Preface

In the last decade, nanomaterials have become a double-edged sword. On the one hand, there has been an increase in the production of nanomaterials, since they have proven their limitless potential not only for technological applications, but also for medical ones. On the other hand, the increasing use of these nanomaterials has raised concerns regarding their safety for environmental and human health, due to their potential toxicity. Their faith in the human body, along with their interactions with different tissues, became of vital importance. The toxic effects of nanomaterials depend on their type, synthesis, surface geometry, diameter, length, and functionalization.

This book discusses the main and new aspects related to nanomaterials' toxicity divided into four main areas: Assessment of nanomaterials' toxicity; Environmental and health impact of nanomaterials; Modulation of nanomaterials' toxicity; Characterization and applications of nanomaterials.

The overall idea of the book is to provide the reader with an evidence–based, comprehensive, and up-to-date overview of the current state of the art of nanomaterials' toxicity, including their synthesis and characterization, environmental impact, tests to assess their toxicity *in vitro* and *in vivo*, ways to modulate their impact on living organisms, and their beneficial use in biomedical applications.

At the beginning of the book, Professor Gustavo Nascimento presents an overview of a challenging up-to-date subject, nanofibers. In the Prologue, the main existing results regarding the synthesis, characterization through Raman spectroscopy, and applications of polyaniline nanofibers are reviewed.

In Chapter 2 the authors discuss the most recommended and frequently used methods, including both *in vivo* and *in vitro* tests, which are the most suitable ones for the assessment of nanomaterials' toxicity. Also, toxicity of the environment is taken into account, along with toxicity related to human health. Finally, the need for the standardization of these methods is discussed.

Chapter 3 focuses on carbon nanomaterials and presents new tools and methodologies to assess the exposure and risk evaluation of hazards used in health, safety, and environmental management of these kinds of structures. Possible relations between safety aspects and biokinetics interaction of living organisms according to the exposure route, along with the major protocols, standards, and guidelines on the safe handling of nanomaterials, are also presented.

The environmental impact of urban atmospheric nanoparticles is presented in Chapter 4, with a focus on the oxidative stress produced by this type of nanomaterial. The authors discuss different mechanisms involved in the interaction between these nanomaterials and living organisms, including cellular internalization, activation of signaling pathways, decrease of cellular antioxidants, activation of the proinflammatory cascade, lipid peroxidation, and activation of the cellular signaling pathway leading to apoptosis, with impacts on human health.

**II**

**Chapter 7 113**

Applications of Nanomaterials **127**

**Chapter 8 129**

**Chapter 9 151**

**Chapter 10 171**

**Chapter 11 199**

**Chapter 12 221**

*by Josef Mašek, Eliška Mašková, Daniela Lubasová, Roman Špánek, Milan Raška* 

Stupendous Nanomaterials: Carbon Nanotubes Synthesis, Characterization,

Phosphate-Mineralization Microbe Repairs Heavy Metal Ions That Formed

*by Crina Anastasescu, Mihai Anastasescu, Ioan Balint and Maria Zaharescu*

Electrospinning Technology: Designing Nanofibers toward Wound Healing

*by Daniela Sousa Coelho, Beatriz Veleirinho, Thaís Alberti, Amanda Maestri,* 

Nanomaterials in Soil and Water *by Xiaoniu Yu and Qiwei Zhan*

SiO2-Based Materials for Immobilization of Enzymes

*Rosendo Yunes, Paulo Fernando Dias and Marcelo Maraschin*

*by Kalaiselvan Shanmugam, J. Manivannan and M. Manjuladevi*

Applications of Cadmium Telluride (CdTe) in Nanotechnology

Nanofibers in Mucosal Drug and Vaccine Delivery

**Section 5**

Application

*and Jaroslav Turánek*

and Applications

*by Akeel M. Kadim*

The toxicity of tungsten nanoparticles with respect to normal human skin fibroblast cells is evaluated in Chapter 5. The authors have analyzed the cytotoxic effects of tokamak dust produced in laboratory cell lines on human fibroblasts and have demonstrated that the effects are dose dependent. At low concentrations (<100 µg/mL), tungsten nanoparticles proved to have no toxic effects, while at concentrations up to 2 mg/mL they can exert toxic effects on the cells.

Chapter 6 focuses on the methods used for the synthesis of nanomaterials, methods by which shapes and sizes could be controlled, and also looks at the methods used to characterize the biomaterials. The manipulation of nanomaterials' shape and size could lead to less toxic nanomaterials.

A new method for the treatment of heavy metal ions in soil or water is presented in Chapter 7. Heavy metal ions can be mineralized by phosphate-mineralization microbes and stable phosphate nanomaterials are formed. This is a mineralization method that can remove heavy metal pollutants from soil or water. In addition, heavy metal pollution can degrade the environment and be a threat to human health.

Chapter 8 focuses on the use of SiO2-based nanomaterials as support for compounds with biological activity such as antibodies and enzymes. The authors emphasize the synthesis of SiO2 nanomaterials with different morphologies, their physicochemical characteristics, the biocatalytic activity of immobilized enzymes on simple SiO2, and their behavior dependent on the morphology of SiO2 inorganic carriers obtained by the sol-gel method.

Chapter 9 is a revision of the density function theory calculation methods of the vibrational zero point for organic molecules containing silicon atoms. This class of molecules are the building blocks of nanomaterials. In addition, the authors provide an extensive amount of calculated data compared to other literature. The chapter gives abundant material for the spectroscopic characterization of advanced materials.

Chapter 10 gives a detailed calculation of the vibrational modes, proton and carbon nuclear magnetic resonance spectra, and other different properties for 5-nitro-1,3-benzodioxole and derivatives. The non-linear optical behavior of the examined molecule is investigated by the determination of hyperpolarizability. This result indicates that 5-nitro-1,3-benzodioxole is a good candidate for non-linear optical study.

A broad review of the synthesis and characterization of carbon nanotubes is described in Chapter 11. Since their discovery, carbon nanotubes have offered tremendous opportunities for the development of new materials and composites. This chapter provides a report on recent advances in the science of carbon nanotubes and their potential applications.

Chapter 12 focuses on a number of applications of cadmium telluride quantum dots (CdTe QDs) in nanotechnology. A hybrid device fabricated from three layers—an organic polymer, an electron injector from organic molecules, and a semiconductor material (CdTe QDs)—proved to be effective in white light generation. The synthesis, characterization, and evaluation of optical, electrical, morphological, and electroluminescent properties of CdTe QDs and of the obtained device are presented and discussed by the author.

**V**

Even though the knowledge regarding the real impact of nanomaterials on the environment and human health is still limited, we hope that this book will provide a useful tool for the reader to understand the complex field of nanotechnology and

**Dr. Simona Clichici and Dr. Adriana Filip**

Centre for Natural Sciences and Humanities,

University of Medicine and Pharmacy,

Professor,

Professor,

Department of Physiology,

Federal University of ABC, Santo André, Brazil

**Dr. Gustavo M. do Nascimento**

Cluj-Napoca, Romania

nanomedicine.

Even though the knowledge regarding the real impact of nanomaterials on the environment and human health is still limited, we hope that this book will provide a useful tool for the reader to understand the complex field of nanotechnology and nanomedicine.

## **Dr. Simona Clichici and Dr. Adriana Filip** Professor, Department of Physiology, University of Medicine and Pharmacy,

Cluj-Napoca, Romania

## **Dr. Gustavo M. do Nascimento** Professor, Centre for Natural Sciences and Humanities, Federal University of ABC, Santo André, Brazil

**IV**

The toxicity of tungsten nanoparticles with respect to normal human skin fibroblast cells is evaluated in Chapter 5. The authors have analyzed the cytotoxic effects of tokamak dust produced in laboratory cell lines on human fibroblasts and have demonstrated that the effects are dose dependent. At low concentrations (<100 µg/mL), tungsten nanoparticles proved to have no toxic effects, while at concentrations up to

Chapter 6 focuses on the methods used for the synthesis of nanomaterials, methods by which shapes and sizes could be controlled, and also looks at the methods used to characterize the biomaterials. The manipulation of nanomaterials' shape and size

A new method for the treatment of heavy metal ions in soil or water is presented in Chapter 7. Heavy metal ions can be mineralized by phosphate-mineralization microbes and stable phosphate nanomaterials are formed. This is a mineralization method that can remove heavy metal pollutants from soil or water. In addition, heavy metal pollution can degrade the environment and be a threat to human

Chapter 8 focuses on the use of SiO2-based nanomaterials as support for compounds with biological activity such as antibodies and enzymes. The authors emphasize the synthesis of SiO2 nanomaterials with different morphologies, their physicochemical characteristics, the biocatalytic activity of immobilized enzymes on simple SiO2, and their behavior dependent on the morphology of SiO2 inorganic carriers

Chapter 9 is a revision of the density function theory calculation methods of the vibrational zero point for organic molecules containing silicon atoms. This class of molecules are the building blocks of nanomaterials. In addition, the authors provide an extensive amount of calculated data compared to other literature. The chapter gives abundant material for the spectroscopic characterization of advanced

Chapter 10 gives a detailed calculation of the vibrational modes, proton and carbon nuclear magnetic resonance spectra, and other different properties for 5-nitro-1,3-benzodioxole and derivatives. The non-linear optical behavior of the examined molecule is investigated by the determination of hyperpolarizability. This result indicates that 5-nitro-1,3-benzodioxole is a good candidate for non-linear optical

A broad review of the synthesis and characterization of carbon nanotubes is described in Chapter 11. Since their discovery, carbon nanotubes have offered tremendous opportunities for the development of new materials and composites. This chapter provides a report on recent advances in the science of carbon nanotubes

Chapter 12 focuses on a number of applications of cadmium telluride quantum dots (CdTe QDs) in nanotechnology. A hybrid device fabricated from three layers—an organic polymer, an electron injector from organic molecules, and a semiconductor material (CdTe QDs)—proved to be effective in white light generation. The synthesis, characterization, and evaluation of optical, electrical, morphological, and electroluminescent properties of CdTe QDs and of the obtained device are

2 mg/mL they can exert toxic effects on the cells.

could lead to less toxic nanomaterials.

obtained by the sol-gel method.

and their potential applications.

presented and discussed by the author.

health.

materials.

study.

**1**

Section 1

Prologue

Section 1 Prologue

**3**

**Chapter 1**

**1. Introduction**

**2. Nanofibers**

(PANI) will be discussed.

**3. Nanofibers of conductive polymers**

Prologue: Nanofibers

The preparation of polymers with morphology well determined in the nanometric range is one of the great challenges in the polymer science and technology. The possibility to prepare nanofibers (or nanofibers) brings the opportunity to produce polymers with new or reinforced properties. Many ways have been developed to synthesize polymeric nanofibers, for instance, the polymerization into media having large organic acids. The interfacial polymerization can also form nanofibers at an aqueous-organic interface. Hence, a great variety of "bottom-up" approaches, such as electrospinning, interfacial, seeding, and micellar, can be employed to obtain pure polymeric nanofibers. The preparation of nanostructured polymers by self-assembly with reduced post-synthesis processing warrants further applications, especially in the field of biotechnology and removable resources. The notable applications include tissue engineering, biosensors, filtration, wound dressings, drug delivery, and enzyme immobilization. In this chapter, the state-of-the-art results of synthesis, spectroscopic characterization, and applications of polyaniline nanofibers will be reviewed. The main goal of this work is to contribute to the rationalization of some

important results obtained in this wonder area of polymeric nanofibers.

one of the focuses in the science of advanced materials.

Despite that nanofibers are produced for a long time, only in recent years, the scientific interest in this field has rapidly increased. The reason for that is, probably, owing to the improvement of the synthetic pathways in the production of better nanofibers. In addition, the combination of spectroscopic and microscopic techniques leads to a better corrletion between structure and properties of nanofibers. **Figure 1** shows that in 2018, more than 6000 papers having "nanofiber" or "nanofibre" as keyword were published. In addition, **Figure 2** shows that at least 20 different research fields have more than 1000 papers published related to "nanofiber" or "nanofibre." These two graphs clearly show that nanofibers are

Our group has dedicated to the preparation and characterization of polyaniline nanofibers [1–10]. Among the different techniques used for structural investigation, resonance Raman spectroscopy is the most important technique for these systems. Thus, in this chapter, mainly the Raman results obtained for polyaniline

Nowadays, the preparation of conductive polymers with organized morphology and structure is a desired deal. Since the discovery of poly(acetylene) doping process

*Gustavo M. Do Nascimento*

## **Chapter 1** Prologue: Nanofibers

*Gustavo M. Do Nascimento*

## **1. Introduction**

The preparation of polymers with morphology well determined in the nanometric range is one of the great challenges in the polymer science and technology. The possibility to prepare nanofibers (or nanofibers) brings the opportunity to produce polymers with new or reinforced properties. Many ways have been developed to synthesize polymeric nanofibers, for instance, the polymerization into media having large organic acids. The interfacial polymerization can also form nanofibers at an aqueous-organic interface. Hence, a great variety of "bottom-up" approaches, such as electrospinning, interfacial, seeding, and micellar, can be employed to obtain pure polymeric nanofibers. The preparation of nanostructured polymers by self-assembly with reduced post-synthesis processing warrants further applications, especially in the field of biotechnology and removable resources. The notable applications include tissue engineering, biosensors, filtration, wound dressings, drug delivery, and enzyme immobilization. In this chapter, the state-of-the-art results of synthesis, spectroscopic characterization, and applications of polyaniline nanofibers will be reviewed. The main goal of this work is to contribute to the rationalization of some important results obtained in this wonder area of polymeric nanofibers.

## **2. Nanofibers**

Despite that nanofibers are produced for a long time, only in recent years, the scientific interest in this field has rapidly increased. The reason for that is, probably, owing to the improvement of the synthetic pathways in the production of better nanofibers. In addition, the combination of spectroscopic and microscopic techniques leads to a better corrletion between structure and properties of nanofibers. **Figure 1** shows that in 2018, more than 6000 papers having "nanofiber" or "nanofibre" as keyword were published. In addition, **Figure 2** shows that at least 20 different research fields have more than 1000 papers published related to "nanofiber" or "nanofibre." These two graphs clearly show that nanofibers are one of the focuses in the science of advanced materials.

Our group has dedicated to the preparation and characterization of polyaniline nanofibers [1–10]. Among the different techniques used for structural investigation, resonance Raman spectroscopy is the most important technique for these systems. Thus, in this chapter, mainly the Raman results obtained for polyaniline (PANI) will be discussed.

## **3. Nanofibers of conductive polymers**

Nowadays, the preparation of conductive polymers with organized morphology and structure is a desired deal. Since the discovery of poly(acetylene) doping process

#### **Figure 1.**

*Number of publications by year having the keyword "nanofiber" or "nanofibre" in the text. The research was done in November 25, 2018, using Web of Science database. The total score found are 54,611 papers.*


#### **Figure 2.**

*Number of publications by year having the keyword "nanofiber" or "nanofibre" in the text divided by the main research areas or categories. The research was done in November 25, 2018, by using Web of Science database.*

in the early 1970s [11–16] and posterior investigation of its properties mainly done by Hideki Shirakawa, Alan J. Heeger, and Alan G. MacDiarmid (see **Figure 3**), the field of conductive polymers brings many contributions to different applications: from batteries to organic light-emitting diode (OLED) displays. The preparation of nanostructured conductive polymers can turn the polymer more efficiently to applications. The doping process [17–25] in conjugated polymers is characterized by the passage from an insulating or semiconducting state with low conductivity, typically ranging from 10−10 to 10−5 Scm−1, to a "metallic" regime (ca. 1–104 Scm−1; see **Figure 3**).

Reversibility is one main characteristic of chemical doping; in fact, the polymer can return to its original state without major changes in its structure. Counterions stabilize the doped state in the polymeric chain. The conductivity can be modulated only by adjusting the doping level, varying from non-doped insulating state to highly doped or metallic. All conductive polymers (and their derivatives), for example, among others, may be doped by p (oxidation) or n (reduction) through chemical and/or electrochemical process [16–18]. The doping process can also be characterized by no loss or gain of electrons from external

**5**

**Figure 4.**

internal redox process.

(polarons) ring (LUMO) [25].

agents. This is the point for polyanilines (see **Figure 4**), and this process is named

*Generalized representation of chemical structure of PANI and its most common forms.*

*The Nobel winners (Hideki Shirakawa, Alan J. Heeger, and Alan G. MacDiarmid) and the chemical structures of the most common conductive polymers. The conductivity values for different materials are displayed in comparison with conducting polymers before and after the doping process. The doping causes (addition of nonstoichiometric chemical species in quantities commonly low ≤10%) dramatic changes in the* 

*electronic, electrical, magnetic, optical, and structural properties of the polymer.*

PANI-ES is formed after protonation with the appearance of the free radical tail of band in the NIR spectral region (starting from ca. 1.6 eV or 780 nm), which is attributed to a charge transfer from the highest occupied energy level of the benzene ring (HOMO) to the lowest unoccupied energy level of a semiquinone

*Prologue: Nanofibers*

**Figure 3.**

*DOI: http://dx.doi.org/10.5772/intechopen.83632*

*Prologue: Nanofibers DOI: http://dx.doi.org/10.5772/intechopen.83632*

#### **Figure 3.**

*Nanomaterials - Toxicity, Human Health and Environment*

in the early 1970s [11–16] and posterior investigation of its properties mainly done by Hideki Shirakawa, Alan J. Heeger, and Alan G. MacDiarmid (see **Figure 3**), the field of conductive polymers brings many contributions to different applications: from batteries to organic light-emitting diode (OLED) displays. The preparation of nanostructured conductive polymers can turn the polymer more efficiently to applications. The doping process [17–25] in conjugated polymers is characterized by the passage from an insulating or semiconducting state with low conductivity, typically ranging

*Number of publications by year having the keyword "nanofiber" or "nanofibre" in the text divided by the main research areas or categories. The research was done in November 25, 2018, by using Web of Science database.*

*Number of publications by year having the keyword "nanofiber" or "nanofibre" in the text. The research was done in November 25, 2018, using Web of Science database. The total score found are 54,611 papers.*

Reversibility is one main characteristic of chemical doping; in fact, the polymer can return to its original state without major changes in its structure. Counterions stabilize the doped state in the polymeric chain. The conductivity can be modulated only by adjusting the doping level, varying from non-doped insulating state to highly doped or metallic. All conductive polymers (and their derivatives), for example, among others, may be doped by p (oxidation) or n (reduction) through chemical and/or electrochemical process [16–18]. The doping process can also be characterized by no loss or gain of electrons from external

Scm−1; see **Figure 3**).

from 10−10 to 10−5 Scm−1, to a "metallic" regime (ca. 1–104

**4**

**Figure 1.**

**Figure 2.**

*The Nobel winners (Hideki Shirakawa, Alan J. Heeger, and Alan G. MacDiarmid) and the chemical structures of the most common conductive polymers. The conductivity values for different materials are displayed in comparison with conducting polymers before and after the doping process. The doping causes (addition of nonstoichiometric chemical species in quantities commonly low ≤10%) dramatic changes in the electronic, electrical, magnetic, optical, and structural properties of the polymer.*

#### **Figure 4.**

*Generalized representation of chemical structure of PANI and its most common forms.*

agents. This is the point for polyanilines (see **Figure 4**), and this process is named internal redox process.

PANI-ES is formed after protonation with the appearance of the free radical tail of band in the NIR spectral region (starting from ca. 1.6 eV or 780 nm), which is attributed to a charge transfer from the highest occupied energy level of the benzene ring (HOMO) to the lowest unoccupied energy level of a semiquinone (polarons) ring (LUMO) [25].

PANI nanofibers can be prepared by using different routes, and the resulting polymer shows improvement in its electrical, thermal, and mechanical stabilities. The conventional synthesis of polyaniline, based on the oxidative polymerization of aniline in the presence of a strong acid dopant, typically results in an irregular granular morphology with a very small percentage of nanoscale fibers. Highly uniform PANI nanofibers with diameter ranging from 30 to 120 nm, depending on the dopant, are prepared by interfacial polymerization [26, 27]. The diffusion of the formed product from the interfacial solvent-solvent region to the bulk of the solvent can suppress uncontrolled polymer growth by isolating the fibers from the excess of reagents. In fact, the addition of certain surfactants to such an interfacial system grants further control over the diameter of the nanofibers. Isolation of the nanostructured PANI from the solution can be achieved by filtration in a nanoporous filters or dialyzed, and then the cleaned solution containing the nanofibers is centrifuged in order to separate the nanofibers from the solution.

Another approach is the synthesis of PANI nanofibers or nanotubes by making use of large organic acids. These acids form micelles upon which aniline is polymerized and doped. Fiber with diameters from 30 to 60 nm can be modulated by reagent ratios [28–31]. PANI nanofibers can also be obtained in ionic liquids (ILs) as synthetic media [2, 6]. There is a large variety of ionic liquids, and the most used ones are derived from imidazolium ring, pyridinium ring, quaternary ammonium, and tertiary phosphonium cations. The most unusual characteristic of these systems is that, although they are liquids, they present structural organization and can act as a template-like system, and PANI nanofibers are obtained when the aniline is polymerized in these media.

### **4. Raman spectroscopy of polyaniline nanofibers**

Raman spectroscopy is a technique par excellence for probing the vibrational frequencies by inelastic scattering the incident light (see **Figure 5**) [32–35]. In the conventional Raman spectroscopy, the intensities of the Raman bands are linearly proportional to the intensity of the incident light and proportional to the square of the polarizability tensor. However, when the laser line falls within the region of a permitted electronic transition, the Raman bands that are tightly coupled or associated with the excited electronic state have a tremendous increase of about 105–6 times; this is what characterizes the resonance Raman effect. In the case of multi-chromophoric system, like polyaniline, just by tuning an appropriate laser radiation on an electronic transition of the polymer, the spectrum changes dramatically (see **Figure 6**).

PANI shows a characteristic Raman bands for each oxidized or protonated form [36–40]. The presence of a free carrier tail absorption in the UV–VIS–NIR spectra for both PANI nanofibers/nanotubes prepared with NSA (β-naphthalenesulfonic acid) or with DBSA (dodecybenzenesulfonic acid) confirmed that polymeric chains have an extended conformation. In addition, the band at 609 cm−1 is sensible to conformation changes of the PANI chains [1, 3]. The studies of doping and heating behavior of PANI-NSA nanofibers show the loss of the fibrous morphology of PANI after treatment with HCl solution [4]. However, the PANI nanofibers are more susceptible to cross-linking (bands at 578 and 1340 cm−1; see **Figure 6**) than conventional PANI, and after heating at 200°C, it is possible to dope the polymer with HCl and maintain the nanostructured morphology.

PANI nanofibers prepared from interfacial polymerization were also characterized by Raman spectroscopy. Bands at 200 and 296 cm−1 related to Cring-N-Cring deformation and lattice modes of polaron segments of PANI practically disappear in the Raman spectra of PANI nanofibers. The changes indicate the increase of the

**7**

**Figure 6.**

*comparison the SEM images are also given.*

*Prologue: Nanofibers*

**Figure 5.**

*DOI: http://dx.doi.org/10.5772/intechopen.83632*

*(νas) with higher energy than Eo (Eas > Eo).*

torsion angles of the Cring-N-Cring segments. In addition, the FTIR spectra for PANI nanofibers display higher changes in the region from 2000 to 4000 cm−1. Both data are associated to the formation of bipolarons (protonated, spinless units) in the PANI nanofiber backbone higher than the conventional PANI. The PANI nanofiber morphology permits major diffusion of the ions inside the polymeric matrix leading to a more effective protonation of the polymeric chain [5]. In addition, only for PANI nanofibers with a diameter of 30.0 nm, low dispersion of the νC〓N band is seen (see **Figure 7**). The Raman dispersion is associated to the electron–phonon coupling into a conjugated structure. In other words, very low D values indicated more electronic homogeneity into the PANI nanofibers, due to the stacking of

*Resonance Raman spectra of PANI-NSA after heating at indicated temperatures and doping with HCl. For* 

*Schematic representation of Raman effect. The Raman scattering was discovered by C. V. Raman and is characterized by inelastic scattering of the incident radiation (νo) with laser energy (EO). The scattered light has two components: Stokes radiation (νs) with lower energy than Eo (Es < Eo) and the anti-stoke radiation* 

quinoid-quinoid rings, leading to high torsion Cring-N-Cring angles.

#### **Figure 5.**

*Nanomaterials - Toxicity, Human Health and Environment*

PANI nanofibers can be prepared by using different routes, and the resulting polymer shows improvement in its electrical, thermal, and mechanical stabilities. The conventional synthesis of polyaniline, based on the oxidative polymerization of aniline in the presence of a strong acid dopant, typically results in an irregular granular morphology with a very small percentage of nanoscale fibers. Highly uniform PANI nanofibers with diameter ranging from 30 to 120 nm, depending on the dopant, are prepared by interfacial polymerization [26, 27]. The diffusion of the formed product from the interfacial solvent-solvent region to the bulk of the solvent can suppress uncontrolled polymer growth by isolating the fibers from the excess of reagents. In fact, the addition of certain surfactants to such an interfacial system grants further control over the diameter of the nanofibers. Isolation of the nanostructured PANI from the solution can be achieved by filtration in a nanoporous filters or dialyzed, and then the cleaned solution containing the nanofibers is

Another approach is the synthesis of PANI nanofibers or nanotubes by making use of large organic acids. These acids form micelles upon which aniline is polymerized and doped. Fiber with diameters from 30 to 60 nm can be modulated by reagent ratios [28–31]. PANI nanofibers can also be obtained in ionic liquids (ILs) as synthetic media [2, 6]. There is a large variety of ionic liquids, and the most used ones are derived from imidazolium ring, pyridinium ring, quaternary ammonium, and tertiary phosphonium cations. The most unusual characteristic of these systems is that, although they are liquids, they present structural organization and can act as a template-like system, and PANI nanofibers are obtained when the aniline is

Raman spectroscopy is a technique par excellence for probing the vibrational frequencies by inelastic scattering the incident light (see **Figure 5**) [32–35]. In the conventional Raman spectroscopy, the intensities of the Raman bands are linearly proportional to the intensity of the incident light and proportional to the square of the polarizability tensor. However, when the laser line falls within the region of a permitted electronic transition, the Raman bands that are tightly coupled or associated with the excited electronic state have a tremendous increase of about 105–6 times; this is what characterizes the resonance Raman effect. In the case of multi-chromophoric system, like polyaniline, just by tuning an appropriate laser radiation on an electronic

transition of the polymer, the spectrum changes dramatically (see **Figure 6**).

PANI shows a characteristic Raman bands for each oxidized or protonated form [36–40]. The presence of a free carrier tail absorption in the UV–VIS–NIR spectra for both PANI nanofibers/nanotubes prepared with NSA (β-naphthalenesulfonic acid) or with DBSA (dodecybenzenesulfonic acid) confirmed that polymeric chains have an extended conformation. In addition, the band at 609 cm−1 is sensible to conformation changes of the PANI chains [1, 3]. The studies of doping and heating behavior of PANI-NSA nanofibers show the loss of the fibrous morphology of PANI after treatment with HCl solution [4]. However, the PANI nanofibers are more susceptible to cross-linking (bands at 578 and 1340 cm−1; see **Figure 6**) than conventional PANI, and after heating at 200°C, it is possible to dope the polymer

PANI nanofibers prepared from interfacial polymerization were also characterized by Raman spectroscopy. Bands at 200 and 296 cm−1 related to Cring-N-Cring deformation and lattice modes of polaron segments of PANI practically disappear in the Raman spectra of PANI nanofibers. The changes indicate the increase of the

centrifuged in order to separate the nanofibers from the solution.

**4. Raman spectroscopy of polyaniline nanofibers**

with HCl and maintain the nanostructured morphology.

polymerized in these media.

**6**

*Schematic representation of Raman effect. The Raman scattering was discovered by C. V. Raman and is characterized by inelastic scattering of the incident radiation (νo) with laser energy (EO). The scattered light has two components: Stokes radiation (νs) with lower energy than Eo (Es < Eo) and the anti-stoke radiation (νas) with higher energy than Eo (Eas > Eo).*

#### **Figure 6.**

*Resonance Raman spectra of PANI-NSA after heating at indicated temperatures and doping with HCl. For comparison the SEM images are also given.*

torsion angles of the Cring-N-Cring segments. In addition, the FTIR spectra for PANI nanofibers display higher changes in the region from 2000 to 4000 cm−1. Both data are associated to the formation of bipolarons (protonated, spinless units) in the PANI nanofiber backbone higher than the conventional PANI. The PANI nanofiber morphology permits major diffusion of the ions inside the polymeric matrix leading to a more effective protonation of the polymeric chain [5]. In addition, only for PANI nanofibers with a diameter of 30.0 nm, low dispersion of the νC〓N band is seen (see **Figure 7**). The Raman dispersion is associated to the electron–phonon coupling into a conjugated structure. In other words, very low D values indicated more electronic homogeneity into the PANI nanofibers, due to the stacking of quinoid-quinoid rings, leading to high torsion Cring-N-Cring angles.

**Figure 7.** *Raman dispersion of PANI nanofibers.*

### **5. Conclusion**

The structural studies of the polyaniline nanofibers by using resonance Raman spectroscopy, as the main technique, have been decisive to elucidate intra- and interchain interactions and chemical and thermal stabilities of PANI nanofibers. The presence of phenoxazine rings is observed in PANI nanofibers formed in micellar media. The presence of these rings is crucial for stacking and stabilization of the fibers. In addition, the changes in bands at low energies are associated with an increase in the torsion angles of Cring-N-Cring segments due to the formation of bipolarons (protonated, spinless units) in the PANI nanofibers. The major diffusion of the ions inside the nanofiber gives a more effective protonation. However, only with the previous thermal treatment, it is possible to retain the nanofiber morphology.

Hence, the π-stacking between quinoid rings and the presence of π-π stacking formed by phenoxazine rings can be the driving forces for the formation of the fiber morphology of PANI. The quality of the PANI nanofibers can be monitored by the influence over the Raman dispersion curves. Finally, the example of characterization of PANI nanofibers by using Raman spectroscopy can be applied to other nanofiber materials with the improvement of future nanofiber structural studies.

### **Author details**

Gustavo M. Do Nascimento Federal University of ABC-CCNH, Brazil

\*Address all correspondence to: gustavo.morari@ufabc.edu.br

© 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.

**9**

*Prologue: Nanofibers*

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[11] Shirakawa H, Ikeda S. Infrared spectra of poly(acetylene). Polymer

Cyclotrimerization of acetylene by tris(acetylacetonato)titanium(III) diethylaluminum chloride system. Journal of Polymer Science. 1974;**12**:929

[13] Chiang CK, Druy MA, Gau SC, Heeger AJ, Louis EJ, MacDiarmid AG, et al. Synthesis of highly conducting films of derivatives of polyacetylene (CH)x. Journal of the American Chemical Society. 1978;**100**:1013

[14] Chiang CK, Fincher CR Jr, Park YW, Heeger AJ, Shirakawa H, Louis EJ, et al. Electrical-conductivity in doped polyacetylene. Physical Review Letters.

[15] Shirakawa H. The discovery of polyacetylene film: The dawning of an era of conducting polymers (Nobel Lecture). Angewandte Chemie, International Edition. 2001;**40**:2575

[16] Shirakawa H, Louis EJ, MacDiarmid AG, Chiang CK, Heeger AJ. Synthesis of electrically conducting organic polymers-halogen derivatives of polyacetylene, (CH)X. Journal of the Chemical Society, Chemical Communications. 1977;**16**:578

[17] MacDiarmid AG. "Synthetic Metals": A novel role for organic

Papers. 2013;**67**:933

Nova Publishers; 2014

Journal. 1971;**2**:231

1977;**39**:1098

[12] Shirakawa H, Ikeda S.

[1] Do Nascimento GM, Silva CHB, Temperini MLA. Electronic structure and doping behavior of PANI-NSA nanofibers investigated by resonance raman spectroscopy. Macromolecular Rapid Communications. 2006;**27**:255

[2] Rodrigues F, Do Nascimento GM, Santos PS. Dissolution and doping of polyaniline emeraldine base in imidazolium ionic liquids investigated by spectroscopic techniques. Macromolecular Rapid Communications. 2007;**28**:666

[3] Do Nascimento GM, Silva CHB, Izumi CMS, Temperini MLA. The role of cross-linking structures to the formation of one-dimensional nanoorganized polyaniline and their Raman fingerprint. Spectrochimica Acta Part A.

[4] Do Nascimento GM, Silva CHB, Temperini MLA. Spectroscopic characterization of the structural changes of polyaniline nanofibers after heating. Polymer Degradation and

[5] Do Nascimento GM, Kobata PYG, Temperini MLA. Structural and vibrational characterization of polyaniline nanofibers prepared from interfacial polymerization. The Journal of Physical Chemistry. B.

[6] Rodrigues F, Do Nascimento GM, Santos PS. Studies of ionic liquid solutions by soft X-ray absorption spectroscopy. Journal of Electron Spectroscopy and Related Phenomena.

[7] Do Nascimento GM. In: Kumar A, editor. (Org.)Nanofibers. 1st ed. Austria/Croacia: InTech; 2010

[8] Do Nascimento GM. X-ray absorption spectroscopy of

## **References**

*Nanomaterials - Toxicity, Human Health and Environment*

**8**

**5. Conclusion**

**Author details**

Gustavo M. Do Nascimento

*Raman dispersion of PANI nanofibers.*

**Figure 7.**

provided the original work is properly cited.

Federal University of ABC-CCNH, Brazil

© 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,

materials with the improvement of future nanofiber structural studies.

\*Address all correspondence to: gustavo.morari@ufabc.edu.br

The structural studies of the polyaniline nanofibers by using resonance Raman spectroscopy, as the main technique, have been decisive to elucidate intra- and interchain interactions and chemical and thermal stabilities of PANI nanofibers. The presence of phenoxazine rings is observed in PANI nanofibers formed in micellar media. The presence of these rings is crucial for stacking and stabilization of the fibers. In addition, the changes in bands at low energies are associated with an increase in the torsion angles of Cring-N-Cring segments due to the formation of bipolarons (protonated, spinless units) in the PANI nanofibers. The major diffusion of the ions inside the nanofiber gives a more effective protonation. However, only with the previous thermal treatment, it is possible to retain the nanofiber morphology. Hence, the π-stacking between quinoid rings and the presence of π-π stacking formed by phenoxazine rings can be the driving forces for the formation of the fiber morphology of PANI. The quality of the PANI nanofibers can be monitored by the influence over the Raman dispersion curves. Finally, the example of characterization of PANI nanofibers by using Raman spectroscopy can be applied to other nanofiber

[1] Do Nascimento GM, Silva CHB, Temperini MLA. Electronic structure and doping behavior of PANI-NSA nanofibers investigated by resonance raman spectroscopy. Macromolecular Rapid Communications. 2006;**27**:255

[2] Rodrigues F, Do Nascimento GM, Santos PS. Dissolution and doping of polyaniline emeraldine base in imidazolium ionic liquids investigated by spectroscopic techniques. Macromolecular Rapid Communications. 2007;**28**:666

[3] Do Nascimento GM, Silva CHB, Izumi CMS, Temperini MLA. The role of cross-linking structures to the formation of one-dimensional nanoorganized polyaniline and their Raman fingerprint. Spectrochimica Acta Part A. 2008;**71**:869

[4] Do Nascimento GM, Silva CHB, Temperini MLA. Spectroscopic characterization of the structural changes of polyaniline nanofibers after heating. Polymer Degradation and Stability. 2008;**93**:291

[5] Do Nascimento GM, Kobata PYG, Temperini MLA. Structural and vibrational characterization of polyaniline nanofibers prepared from interfacial polymerization. The Journal of Physical Chemistry. B. 2008;**112**:11551

[6] Rodrigues F, Do Nascimento GM, Santos PS. Studies of ionic liquid solutions by soft X-ray absorption spectroscopy. Journal of Electron Spectroscopy and Related Phenomena. 2007;**155**:148

[7] Do Nascimento GM. In: Kumar A, editor. (Org.)Nanofibers. 1st ed. Austria/Croacia: InTech; 2010

[8] Do Nascimento GM. X-ray absorption spectroscopy of

nanostructured polyanilines. Chemical Papers. 2013;**67**:933

[9] Do Nascimento GM. In: Michaelson L, editor. (Org.)Advances in Conducting Polymers Research. 1st ed. New York: Nova Publishers; 2014

[10] Do Nascimento GM. Raman dispersion in polyaniline nanofibers. Vibrational Spectroscopy. 2017;**90**:89

[11] Shirakawa H, Ikeda S. Infrared spectra of poly(acetylene). Polymer Journal. 1971;**2**:231

[12] Shirakawa H, Ikeda S. Cyclotrimerization of acetylene by tris(acetylacetonato)titanium(III) diethylaluminum chloride system. Journal of Polymer Science. 1974;**12**:929

[13] Chiang CK, Druy MA, Gau SC, Heeger AJ, Louis EJ, MacDiarmid AG, et al. Synthesis of highly conducting films of derivatives of polyacetylene (CH)x. Journal of the American Chemical Society. 1978;**100**:1013

[14] Chiang CK, Fincher CR Jr, Park YW, Heeger AJ, Shirakawa H, Louis EJ, et al. Electrical-conductivity in doped polyacetylene. Physical Review Letters. 1977;**39**:1098

[15] Shirakawa H. The discovery of polyacetylene film: The dawning of an era of conducting polymers (Nobel Lecture). Angewandte Chemie, International Edition. 2001;**40**:2575

[16] Shirakawa H, Louis EJ, MacDiarmid AG, Chiang CK, Heeger AJ. Synthesis of electrically conducting organic polymers-halogen derivatives of polyacetylene, (CH)X. Journal of the Chemical Society, Chemical Communications. 1977;**16**:578

[17] MacDiarmid AG. "Synthetic Metals": A novel role for organic polymers (Nobel Lecture). Angewandte Chemie, International Edition. 2001;**40**:2581

[18] Nigrey PJ, MacDiarmid AG, Heeger AJ. Electrochemistry of polyacetylene, (CH)X- Electrochemical doping of (CH)X films to the metallic state. Journal of the Chemical Society, Chemical Communications. 1979;**14**:594

[19] Han CC, Elsenbaumer RL. Protonic acids- generally applicable dopants for conducting polymers. Synthetic Metals. 1989;**30**(1):123

[20] Heeger AJ. Semiconducting and metallic polymers: The fourth generation of polymeric materials (Nobel Lecture). Angewandte Chemie, International Edition. 2001;**40**:2591

[21] MacDiarmid AG, Epstein AJ. Polyanilines- A novel class of conducting polymers. Faraday Discussions of the Chemical Society. 1989;**88**:317

[22] MacDiarmid AG, Epstein AJ. Conducting Polymers, Emerging Technologies. New Jersey: Technical Insights; 1989. p. 27

[23] MacDiarmid AG, Chiang JC, Richter AF, Sonosiri NLD. In: Alcácer L, editor. Conducting Polymers. Dordrecht: Reidel Publications; 1989

[24] MacDiarmid AG, Epstein AJ. In: Prasad PN, editor. Frontiers of Polymers and Advanced Materials. Vol. 251. New York: Plenum Press; 1994

[25] Huang WS, MacDiarmid AG. Optical properties of polyaniline. Polymer. 1993;**34**:1833

[26] Huang J, Kaner RB. Nanofiber Formation in the chemical polymerization of aniline: A mechanistic study. Angewandte Chemie, International Edition. 2004;**43**:5817

[27] Huang J, Kaner RB. A general chemical route to polyaniline nanofibers. Journal of the American Chemical Society. 2004;**126**:851

[28] Zhang ZM, Wei ZX, Wan MX. Nanostructures of polyaniline doped with inorganic acids. Macromolecules. 2002;**35**:5937

[29] Qiu HJ, Wan MX, Matthews B, Dai LM. Conducting polyaniline nanotubes by template-free polymerization. Macromolecules. 2001;**34**:675

[30] Wei ZX, Wan MX. Hollow microspheres of polyaniline synthesized with an aniline emulsion template. Advanced Materials. 2002;**14**:1314

[31] Gao H, Jiang T, Han B, Wang Y, Du J, Liu Z, et al. Aqueous/ionic liquid interfacial polymerization for preparing polyaniline nanoparticles. Polymer. 2004;**45**:3017

[32] Batchelder DN. In: Brässler H, editor. Optical Techniques to Characterize Polymer Systems. Amsterdam: Elsevier; 1987

[33] Batchelder DN, Bloor D. Advances in Infrared and Raman Spectroscopy. London: Wiley-Heyden; 1984

[34] Clark JH, Dines TJ. Resonance raman spectroscopy, and its application to inorganic chemistry. New analytical methods (27). Angewandte Chemie (International Ed. in English). 1986;**25**:131

[35] McHale JL. Molecular Spectroscopy. US: Prentice-Hall; 1999

[36] Sariciftci NS, Bartonek M, Kuzmany H, Neugebauer H, Neckel A. Analysis of various doping mechanisms in polyaniline by optical, FTIR and Raman spectroscopy. Synthetic Metals. 1989;**29**:193

**11**

*Prologue: Nanofibers*

1994;**50**:12496

201;**1995**:69

*DOI: http://dx.doi.org/10.5772/intechopen.83632*

[37] Furukawa Y, Ueda F, Hydo Y, Harada I, Nakajima T, Kawagoe T. Vibrational spectra and structure of polyaniline. Macromolecules. 1988;**21**:1297

[38] Quillard S, Louarn G, Lefrant S, MacDiarmid AG. Vibrational analysis of polyaniline: A comparative study of leucoemeraldine, emeraldine, and pernigraniline bases. Physical Review B.

[39] Berrada K, Quillard S, Louarn G, Lefrant S. Polyanilines and

study of the Raman spectra of leucoemeraldine, emeraldine and pernigraniline. Synthetic Metals.

Chemistry. 1996;**100**:6998

substituted polyanilines: A comparative

[40] Louarn G, Lapkowski M, Quillard S, Pron A, Buisson JP, Lefrant S. Vibrational properties of polyaniline - Isotope effects. The Journal of Physical *Prologue: Nanofibers DOI: http://dx.doi.org/10.5772/intechopen.83632*

*Nanomaterials - Toxicity, Human Health and Environment*

[27] Huang J, Kaner RB. A general chemical route to polyaniline nanofibers. Journal of the American Chemical Society. 2004;**126**:851

[28] Zhang ZM, Wei ZX, Wan MX. Nanostructures of polyaniline doped with inorganic acids. Macromolecules.

[29] Qiu HJ, Wan MX, Matthews B, Dai LM. Conducting polyaniline nanotubes by template-free polymerization. Macromolecules.

[30] Wei ZX, Wan MX. Hollow microspheres of polyaniline

synthesized with an aniline emulsion template. Advanced Materials.

[31] Gao H, Jiang T, Han B, Wang Y, Du J, Liu Z, et al. Aqueous/ionic liquid interfacial polymerization for preparing polyaniline nanoparticles. Polymer.

[32] Batchelder DN. In: Brässler H, editor. Optical Techniques to Characterize Polymer Systems. Amsterdam: Elsevier; 1987

London: Wiley-Heyden; 1984

[34] Clark JH, Dines TJ. Resonance raman spectroscopy, and its application to inorganic chemistry. New analytical methods (27). Angewandte Chemie (International Ed. in English).

[35] McHale JL. Molecular Spectroscopy.

Kuzmany H, Neugebauer H, Neckel A. Analysis of various doping mechanisms in polyaniline by optical, FTIR and Raman spectroscopy. Synthetic Metals.

[33] Batchelder DN, Bloor D. Advances in Infrared and Raman Spectroscopy.

2002;**35**:5937

2001;**34**:675

2002;**14**:1314

2004;**45**:3017

1986;**25**:131

1989;**29**:193

US: Prentice-Hall; 1999

[36] Sariciftci NS, Bartonek M,

polymers (Nobel Lecture). Angewandte

polyacetylene, (CH)X- Electrochemical doping of (CH)X films to the metallic

[19] Han CC, Elsenbaumer RL. Protonic acids- generally applicable dopants for conducting polymers. Synthetic Metals.

Chemie, International Edition.

[18] Nigrey PJ, MacDiarmid AG, Heeger AJ. Electrochemistry of

state. Journal of the Chemical Society, Chemical Communications.

[20] Heeger AJ. Semiconducting and metallic polymers: The fourth generation of polymeric materials (Nobel Lecture). Angewandte Chemie, International Edition. 2001;**40**:2591

[21] MacDiarmid AG, Epstein AJ.

[22] MacDiarmid AG, Epstein AJ. Conducting Polymers, Emerging Technologies. New Jersey: Technical

Insights; 1989. p. 27

Reidel Publications; 1989

Polymer. 1993;**34**:1833

Formation in the chemical polymerization of aniline: A mechanistic study. Angewandte Chemie, International Edition.

Polyanilines- A novel class of conducting polymers. Faraday Discussions of the Chemical Society. 1989;**88**:317

[23] MacDiarmid AG, Chiang JC, Richter AF, Sonosiri NLD. In: Alcácer L, editor. Conducting Polymers. Dordrecht:

[24] MacDiarmid AG, Epstein AJ. In: Prasad PN, editor. Frontiers of Polymers and Advanced Materials. Vol. 251. New York: Plenum Press; 1994

[25] Huang WS, MacDiarmid AG. Optical properties of polyaniline.

[26] Huang J, Kaner RB. Nanofiber

2001;**40**:2581

1979;**14**:594

1989;**30**(1):123

**10**

2004;**43**:5817

[37] Furukawa Y, Ueda F, Hydo Y, Harada I, Nakajima T, Kawagoe T. Vibrational spectra and structure of polyaniline. Macromolecules. 1988;**21**:1297

[38] Quillard S, Louarn G, Lefrant S, MacDiarmid AG. Vibrational analysis of polyaniline: A comparative study of leucoemeraldine, emeraldine, and pernigraniline bases. Physical Review B. 1994;**50**:12496

[39] Berrada K, Quillard S, Louarn G, Lefrant S. Polyanilines and substituted polyanilines: A comparative study of the Raman spectra of leucoemeraldine, emeraldine and pernigraniline. Synthetic Metals. 201;**1995**:69

[40] Louarn G, Lapkowski M, Quillard S, Pron A, Buisson JP, Lefrant S. Vibrational properties of polyaniline - Isotope effects. The Journal of Physical Chemistry. 1996;**100**:6998

**13**

Section 2

Assessment of

Nanomaterial's Toxicity

Section 2
