Advanced Carbon Materials and Technology E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Advance Materials Series
• Sprache: Englisch

Seitenzahl: 721

Veröffentlichungsjahr: 2013

Beschreibung

The expansion of carbon materials is multidisciplinary and is related to physics, chemistry, biology, applied sciences and engineering. The research on carbon materials has mostly focused on aspects of fundamental physics as they unique electrical, thermal and mechanical properties applicable for the range of applications. The electrons in graphene and other derived carbon materials behave as dirac fermions due to their interaction with the ions of the lattice. This direction has led to the discovery of new phenomena such as Klein tunneling in carbon based solid state systems and the so-called half-integer quantum Hall effect. Advanced Carbon Materials and Technology presents cutting-edge chapters on the processing, properties and technological developments of graphene, carbon nanotubes, carbon fibers, carbon particles and other carbon based structures including multifunctional graphene sheets, graphene quantum dots, bulky balls, carbon balls, and their polymer composites. This book brings together respected international scholars writing on the innovative methodologies and strategies adopted in carbon materials research area including * Synthesis, characterization and functionalization of carbon nanotubes and graphene * Surface modification of graphene * Carbon based nanostructured materials * Graphene and carbon nanotube based electrochemical (bio)sensors for environmental monitoring * Carbon catalysts for hydrogen storage materials * Optical carbon nanoobjects * Graphene and carbon nanotube based biosensors * Carbon doped cryogel films * Bioimpact of carbon nanomaterials * Photocatalytic nature of carbon nanotube based composites * Engineering behavior of ash fills * Fly ash syntactic foams microstructure

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Part 1: Graphene, Carbon Nanotubes and Fullerenes

Chapter 1: Synthesis, Characterization and Functionalization of Carbon Nanotubes and Graphene: A Glimpse of Their Application

1.1 Introduction

1.2 Synthesis and Characterization of Carbon Nanotubes

1.3 Synthesis and Characterization of Graphene

1.4 Methods Used in Our Lab: CVD, Thermal Exfoliation, Arc Discharge and Chemical Reduction

1.5 Functionalization of Carbon Nanotubes and Graphene

1.6 Applications

1.7 Conclusion

Acknowledgements

References

Chapter 2: Surface Modification of Graphene

2.1 Introduction

2.2 Surface-Modified Graphene from GO

2.3 Application of Surface-Modified Graphene

2.4 Conclusions and Future Directions of Research

Acknowledgement

References

Chapter 3: Graphene and Carbon Nanotube-based Electrochemical Biosensors for Environmental Monitoring

3.1 Introduction

3.2 Applications of Electrochemical Biosensors

3.3 Conclusions and Future Perspectives

References

Chapter 4: Catalytic Application of Carbon-based Nanostructured Materials on Hydrogen Sorption Behavior of Light Metal Hydrides

4.1 Introduction

4.2 Different Carbon Allotropes

4.3 Carbon Nanomaterials as Catalyst for Different Storage Materials

4.4 Key Results with MgH2, NaAlH4 and Li-Mg-N-H Systems

4.5 Summary

Acknowledgements

References

Chapter 5: Carbon Nanotubes and Their Applications

5.1 Introduction

5.2 Carbon Nanotubes Structure

5.3 Carbon Nanotube Physical Properties

5.4 Carbon Nanotube Synthesis and Processing

5.5 Carbon Nanotube Surface Modification

5.6 Applications of Carbon Nanotubes

5.7 Conclusion

References

Chapter 6: Bioimpact of Carbon Nanomaterials

6.1 Biologically Active Fullerene Derivatives

6.2 Biologically Active Graphene Materials

6.3 Bioimpact of Carbon Nanotubes

6.4 Genotoxicity of Carbon Nanomaterials

6.5 Ecotoxicological Effects of Carbon Nanomaterials

References

Part 2: Composite Materials

Chapter 7: Advanced Optical Materials Modified with Carbon Nano-Objects

7.1 Introduction

7.2 Photorefractive Features of the Organic Materials with Carbon Nanoparticles

7.3 Homeotropic Alignment of the Nematic Liquid Crystals Using Carbon Nanotubes

7.4 Thin Film Polarization Elements and Their Nanostructurization via CNTs

7.5 Spectral and Mechanical Properties of the Inorganic Materials via CNTs Application

7.6 Conclusion

Acknowledgments

References

Chapter 8: Covalent and Non-Covalent Functionalization of Carbon Nanotubes

8.1 Introduction

8.2 Functionalization of Carbon Nanotubes

8.3 Covalent Functionalization

8.4 Non-Covalent Functionalization

8.5 Functionalization of CNT with Nanoparticles

8.6 Conclusion

Acknowledgment

References

Chapter 9: Metal Matrix Nanocomposites Reinforced with Carbon Nanotubes

9.1 Introduction

9.2 Carbon Nanotubes

9.3 Processing and Microstructural Characterization of Metal Matrix Nanocomposites

9.4 Mechanical Properties of Carbon Nanotube Reinforced Metal Matrix Nanocomposites

9.5 Strengthening Mechanisms

9.6 Thermal Properties of Carbon Nanotube Reinforced Metal Matrix Nanocomposites

9.7 Tribological Properties of Carbon Nanotube Reinforced Metal Matrix Nanocomposites

9.8 Challenges

9.9 Concluding Remarks

References

Part 3: Fly Ash Engineering and Cryogels

Chapter 10: Aluminum/Fly Ash Syntactic Foams: Synthesis, Microstructure and Properties

10.1 Introduction

10.2 Hollow Particles

10.3 Synthesis Methods

10.4 Microstructure of Aluminum/Fly Ash Composites

10.5 Properties of Aluminum/Fly Ash Syntactic Foams

10.6 Applications

10.7 Conclusion

Acknowledgments

References

Chapter 11: Engineering Behavior of Ash Fills

11.1 Background

11.2 Engineering Evaluation of Cemented Ash Fill

11.3 Problems of Uncemented Ash Fill

11.4 Ash as a Structural Fill

11.5 Conclusions

References

Chapter 12: Carbon-Doped Cryogel Thin Films Derived from Resorcinol Formaldehyde

12.1 Introduction

12.2 Experimental Procedure

12.3 Results and Discussion

12.4 Conclusion

Acknowledgements

References

Index

Advanced Carbon Materials and Technology

Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106

Advance Materials SeriesThe Advance Materials Series is intended to provide recent advancements of the fascinating field of advanced materials science and technology, particularly in the area of structure, synthesis and processing, characterization, advanced-state properties, and applications. The volumes will cover theoretical and experimental approaches of molecular device materials, biomimetic materials, hybrid-type composite materials, functionalized polymers, superamolecular systems, information- and energy-transfer materials, biobased and biodegradable or environmental friendly materials. Each volume will be devoted to one broad subject and the multidisciplinary aspects will be drawn out in full.

Series Editor: Dr. Ashutosh TiwariBiosensors and Bioelectronics CentreLinkoping UniversitySE-581 83 LinkopingSwedenE-mail: [email protected] Editors: Swapneel Despande and Sudheesh K. Shukla

Publishers at ScrivenerMartin Scrivener([email protected])Phillip Carmical ([email protected])

Copyright © 2014 by Scrivener Publishing LLC. All rights reserved.

Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts.Published simultaneously in Canada.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or other -wise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, [phone], fax [phone], or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, [phone], fax [phone], or online at http://www.wiley.com/go/permission.

Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at [phone], outside the United States at [phone] or fax [phone].

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com.

For more information about Scrivener products please visit www.scrivenerpublishing.com.

Cover design by Russell Richardson

Library of Congress Cataloging-in-Publication Data:

ISBN 978-1-118-68623-2

Preface

The expansion of carbon materials is the focal point of materials research and technology which is mostly related to physics, chemistry, biology, applied sciences and engineering. Research on carbon materials has mainly focused on the aspects of fundamental physics that have unique electrical, thermal and mechanical properties applicable for a range of applications. The electrons in graphene and other derived carbon materials behave as dirac fermions due to their interaction with the ions of the lattice. This direction has led to the discovery of new phenomena such as Klein tunneling in carbon-based solid state systems, and the so-called half-integer quantum Hall effect due to a special type of Berry phase. In pursuit of the same goal, Advanced Carbon Materials and Technology offers detailed, up-to-date chapters on the processing, properties and technological developments of graphene, carbon nanotubes, carbon fibers, carbon particles and other carbon-based structures, including multifunctional graphene sheets, graphene quantum dots, bulky balls, carbon balls, and their polymer composites.

Nanoscaled materials have properties which make them useful for enhancing surface-to-volume ratio, reactivity, strength and durability. The chapter entitled, “Synthesis, Characterization and Functionalization of Carbon Nanotubes and Graphene: A Glimpse of Their Application,” encompasses the principles of nanotubes and graphene production, new routes of preparation and numerous methods of modification essential for various potential applications. The chapter on, “Surface Modification of Graphene,” covers a range of covalent and non-covalent approaches. In the chapter, “Graphene and Carbon Nanotube-Based Electrochemical Biosensors for Environmental Monitoring,” the use of carbon nanotubes and numerous graphene-based affinity electrodes for the development of novel tools for monitoring environmental pollution are described. The chapter on, “Catalytic Application of Carbon-Based Nanostructured Materials on Hydrogen Sorption Behavior of Light Metal Hydrides,” describes the state-of-the-art of carbon nanotubes, carbon nanofibers and graphene as a catalyst for the aforesaid hydrogen storage materials. An informal presentation about recent progress in the advances in synthetic techniques for large-scale production of carbon nanotubes, their purification and chemical modification, and the emerging technologies they enable are presented in the chapter, “Carbon Nanotubes and Their Applications.” Moreover, a chapter dedicated to the, “Bioimpact of Carbon Nanomaterials,” discusses graphene, nanotubes and fullerenes, along with their nanotoxicity, nanoecotoxicity, and various biomedical applications.

Carbon nano-objects including fullerenes, carbon nanotubes, carbon quantum dots, shungites and graphenes, show unique photorefractive characteristics. The chapter on, “Advanced Optical Materials Modified with Carbon Nano-Objects,” illustrates the spectral, photoconductive, photorefractive and dynamic properties of the optical carbon objects-based nanomaterials. “Covalent and Non-Covalent Functionalization of Carbon Nanotube: Applications,” deals with the photocatalytic nature of carbon nanotube-based composites. Illustrated in, “Metal Matrix Nanocomposites Reinforced with Carbon Nanotubes,” are the preparation and properties of nanocomposites based on aluminium, copper, magnesium, nickel and titanium with reinforced matrix of nanofiller carbon materials (e.g., nanoplatelets, nanoparticles, nanofibers and carbon nanotubes) using various processing techniques. The chapter also discusses reinforcement using carbon nanotubes, interfacial bonding, thermal, mechanical, and tribological properties and tne challenges related to the synthesis of composites.

Fly ash, a waste by-product of coal thermal power plants, is a carbon-based lightweight material. Fly ash is generally inexpensive and is considered to be an environmental hazard, thus utilization of fly ash in composites proves to be both economically and environmentally beneficial. In this way, use of fly ash in developing advanced composites is very encouraging for the next generation of advanced lightweight composites. The discussion in, “Aluminum/Fly Ash Syntactic Foams: Synthesis, Microstructure and Properties,” is focused on the methods of synthesis for fly ashfilled aluminum matrix composites along with their microstructure and mechanical properties, and the tribological properties of Al/fly ash syntactic foams. The chapter entitled, “Engineering Behavior of Ash Fills,” covers the extensive characterization, hardening, bearing capacity and settlement of ash fill technology. The chapter on, “Carbon-Doped Cryogel Thin Films Derived from Resorcinol Formaldehyde,” presents results of the structural and optical properties of carbon-doped cryogel thin films derived from resorcinol formaldehyde.

This book is written for a large readership, including university students and researchers from diverse backgrounds such as chemistry, materials science, physics, pharmacology, medical science and engineering, with specializations in the civil, environmental and biomedical fields. It can be used not only as a textbook for both undergraduate and graduate students, but also as a review and reference book for researchers in materials science, bioengineering, medicine, pharmacology, biotechnology and nanotechnology. We hope that the chapters of this book will provide the readers with valuable insight into state-of-the-art advanced and functional carbon materials and cutting-edge technologies.

EditorsAshutosh Tiwari, PhDS.K. Shukla, PhD

Managing EditorsSwapneel DespandeSudheesh K. Shukla

Part 1

GRAPHENE, CARBON NANOTUBES AND FULLERENES

Chapter 1

Synthesis, Characterization and Functionalization of Carbon Nanotubes and Graphene: A Glimpse of Their Application

Mahe Talat and O.N. Srivastava*

Nanoscience and Nanotechnology Unit, Department of Physics, Banaras Hindu University, Varanasi, India

*Corresponding author: [email protected]

Abstract

Since the discovery of nanomaterials, carbon nanotubes structures have attracted great interest in most areas of science and engineering due to their unique physical and chemical properties and are supposed to be a key component of nanotechnology. The most recent addition to the family of carbon nanostructures is graphene. Graphene is a one-atom-thick material consisting of sp2-bonded carbon with a honeycomb structure. It resembles a large polyaromatic molecule of semi-infinite size. In the past five years, graphene-based nanomaterials have been the focus of not only material scientists but also engineers and medical scientists. The interesting and exciting properties of single-layer graphene sheets have excited the scientific community especially in the areas of materials, physics, chemistry and medical science. The state-of-the-art CNT production encompasses numerous methods and new routes are continuously being developed. The most common synthesis techniques are arc discharge, laser ablation, high pressure carbon monoxide (HiPCO) and chemical vapor deposition (CVD) with many variants. Most of these processes take place in vacuum or with process gases. By choosing appropriate experimental parameters, large quantities of nanotubes can be synthesized by these methods. It is possible to control some properties of the final product, such as type of CNTs synthesized (MWNTs vs. SWNTs), the quality of the nanotubes, the amount and type of impurities, and some structural CNT features. In this chapter we discuss some of the methods employed in our lab for the synthesis and characterization of the CNTs and graphene. For application in biomedical and targeted drug delivery, the major limitation of these nanomaterials is their poor solubility, agglomeration and processibility. Functionalization of CNTs and GS is, therefore, necessary to attach any desired compounds including drug and also to enhance the solubility and biocompatibility of these nanomaterials. Two types of functionalization methods, i.e., covalent and non-covalent methods are generally being adopted. We deliberate these two procedures of functionalization of CNTs and GS. The merits of these two modes of functionalization will also be discussed.

Keywords: Synthesis, characterization, application, CNT, graphene

1.1 Introduction

The most recent addition to the family of carbon nanostructures is graphene. Graphene is a one-atom-thick material consisting of sp2-bonded carbon with a honeycomb structure. It resembles a large polyaromatic molecule of semi-infinite size. In the past five years, graphene-based nanomaterials have been the focus of not only material scientists but also engineers and medical scientists. The interesting and exciting properties of single-layer graphene sheets, such as high mechanical strength, high elasticity and thermal conductivity, demonstration of the room-temperature quantum Hall effect, very high room temperature electron mobility, tunable optical properties, and a tunable band gap have excited the scientific community especially in the areas of materials, physics, chemistry and medical science. Following the series of Nobel Prizes awarded after the discovery of fullerenes, another nano star—graphene—received the 2010 Nobel Prize in Physics “for groundbreaking experiments regarding the two-dimensional material graphene” performed by Andre Geim and Konstantin Novoselov [2].

Therefore, the discovery and subsequent applications of these carbon nanomaterials have allowed the development of an entire branch of nanotechnology based on these versatile materials.

1.2 Synthesis and Characterization of Carbon Nanotubes

The first experimental evidence of carbon nanotubes (CNTs) came in 1991 [3] in the form of multi-wall nanotubes (MWNT), which motivated a sudden increase in nanotubes synthesis research. In 1993, the first experimental evidence of single-wall nanotubes (SWNT) was introduced [4]. Since then, the synthesis methods for CNTs have been developed tremendously. Production methods for carbon nanotubes (CNTs) can be broadly divided into two categories, chemical and physical, depending upon the process used to extract atomic carbon from the carbon-carrying precursor. Chemical methods rely upon the extraction of carbon solely through catalytic decomposition of precursors on the transition metal nanoparticles, whereas physical methods also use high energy sources, such as plasma or laser ablation to extract the atomic carbon. However, the most common synthesis techniques are arc discharge, laser ablation, high pressure carbon monoxide (HiPCO) and chemical vapor deposition (CVD) with many variants [5]. Most of these processes take place in vacuum or with process gases. By choosing appropriate experimental parameters, large quantities of nanotubes can be synthesized by these methods. It is possible to control some properties of the final product, such as type of CNTs synthesized (MWNTs vs SWNTs), the quality of the nanotubes, the amount and type of impurities, and some structural CNT features [6]. Other reported methods include plastic pyrolysis [7], diffusion flame synthesis and electrolysis using graphite electrodes immersed in molten ionic salts [8] and ball-milling of graphite [9].

In this chapter, we will discuss the method of synthesis of CNTs employed in our lab such as spray pyrolysis, arc discharge method and synthesis of CNTs by low pressure chemical vapor deposition (LPCVD) method, and catalytic decomposition of hydrocarbon gases, e.g., methane and ethylene, onto the Ferritin/Fe- SiO2- Si substrates.

Synthesis of CNTs was carried out using spray pyrolysis-assisted CVD method, where ferrocene (C10H10Fe) was used as a source of iron (Fe) which acts as a catalyst for the growth of CNTs. Castor oil was used as the carbon source; castor oil contains carbon, hydrogen and lower amount of oxygen. The spray pyrolysis setup consisted of a nozzle (inner diameter ~ 0.5 mm) attached to a ferrocene-castor oil supply used for releasing the solution into a quartz tube (700 mm long and inner diameter 25 mm), which was mounted inside a reaction furnace [10].

Spray pyrolysis of castor oil-ferrocene solution at ~ 850°C in Ar atmosphere leads to a uniform thick black deposition on the inner wall of the quartz tube at the reaction hot zone (~ 850°C). Figure 1.1(a) shows the SEM morphology of the as-grown CNTs. The length of CNTs was ~ 5–10 μm. Structural details of the as-grown CNTs sample were further investigated by TEM. Typical TEM image of the as-grown CNTs is shown in Figure 1.1(b). The TEM investigation of the as-grown CNTs confirms that the CNTs are multi-walled in nature. These nanotubes have varying diameters ranging from ~ 20–60 nm. In the spray pyrolysis reaction, the castor oil-ferrocene solution was atomized via spray nozzle and sprayed through carrier gas (Ar). The Fe particles (liberated by the decomposition of ferrocene) were deposited on the inner walls of the quartz tube. The carbon species released from decomposition of castor oil and also from ferrocene got adsorbed on the Fe particles and diffused rapidly along the axial direction leading to the formation of CNTs. A study was also done using castor oil-ferrocene with ammonia solution so as to develop CNTs containing nitrogen, i.e., C-N nanotubes. This was done keeping in view the fact that nitrogen-doped CNTs are considered as one of the important ingredients of CNT-based electronics. Figure 1.2(a) shows a typical SEM micrograph of as-grown C-N nanotubes, which reveals the wavy morphology of nanotubes. These wavy nanotubes are most likely due to pentagonal and heptagonal defects that are introduced in the hexagonal sheets. TEM images of the as-grown C-N nanotubes are shown in Figure 1.2(b). These CNTs have bamboo-shaped structures. The TEM image in Figure 1.2(b) shows that the nanotubes have a range of diameters varying from ~ 50–80 nm. It is suggested that the bamboo-shaped morphologies arise from the incorporation of pyridine-like N atoms within the carbon framework [11]. Also, no encapsulated metal particle was found inside the nanotubes.

Figure 1.1 SEM (a) and TEM (b) micrographs of the as-grown CNTs obtained by spray pyrolysis of castor oil-ferrocene solution at ~ 850°C [11].

Figure 1.2 SEM (a) and TEM (b) micrographs of the as-grown C-N nanotubes obtained by spray pyrolysis of castor oil-ferrocene with ammonia solution at ~ 850°C [11].

Another method used is arc discharge method where SWNTs webs have been synthesized using Fe as catalysts by this method in argon atmosphere. SWNTs has been synthesized by using electric arc discharge of graphite cathode (3cmx1cmx1cm) and Fe as well as Ni-Y filled anode (5cmx0.8cmx0.8) at 200 torr pressure of argon gas. The SWNTs webs have been synthesized using Fe as catalysts by arc discharge method in argon atmosphere. Figure 1.3 shows the low magnification SEM micrographs of as-synthesized SWNTs web. The inset of Figure 1.3(a) shows the optical photograph of the as-deposited web on the chamber walls. The length of these webs is around 4 to 6 cm. The webs are ~75 to 100 μm thick, which abundantly contains the SWNTs, as is clear from Figure 1.3(b). Figure 1.3(c) shows the SEM image from the inner region between the two webs, dominantly containing SWNTs. A few SWNTs are also visible in Figure 1.3(d), which are coming out from these bundles.

Figure 1.3 (a–d) SEM micrographs of as synthesized SWNTs webs, Inset of Fig. 1.3(a) shows the optical photograph of SWNTs web, some SWNTs which are coming out of the bundle.

Figure 1.4 shows the transmission electron micrographs of SWNTs bundles. Figure 1.4(a) reveals the bundles containing large amount of SWNTs along with the catalyst particle which have been used to synthesize these SWNTs. Figure 1.4(b) shows the HRTEM image of as synthesized SWNTs as shown in Figure 1.4(a). Figure 1.4(c,d) are from the different regions of the samples containing SWNTs bundles and also catalysts particles and some amorphous carbon which have been coated onto the SWNTs bundles. The diameter of individual SWNTs is found to be approximately 1.6 nm. (Synthesis of SWNTs and graphene by electric arc discharge method in Ar atmosphere, S. Awasthi, K. Awasthi and O.N. Srivastava, J Nanosci Nanotech [under submission].)

Figure 1.4 (a–d) HRTEM micrographs of SWNTs web from different regions.

Raman analysis of as-synthesized SWNTs webs was also done. In Figure 1.5, the presence of RBM at 132 cm−1 confirms the formation of SWNTs. The diameter of SWNTs as calculated from RBM is found to be 1.91 nm, which is in good agreement with the HRTEM results. Since G peak is related to the sp2 bonding and is common to all the graphitic materials, and D peak is the defect-induced peak, showing the mixed state of sp2-sp3 bonding, the intensity ratio of the D peak to the G peak can be used to quantify the quality of the graphitic samples. In the present case, this ratio was found to be ~0.08, which confirms that the as-synthesized nanotubes are highly crystalline and defect free in nature.

Figure 1.5 Raman spectrum of as-synthesized SWNTs webs.

Through synthesis of CNTs by low pressure chemical vapor deposition (LPCVD) method we have grown CNTs (single-walled) by LPCVD method on Ferritin-based Fe catalyst. The SWNTs were grown using LPCVD unit (Automate, USA) (Fig.1.6). The substrate, i.e., ferritin-SiO2-Si (supplied by Automate USA), was placed into the center of a 50 mm quartz tube reactor. First, the iron oxide particles were reduced under a H2 pressure of 200 mbar at 800°C for 10 min. CNTs growth was then performed on the substrate at 800°C for 15 and 30 min under flows of 1400 sccm of methane, 100 sccm of ethylene and 500 sccm of H2. After CVD reaction, the furnace was switched off and allowed to cool down to room temperature under Ar gas flow of 500 sccm. (Synthesis of SWNTs and graphene by electric arc discharge method in Ar atmosphere, S. Awasthi, K. Awasthi and O.N. Srivastava, J Nanosci Nanotech [under submission].)

Figure 1.6 SEM images of as-grown CNTs using ferritin-SiO2-Si substrate at different temperatures.

1.3 Synthesis and Characterization of Graphene

Graphite is stacked layers of many graphene sheets, bonded together by week van der Waals force. Thus, in principle, it is possible to produce graphene from a high purity graphite sheet, if these bonds can be broken. Exfoliation and cleavage use mechanical and chemical energy, respectively, for breaking these weak bonds and separate out individual graphene sheets. To scale up the production, various synthetic methods are being developed. Some of the methods listed are presented below.

1.3.1 Micromechanical Cleavage of Highly Oriented Pyrolytic Graphite

The remarkably simple yet efficient method developed by Novoselov and Geim consists in using common adhesive tape to repeat the stick and peel process a dozen times which statistically brings a 1mm-thick graphite flake to a monolayer thin sample. The first piece of graphene sheet was obtained via manual mechanical cleavage of graphite with a Scotch tape [12], which seems to break the rule that no 2D crystals can exist under ambient conditions and shows us many unusual properties [12]. The exfoliated graphene manifests a unique structure and superior properties, although this production method is not applicable on a large scale. Inspired by this pioneering work, several alternative techniques have been developed for fabricating graphene materials.

Graphene has been made by four different methods. This approach, which is also known as the “Scotch tape” or peel-off method, was based on earlier work on micromechanical exfoliation from patterned graphite [13], and the fourth was the creation of colloidal suspensions. Micromechanical exfoliation has yielded small samples of graphene that are useful for fundamental study, although large-area graphene films (up to ~1cm2) of single- to few-layer graphene have been generated by CVD growth on metal.

1.3.2 Chemical Vapor Deposition Growth of Graphene either as Stand Alone or on Substrate

Another feasible method is by chemical vapor deposition (CVD) and epitaxial growth, such as decomposition of ethylene on nickel surfaces [14]. These early efforts (which started in 1970) were followed by a large body of work by the surface-science community on “monolayer graphite” [15]. Epitaxial growth on electrically insulating surfaces such as SiC has also been used for the growth of graphene [16, 17]. One of the highly popular techniques of graphene growth is thermal decomposition of Si on the (0001) surface plane of single crystal of 6H-SiC [18]. Graphene sheets are found to be formed when H2-etched surface of 6H-SiC was heated to temperatures of 1250 to 14500°C for a short time (1–20 minutes). Graphene epitaxially grown on this surface typically has 1 to 3 graphene layers; the number of layers being dependent on the decomposition temperature. In a similar process, Rollings et al. have produced graphene films as low as one atom thick [19]. The first report on planar few-layer graphene (PFLG) synthesized by CVD was in 2006 [20]. In this work, a natural, eco-friendly, low-cost precursor, camphor, was used to synthesize graphene on Ni foils. Camphor was first evaporated at 1800°C and then pyrolyzed in another chamber of the CVD furnace at 700 to 850°C using argon as the carrier gas. Large-area, high quality graphene can also be grown by thermal CVD on catalytic transition metal surfaces such as nickel and copper [21, 22]. Reina et al. prepared single- to few-layer graphene on polycrystalline Ni film of 1–2 cm2 [23]. The Ni film (500 nm thick) was evaporated on a SiO2/Si substrate and was annealed in Ar+H2 atmosphere at 900 to 10000°C, for 10 to 20 minutes. This annealing step created Ni grains of 5 to 20 μm in size. After CVD at 900 to 10000°C for 5 to 10 minutes, using 5 to 25 sccm CH4 and 1500 sccm H2, graphene was found to form on the Ni—the size of each graphene being restricted by the Ni grain size. For Ni, mixed mono-and bi-layer graphene coverage of 87% has been reported [24, 25], while for Cu foils, an average of 95% of surfaces were covered by mono-layer graphene [26]. The graphene was later transferred to any substrate, keeping its electrical properties unchanged, thus making them suitable for various electronic applications. Typical CVD graphene growth uses gaseous hydrocarbons at elevated temperatures as the carbon source, such as methane, ethylene [27-29] and acetylene [3]. Single-layer graphene were synthesized from ethanol on Ni foils in an Ar atmosphere under atmospheric pressure by flash cooling after CVD, but a wide variation in graphene layer number was observed over the metal surface [31]. Single-and few-layer graphene films were grown employing a vacuum-assisted CVD technique on Cu foils using n-hexane as a liquid precursor [32]. Copper appears to have a small affinity for oxygen that allows for graphene growth even if the source of carbon is a solid, such as the sugar as reported recently [33]. Graphene, thus synthesized and transferred onto a glass substrate, has shown 90% optical transmittance [34].

1.3.3 Chemical and Thermal Exfoliation of Graphite Oxide

Some recent success in regards to graphene includes chemical exfoliation through the formation of derivatized graphene sheets such as GO [35, 36], r-GO [37], or halogenated graphene, solvent-assisted ultrasonic exfoliation [38]. Graphite oxide was first prepared in the nineteenth century [39], and since then it has been mainly produced by the following methods pronounced by Brodie, Staudenmaier [40] and Hummers [41]. All three methods involve oxidation of graphite in the presence of strong acids and oxidants. The level of the oxidation can be varied on the basis of the method, the reaction conditions and the precursor graphite used. Although extensive research has been done to reveal the chemical structure of graphite oxide, several models are still being worked out. Graphite oxide consists of a layered structure of “graphene oxide” sheets that are strongly hydrophilic such that intercalation of water molecules between the layers readily occurs [42]. The interlayer distance between the graphene oxide sheets increases reversibly from 6 to 12 Å with increasing relative humidity [43]. Notably, graphite oxide can be completely exfoliated to produce aqueous colloidal suspensions of graphene oxide sheets by simple sonication [44] and by stirring the water/graphite oxide mixture for a long enough time [45]. The second approach is the oxidation-exfoliation-reduction of graphite powder [46]. Severe oxidation treatment converts graphite to hydrophilic graphite oxide which can be exfoliated into single-layer graphite oxide (graphene oxide) via stirring or mild sonication in water. Graphene oxide can be regarded as a functionalized graphene containing hydroxyl, epoxy and carboxylic groups, providing reaction sites for chemical modifications [47]. Reducing graphene oxide can partly restore its graphitic structure as well as conductivity [48]. Although reduced graphene oxide (r-GO), (also called chemically modified graphene [CMG], chemically converted graphene [CCG] or graphene), has considerable defects, it is one of the most widely used graphene-based renewable energy materials due to its low cost, facile preparation process, large productivity, and potential for functionalization [49].

1.3.4 Arc-Discharge Method

The arc-discharge method has also been used to prepare graphene sheets. Rao et al. reported for the first time that the arc-discharge method can also be used for the synthesis of graphene sheets [50]. By using graphite rods as electrodes, they have synthesized pure graphene with mainly 2–4 layers in the inner wall region of the arc chamber under relatively high pressure of hydrogen without any catalyst. Moreover, through this method, nitrogen-doped and boron-doped graphene sheets can also be easily synthesized with boron sources (B2H6) or nitrogen sources (pyridine) mixed into the hydrogen gas. However, the size and thickness of the pure graphene sheets still have room to improve, and the properties of the N- and B-doped graphene sheets synthesized also need further studies.

1.4 Methods Used in Our Lab: CVD, Thermal Exfoliation, Arc Discharge and Chemical Reduction

Figure 1.7 The XRD patterns of graphite, graphite oxide and graphene samples.

Few-layer graphene (FLG) has been synthesized by using electric-arc discharge of graphite electrodes in argon ambience at different pressure. The arc was maintained by continuously translating the anode to keep a constant distance of ~1 mm from the cathode. The deposits collected from the inner walls of the arc chamber have been characterized and Figure 1.8(a,b) shows the TEM images of as-synthesized FLG at 350 torr pressure of argon. Distinct features of the micrographs are the large-area graphene sheet-like structures as can clearly be seen in the Figure 1.8. Few-layer graphene nanosheets are clearly visible in the images. The Figure 1.8(b) shows the HRTEM image of the large-area graphene with minimum number of layers equal to four. The width of these graphene nanosheets is ~100–200 nm.

Figure 1.8 TEM micrographs of as-synthesized graphene nanosheets at 350 torr argon pressure.

1.4.1 Raman Spectra

It is worth mentioning that an extensive analysis of graphene has been reported by Ferrari et al. [53], who have demonstrated that the second order Raman peak centered at 2700 cm–1 (2D peak) is the characteristic graphene feature and can be very useful in identifying the number of layers in a few-layer graphene sample. The number of layers in a graphene film can be estimated from the intensity, shape and position of the G and 2D bands. While the 2D band changes its shape, width and position with an increasing number of layers, the G-band peak position shows a down-shift with the number of layers. From XRD and TEM analysis it has been found that at 350 torr the minimum numbers of graphene layer are formed. By monitoring the width and position of this 2D peak one can deduce the number of layers from graphene samples. In Figure 1.9 at 350 torr, the 2D peak is at 2687cm−1, confirming the formation of FLG.

Figure 1.9 Raman Spectra at 350 torr.(Synthesis of SWNTs and graphene by electric arc discharge method in Ar atmosphere, S. Awasthi, K. Awasthi and O.N. Srivastava, J Nanosci Nanotech [under submission].)

Synthesis of large-area, high-quality and uniform graphene films on metal substrate by chemical vapor deposition (CVD) is shown in Figure 1.10. Chemical vapor deposition (CVD) is one of the main interesting synthetic procedures because it employs hydrocarbon decomposition over substrates, where metal nanoparticles have been placed. A one meter long quartz tube is used in the CVD system in our laboratory. The CVD system has a two zone furnace and the diameter of the quartz tube is 2 inches. The quartz tube is adjusted in the two zone CVD furnace. The solid carbon precursor (sugar) is placed in an alumina boat and placed on the middle portion in the first zone furnace. Alloy pieces are placed in a second alumina boat and it is placed in the second zone furnace. The distance between substrate and precursor is nearly 22 cm. In the first few (15) minutes only high purity gas flows. After that, the heating starts in the second zone (substrate) furnace set at 850°C in the presence of 200 sccm flow rate of argon gas. In the metal substrate we used copper and gold foil, and copper-gold alloy (Cu3Au2) as a substrate. Next, CH4 was introduced at a flow rate of 30 sccm and H2 at 50 sccm for annealing. After this the solid carbon precursor was vaporized and deposited on the substrate in the form of graphene.

Figure 1.10 CVD set-up.

In Figure 1.11(a) given below, Raman spectra of graphene was deposited on Cu3Au2 substrate. The appearance of a well-pronounced 2D peak at 2685cm−1 reveals the formation of high quality (probably single-layer) graphene. While in Figure 1.11(b), the growth of a large graphene island on Cu3Au2 substrate is visible in the image captured by Raman spectrophotometer.

Figure 1.11 (a) Raman spectra of graphene deposited on Cu3Au2 substrate; (b) image captured by Raman spectrophotometer.

1.4.2 Electrochemical Exfoliation

The electrochemical methods of preparing GN flakes involve the application of cathodic or anodic potentials or currents in either aqueous (acidic or other media) or non-aqueous electrolytes. One of the most important parameters for consideration of scaling-up the electrochemical technology is the yield of GN flakes. Single- or multi-layered GN flakes can easily be produced in short periods of time. It is a simple and fast method to exfoliate graphite into thin graphene sheets, mainly AB-stacked bilayered graphene with large lateral size (several to several tens of micrometers). In this method we take a chemical mixed with deionized water; graphite is used as an anode and platinum is used as cathode, and voltage is applied. Within a few minutes whole graphite foil is exfoliated into thin graphene sheets and dispersed into whole electrolyte (Figure 1.12). The electrical properties of these exfoliated sheets are radially superior to commonly used reduced graphene oxide, whose preparation typically requires many steps including oxidation of graphite and high temperature reduction.

Figure 1.12 A set up in our lab showing (a) before exfoliation; (b) after exfoliation.

1.5 Functionalization of Carbon Nanotubes and Graphene

Beyond synthesis by different techniques, it appears immediately clear that CNTs and graphene need processing after their synthesis. To address this issue, purification methods and, above all, functionalization approaches, are essential to allow manipulation and further application of this material. Usually, metal nanoparticles and amorphous carbon are present as a synthetic residue. In general, these carbon nanomaterials are a fluffy powder difficult to manage, while chemical functionalization contributes to the preparation of more homogenous and soluble material. SWNTs are highly polarizable smooth-sided carbon compounds with attractive interaction of 0.5 eV per nanometer of inter-tube contact. This extreme cohesive force makes it difficult to disperse SWNTs into individual state. Pristine SWNTs tend to agglomerate in the polymer matrix and form bundles. Similarly, pristine graphene is also hydrophobic, so producing stable suspension of graphene in water or organic solvents is an important issue for the fabrication of many graphene-based devices [54, 55]. Prevention of aggregation was of particular importance for graphene sheets because most of their unique properties were only associated with individual sheets and keeping them well separated was required. Strategies for functionalizing these carbon nanomaterials are important for the pursuit of these applications so these materials should be dispersed uniformly and form stable suspension. In recent years, new functionalization methods have been developed to disperse these carbon nanomaterials which allow their application [56, 57] A wide variety of functionalizations have been reported in the literature [58–60], the most important of which are summarized in Scheme 1.1. We can categorize mainly covalent and non-covalent approaches.

Scheme 1.1 A wide variety of functionalizations adapted from ref. [61].

1.5.1 Covalent Functionalization

In this method CNTs are functionalized by nonreversible attachment of appendage on the sidewalls and/or on the tips. Also in this case, many different approaches are reported [13]. Briefly, reactions can be performed at the sidewall site (sidewall functionalization) or at the defect sites (defect functionalization), usually localized on the tips. In the first case, fluorination with elemental fluorine at high temperature (400–600°C) has been explored, accomplishing further substitutions with alkyl groups. Furthermore, radical addition via diazonium salt has been proposed by Tour’s group [62]. On the other hand, cycloadditions have found wide interest. Cycloadditions have been reported, such as carbene [2+1] cycloadditions or Diels-Alder via microwave (MW) irradiation cycloaddition. Side defects functionalization occurs via amidation or esterification reactions of carboxylic residues obtained on CNTs. Moreover, it is feasible that in general caps (i.e., tips when they are not cut) are more reactive than sidewalls because of their mixed pentagonal-hexagonal structure. The f-MWCNTs are not modified in their electronic structure and new properties can be added by means of functionalization. Instead, electronic properties of SWCNTs are perturbed by covalent functionalization and double bonds are irreversibly lost. This may affect conductive property, preventing further CNT applications.

1.5.2 Non-Covalent Functionalization

Recently, non-covalent functionalization has been preferred as it has several advantages over covalent functionalization. Noncovalent functionalization preserves the structural and electrical properties of CNTs and graphene which may be advantageous for future application. Noncovalent functionalization of these carbon nanonmaterials is basically through van der Waals, electrostatic and π-stacking interaction, etc. [63]. CNTs wrapping by polymers, including DNA, have been studied [64]; also, proteins are able to non-convalently interact with CNTs and these are often used for biosensor applications [65]. Furthermore, these procedures are usually quite simple and quick, and involve simple steps like ultrasonication, filteration, magnetic stirring and centrifugation, etc., and also do not perturb the electronic structure of CNTs, graphene and SWCNTs in particular.

These functionalization methods generally involve the conjugation of these carbon nanomaterials with the biological species like protein, carbohydrates and nucleic acid, etc.

In our lab we have functionalized CNT and graphene both by covalent and non-covalent methods. Covalent functionalization with amine groups of CNTs was achieved after such steps as carboxylation, acylation and amidation [66]. These CNTs were treated with a concentrated H2SO4/HNO3 mixture to form a stable aqueous suspension containing individual oxidized CNTs with carboxyl groups (Figure 1.13). Then carboxylated CNTs were treated with ethylenediamine [NH2(CH2)2NH2], forming an active amine group on the nanotubes surface. The optical image of as-synthesized CNTs and amino-functionalized CNTs is also shown in Figure 1.14(a).

Figure 1.13 Schematic of the reaction scheme to form carbon nanotube (CNT) with amino functionalization [66].

Figure 1.14 (a) As synthesized CNTs; (b) Amino functionalized CNTs.

Several reports are available for functionalizing graphene and CNTs by biomolecules. The biological molecules which possess hydrophobic and hydrophilic moieties provide a more efficient means to solubilize the nanomaterial in water than the use of surfactants and polymers. Molecules containing aromatic groups or electron-rich environments have also been reported to modify nanotubes/nanosheets via -π stacking. The non-covalent approaches are based on interactions of the hydrophobic part of the adsorbed molecules with nanotube sidewalls through van der Waals, -π, CH-, and other interactions, and aqueous solubility is provided by the hydrophilic part of the molecules. If any, the charging of the nanotube surface by adsorbed ionic molecules additionally prevents nanotube aggregation by the coulombic repulsion forces between modified CNTs. In the last few years, the non-covalent treatment of CNTs with surfactants and polymers has been widely used in the preparation. On the basis of these observations, we explored the use of a novel amino-acid-based non-covalent functionalization of graphene and CNTs using amino acid L-cysteine.

Purified CNTs and graphene were dispersed in double distilled water and sonicated for one hour at room temperature for CNTs and one and a half hours for graphene to obtain homogeneous solution. Then, 0.1 M of L-cysteine was added and sonicated for 30 min followed by 2 h for CNTs and 3 h for graphene of constant stirring to each solution. The CNTs and graphene so obtained were thoroughly washed with double-distilled water in centrifuge at 10,000 rpm for 10 min and the solution phase was discarded. This washing was repeated five times in order to remove any unbound L-cysteine.

1.5.3 FTIR Analysis of CNTs and FCNTs

The presence of functional groups after the functionalization of CNTs and functionalized CNTs by FTIR spectroscopy are shown in Figure 1.15. Figure 1.15(a) shows the FTIR spectra of purified CNTs, the band at 3450cm−1 is attributed to the presence of –OH group on the surface of CNTs and is believed to be due to the oxidation during the purification of nanotubes. The peak present at 1585 cm−1 corresponds to the C=C stretching vibration of CNTs. In the FTIR spectra of amino FCNTs, Figure 1.15(b), the peak at 3430 cm−1 is due to the NH2 stretch of the amine group overlapped with –OH stretching vibration. The presence of peaks at 1472 and 1385cm−1 correspond to the N-H and C-N bond stretching of amine group, respectively. The peaks at 2955 and 2835 cm−1 are due to the –CH stretching of CH2 group.

Figure 1.15 FTIR spectra of (a) CNTs and (b) FCNTs FTIR analysis of CNTs and FCNTs.

The TEM image of GS reveals a wrinkled paper-like structure (Figure 1.16a). The inset in Figure 1.16(a) is the selected area electron diffraction pattern (SAED) of GS, showing a clear diffraction spot. The diffraction spots were indexed to hexagonal graphite crystal structure, whereas the TEM images of FGS shows a smoothened surface which is due to the functionalization by L-cysteine Figure 1.16(b).

Figure 1.16 TEM images of (a) GS and (b) FGS.

1.6 Applications

Nanomaterials have become the focus of scientific research in the past few years because of their unique electronic, chemical, optical, thermal and mechanical properties. Among the numerous active nanomaterials, carbon nanomaterials are at the forefront of research in a variety of physical and chemical disciplines. Both multi- and single-walled carbon nanotubes and graphene sheets (GS) show great promise for advancing the fields of biology [67], medicine [68], electronics [69], composite material [70], energy technology [71], etc. Currently there is a flurry of activity amongst scientists to exploit the unique properties of these carbon nanomaterials for potential application. We have also used these carbon nanomaterials for various applications such as drug delivery, biosensing, protein immobilization, protein and DNA immobilization, hydrogen storage, etc. Some of the applications used in our lab are discussed briefly below.

a) Targeted killing of Leishmania donovani in vivo and in vitro with amphotericin B attached to functionalized car bon nanotubes and graphene

The development of new drug delivery systems is attractive as it allows optimization of the pharmacological profile and the therapeutic properties of existing drugs. Within the family of nanomaterials, carbon nanotubes and graphene have emerged as a new and efficient tool for transporting therapeutic molecules, due to their unique physical and chemical properties. By employing the drug delivery system of f-CNTs to the known antileishmanial drug AmB, we found that antileishmanial efficiency is significantly increased in both in vivo and in vitro settings. This, together with low cytotoxicity of f-CNT–AmB, means that it is a viable compound for further drug development [72]. The synthesis of f-CNT–AmB was performed on a large scale and it was stored at room temperature for at least six months without any loss of efficacy.

Encouraging in vitro/in vivo results have prompted us to carry out further research on graphene-based drug delivery for Leishmaniasis treatment. The results obtained by targeted drug delivery were more promising as compared to CNT-based drug delivery. The probable reason could be due to the large surface area of graphene enabled to load more drug, thereby improving the bioavailability of drug to the cells. Figure 1.17 below shows the drug-attached graphene and Figure 1.18 shows the improved efficacy of graphene-based drug delivery as compared to CNT.

Figure 1.17 The presence of black particles on the surface of nanotube represents the attachment of AmB with CNT [72].

Figure 1.18 SEM image of graphene attached to the amphoteric drug.

b) Attachment of biomolecules (protein and DNA) with amino f-CNTs

The biomolecules (e.g., bovine serum albumin [BSA] protein and DNA) have been attached to the multi-walled CNTs through interaction between amino f-CNTs and biomolecules. The as-synthesized CNTs, f-CNTs and amino f-CNTs with BSA protein and DNA samples have been characterized by TEM and FTIR spectroscopy. The TEM observations clearly confirm the attachment of BSA protein and DNA to the amino f-CNTs. The FTIR (Figure 1.20) results show the presence of carboxylic (at 1720 cm−1 C=O) and amino groups (at 3540 cm−1 N-H) in the f-CNTs. The attachment of biomolecules (BSA protein and DNA) to amino f- CNTs is confirmed by the shift of the C=O (amide bond) peak in the amino f-CNTs- BSA protein/DNA samples [73].

Figure 1.19In vivo Efficacy of Gr-AmB.

Figure 1.20 FTIR spectrum of the attachment of biomolecules (BSA protein and DNA) [73].

Figure 1.21 (a) TEM images of as prepared amino f-MWCNT-BSA protein sample. (b) TEM images of as-prepared amino f-MWCNT-DNA sample [73].

c) Immobilization of beta-Galactosidase onto functionalized graphene and its analytical applications

Beta-galactosidase is a vital enzyme with diverse application in molecular biology and industries. It was covalently attached onto functionalized graphene nano-sheets for various analytical applications based on lactose reduction. The enzyme was coupled to the functionalized graphene with the help of a spacer arm (cysteamine) and a crosslinker (glutaraldehyde). The functionalized graphene was dissolved in phosphate buffer to make a final preparation. Functionalized graphene-coupled enzyme stored at 4°C showed excellent reusability with negligible loss up to three cycles, and a retention of more than 92% enzymatic activity after 10 cycles of repeated use [74].

d) Carbon nanomaterials and hydrogen storage

Our group has synthesized helical carbon nanofibers (HCNFs) by employing hydrogen storage intermetallic LaNi5 as the catalyst precursor. It was observed that oxidative dissociation of LaNi5 alloy occurred during synthesis. In order to explore the application potential of the present as-synthesized CNFs, they were used as a catalyst for enhancing the hydrogen desorption kinetics of sodium aluminum hydride (NaAlH4). It was observed that the present as-synthesized HCNFs, with metallic impurities, indeed work as an effective catalyst [75]. Thus there is an enhancement of w5 times in kinetics when as-synthesized HCNFs are used as the catalyst.

Figure 1.22 Transmission electron micrograph (TEM) images of functionalized (a) and coupled (b) graphene showing fine transparent sheets with insets showing the characteristic Selected-area electron diffraction pattern (SAD). Functionalized graphene sheets appear transparent, whereas islands of immobilized enzyme can be seen in dark shades.

1.7 Conclusion

In this chapter we have discussed some of the recent progress in CNT and graphene synthesis and its applications. The research in this area is still in its infancy and much more work is needed to realize the technological potential of graphene and CNTs. We should expect many other applications that exploit the unique properties of CNT and graphene to appear in the coming years. Keeping this in view we have synthesized these nanomaterials by applying different routes so as to explore and exploit its enormous potential, and also to obtain a high quality material for different applications from drug delivery, energy storage to electronics.

Acknowledgements

The authors are grateful to the Nano Science and Technology Initiative, Department of Science and Technology (DST), India, for financial support. We would also like to thank Prof. C.N.R. Rao and all the lab members who are engaged and contributed in this nanoscience research. The financial support from CSIR, and MNRE, New Delhi, are also gratefully acknowledged. M.T. thanks UGC-D.S. Kothari Fellowship for the financial support.

References

1. S. Iijima, and T. Ichihashi, Single-shell carbon nanotubes of 1-nm diameter, Nature, 1993. 363(6430): p. 603–605.3.

2. A.K. Geim, and K.S. Novoselov. The rise of graphene. Nature Mater. 6, 183–191 (2007).

3. S. Iijima, Helical microtubules, Nature 354, 56–58, 1991.

4. D.S. Bethune, et al., Cobalt-catalyzed growth of carbon nanotubes with single-atomic-layer walls, Nature, 1993. 363(6430): p. 605–607.

5. J. Prasek, J. Drbohlavova, J. Chomoucka, J. Hubalek, O. Jasek, V. Adam, and R. Kizek. Methods for carbon nanotubes synthesis—review, J. Mater. Chem. 21, 15872–15884, 2011.

6. K. Shen, H. Xu, Y. Jiang, T. Pietraß, The role of carbon nanotube structure in purification and hydrogen adsorption, Carbon 42, 2315–2322, 2004.

7. W.D. Zhang, L. Shen, I.Y. Phang, T. Liu, Surface energy components of a dye-ligand immobilized pHEMA membranes: Effects of their molecular attracting forces for non-covalent interactions with IgG and HSA in aqueous media, Macromolecules 37, 256–259, 2004.

8. S. Nakazawa, T. Yokomori, M. Mizomoto, Flame synthesis of carbon nanotubes in a wall stagnation flow, Chem. Phys. Lett. 403, 158–162, 2005.

9. X. Lu, M. Yu, H. Huang, and R.S. Ruoff, Tailoring graphite with the goal of achieving single sheets, Nanotechnology 10, 269–272, 1999.

10. A. Srivastava, C. Galande, L. Ci, L. Song, C. Rai, D. Jariwala, et al., Novel liquid precursor-based facile synthesis of large-area continuous, single, and few-layer graphene films, Chem. Mater. 22 (11), 3457–3461, 2010.

11. C.J. Lee, S.C. Lyu, H.W. Kim, J.H. Lee, and K.I. Cho, Chem. Phys. Lett. 359, 115, 2002.

12. K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, and A.A. Firsov, Electric field effect in atomically thin carbon films, Science 306, 666–669, 2004.

13. X. Lu, M. Yu, H. Huang, and R.S. Ruoff, Tailoring graphite with the goal of achieving single sheets, Nanotechnology 10, 269–272, 1999.

14. M. Eizenberg and J.M. Blakely. Carbon monolayer phase condensation on Ni(111), Surf. Sci. 82, 228–236, 1970.

15. T. Aizawa, R. Souda, S. Otani, Y. Ishizawa, and C. Oshima, Anomalous bond of monolayer graphite on transition-metal carbide surfaces, Phys. Rev. Lett. 64, 768–771, 1990.

16. C. Berger, Z. Song, X. Li, X. Wu, N. Brown, C. Naud, D. Mayou, T. Li, J. Hass, A.N. Marchenkov, E.H. Conrad, P.N. First, and W.A. Heer, Electronic confinement and coherence in patterned epitaxial graphene, Science 312, 1191–1196, 2006.

17. K.V. Emtsev, A. Bostwick, K. Horn, J. Jobst, et al., Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide, Nature Mater. 8, 203–207, 2009.

18. C. Berger, Z. Song, T. Li, X. Li, A.Y. Ogbazghi, R. Feng, Z. Dai, et al., Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics, J. Phys. Chem. B 108 (52), 19912–19916, 2004.

19. E. Rollings, G.H. Gweon, S.Y. Zhou, B.S. Mun, J.L. McChesney, B.S. Hussain, A.V. Fedorov, et al., Sythesis and characterization of atomically-thin graphite films on a silicon carbide substrate, J. Phys. Chem. Solids 67, 2172–2177, 2006.

20. P.R. Somani, S.P. Somani, and M. Umeno. Planer nanographenes from camphor by CVD, Chemical Physics Letters 430, 56–59, 2006.

21. S. Bae, H. Kim, Y. Lee, X. Xu, J.-S. Park, Y. Zheng, et al., Roll-to-roll production of 30-inch graphene films for transparent electrodes, Nat. Nano. 5(8), 574–578, 2010.

22. Q. Liu, W. Ren, D.W. Wang, Z.G. Chen, S. Pei, B. Liu, F. Li, H. Cong, C. Liu, and H.M. Cheng, In situ assembly of multi-sheeted buckybooks from single-walled carbon nanotubes, ACS Nano 3(3), 707–713, 2009.

23. A. Reina, S. Thiele, X.T. Jia, S. Bhaviripudi, M.S. Dresselhaus, J.A. Schaefer, et al., Growth of large-area single- and bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces, Nano Res. 2(6), 509–516, 2009.

24. A. Reina, X. Jia, J. Ho, D. Nezich, H. Son, V. Bulovic, M.S. Dresselhaus, and J. Kong, Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition chemical vapor deposition, Nano Lett. 9, 30–35, 2009.

25. K.S. Kim, Y. Zhao, H. Jang, S.Y. Lee, J.M. Kim, K.S. Kim, J.H. Ahn, P. Kim, J.Y. Choi, and B.H. Hong, Large-scale pattern growth of graphene films for stretchable transparent electrodes, Nature 457, 706–710, 2009

26. X. Li, W. Cai, J. An, S. Kim, et al., Large-area synthesis of high-quality and uniform graphene films on copper foils, Science 324, 1312–1314, 2009.

27. P.W. Sutter, J.I. Flege, E.A. Sutter, Epitaxial graphene on ruthenium, Nat. Mater. 7, 406–411, 2008.

28. H. Ueta, M. Saida, C. Nakai, Y. Yamada, M. Sasaki, S. Yamamoto, Highly oriented monolayer graphite formation on Pt (111) by a supersonic methane beam, Surf Sci. 560(1–3), 183–190, 2004.

29. J. Coraux, A.T. N’Diaye, C. Busse, T. Michely, Structural coherency of graphene on Ir(111), Nano Lett. 8(2), 565–570, 2008.

30. G. Nandamuri, S. Roumimov, and R. Solanki, Chemical vapor deposition of graphene films. Nanotechnology 21(14), 145604 (1–4), 2010.

31. Y. Miyata, K. Kamon, K. Ohashi, R. Kitaura, M. Yoshimura, H. Shinohara, A simple alcohol-chemical vapor deposition synthesis of single-layer graphenes using flash cooling, Appl. Phys. Lett. 96, 263105–263107, 2010.

32. A. Srivastava, C. Galande, L. Ci, L. Song, C. Rai, D. Jariwala, et al., Novel liquid precursor-based facile synthesis of large-area continuous, single, and few-layer graphene films, Chem. Mater. 22(11), 3457–3461, 2010.

33. Z. Sun, Z. Yan, J. Yao, E. Beitler, Y. Zhu, and J.M. Tour, Growth of graphene from solid carbon sources, Nature 468, 549–552, 2010.

34. W. Choi, I. Lahiri, R. Seelaboyina, Y.S. Kang. Synthesis of graphene and its applications: A review, Critical Reviews in Solid State and Materials Sciences, 35(1), 52–71, 2010.

35. M. Hirata, T. Gotou, S. Horiuchi, M. Fujiwara, M. Ohba, Thin-film particles of graphite oxide high-yield synthesis and flexibility of the particles, Carbon 42, 2929–2937, 2004.

36. D.A. Dikin, S. Stankovich, E.J. Zimney, R.D. Piner, G.H.B. Dommett, G. Evmenenko, S.T. Nguyen, and R.S. Ruoff, Preparation and characterization of graphene oxide paper, Nature 448, 457–460, 2007.

37. V.C. Tung, M.J. Allen, Y. Yang, and R.B. Kaner, High-throughput solution processing of large-scale grapheme, Nature Nanotech 4, 25–29, 2009.

38. Y. Hernandez, et al., High-yield production of graphene by liquid-phase exfoliation of graphite, Nature Nanotechnology 3, 563–568, 2008.

39. B.C. Brodie, Sur le poids atomique du graphite. Ann. Chim. Phys. 59, 466 (1860).

40. L. Staudenmaier, Verfahren zur Darstellung der Graphitsaure. Ber. Deut. Chem. Ges. 31, 1481 (1898).

41. W.S. Hummers and R.E. Offeman, Preparation of graphitic oxide, J. Am. Chem. Soc. 80, 1339–1339, 1958.

42. A. Buchsteiner, A. Lerf, and J. Pieper, Water dynamics in graphite oxide investigated with neutron scattering, J. Phys. Chem. B 110, 22328–22338, 2006.

43. A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, and C.N. Lau, Superior thermal conductivity of single-layer graphene, Nano Lett. 8, 902–907, 2008.

44. S. Stankovich, D.A. Dikin, R.D. Piner, K.A. Kohlhaas, A. Kleinhammes, et al., Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide, Carbon 45, 1558–1565, 2007.

45. I. Jung, et al., Simple approach for high-contrast optical imaging and characterization of graphene-based sheets, Nano Lett. 7, 3569–3575, 2007.

46. S. Park and R.S. Ruoff, Chemical methods for the production of graphenes, Nature Nanotechnology 4, 217–224, 2009.

47. D.R. Dreyer, S. Park, C.W. Bielawski, and R.S. Ruoff, The chemistry of graphene oxide, Chem. Soc. Rev. 39, 228–240, 2010.

48. C. Zhu, S. Guo, Y. Fang, and S. Dong, Reducing sugar: New functional molecule for the green synthesis of graphene nanoshests, ACS Nano 4, 2429–2437, 2010.

49. Y. Sun, Q. Wu, and G. Shi. Graphene based new energy materials, Energy Environ. Sci. 4, 1113–1132, 2011.

50. C.N.R. Rao, A.K. Sood, K.S. Subrahmanyam, A. Govindaraj, Epitaxial graphite: 2D electron gas properties and a route toward graphene-based, Angew. Chem. Int. Ed. 48, 7752–7777, 2009.

51. C. Schafhaeutl, On the combination of carbon with silicon and iron, and other metals, forming the different species of cast iron, steel, and malleable iron, Phil. Mag. 16, 570–590, 1840.

52. H.C. Schniepp, J.L. Li, M.J. McAllister, H. Sai, M.H. Alonso, D.H. Adamson, R.K. Prud’homme, R. Car, D.A. Saville, and I.A. Aksay, Functionalized single graphene sheets derived from splitting graphite oxide, J. Phys. Chem. B, 110 (17), 8535–8539, 2006.

53. A.C. Ferrari, J.C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri, S. Piscanec, D. Jiang, K.S. Novoselov, S. Roth, and A.K. Geim, Raman spectrum of graphene and graphene layers, Phys. Rev. Lett. 97, 187401, 2006.

54. D. Li, M.B. Müller, S. Gilje, R.B. Kaner, G.G. Wallace, Processable aqueous dispersion of graphene nanosheets, Nat. Nanotechnol. 2008;3:101–5.

55. Z. Liu, J.T. Robinson, X. Sun, H. Dai, PEGylated nano-graphene oxide for delivery of water insoluble cancer drugs, J. Am. Chem. Soc. 2008;130:10876–7.

56. Y. Lin, S. Taylor, H. Li, K.A.S. Fernando, L. Qu, W. Wang, L. Gu, B. Zhou, and Y.P. Sun, Advances toward bioapplications of carbon nanotubes, J. Mater. Chem. 14(2004), pp. 527–541.

57. A. Carrillo, J.A. Swartz, J.M. Gamba, R.S. Kane, N. Chakrapani, B. Wei, and P.M. Ajayan, Noncovalent functionalization of graphite and carbon nanotubes with polymer multilayers and gold nanoparticles, Nano Lett. 3(2003), pp.1437–1440.

58. P. Singh, S. Campidelli, S. Giordani, D. Bonifazi, A. Bianco, M. Prato, Organic functionalisation and characterisation of single-walled carbon nanotubes, Chemical Society Reviews 2009, 38, 2214–2230.

59. A. Hirsch, Functionalization of single-walled carbon nanotubes, Angewandte Chemie - International Edition 2002, 41, 1853–1859.

60. D. Tasis, N. Tagmatarchis, A. Bianco, M. Prato, Chemistry of carbon nanotubes. Chemical Reviews 2006, 106, 1105–1136.

61. A. Hirsch, Functionalization of single-walled carbon nanotubes, Angewandte Chemie-International Edition 41(11), 1853–1859 (2002).