterized by chemical stability and non-solubility in the aqueous medium, which facilitates the process of separation after the desired reactions. Moreover, photocatalytic stimulation is primarily aimed at environmental applications; therefore, non-toxicity of titanium dioxide is also favorable. Other n-type semiconductor binary oxides with a d-transition metal such as WO3 , Fe2 O3 , Nb2 O5 , V<sup>2</sup> O5 , NiO, Ta2 O5 , ZrO2 , CuO, and Cu2 O have been studied. In addition, binary metal oxides of elements other than transition metals such as ZnO, Ga2 O3 , Sb2 O3 , Bi2 O3 , and CeO2 had also some attention. Although ZnO suffers from photocorrosion, it is photocatalytic activity is comparable with TiO2 . Furthermore, the photocorrosion process can be controlled by monitoring of the operational factors such as the pH, additives, and ZnO crystal growth.

[2–4] NiO, [5] WO3

the photocatalytic H<sup>2</sup>

**3.3. Multiple compounds**

and 5 s in Sn2+ or 4d in Ag+

lyst. For instance, the Bi2

transfer channel [29].

Bi2 WO6

The photocatalytic activity of Bi2

of organic pollutants and water splitting.

WO6

WO6

as an enhanced photocatalyst.

**3.2. Non-oxidic binary compounds**

time to fabricate GO/ZnS, GO/CdS, and GO/Bi2

, [6] CuO, [7], and Mn<sup>3</sup>

group 16 in the periodic table. Chalcogenide such as CdS, ZnS, Sb<sup>2</sup>

their poor photocatalytic activity for oxidation of organic pollutants [26].

hole pair recombination in metal sulfides due to the introduction of GO.

upon irradiation with UV-visible or visible light, respectively [28].

O4

Many photocatalytic substances contain no oxygen, but still have another element of

CdTe give a good example of such materials. Sulfides other than zinc sulfide have an absorption edge compatible with solar energy utilization rather than photocatalytic processes. Unfortunately, sulfides have the disadvantage of photo-induced corrosion. Cadmium selenides and tellurides have a valence band redox potential lower than 1.23 V. This explains

A simple and high-yield room-temperature solid-state method was employed for the first

sulfide composites were used as photocatalysts for the degradation of methyl orange under UV irradiation. The composites exhibited superior photocatalytic activity to pure metal sulfides, owing to the high specific surface area, and the reduction of photo-induced electron-

However, incorporation of non-oxidic binary compounds alone with GO is superfluous. They are often introduced to the GO surface with each other or with different photocatalytic materials. The association of ZnS-CdS with GO to form the ZnS-CdS/GO heterostructure for

rate. Moreover, doping ZnS-CdS/GO heterostructure with 2 wt% Pt nanoparticles to serve as co-catalysts, the hydrogen generation rate is significantly elevated to 1.68 and 0.78 mmol h−1

Metallates of elements of the middle region of the periodic table and cations with filled or partially filled orbitals in their outer shell, which may hybridize with the oxygen 2p orbitals. Aluminates, ferrites, niobates, tantalates, titanates, tungstates, and vanadates are some examples of these metallates. While the examples of those cations are 6 s orbitals in Pb2+ and Bi3+,

and oxyhalides have also been investigated for evaluation of their activity in the degradation

Incorporation of metallates with GO has also been investigated as an enhanced photocata-

refluxing method in the presence of GO. The photocatalytic degradation of rhodamine B under visible light irradiation was utilized to evaluate the photocatalytic performance.

. The enhanced photocatalytic activity could be attributed to that GO as charge

gas generation result in the duplication of the recorded production

. Various ternary and quaternary oxides, oxynitrides, oxysulfides,

/GO photocatalysts were successfully prepared via in situ

/graphene was greatly enhanced compared to pure

S3

, [8] have been also incorporated with GO to serve

Immobilization Impact of Photocatalysts onto Graphene Oxide

http://dx.doi.org/10.5772/intechopen.78054

S3 , Bi2 S3

composites [27]. The synthesized GO/metal

, MoS, CdSe, and

111

GO has been explored as electron acceptor molecule for making composite with TiO2 . The effects of particle size GO content and targeted pollutants for different TiO<sup>2</sup> and GO composites have been represented by examples in **Table 1**. Moreover, other metal oxides such as ZnO,


**Table 1.** Summary of TiO2 and GO composites used as photocatalyst. [2–4] NiO, [5] WO3 , [6] CuO, [7], and Mn<sup>3</sup> O4 , [8] have been also incorporated with GO to serve as an enhanced photocatalyst.

### **3.2. Non-oxidic binary compounds**

**3.1. Binary metal oxides**

110 Graphene Oxide - Applications and Opportunities

**Composites TiO2**

been studied in the field of photocatalysis. TiO<sup>2</sup>

, CuO, and Cu2

other than transition metals such as ZnO, Ga2

semiconductor binary oxides with a d-transition metal such as WO3

operational factors such as the pH, additives, and ZnO crystal growth.

 **particle** 

**size**

/GO — GO:TiO2

/GO 10 nm GO:TiO2

effects of particle size GO content and targeted pollutants for different TiO<sup>2</sup>

) is the first and most important binary transition metal oxides that have

O have been studied. In addition, binary metal oxides of elements

non-solubility in the aqueous medium, which facilitates the process of separation after the desired reactions. Moreover, photocatalytic stimulation is primarily aimed at environmental applications; therefore, non-toxicity of titanium dioxide is also favorable. Other n-type

> O3 , Sb2 O3 , Bi2 O3

tion. Although ZnO suffers from photocorrosion, it is photocatalytic activity is comparable

ites have been represented by examples in **Table 1**. Moreover, other metal oxides such as ZnO,

/GR 30 nm 0.5 wt% Dodecylbenzenesulfonate [9]

/GO — 10 mg Methylene blue [11]

GO 57 nm 3.3 wt% Diphenhydramine methyl [12]

/GO 50 nm thickness 10 wt% Methylene blue [13]

/GO 20–40nm 4.6 wt% Methyl orange [14]

/GO 30 nm 10 wt% Methylene blue [15]

/GO 10 nm 0.03 mg GO Methylene blue [17]

/GO 4–5 nm 3.3–4.0 wt% Diphenhydramine and methyl orange [18]

/GO 15 nm ~10% Rhodamine B [19]

/GO 6–9 nm 1 wt% Methylene blue [21]

B/GO/TiO2 51 nm 4-Nitrophenol [24]

and GO composites used as photocatalyst.

/GO 30–50 nm 3–4 wt% Oxytetracycline and Congo Red [22]

/GO 17 nm Enrofloxacin [23]

/GO Acid Blue 40 [25]


GO has been explored as electron acceptor molecule for making composite with TiO2

. Furthermore, the photocorrosion process can be controlled by monitoring of the

is characterized by chemical stability and

, Fe2 O3 , Nb2 O5 , V<sup>2</sup> O5 , NiO,

had also some atten-

and GO compos-

. The

, and CeO2

**GO content Pollutant Ref.**

= 1.5 wt Methyl orange [16]

= 3:2 wt Methyl orange [20]

Titanium oxide (TiO2

Ta2 O5 , ZrO2

with TiO2

Pt-GO-TiO2


TiO2

TiO2

TiO2

TiO2

TiO2

TiO2

TiO2

TiO2

TiO2

TiO2

TiO2

TiO2

Co3 O4 /TiO2

Fe3 O4 /TiO2

La/TiO2

**Table 1.** Summary of TiO2

Many photocatalytic substances contain no oxygen, but still have another element of group 16 in the periodic table. Chalcogenide such as CdS, ZnS, Sb<sup>2</sup> S3 , Bi2 S3 , MoS, CdSe, and CdTe give a good example of such materials. Sulfides other than zinc sulfide have an absorption edge compatible with solar energy utilization rather than photocatalytic processes. Unfortunately, sulfides have the disadvantage of photo-induced corrosion. Cadmium selenides and tellurides have a valence band redox potential lower than 1.23 V. This explains their poor photocatalytic activity for oxidation of organic pollutants [26].

A simple and high-yield room-temperature solid-state method was employed for the first time to fabricate GO/ZnS, GO/CdS, and GO/Bi2 S3 composites [27]. The synthesized GO/metal sulfide composites were used as photocatalysts for the degradation of methyl orange under UV irradiation. The composites exhibited superior photocatalytic activity to pure metal sulfides, owing to the high specific surface area, and the reduction of photo-induced electronhole pair recombination in metal sulfides due to the introduction of GO.

However, incorporation of non-oxidic binary compounds alone with GO is superfluous. They are often introduced to the GO surface with each other or with different photocatalytic materials. The association of ZnS-CdS with GO to form the ZnS-CdS/GO heterostructure for the photocatalytic H<sup>2</sup> gas generation result in the duplication of the recorded production rate. Moreover, doping ZnS-CdS/GO heterostructure with 2 wt% Pt nanoparticles to serve as co-catalysts, the hydrogen generation rate is significantly elevated to 1.68 and 0.78 mmol h−1 upon irradiation with UV-visible or visible light, respectively [28].

### **3.3. Multiple compounds**

Metallates of elements of the middle region of the periodic table and cations with filled or partially filled orbitals in their outer shell, which may hybridize with the oxygen 2p orbitals. Aluminates, ferrites, niobates, tantalates, titanates, tungstates, and vanadates are some examples of these metallates. While the examples of those cations are 6 s orbitals in Pb2+ and Bi3+, and 5 s in Sn2+ or 4d in Ag+ . Various ternary and quaternary oxides, oxynitrides, oxysulfides, and oxyhalides have also been investigated for evaluation of their activity in the degradation of organic pollutants and water splitting.

Incorporation of metallates with GO has also been investigated as an enhanced photocatalyst. For instance, the Bi2 WO6 /GO photocatalysts were successfully prepared via in situ refluxing method in the presence of GO. The photocatalytic degradation of rhodamine B under visible light irradiation was utilized to evaluate the photocatalytic performance. The photocatalytic activity of Bi2 WO6 /graphene was greatly enhanced compared to pure Bi2 WO6 . The enhanced photocatalytic activity could be attributed to that GO as charge transfer channel [29].
