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1、Advanced Materials Science and Engineering of CarbonMichio INAGAKIProfessor Emeritus of Hokkaido University,228-7399 Nakagawa,Hosoe-cho,Kita-ku,Hamamatsu 431-1304,JapanFeiyu KANGDean and Professor,Graduate School at Shenzhen,Tsinghua University,University Town,Shenzhen City,Guangdong Province 518055

2、,ChinaMasahiro TOYODAProfessor of Oita University,700 Dannoharu,Oita 870-1192,JapanHidetaka KONNOProfessor Emeritus of Hokkaido University,702,1-1 Nishi-10,Minami-15,Chuou-ku,Sapporo 064-0915,JapanAMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO

3、Butterworth-Heinemann is an imprint of ElsevierButterworth-Heinemann is an imprint of ElsevierThe Boulevard,Langford Lane,Kidlington,Oxford,OX5 1GB,UK225 Wyman Street,Waltham,MA 02451,USAFirst published 2014Copyright 2014 Tsinghua University Press Limited.Published by Elsevier Inc.All rights reserve

4、d.No part of this publication may be reproduced or transmitted in any form or by any means,electronic or mechanical,including photocopying,recording,or any information storage and retrieval system,without permission in writing from the publisher.Details on how to seek permission,further information

5、about the Publishers permissions policies and our arrangement with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency,can be found at our website: book and the individual contributions contained in it are protected under copyright by the Publisher(other than as m

6、ay be noted herein).NoticesKnowledge and best practice in this field are constantly changing.As new research and experience broaden our understanding,changes in research methods,professional practices,or medical treatment may become necessary.Practitioners and researchers must always rely on their o

7、wn experience and knowledge in evaluating and using any information,methods,compounds,or experiments described herein.In using such information or methods they should be mindful of their own safety and the safety of others,including parties for whom they have a professional responsibility.To the ful

8、lest extent of the law,neither the Publisher nor the authors,contributors,or editors,assume any liability for any injury and/or damage to persons or property as a matter of products liability,negligence or otherwise,or from any use or operation of any methods,products,instructions,or ideas contained

9、 in the material herein.British Library Cataloguing in Publication DataA catalogue record for this book is available from the British LibraryLibrary of Congress Cataloguing in Publication DataA catalog record for this book is available from the Library of CongressISBN:978-0-12-407789-8Printed and bo

10、und in the United States13 14 15 16 10 9 8 7 6 5 4 3 2 1For information on all Butterworth-Heinemann publications visit our website at xiPrefaceCarbon materials,the targeted materials of the present book,are very important in many fields of science,engineering,and technology,and so papers reporting

11、on“carbon material”are published in journals in a wide range of specialties.Even focusing on a specific subjectfor example,carbon nanotubes,template carbonization,anode materials for lithium-ion batteries,and so onhuge numbers of scientific papers are published.Therefore,the search of related refere

12、nces published in journals without omission is an onerous and time-consuming task.Naturally,it is not easy to provide a comprehensive overview of a particular subject within the science of carbon and cover the whole range of material released.That is what makes it so challenging;and above all,compre

13、hensive summary and review of the published results are remarkably helpful to many people and vital to further development of the field.In the present book,the authors attempt to give summaries and reviews on selected themes concerning carbon materials,based on the material and information,as much a

14、s is obtainable to us.Principal results in advanced materials science and engineering of carbon materials are reviewed with reference to a vast number of papers published in scientific journals.The book is organized into 17 chapters,including the introduction in Chapter 1.Chapters 2 to 10 are focuse

15、d on issues of formation and preparation of carbon materials,and Chapters 11 to 17 cover different applications.In Chapters 2 and 3,carbon nanotubes and graphene are reviewed,with emphasis on their formation.Processes with specific procedures and the resultant carbon materials are reviewed in Chapte

16、rs 4 to 10:they cover carbonization under pressure;graphitization under high pressure,including stress graphitization;glass-like carbons,with special attention to their activation and graphitization;template carbonization to control morphology and pore structure;carbon nanofibers prepared via electr

17、ospinning;carbon foams creating new applications;and nanoporous carbon membranes including carbon fiber webs.In Chapters 11 to 17,carbon materials used in specific fields are reviewed:electrochemical capacitors;lithium-ion rechargeable batteries;photocatalysis;spilled-oil recovery;adsorption of hydr

18、ogen,methane,vol-atile organic compounds,and metal ions;highly-oriented and highly-crystalline graphite,emphasizing its high thermal conductivity;and isotropic high-density graphite,emphasizing its nuclear applications.To understand the advanced science and engineering of carbon materials,a wide ran

19、ge of fundamental knowledge in the field of carbon materials is essential;that is,knowledge of aspects such as carbonization,graphitization,intercalation,and so on,in addition to basic knowledge of chemistry,physics,biology,and other subjects.For readers convenience,it is recommended to consult Carb

20、on Materials Science and Engineering:From Fundamentals to Applications,published by Tsinghua University Press.The book will supply fundamental knowledge on carbon materials and help in the understanding of the broad range of topics in the present book.It would give great pleasure to the authors if t

21、he content of this book can provide useful information which may be used to inspire the readers to new research directions.xiiiAcknowledgmentsThe authors would like to express their sincere thanks to the people who kindly provided the data and figures for this book.They also thank all of the people

22、who have taken care of this book in Tsinghua University Press and also in Elsevier.1Advanced Materials Science and Engineering of Carbon.http:/dx.doi.org/10.1016/B978-0-12-407789-8.00001-6Copyright 2014 Tsinghua University Press Limited.Published by Elsevier Inc.All rights reserved.CHAPTERCarbon mat

23、erials have always played important roles for human beings;for example,charcoals as a heat source and adsorbent since prehistoric times,flaky natural graph-ite powder as pencil lead and soot in black ink in the development of communication techniques,graphite electrodes in steel production,carbon bl

24、acks for reinforcing tires in the development of motorization,graphite membrane switches making computers and control panels thinner and lighter,carbon fibers for reinforcing plastics,high-purity graphite blocks in nuclear reactors,compounds of graphite with fluorine in lithium primary batteries,gra

25、phite in lithium-ion secondary batteries.Many carbon materials have been developed and more will be developed in the future.They are widely used from the home to the industrial setting.In Figure 1.1,some examples of applications of carbon materials are illustrated,in order to show how widely they ar

26、e used,although listing every application is not possible here.In the aircraft and aerospace fields,carbon-fiber-reinforced plastics are used in body parts.In automobiles,carbon-fiber-reinforced carbons are used in brakes;carbon/metal composites in brushes;carbon blacks in tires;and activated carbon

27、s to create comfortable space in the car,and also in the canister to save gasoline and to avoid air contamination.In the building and civil engineering fields,carbon-fiber-reinforced concrete is successfully used in buildings and bridges exposed to sea water to avoid erosion by salts.Carbon fibers a

28、re used for reinforcing the piers of expressways.In electronic devices such as computers and mobile phones,carbon materials are used in power sources as electrodes of primary and secondary batteries,and conductive graph-ite sheets printed on polymer films are used as switches and conducting leads,he

29、lping to make the devices greatly lighter and thinner.To produce semiconductors for elec-tronic devices,like silicon single crystals,carbon/carbon composites for heaters and high-density graphite for crucibles and susceptors are essential.Carbon materials also find their way into sustainable energy

30、development:the blades of windmills consist of carbon-fiber-reinforced composites.To stabilize the varying electricity produced by windmills and solar cells,lithium-ion rechargeable batteries and electrochemical capacitors are essential devices,both using carbon materials as electrodes.Electric cond

31、uctive carbon rods and carbon blacks support the development of primary batter-ies.Compounds of graphite with fluorine,graphite fluorides,improve the performance of primary batteries,and the reaction of lithium intercalation/deintercalation into the galleries of graphite is greatly furthering the de

32、velopment of lithium-ion rechargeable batteries.In addition,carbon nanotubes and fullerenes are promoting the development of nanotechnology in various fields of science and engineering.Introduction1CHAPTER 1 Introduction2Carbon materials are predominantly composed of carbon atoms,only the sin-gle el

33、ement,but they have widely diverse structures and properties.Diamond has a three-dimensional structure,graphite has a two-dimensional nature,while carbon nanotubes are one-dimensional,and buckminsterfullerene,C60,is zero-dimensional.Fullerenes behave as molecules,although other carbon materials do n

34、ot.Graphite is an electrical conductor and its conductivity is strongly enhanced by AsF5 intercala-tion,becoming almost comparable to that of metallic copper,whereas diamond is completely insulating.Diamond,the hardest material,is used for cutting tools,and graphite is so soft that it can be used as

35、 a lubricant.1.1 Classification of carbon materialsClassification of carbon materials has been done on various different bases;for example,the chemical nature of the carbon-carbon bonds(structures),the production procedure,structural change at high temperatures,nanotexture,and time of Aircraft and a

36、erospaceAutomobilesCivil engineeringSustainable energyElectronicsPressure bombsIndustrial equipmentFIGURE 1.1 Carbon Materials Supporting Our Lives1.1 Classification of carbon materials3appearance 1,2.Carbon materials have been named from different viewpoints.Structurally,they can be divided into di

37、amond,graphite,fullerenes,carbynes,glass-like carbons,etc.,and by production procedure into artificial graphite,intercalation compounds,activated carbons,carbon/carbon composites,etc.In Figure 1.2,some representative carbon materials are shown.Those in bold italics are listed in relation to carbon f

38、amilies classified on the basis of carbon-carbon bonds,together with some information on the diversity in each family.Based on the nature of the carbon-carbon bonding,four carbon families have been defined and named after representative carbon materials:the diamond family constructed by C-C bonds ba

39、sed on sp3 orbitals,the graphite family with bonds based on planar sp2 orbitals,fullerenes on curved sp2 orbitals,and carbynes on sp orbitals.In the graphite and fullerene families,the two electrons per one carbon atom have a pronounced influence on the properties.Commonly known carbon materials are

40、 shown in Figure 1.2.Most carbon materi-als that have been produced on an industrial scale belong to the graphite family.The fundamental structural unit is a stack of layers of carbon hexagons,i.e.graphite-like hexagonal carbon layers.These hexagonal carbon layers have strong anisotropy because of s

41、trong covalent bonding due to sp2 orbitals in the layer,but weak bonding of van der Waals force between electron clouds of stacked layers.When these layers are large enough,they stack with specific regularity:ABAB stacking results in graphite crystals belonging to the hexagonal crystal system 3 C2s2

42、2p22sp3spPlanarCurvedFullerenessp+2Chain length,etcDiamondCarbyneGraphiteCrystallineCubicHexagonalNon-crystallineDiamond-likecarbon(DLC)Carbon nanotubesSingle wallChiralitySingle wall C60,C70,Multi-walledetc.ChiralityMulti-walledCrystallineHexagonalRhombohedralNon-crystallineTurbostraticGraphitizati

43、on degreeP1=1.00d002=0.3354 nmP1=0.00d0020.344 nmNanotextureOrientedNot-orientedPlanar orientation Axial orientationPoint orientation Random orientationActivated carbonsGlass-like carbonsCarbon blacksCarbon fibersC/C CompositesArtificial graphiteHigh-density isotropic graphiteNanotextureOrientedNot

44、orientedC/C CompositesHigh density isotropic graphiteIntercalation compoundsPyrolytic carbonsFIGURE 1.2 Classification of Carbon MaterialsCHAPTER 1 Introduction4and ABCABC stacking results in graphite crystals belonging to the rhombohedral crystal system 4;the latter crystals being in metastable pha

45、se under atmospheric pressure.When the layers are too small,there is no stacking regularity even though they stack in parallel.The structure,where layers are just stacked without regular-ity,cannot be called graphite and has been named turbostratic 5.It is known to be common in various layered compo

46、unds,such as clays.Turbostratic stacking is also metastable under normal conditions,around room temperature under atmospheric pressure,and it is thought to be stabilized by the presence of hydrogen and other foreign atoms,which bond to carbon atoms located at the edges of the layers and also by dang

47、ling bonds with neighboring layers.The spacing between two layers that stack without regularity(turbostratic stacking),is larger than that of graphitic stacking.Interlayer spacing of graphite crystals has been accurately determined to be 0.3354 nm 6.Interlayer spacing of turbostratic stacking is rep

48、orted to be 0.344 nm 7,but now it is understood not to be a unique value,because of the presence of foreign atoms at the edges of layers.A turbostratic structure is commonly observed after the carbonization of many carbon precursors,because carbonization occurs at temperatures as low as 7001300 C.By

49、 heat treatment at higher temperatures,carbon layers grow in both directions,parallel to the layers(increase in the crystallite size La)and perpendicu-lar to the layers(increase in the thickness of parallel stacking,which is measured as crystallite size Lc).This crystallite growth was known to depen

50、d strongly on carbons prepared at low temperatures,and it was proposed to classify carbons into two groups,graphitizing and non-graphitizing carbons 7,later named graphitiz-able and non-graphitizable carbons 8 or soft and hard carbons 9.However,this classification into graphitizing and non-graphitiz

51、ing is not critical,mainly because carbon materials with a variety of nanotextures have been developed and they show very different behaviors under high-temperature treatment.During crystallite growth,the average interlayer spacing,usually measured by X-ray powder diffraction analysis,increases grad

52、ually with increase in heat treat-ment temperature,so that graphitic stacking with the spacing of 0.3354 nm occurs randomly in the crystallite with turbostratic stacking,as shown schematically in Figure 1.3 for a certain moment during heat treatment.The development of graphitic stacking(graphitizati

53、on degree)can be determined exactly by the probability of incidence in neighboring layers P1,which can be done by Fourier analysis of the X-ray powder pattern 10.Since the procedure to deter-mine P1 is not simple,however,the average interlayer spacing,d002,is often used as a convenient parameter for

54、 the graphitization degree,which can be measured from the diffraction angle of 00l diffraction lines.In Figure 1.4,change in the average d002 with heat treatment temperature is shown for different carbon materials,demonstrat-ing how widely the behavior of carbon materials varies.From measured d002,d

55、ifferent parameters,such as p and g,have been proposed to evaluate the graphitization degree,by making various assumptions 7,11,12.However,the value d002 itself is now used as a measure of graphitization degree,often coupled with the crystallite sizes of Lc,La,and Lc(112).The specifications for 1.2

56、Nanotexture of carbon materials5the analysis of these X-ray diffraction parameters,d002,c0(=2d002),a0,Lc,La,and Lc(112),have been proposed in the international journal Carbon 13.The relation-ship between d002 and P1 was reported to be linear 10,14,but it is now known not to be a simple linear relati

57、onship,as shown in Figure 1.5,on the basis of the measure-ment of various carbon materials 13.1.2 Nanotexture of carbon materialsThe preferred orientation of the anisotropic carbon layers in a carbon material is known to be important to understand the properties and structural changes at high temper

58、atures.Based on a scheme of preferred orientation of carbon layers,the nano-texture of carbon materials has been used to classify them into two groups,random LcGraphitic stackingLaTurbostratic stackingFIGURE 1.3 Structural Model of a Partially-graphitized Carbonmd002/nmr spacing Vapor-grownInterlaye

59、rVapor growncarbon fiberIHeat treatment temperature/C FIGURE 1.4 Changes in the Interlayer Spacing,d002,with Heat Treatment Temperature for Various Carbon MaterialsCHAPTER 1 Introduction6and oriented,and the latter into a further three:planar,axial,and point orientations 15,16.This classification is

60、 shown in Figure 1.6,together with some examples of carbon materials for each nanotexture.Nanotexture with a planar orientation scheme can be represented by graphite,flaky natural graphite,kish graphite,and highly oriented pyrolytic graphite(HOPG),in which the orientation degree is almost 100%.In py

61、rolytic carbons,which have been prepared by chemical vapor deposition(CVD)of gaseous hydrocarbon precur-sors,such as methane,propane,and benzene,various degrees of planar orientation are obtained,depending on the preparation conditions and also on the heat treatment temperature.In cokes,particularly

62、 needle-like coke,planar and axial orientation schemes are mixed and the orientation degree depends strongly on the heat treatment temperature.In the axial orientation scheme,co-axial and radial modes have to be differentiated.The extreme of co-axial orientation(orientation degree of 100%)is Planar

63、orientationNatural graphiteSynthetic graphitePVC cokeCoke ACoke BCoke CPyrolytic carbon APyrolytic carbon BAxial orientationMesophase-pitch-based carbon fibers AMesophase-pitch-based carbon fibers BVapor-grown carbon fibers AVapor-grown carbon fibers BVapor-grown carbon fibers CRandom orientationGla

64、ss-like carbonIsotropic carbon0.3500.35280.3450.3400.3350.00.51.0P1d002/nmFIGURE 1.5 The Relationship Between Interlayer Spacing,d002,and Degree of Graphitization,P1From 131.2 Nanotexture of carbon materials7found in carbon nanotubes(CNTs).Both co-axial and radial modes,in addition to various degree

65、s of axial orientation,can be found in the cross-section of carbon fibers.The co-axial mode associated with a central hollow tube is found in vapor-grown carbon fibers.In mesophase-pitch-based carbon fibers,both co-axial and radial modes,and even intermediate modes,are formed.Isotropic-pitch-based c

66、arbon fibers,how-ever,have a uniquely random orientation.Polyacrylonitrite(PAN)-based and phenol-based carbon fibers have random orientation along the fiber axis,as well as in the cross-section.In the point orientation scheme,concentric and radial modes are found.All fullerene molecules are the extr

67、emes of concentric point orientation.In carbon blacks,various degrees of concentric point orientation are found,depending on the size of primary particles and the heat treatment temperature.Radial point orientation is realized in carbon spherules,which have been synthesized from the mixture of polye

68、thylene and poly(vinyl chloride)under pressure 17.In mesocarbon microbeads(MCMBs),which are mesophase spheres separated from the isotropic pitch matrix,radial point orientation can be found near the surface,but not at the center 18.Even in random orientation schemes,the fundamental structure is base

69、d on hexagonal car-bon layers,though they form minute closed shells as found in glass-like carbons.These nanotextures depend strongly on the precursors;in general,thermoplas-tic precursors tending to give oriented nanotexture but thermosetting precursors random nanotexture.However,carbonization cond

70、itions,not only temperature and residence time but also heating rate,pressure,etc.,have an additional influence on the resultant nanotextures.Carbonization under high pressure is known to give a specific nanotexture,different from that obtained under normal pressure 19.These nanotextures established

71、 in the process of carbonization govern the struc-tural change at high temperatures from 1500 to 3000 C,as shown in Figure 1.4.In carbons where the nanotexture consists of planar orientation,such as needle-like RandomnanotextureOrientednanotextureFlaky graphitesPyrolytic carbonsCokesCarbon nanotubes

72、Carbon fibersFullerenesCarbon blacksGlass-likecarbonsRandomorientationPlanar orientationReferenceplaneReferenceaxisReferencepointRadialRadialPoint orientationConcentricAxial orientationCo-axialFIGURE 1.6 Classification of the Nanotexture of Carbon Materials,with ExamplesCHAPTER 1 Introduction8coke,t

73、he transformation of turbostratic stacking to graphitic stacking and the crys-tallite growth both parallel and perpendicular to the carbon layers occur easily;in other words,graphitization proceeds more easily with increasing temperature,and can reach high graphitization degrees.In carbons with nano

74、textures of a random ori-entation scheme,on the other hand,the development of graphite structure is strongly depressed and limited to a low graphitization degree even at a temperature as high as 3000 C,as in glass-like carbon.Carbons with point orientation show intermediate behavior,depending on the

75、 size of the primary particles(Figure 1.4);thermal black having a diameter of a few hundreds of nanometers and furnace black about 30 nm size.Vapor-grown carbon fibers with axial orientation show very similar behavior to needle-like coke(Figure 1.4).In order to overcome the depression in the develop

76、ment of graphite structure due to the nanotexture established through carbonization,heat treatment under severe conditions,much more severe than necessary to modify the nanotexture during car-bonization,is known to be required,in such a way as to melt at a high temperature above 3400 C under moderat

77、e pressure 20 or to heat-treat at a temperature above 1600 C under high pressure at 0.31 GPa 21.1.3 Microtexture of carbon materialsMost particles with planar and axial orientation,such as cokes,carbon fibers,and carbon nanotubes,are also anisotropic and by agglomeration they can create further vari

78、ety in texture.In order to understand the properties of different carbon materi-als,therefore,it is necessary to take into consideration the texture formed by the preferred orientation of these anisotropic particles,in addition to the nanotexture and graphitization degree of each particle.The textur

79、e due to the preferred orienta-tion of anisotropic particles may be called the microtexture,because the particles are often of micrometer or millimeter size.The microtexture is usually created during the forming process of bulky carbon materials.In large-sized graphite electrodes for metal refining,

80、for example,the particles of needle-like coke tend to be oriented along the rod axis during the forming process by extrusion with pitch binder.To prepare carbon-fiber-reinforced plastics(composites),different microtextures based on the orientation of carbon fibers have been applied in order to get h

81、igh strength and high modulus of the composites.Some examples are shown in Figure 1.7.Two methods have been employed for realizing the isotropy of the bulk of car-bon materials that fundamentally consist of anisotropic structural units or crys-tallites:(1)the random aggregation of micrometer-or mill

82、imeter-sized particles,even though those particles are anisotropic,and(2)the random agglomeration of nanometer-sized crystallites in the bulk.The former is realized in so-called isotropic high-density graphite blocks,where small coke particles are formed by using binder pitch under isostatic pressin

83、g.The latter,random aggregation of nanometer-sized carbon layers,has been realized in glass-like carbons,which are isotropic and have a non-graphitizing nature.1.3 Microtexture of carbon materials9Pores in the formed carbons influence the bulk properties of the carbon mate-rials.In such a case,the m

84、icrotexture,including the shape and size of pores in addition to that due to the orientation of anisotropic particles,has to be taken into account.Optical microscopy images of polished sections of six isotropic high-density graphite blocks with different bulk densities from 1.735 to 1.848 g/cm3 are

85、shown in Figure 1.8 22.Although the difference in bulk density looks rather small,a marked difference is seen in the micrographs,showing different shapes,sizes,and distributions of pores in the cross-sections.Different pore parameters of ChoppedfibersRandom One-directionalLongfibersThree-dimensional

86、Two-directionalThree-directionalFIGURE 1.7 Microtextures Formed by Carbon FibersFIGURE 1.8 Pores Observed in Isotropic High-density Graphite Blocks.Bulk density increas-ing from A to FFrom 22CHAPTER 1 Introduction10these carbon materials,such as density,average cross-sectional area,roundness,fractal

87、 dimension,etc.,have been determined with the help of image analysis.The mechanical properties,such as elastic modulus,bending strength,and fracture toughness(KIc),showed close dependence on the pore parameters.1.4 Specification of carbon materialsCarbon materials are used in many different fields o

88、f science and engineering.They appear in various scientific and technological reports,describing their preparation and applications,not only as functional materials but also as parts of devices.In those cases,sufficient information on the carbon materials has to be presented.Commonly used names of c

89、arbon materials,such as coke,carbon fiber,and carbon nanotube,give a priori some information:the carbon family to which they belong and even the nanotexture they have.In many cases,however,more information is required to understand correctly the carbon materials used.Carbon fibers are prepared from

90、different precursors by varying processes,and consequently they have different nanotextures and structures.The precursor used enables estimation of the nanotexture of the resultant carbon fiber:PAN,isotropic-pitch,and phenol are known to give random nanotexture in the cross-section,but mesophase-pit

91、ch-based carbon fibers can have a wide range of nano-textures(straight radial,corrugate radial,concentric,etc.),and vapor-grown carbon fibers have concentric axial nanotexture.The heat treatment temperature of the car-bon fiber is also important information for understanding the structure and proper

92、-ties of the fibers;vapor-grown carbon fibers can have the interlayer spacing,d002,close to graphite(0.3354 nm)after heat treatment at 3000 C,but isotropic-pitch-based carbon fibers are far from graphite values even after 3000 C heat treatment,as shown in Figure 1.9A.Crystallite magnetoresistance(/)

93、cr shows very marked difference among carbon fibers prepared from different precursors and under dif-ferent conditions,as shown in Figure 1.9B.In addition,it has to be pointed out that the word“graphitized,”which has been used,for example,in expressions like“graphitized carbon fibers,”does not alway

94、s mean the development of graphitic structure in the carbon fibers,but that a high temperature of 25003000 C was applied.In order to specify the carbon fiber correctly,therefore,not only the pre-cursor and heat treatment temperature but also some structural parameters,such as d002 or(/)cr,and nanote

95、xture in the cross-section have to be presented,particu-larly in the case of mesophase-pitch-based carbon fibers.In the case of carbon nanotubes,the situation is more complicated,mainly because there is no consistent definition of carbon nanotube and also because many people want to use“carbon nanot

96、ube”in publications even without unambiguous identification of the structure and nanotexture.It is regrettable to say that the terms“carbon nanotube”and“graphene”have not,in many papers published,been used in a precise sense according to the definitions.The present authors have proposed that a carbo

97、n nanotube has to consist of straight layers,as shown by its 002 lattice fringes 1.4 Specification of carbon materials11in the transmission electron microscopy(TEM)image in Figure 1.10A,as this is the reason why the name“carbon nanotube”was first proposed.According to this definition,the fibrous car

98、bon consisting of small carbon layers preferentially oriented along its fiber axis,as in the example shown in Figure 1.10B,should not be called carbon nanotube.These two fibrous carbons have quite different properties,particu-larly their electronic,mechanical,and chemical properties.In reports where

99、 the term“carbon nanotube”is used,therefore,it is strongly recommended to show how the carbon layers are extended on the wall of tubes,by TEM imaging or other techniques.Carbon blacks are named by the production process during gas-phase carboniza-tion,such as thermal black,furnace black,acetylene bl

100、ack,which suggests to us some information on the size of primary particles and the aggregation(so-called structure):thermal black has large particle size and almost no structure,but furnace 0.3450.3400.3351,0002,0003,000PAN-basedMesophase-pitch-basedIsotropic-pitch-basedVapor-grownHeat treatment tem

101、perature/CHeat treatment temperature/CInterlayer spacing d002/nmCrystallite magnetoresistance(/)cr/%1601401201008060402001500200025003000350020Vapor-grownPAN-basedunder stretching gMesophase-pitch-basedIsotropic-pitch-basedPAN-based(A)(B)FIGURE 1.9 Changes in the Structure Parameters with Heat Treat

102、ment Temperature for Carbon Fibers(A)Interlayer spacing,d002 and(B)crystallite magnetoresistance,(/)cr.(B)(A)5 nm5 nmFIGURE 1.10 002 Lattice Fringe Images of Fibrous Carbons(A)Carbon nanotube and(B)carbon nanofiber.CHAPTER 1 Introduction12black has small particle size and well-developed structure.In

103、 furnace black,the size distribution of primary particles,ranging from 5 to 100 nm,and the degree of struc-ture development are known to be very important for reinforcing rubber.1.5 Construction of the present bookIn 2006,the authors(M.I.and F.K.)published a book entitled Carbon Materials Science an

104、d Engineering:From Fundamentals to Applications from Tsinghua University Press.The book was written with the aim of giving the fundamentals in science and engineering on all carbon materials,in relation to their applications.The principal readers of the book were assumed to be beginners in carbon sc

105、ience and engineering,such as young researchers,scientists,and graduate students who were studying or intending to study carbon materials.In the present book,advanced materials science and engineering of carbon materials are reviewed over 17 chapters,including this introduction.Chapters 2 to 10 are

106、focused on the issues of formation and preparation of carbon materials,and Chapters 11 to 17 cover different applications.In Chapters 2 and 3,carbon nano-tubes and graphene are reviewed,with emphasis on their formation.Since funda-mental carbonization and graphitization processes were described in o

107、ur previous book,processes containing additional and/or specific procedures and the formed carbon materials are reviewed in Chapters 4 to 10:carbonization under pressure(Chapter 4);graphitization under high pressure(Chapter 5);glass-like carbons,with special attention given to the activation and gra

108、phitization(Chapter 6);template carbonization to control morphology and pore structure(Chapter 7);carbon nano-fibers prepared via electrospinning(Chapter 8);carbon foams creating new appli-cations(Chapter 9);and nanoporous carbon membranes,including carbon-fiber webs(Chapter 10).In Chapters 11 to 17

109、,carbon materials used in specific fields are reviewed:electrochemical capacitors(Chapter 11);lithium-ion rechargeable batteries(Chapter 12);photocatalysis(Chapter 13);spilled-oil recovery(Chapter 14);adsorption of hydrogen,methane,volatile organic compounds(VOCs),and metal ions(Chapter 15),highly-o

110、riented and highly-crystallized graphite,with emphasis on its high thermal conductivity(Chapter 16);and isotropic high-density graphite,emphasizing its nuclear applications(Chapter 17).In a footnote to the first page of each chapter,the location in our previous book of fundamental information on eac

111、h topic is indicated,as prerequisite for readers.References 1 Inagaki M.New Carbons.Control of Structure and Functions 2000:13,Elsevier.2 Inagaki M,Kang F.Carbon Materials Science and Engineering 2006:2331,Tsinghua University Press.3 Bernal JD.Proc Roy Soc A 1924;106:74973.4 Lipson H,Stokes AR.Natur

112、e 1942;149:328.References13 5 Warren BE.J Chem Phys 1934;2:5516.6 Nelson JB,Riley DP.Proc Phys Soc A 1945;57:47785.7 Franklin RE.Acta Cryst 1951;4:25361.8 International Committee for Characterization and Terminology of Carbon.Carbon 1982;20:4459.9 Mrozowski S.Proceedings of the First and Second Conf

113、erences on Carbon.University of Buffalo:Waverly Press;1956;3145.10 Houska SR,Warren BE.J Appl Phys 1954;25:150310.11 Bacon GE.Acta Cryst 1951;4:55861.12 Maire J,Mering J.Chem Phys Carbon 1979;6:12590.13 Iwashita N,Inagaki M.Carbon 1993;31:110713.14 Noda T,Iwatsuki M,Inagaki M.TANSO 1966;No.47:1422 i

114、n Japanese.15 Inagaki M.TANSO 1985;No.122:114122 in Japanese.16 Inagaki M.New Carbon Mater 1999;14:13.17 Hishiyama Y,Yoshida A,Inagaki M.Carbon 1982;20:7984.18 Augie D,Oberlin M,Oberlin A,et al.Carbon 1980;18:33746.19 Inagaki M,Park KC,Endo M.New Carbon Mater 2010;25:40920.20 Noda T,Inagaki M.Bull C

115、hem Soc Jpn 1964;37:170910.21 Inagaki M,Meyer RA.Chem Phys Carbon 1999;26:149244.22 Oshida K,Ekinaga N,Endo M,Inagaki M.TANSO 1996;No.173:142147 in Japanese.15Advanced Materials Science and Engineering of Carbon.http:/dx.doi.org/10.1016/B978-0-12-407789-8.00002-8Copyright 2014 Tsinghua University Pr

116、ess Limited.Published by Elsevier Inc.All rights reserved.CHAPTERCarbon materials can be classified into three categories on the basis of their period of development:classic carbons,new carbons,and nanocarbons 1.Classic carbons include synthetic graphite blocks mainly used as electrodes,carbon black

117、s,and activated carbons,for which production procedures were developed before the 1960s.In the 1960s,carbon materials different from these classic carbons were invented:carbon fibers from various precursors,including vapor-grown carbon fibers;pyrolytic carbons produced via chemical vapor deposition

118、processes;glass-like carbons with high hardness and gas impermeability;high-density isotropic carbons produced by isostatic pressing;intercalation compounds with different functionalities,such as high electrical conductivity;and diamond-like carbons as transparent carbon sheets.These newly developed

119、 carbon materials are classified as new carbons.Since the 1990s,various fullerenes with closed-shell structure,carbon nanotubes with nanometer diameters,and graphene flakes of only a few atoms thickness have attracted attention from nanotechnology;these are classified as nanocarbons.If these carbon

120、materials are considered from the point of view of their texture,however,they may be classified into two groups:nanotextured and nano-sized carbons 2.Most carbon materials in the new carbon category are classified as nanotextured carbon,because their nanotexture is controlled via different pro-cesse

121、s in their production,in addition to the structural control.On the other hand,fullerenes,carbon nanotubes,and graphene can be classified as nano-sized carbon,because the shell size of fullerenes,diameter of carbon nanotubes,and thickness of graphene flakes are on the nanometer scale.Carbon blacks in

122、 classic carbon are composed of nano-sized particles,but they are not usually classified as nano-carbons because they have various applications as a mass,not as individual nano-sized particles.These two classifications for carbon materials are summarized in Figure 2.1.In this chapter,synthesis of ca

123、rbon nanotubes(CNTs),representative nano-carbons,and their formation into yarns,sheets,and sponges are summarized.The formation of CNTs is very important for developing their applications in different engineering fields.Carbon Nanotubes:Synthesis and Formation2Prerequisite for readers:Chapters 2.3(N

124、anotexture development in carbon materials)and 3.4(Fibrous carbons)in Carbon Materials Science and Engineering:From Fundamentals to Applications,Tsinghua University Press.CHAPTER 2 Carbon Nanotubes:Synthesis and Formation162.1 Synthesis of carbon nanotubesCarbon nanotubes(CNTs)are synthesized at the

125、 first stage of growth of so-called vapor-grown carbon fibers 36,as shown in Figure 2.2,and are found in the carbon deposits on graphite anodes during arc discharge 710.Under similar arc discharge conditions,fibrous carbon composed of a scroll of carbon layers was obtained in 1960,and was called“gra

126、phite whisker”11.Arc discharge between graphite electrodes forms carbon nanotubes together with other forms of amorphous carbon,such as carbon blacks and pyrolytic carbons,but with difficulty in controlling the structure of CNTs,i.e.thickness(single-,double-,or multi-walled),diameter,and length.In o

127、rder to obtain CNTs of high purity,different techniques such as laser-abrasion,modified arc discharge,and catalytic chemical vapor deposition have been proposed 12.Since catalytic chemical vapor deposition(CCVD)was thought to be practical for large-scale production,it has been applied using various

128、carbon precursors and various catalytic metals,either supported on a substrate or float-ing as fine particles 1321.The so-called HiPco process,using the disproportionation reaction of high-pressure and high-temperature CO with iron pentacarbonyl as a cata-lyst precursor,is producing single-walled CN

129、Ts(SWCNTs)almost free from amor-phous carbon 2224.Double-walled CNTs(DWCNTs)were successfully obtained in a high yield by the catalytic CVD method by placing a Mo catalyst on Al2O3 at the end of the furnace and an Fe catalyst on MgO at the center of the furnace 25,26.It was thought that the Mo catal

130、yst worked as the moderator for enhancing the active carbon species,and the Fe catalyst was the catalyst for nanotube formation.A CH4/Ar gas mixture was fed onto the catalysts,heated at 875 C for 10 min.The yield of DWCNTs was more than 95%after purification.Long DWCNTs have been synthesized with a

131、relatively high production rate of 0.5 g/h in a quartz tube(45 mm in diameter and 180 cm in length)heated to a temperature of 1100 C,by introducing a xylene solution of ferrocene with a small amount of sulfur at a rate of 0.050.15 cm3/min under a flow of argon and hydrogen at rates of 25003500 and 5

132、00 cm3/min,respectively 27.Conventional carbonsNewly developed carbonsGraphite electrodesCarbon blacksActivated carbonsNatural diamondCarbon fibersPyrolytic carbonsGlass-like carbonsHigh-density isotropic carbonsIntercalation compoundsDiamond-like carbonsFullerenesCarbon nanotubesGrapheneClassiccarb

133、onsNewcarbonsNano-carbonsNano-sizedNanotexturedNanocarbonsFIGURE 2.1 Classification of Carbon Materials2.1 Synthesis of carbon nanotubes17Although the yield and growth rate of CNTs with uniform structure,either sin-gle-,double-,or multi-walled,were markedly improved by using catalysts under controll

134、ed conditions,the resultant CNTs usually contained the minute metal par-ticles used as a catalyst at their tips.Therefore,opening of the tips by oxidation and removal of the metal particles through either dissolution by acid or evaporation as halides were essential for getting chemically pure CNTs.C

135、NTs aligned in parallel with each other have been prepared from differ-ent hydrocarbon gases on different metal catalysts.By CVD of 2-amino-4,6-di-chloro-s-triazine at 950 C on a Co film(10100 nm thick)deposited on a silica substrate by laser etching,well-aligned CNTs were synthesized,of lengths up

136、to about 50 m and fairly uniform diameters(3050 nm);these were produced in high yield without noticeable amounts of other forms of carbon 28.CVD of acetylene on iron/silica substrates produced CNTs(2040 nm diameter)aligned perpendicularly to the substrate surfaces 29.The lengths of CNTs increased wi

137、th growth time,and reached about 2 mm after 48 h.Well-aligned CNTs over areas up to several square centimeters were grown on nickel-coated glass at 666 C by plasma-enhanced hot-filament CVD of acetylene containing NH3 30.NH3 gas was thought to etch the surface of the nickel catalyst.Nanotubes with c

138、ontrollable diameters from 20 to 400 nm and lengths from 0.1 to 50 m were obtained.CNTs aligned perpendicularly to the substrate(called“arrays”)with well-defined patterns were synthesized by CVD at 700 C under a flow of ethylene at 1000 stan-dard cm3/min(SCCM)on a P-doped porous Si(100)wafer,on whic

139、h an Fe thin film(5 nm thick)was patterned by electron beam evaporation,as shown in Figure 2.3 31.The resultant CNTs were multi-walled and had diameters of 16 2 nm.Growth rate of CNTs was very high;the length of CNTs,i.e.the height of the arrays,reached FIGURE 2.2 Single-walled Carbon Nanotube Forme

140、d at the First Stage of Growth of Vapor-grown Carbon FibersCourtesy of Prof.M.Endo of Shinshu University,JapanCHAPTER 2 Carbon Nanotubes:Synthesis and Formation1830 and 240 m after 5 and 60 min CVD,respectively.In the arrays,CNTs aligned almost perfectly perpendicularly to the substrate,as shown in

141、Figure 2.3F,although CNTs formed on a porous Si wafer without an Fe film were not aligned(Figure 2.3G).The CNT arrays can be formed with a well-defined pattern(Figures 2.3AC),of which the edges and corners are very sharp(Figures 2.3D and E).Instant addition of inert gas(Ar)into the supply of the pre

142、cursor gas(acetylene),as shown in Figure 2.4D,was found to give a distinct straight line on the scanning electron microscopy(SEM)image of the as-grown CNT array(Figure 2.4E),and so the growth kinet-ics and mechanism of the multi-walled CNT(MWCNT)array were discussed with relation to these marks 32.G

143、rowth rate of CNTs by CVD of acetylene was almost constant at 600 C,c.3 m/min,but at 680 C it increased from 17 to 23 m/min during the first 15 min and then tended to be saturated.The growth process was well approximated by the first order reaction Ea=159 5 kJ/mol.The diameter corre-sponding to its

144、maximum population tended to shift to larger sizes with increasing thickness of Fe catalyst:6.2 nm(34 walls)to 9.2 nm(69 walls)with increase in Fe thickness from 0.2 to 5.0 nm 33.The presence of a buffer layer of Al2O3 or SiO2 in between the substrate and catalyst layer was essential for the synthes

145、is of CNT arrays,no formation of CNT array being observed on a flexible stainless steel foil either with or without a thin film of iron 34.Preheating of precursor gas(C2H4/H2)FIGURE 2.3 Carbon Nanotube Arrays.(A-F)SEM images with different magnifications,(G)TEM images of carbon nanotubes in the arra

146、y.From 312.1 Synthesis of carbon nanotubes19to 770 C lowered the deposition temperature for CNT arrays to 500 C,but did not appreciably change the diameters of the resultant CNTs 35,36.Carbon nanofibers with 10140 nm diameters have been synthesized by using H2/methane gas and a 0.55 nm thick Ni or F

147、e catalyst film through low-power micro-wave plasma-assisted CVD 37.Accelerated growth of SWCNTs and DWCNTs can be achieved by either using an alcohol as the carbon precursor or adding water vapor to the precursor gas 3842.High-purity SWCNTs with a diameter of about 1 nm have been synthesized from a

148、lcohol by using Y-type zeolite powder loaded with Fe/Co nanoparticles;SWCNTs were formed at 550 C from methanol vapor 38.Sheets of vertically aligned SWCNTs with a few micrometers length have been grown by CVD of ethanol vapor by using Co-Mo catalyst particles of about 1.02.0 nm size,which were disp

149、ersed densely on a quartz substrate by a dip-coating method 40.Continuous reduction of catalysts with Ar/H2(3%H2)during CVD was essential for generating dense SWCNTs with vertical alignment.The diameter of SWCNTs decreased with increasing acetonitrile content in ethanol,showing a drastic decrease in

150、 diameter from 2.1 to 0.7 nm by the addition of 0.1%acetonitrile,although the nitrogen content saturated at about 1 at%,as shown in Figure 2.5 42.FurnaceFurnaceQuartz boatSilica padGas flux(SCCM)OutletSi substrate1min2min3min1min2min3min3003000 3002017141180Time(min)(II)Ar(II)Ar5Substrate(A)(B)(D)(E

151、)(C)20 m50 m50 mFIGURE 2.4 Determination of Growth Rate of Carbon Nanotubes Forming in an Array.(A)Illustration of experimental setup,(B)SEM image of a CNT array grown on a silicon substrate,with white line in the middledue to turning off C2H2 inlet,(C)SEM image of a CNT array with a series of line

152、marks,(D)plot of gas flux versus time during CNT growth,(E)image of CNT array captured by a digital camera on an optical microscope.From 32CHAPTER 2 Carbon Nanotubes:Synthesis and Formation20Vertically aligned SWCNTs(called“forests”)have been grown from ethylene on various metal catalysts in either

153、Ar/H2 or He/H2 containing a small amount of water vapor,as shown in Figure 2.6 43;this process was called water-assisted growth because of the acceleration by water vapor,and also named“supergrowth”because of the superior growth rate of CNTs.Dense and vertically aligned SWCNTs with 2.5 mm length cou

154、ld be grown in 10 min by using thin catalyst films of Al2O3 and Fe sputtered on a Si wafer.The ratio of ethylene and water was crucial for the produc-tion.The as-grown SWCNT forest had a very low content of metal catalyst,less than 2 105 mass%,and was free from both amorphous carbon and multi-walled

155、 carbon nanotubes.The SWCNT forest obtained could be easily removed from the substrate 2.52.52.01.51.00.50.00.51.01.52.02.01.51.00.5Mean diameterNitrogen contentNitrogen content in SWCNTs /at%Concentration of CH3CN(%)Concentration of CH3CN/%020406080100012210Mean diameter of SWCNTs /nmFIGURE 2.5 Cha

156、nges in Diameter and Nitrogen Content of SWCNTs with Concentration of Acetonitrile in EthanolThe insert is an enlarged presentation for a region of low CH3CN concentration.From 42A match headSWNT forest (2.5 mm height)Enlarged pictureFIGURE 2.6 Single-walled Carbon Nanotube ForestFrom 432.1 Synthesi

157、s of carbon nanotubes21with a razor blade and the substrate could be re-used for the growth of CNT forests.By using a lithographically patterned catalyst on the substrate,a well-defined verti-cally standing structure of SWCNT forests was produced.In the forest,SWCNTs with a diameter of 3.0 0.07 nm w

158、ere formed,occupying the surface area of the catalyst by about 84 mass%,showing efficient usage of catalyst surface 44.The structure of CNTs and the characteristics of their forests synthesized via the supergrowth process were explored in detail.High growth rate of CNTs was obtained by using an Fe c

159、atalyst layer on an Al2O3 buffer layer;it was possible to obtain an SWCNT forest with a height of 5001000 m after 10 min 45,46.The diameter of CNTs grown by this process depended linearly on the thickness of the Fe catalyst layer;with Fe thicknesses of 1.6,3,and 5 nm,SWCNTs,DWCNTs,and MWCNTs,respec-

160、tively,were formed.The method of gas delivery to the catalyst and the water vapor content in the gas have a strong influence on the yield of SWCNTs as forests 47.As shown in Figure 2.7,three different ways of supplying carbon precursor gas(ethylene)and water vapor were tested with different water co

161、ntents.By supplying both gases from the top(Figure 2.7C),a relatively high yield,more than 3 mg/cm2,was obtained,with a low water content of about 80 ppm.The length of SWCNTs,i.e.the height of the forest,increased with time when both gases were supplied from the top,more than 3 m after 80 min,althou

162、gh growth of SWCNTs was terminated at around 1 m FIGURE 2.7 Yield of Single-walled Carbon Nanotubes Depending on the Water Vapor Con-centration and Method of Gas Delivery(A)Both gases injected from the side,(B)ethylene from the side and water vapor from the top,and(C)both gases from the top.From 47C

163、HAPTER 2 Carbon Nanotubes:Synthesis and Formation22after 20 min when the two gases were supplied from the side(Figure 2.7A)and when a water supply from the top(Figure 2.7B)was employed.The formation of patterned CNT forests(or arrays,i.e.vertically aligned CNTs)has been reviewed 48.2.2 Formation of

164、carbon nanotubes2.2.1 Formation into yarnsFor many applications,ultrathin CNTs are required to be much thicker yarns(called sometime fibers or strands)to make their handling easier.The formation of CNTs into a yarn has been done by three methods:(1)in situ spinning in a CVD furnace,(2)spinning from

165、the suspension of as-prepared CNTs after purification,and(3)spinning from a CNT forest.SWCNTs synthesized by laser a vaporization technique were known to be bun-dled into a rope with a diameter of 520 nm 12,49.Long and thick SWCNTs yarns have been synthesized by CVD of either benzene or n-hexane wit

166、h floating catalyst particles formed from ferrocene and thiophene at 11001200 C 18,50,51.By either inserting a rod or winding up in the lower part of the furnace,as schematically shown in Figures 2.8A and 2.8B,yarns can be prepared from SWCNTs synthesized in the hot zone by the floating catalyst met

167、hod;an example of the twisted yarn obtained being shown in Figure 2.8C 52.Concentration of additive(thiophene),flow rate of carrier gas(H2),and CVD temperature governed the structure of CNTs,whether FeedstockFeedstockHot zoneHot zoneHot zoneHot zoneWind-upWind-up50 m(A)(B)(C)FIGURE 2.8 In Situ Spinn

168、ing of Carbon Nanotubes to Yarns(A and B)Schematic illustrations,and(C)spun yarn.From 522.2 Formation of carbon nanotubes23multi-walled or single-walled.The rate of winding-up(5.520 m/min)influenced the density and strength of the resultant yarns owing to the alignment of CNTs,which improved with a

169、higher rate 53.Yarns prepared from hexane had a high tensile strength(1.46 GPa)and a high Youngs modulus(30 GPa),higher than those from ethanol and ethylene glycol 54.Long yarns,the authors claiming of several kilometers,have been prepared by assembling multiple layers of CNTs concentrically,which w

170、ere produced by CVD of mixed gases of acetone and ethanol with ferrocene and thiophene in flowing hydro-gen,followed by spinning and water-densification 55.The CNT yield from the mixed gases was about 240 mg/h,while that from ethanol alone was about 110 mg/h.The stable spinning could be conducted wi

171、th a velocity in the range of 5 to 20 m/min.CNTs synthesized through arc-discharge and laser-ablation methods have been formed into yarns via their suspension.By immersing a graphitized carbon fiber(CF)bundle into a SWCNT/DMF(N,N-dimethylformamide)suspension and apply-ing a voltage of 12 V between t

172、he CF and the suspension,a cylindrical cloud of the SWCNT was formed around the positive CF,resulting in a yarn with 210 m diam-eter by slow withdrawal from the suspension(electrophoretic drawing)56.The diameter of the yarns depended on the time allowed for the SWCNT cloud assembly before withdrawal

173、 and the rate of withdrawal.SWCNT yarns with a diameter of 1642 m and length of more than 3 cm have been obtained by a withdrawal rate of 0.85 m/s 57.SWCNT yarns have been prepared by injecting a SWCNT suspen-sion in a sodium dodecyl sulfate(SDS)aqueous solution into a PVA(poly(vinyl alcohol)aqueous

174、 solution through a syringe,followed by taking out the yarn in gel,washing out the PVA and SDS with water,and drying 5860.Drying the gel yarns under tension was effective to improve the alignment of CNTs and Youngs modulus 59.Spinning from CNT suspension in SDS solution was performed by injecting in

175、to either an ethanol/glycerol or an ethanol/glycol mixture and then washed out the remaining SDS and glycerol or glycol with water and ethanol to get yarns of pure CNTs 61.SWCNT yarns have also been prepared by adding a SWCNT suspension of lithium dodecyl sulfate aqueous solution into HCl aqueous so

176、lution at a rate of 0.25 cm3/min under rotation at 33 rpm,followed by excluding the HCl in methanol 62.SWCNTs suspended in concentrated sulfuric acid have been formed into yarns via a similar procedure 63,64.Alignment of CNTs in the yarns is improved by using a smaller nozzle 63.The resultant yarns

177、had a bulk density of 0.871.11 g/cm3 64.Nematic liquid crystal solution prepared by suspending 95%)126.By controlling gas flow in a CVD furnace,oriented growth of CNTs has been successfully performed 128133.By introducing CH4/H2 gas with a relatively high flow rate(800/700 standard(SCCM)onto Si wafe

178、rs with mono-dispersed Cu nanoparticles,horizontally-oriented dense SWCNT films were prepared at 925 C 128.By using an extremely low feeding rate of methane at 1.5 SCCM,horizontally aligned SWCNTs with diameter about 2 nm were formed on a SiO2/Si substrate deposited with Fe-Mo catalyst nanoparticles

179、 130.Cross-orientation of SWCNTs has been carried out through two-step CVD by using a Cu catalyst 131.FIGURE 2.12 Shrinkage of a Carbon Nanotube Forest(A)After shrinkage,(B and C)SEM images of side view before and after shrinkage.From 1192.2 Formation of carbon nanotubes29SWCNTs synthesized by the a

180、rc-discharge process have been formed into films by passing through a magnetic field of 0.56 T on different substrates,such as glass,Si,poly(methyl methacrylate(PMMA),and PET 134.SWCNTs deposited randomly on a SiO2/Si substrate have been transferred to another substrate by mechanical force with shea

181、r stress to create well-oriented,dense films 135.The formation of CNT sheets has been reviewed 136,137.2.2.3 Formation into spongesAgglomerates of MWCNTs have been prepared by compression,with bulk den-sity of 0.40.5 g/cm3 and excellent resilience up to 250 MPa 138.By controlling the injection rate

182、of the source gases(dichlorobenzene and ferrocene),sponge-like agglomerates of MWCNTs with densities of 0.0050.025 g/cm3 have been prepared by catalytic CVD that showed high compressibility up to 0.1 MPa and high thickness recovery of 93%139.CNT sponges have shown reversible stress-strain curves wit

183、h marked hysteresis in air and ethanol,and rapid sorption of oil floating on water 140.Highly resilient composites have been prepared by compressing a mixture of natural graphite and MWCNTs 141.FIGURE 2.13 Horizontally Aligned,High-density SWCNTs Grown on a Quartz Substrate(A and B)SEM images of the

184、 film,the bright stripes corresponding to the Cu catalyst,(C)high-magnification SEM,and(D)atomic force microscopy(AFM).image of a 1 0.75 m2 area.From 125CHAPTER 2 Carbon Nanotubes:Synthesis and Formation30Vertically aligned MWCNT arrays,produced by catalytic CVD with xylene and ferrocene,show excell

185、ent mechanical behavior under compression,and high com-pressive strength and recovery rate,by keeping their open-cell nature,as shown in Figure 2.14C 142.Their high resiliency is due to the formation of zigzag buckles of MWCNTs,as shown in Figures 2.14A and 2.14B.On vertically aligned MWCNT mats(arr

186、ays),mechanical behavior under tension and compression has been mea-sured,showing very low stiffness under compression,due to buckling of the CNTs,but being considerably stiff under tension 143.2.3 Applications of carbon nanotubesCNTs are known to have excellent electrical,thermal,and mechanical pro

187、perties.However,it has also been pointed out that it is very difficult to show these intrinsic properties of individual CNTs on their aggregates.In order to address this point,various problems have to be solved:finding efficient methods for preparation of well-characterized CNTs and purification of

188、the prepared CNTs,establishment of charac-terization methods,etc.Many of these problems have not yet been solved completely and considerable efforts are being made to do this.As-prepared CNTs are usually accompanied by various impurities,metal cata-lysts,carbonaceous impurities with amorphous and fu

189、llerene-like structures,and CNT structure variations,such as different wall thickness(single-,double-,and multi-walled),capped and open tubes,and various diameters and lengths of tubes.For the purification of these CNTs,various processeschemical oxidation,physical separa-tion,and a combination of ch

190、emical and physical processeshave been proposed.A comprehensive review on the purification of CNTs has been published 144.In as-grown SWCNTs,nanotubes having metallic and semiconducting prop-erties are usually mixed.Semiconducting SWCNTs have been extracted from as-grown CNTs without detectable rema

191、ining metallic SWCNTs or impurities by(C)(B)252015105002040Compressive strain(%)Compressive stress(MPa)6080100=57%=85%(A)FIGURE 2.14 Compression of Vertically Aligned MWCNTs(A)Before and after compression of 1000 cycles(SEM images),(B)lower part under high magnification(SEM image),and(C)stress-strai

192、n curves under compression.From 1422.3 Applications of carbon nanotubes31using polyfluorene as an extracting agent in toluene,assisted by ultracentrifugation 145.Continuous separation of metallic and semiconducting SWCNTs has been performed by passing an SWCNT/sodium sulfate dispersion through a col

193、umn con-taining agarose gel beads 146:the latter was trapped by the beads and the former passed through the column.Metallic SWCNTs have been separated by using SDS as surfactant and an allyldextran-based gel with multicolumn chromatography 147.Most CNTs are bundled by strong van der Waals forces,whi

194、ch can be troublesome for some applications;for example,bundled SWCNTs have a smaller surface area than that theoretically possible.Debundling of SWCNTs has been performed through intercalation of lithium with solvent molecules between the tubes in dimethyl sulfoxide 148.This process was confirmed n

195、ot to give any change in the quality of SWCNTs by TEM observation and Raman spectroscopy.The effective dispersion of CNTs in solvents and polymers has been reviewed,focusing on the surface modification of CNTs,to give some guidelines 149.MWCNT sheets prepared from a forest by simple drawing have bee

196、n tested in var-ious applications,such as grids for high-resolution transmission microscopy 150,loudspeaker cones 151,anodes for lithium-ion batteries by loading SnO2 nanoparti-cles 152,heating elements for incandescent display 153,stretchable touch panels 154.A transparent conducting flexible sheet

197、 of well-aligned MWCNTs prepared from a forest has been transferred to a polyethylene(PE)sheet by a roll-to-roll tech-nique(Figure 2.15).The MWCNT sheets were reported to possess performance of sheet resistances and transmittances comparable to ITO films.MWCNT yarns prepared by spinning from a fores

198、t have been tested as field elec-tron emitters in high vacuum 155,156.Electron emission I-V curves were measured at the bent part of the yarn,with diameter about 2030 m and 2 cm length at 15002200 K,giving a work function of 4.544.64 eV and thermoionic emission constant of 228824 A/cm2K2,larger than

199、 that for conventional tungsten cathodes 155.On the cross-section of the yarn,which was densified by passing through acetone and FIGURE 2.15 Preparation of a CNT/PE Composite(A)Roll-to-roll setup,and(B)the CNT/PE composite tape.From 153CHAPTER 2 Carbon Nanotubes:Synthesis and Formation32had a diamet

200、er of about 50 m,electron emission performance was measured;the electron emission started at the relatively low voltage of 400 V,current at 1000 V reached 2.1 mA,and current density was 100 A/cm2 156.Sheets have been prepared from SWCNT forests by pressing after the densifica-tion through a liquid c

201、ollapsing process,in which SWCNTs were aligned in one direction along the surface of the sheet(called SWCNT solids)119.These sheets were successfully applied to the electrodes of supercapacitors,giving capacitance as high as 80 F/g and energy density of 69.4 Wh/kg in 1 mol/L Et4NBF4/PC(propyl-ene ca

202、rbonate).electrolyte solution 120,157,158.Their electrochemical properties are unique,characterized by a butterfly-shaped cyclic voltammogram measured in a three-electrode cell,as shown in Figure 2.16 157.Electrochemical doping in semi-conducting CNTs was thought to occur at the interface between th

203、e electrolyte and the nanotube surface,together with electric double layer formation on the surface of CNTs.By controlled oxidation,the SWCNT forest was converted to a material with high surface area of 2240 m2/g,where 85%of carbon atoms were thought to constitute a surface 159.SWCNT films prepared

204、via filtration have been treated with pyrrole after the arylsulfonic acid-functionalization,which gave high values of capacitance(350 F/g),power density(4.8 kW/kg),and energy density(3.3 kJ/kg)in 6 mol/L KOH 160.SWCNT films prepared by spray-drying were reported to give high energy and power densiti

205、es:23 and 70 kW/kg for aqueous gel electrolytes FIGURE 2.16 Cyclic Voltammogram of Single-walled Carbon Nanotube SheetCourtesy of Dr H.Hatori of AIST,Japan2.3 Applications of carbon nanotubes33(PVA/H3PO4 and liquid H3PO4)and an organic electrolyte(LiPF6/EC+DEC),respectively,and 6 Wh/kg for both aque

206、ous and non-aqueous electrolytes 161.SWCNT yarns and sheets have been tested as high-performance components in electronic devices,sensors,and other applications,such as thin film transistors 126,162165,high-current field-effect transistors and sensors in nano-size 124,transparent electrodes of organ

207、ic solar-cells 166,and transparent flexible anodes for organic light-emitting diodes 167.In order to improve the electrical conductivity of CNTs,doping of either K,Br,or I has been proposed 168174.By the intercalation of Br and K into SWCNTs prepared via the laser-ablation method,their electrical re

208、sistivity at 300 K decreased by a factor of 30 169.Doping of polyiodide chains into the interstitial channels in SWCNT ropes was found to be effective to improve the electrical properties,resis-tance of I2-saturated ropes being reduced by almost two orders of magnitude at 300 K 170.Doped I2 reached

209、25 mass%and was stable even in Na/THF solution at 300 C after removing I2 adsorbed on the exterior 172.The presence of poly-iodine anions and the charge transfer between iodine and DWCNTs were confirmed by Raman spectroscopy 171.Iodine-doped DWCNT cables(yarns)gave low electrical resistivity,reachin

210、g around 107 m,and their specific conductivity(conductivity/weight)was reported to be higher than that of copper and aluminum 174.Electrical conductivity improvement by I2 doping has also been reported in SWCNTs 175.Large amounts of CNTs,up to 100 tons/year,have been used as one of the fillers in th

211、e anode of commercial lithium-ion rechargeable batteries,in which the resil-ience and electrical properties of CNTs are believed to play an important role.CNTs have also been successfully used for reinforcement of the cathode of lithium-ion rechargeable batteries 176180.In Figure 2.17,cyclic perform

212、ance is compared for 1501209060010203040Cycle numberCapacity/mA/hMWCNT 4.0 g/cm3Super-P 4.0 g/cm3MWCNT 3.3 g/cm3Super-P 3.3 g/cm3FIGURE 2.17 Cycle Performance of the LiCoO2 Cathode Formed by the Addition of Different Amounts of Conductive Additive(Super P)and MWCNTFrom 179.CHAPTER 2 Carbon Nanotubes

213、:Synthesis and Formation34the LiCoO2 cathode formed using a conventional conductive additive(furnace black,Super-P)and multi-walled carbon nanotube(MWCNT)179.The MWCNTs used were prepared by catalytic CVD and had an average size of 1015 nm in diameter and 1020 m in length.The addition of 3.3 g/cm3 o

214、f MWCNTs into the cathode was effective to improve the cyclic performance 179.The use of 0.5 mass%MWCNTs after graphitization,together with 1 mass%acetylene black,gave cyclic performance much better than that of 1 mass%acetylene black and a little better than that of 3 mass%acetylene black 180.The a

215、ddition of CNTs to the powder of insulating cathode materials,like LiCoO2,was found to give greater structural integrity,higher thermal conductivity,higher density,and shortened electrolyte absorption time,in addition to better electrochemical performance and higher electrical conductivity.The effec

216、tiveness of CNT addition into the anode has been reviewed 181.The addition of a small amount of MWCNTs into conventional carbon fiber/phenol resin composites was found to improve thermal conductivity of the composites 182.Without addition of MWCNTs,the thermal conductivity was relatively high,at abo

217、ut 250 W/mK,because the carbon fibers used had a high conductivity along the fiber axis.By the addition of 7 mass%MWCNTs,thermal conductivity increased to 393 W/mK.This result may encourage the use of CNTs as one of hybrid fillers in conventional composites in order to improve both thermal and mecha

218、nical properties.Effective rein-forcement of rubber has been obtained by using MWCNTs prepared by catalytic CVD after heat treatment at 2800 C 183.The key issues in this reinforcement were to use MWCNTs modified at their surface with fluorinated rubber to generate durable sealants that could be oper

219、ated satisfactorily at high temperatures up to 260 C and high pressure up to 239 MPa.Electrical resistivity,R,and storage modulus,E,are shown as a function of the content of MWCNTs in fluorinated rubber in Figure 2.18.The marked increase in Content of MWCNTs/mass%Electrical resistivity R /cm Storage

220、 modulus E /MPa R E 3.1210126.251091.251072.501045.001011.00101010203016001400120010008006004002000FIGURE 2.18 Changes in Electrical Resistivity,R,at Room Temperature and Storage Modu-lus,E,with the Content of MWCNTs in Fluorine RubberCourtesy of Prof.M.Endo of Shinshu University,Japan2.4 Concluding

221、 remarks35E with increasing MWCNT content is thought to be due to the formation of a cellular structure of MWCNTs.The composites are expected to work as sealants for the probing and production of oil in deeper wells.CNTs have also been tested as an adsorbent for H2 184186.Hydrogen stor-age in CNTs w

222、as revisited and reported to be less than 1.7 mass%at pressures up to 12 MPa at room temperature 186.The results suggest that the hydrogen storage capacity of CNTs is far below the benchmark settled by Department of Energy,USA(DOE).Interaction between carbon atoms in SWCNTs and atomic hydrogen has b

223、een studied by using in situ synchrotron-radiation-based core-level photoelectron spectroscopy and Raman spectroscopy 187.2.4 Concluding remarksThe synthesis of CNTs as forests and sheets by CVD using a catalyst deposited on an insulating buffer layer of SiO2 or Al2O3 is advantageous in its high gro

224、wth rate,lack of included catalyst metal,high purity of CNTs,and homogeneous structure,as well as high alignment vertically to the substrate in the forests and parallel to the substrate in the sheets,respectively.The growth rate of CNTs reaches 250 m/min in the case of the water-assisted synthesis 4

225、3,although it is 323 m/min without water assistance 32.In most cases,catalyst particles stay on the insulating layer,not at the top of CNTs,and so there is no possibility of including metallic catalyst particles during removal of the forest from the substrate by cutting.The remaining catalyst can be

226、 used repeatedly for the synthesis of CNT forests 43.The catalyst works efficiently,the surface of the catalyst being covered by SWCNTs up to 84%44.The forests and sheets thus synthesized contain negligibly small amounts of other forms of carbon,no carbon blacks,and no fullerene-like particles.The C

227、NTs in the forests and sheets possess homogeneous structure,either single-,double-,or multi-walled,which can be controlled by the thickness of catalyst film:1.62 nm thickness of catalyst Fe giving SWCNTs,3 nm Fe giving DWCNTs,and more than 4 nm Fe MWCNTs 46.These advantages of the synthesis process

228、might be a break-through for the development of practical applications for CNTs.Catalysts for the synthesis of the forests are made from transition metals and their alloys.Most of these metals can dissolve carbon atoms at high temperatures,which seems to be an important factor for employing them as

229、catalysts for CNT synthesis,as well as for the graphitization of carbon materials.For the same reason,they are not recommended to be employed as a substrate for the synthesis of graphene via CVD 188.Even using a transition metal as catalyst for CNT synthesis,however,it remains at the surface of the

230、substrate(insulating layer)in other words,at the bot-tom of CNTs during the growth of CNT forests 31,40,43but it exists at the top of the CNTs during the floating catalyst process for CNT synthesis 18.This difference in the location of catalyst particles in the tube is certainly related to the mecha

231、nism of catalytic action of the metal,but unfortunately is not understood at all well.The ratio of Co/Mo bimetallic catalyst governed the formation of SWCNTs from CO at 700 C 189.On the catalyst MoxCoyMg1-x-yO(x=00.09,y=0.050.09),the addition CHAPTER 2 Carbon Nanotubes:Synthesis and Formation36of Mo

232、 was effective in increasing the yield of CNTs,and addition of Co in improving the quality of SWCNTs from methane 16,190.Tungsten acted as a promoter for the synthesis of CNT from methane,as Mo does,although the selectivity was less 191.The composition in NixFe1-x bimetallic catalysts with a constan

233、t mean diameter of 2.0 nm had an effect on the yield of SWCNT via a floating catalyst method:the SWCNT fraction reducing with increasing Fe content in the catalysts,although the yield of as-grown CNTs was almost constant at about 0.65 mg/h 192.These results were explained by higher carbon solubility

234、 of Fe compared to Ni,which results in a larger amount of carbon precipitation and the formation of MWCNTs.In contrast to these transition metals,Cu film is recommended for the CVD deposition of graphene layers,mainly because of no dissolution of carbon and,for the same reason,it is thought not to b

235、e suitable for the acceleration of graphi-tization.However,Cu was reported to be an effective catalyst for the synthesis of sheets in which CNTs aligned in parallel to the substrate surface 73,118,126.The effect of Cu catalysts for the synthesis of CNTs is not yet clearly explained.Undoubtedly,trans

236、parent CNT sheets are very interesting materials.These sheets have to be seriously compared with other transparent conductive sheets,not only CNT sheets prepared from forests,but also ITO films,which are commonly used in various devices,and graphene membranes,which will be explained later in this bo

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276、vier Inc.All rights reserved.CHAPTERThe term“graphene”was first proposed in 1986 as the name for an isolated single two-dimensional sheet of carbon atoms,occurring in a graphite intercalation com-pound 1.In the first-stage structure,a two-dimensional carbon layer has neigh-boring intercalate layers

277、and is isolated from other carbon layers,as schematically shown in Figure 3.1.In structures higher than second stage,however,more than two carbon layers are stacked parallel with the same regularity as in graphite.The carbon layer occurring in the first-stage structure was proposed to be called“grap

278、hene,”which comes from the suffix“-ene”for polycyclic aromatic hydrocarbons,such as naphthalene,anthracene,etc.,and the prefix“graph-”from graphite.“Graphene,”therefore,was defined as an isolated single layer of carbon hexagons consisting of sp2-hybridized C-C bonding with-electron clouds.From the e

279、ngineer-ing point of view,thin flakes consisting of a few layers of carbon atoms,including monolayer graphene,could be very important because of their interesting structural and physical characteristics and also promising potential applications in technologi-cal fields,as reviewed from various viewp

280、oints 26.Preparation of graphene is classified into five routes:(1)mechanical cleavage of graphite crystals,(2)exfoliation of graphite through its intercalation compound,(3)chemical vapor deposition(CVD)on different substrate crystals,(4)organic syn-thesis processes,and(5)other processes.The prepara

281、tion of the graphite intercala-tion compound in route(2)and CVD in route(3)include chemical reactions,but here these two routes are differentiated from the synthesis of graphene via organic synthesis processes.The pyrolysis of organics resulting mostly in the formation of nanoribbons and unzipping o

282、f carbon nanotubes by using metal nanoparticles are classified into route(5).In this chapter,various attempts to prepare graphene are reviewed,with a discus-sion on the probable effectiveness of each method.There have been many papers published in this area,particularly after the Nobel Prize in phys

283、ics for 2010,which was awarded to Profs A.Geim and K.Novoselov of the University of Manchester for their groundbreaking experiments on graphene 7.In many published papers,however,the term“graphene”has not been used in its strict definition,i.e.a single layer of carbon atoms consisting of sp2-hybridi

284、zed bonds.Some authors do not pay Graphene:Synthesis and Preparation3Prerequisite for readers:Chapter 3.2(Highly oriented graphite)in Carbon Materials Science and Engineering:From Fundamentals to Applications,Tsinghua University Press.CHAPTER 3 Graphene:Synthesis and Preparation42enough care to how

285、many layers are stacked in their samples,although they have called them graphene.Here,therefore,the terms either“flake(s)”or“sheet(s)”are used to designate the products of the attempts to prepare graphene,and the term“monolayer graphene”is used only for the products confirmed to be a single layer.3.

286、1 Preparation through the cleavage of graphiteThe cleavage of highly crystalline kish graphite using double-sided adhesive tapes was repeated until the flake became transparent with a thickness of 18108 nm 8,9.On these thin flakes,electrical resistivity(),the Hall coefficient(RH),and transverse magn

287、etoresistance(/)were measured at temperatures between 4.2 and 300 K,as shown in Figure 3.2.The high crystallinity of the thin flakes thus prepared was con-firmed from the presence of a Shubnikovde Haas oscillation in RH(Figure 3.2B).These results show a marked dependence of electronic properties on

288、the thickness of the flakes,i.e.the number of layers stacked.Analysis of these experimental results shows that the overlap energy between conduction and valence bands decreases and the relaxation rate due to lattice defects increases with decreasing number of the layers stacked.Thin flakes with a th

289、ickness of 3-100 nm and lateral size of about 2 m have been obtained through the micromechanical cleavage technique 10,11 from the FIGURE 3.1 Stage Structure of Graphite Intercalation Compounds(Definition of Graphene)3.1 Preparation through the cleavage of graphite4329 nm43 nm52 nm59 nm79 nm95 nm111

290、 nm18 nm23 nm35 nm45 nm20-201234510-310-410-510-60100200300Temperature /KMagnetic field B/T18 nm23 nm35 nm45 nm150100500012345Magnetic field B/TMagnetoresistanceHall coefficient RH/6cm3/CResistivity/cmat 4.2 Kat 4.2 K(A)(B)(C)10FIGURE 3.2 Galvanomagnetic Properties of Thin Graphite Flakes with Vario

291、us Thicknesses(A)Change in resistivity,with temperature,(B)change in the Hall coefficient,RH,with magnetic field,B,and(C)magnetoresistance,/,with BCourtesy of Prof.Y.Ohashi of Keio University,JapanCHAPTER 3 Graphene:Synthesis and Preparation44micropillars formed on highly oriented pyrolytic graphite

292、(HOPG)by using oxy-gen plasma 12.Thin flakes,including monolayer graphene,were visible on the SiO2/Si substrate,although they were optically transparent 13.Electric-field-depen-dent conductance measurement on these flakes showed a marked modulation as a func-tion of gate voltage,the more markedly on

293、 the thinner flakes,as shown in Figure 3.3.The flakes obtained through repeated micromechanical cleavage of graphite were suspended in a liquid and then attached to a micrometer-sized metallic scaffold to iden-tify the monolayer graphene under transmission electron microscopy(TEM)14.The detailed obs

294、ervation by electron microscope(TEM)techniques showed that the flakes exhibited random microscopic out-of-plane deformations,monolayer graphene show-ing more marked deformations than two-layer flakes,in addition to foldings 15.The edges of monolayer graphene were shown to have either zigzag or armch

295、air structure through high-resolution scanning tunneling microscopy(STM)16.Atomically flat flakes have been obtained on the cleaved surface of mica(muscovite)17.The fluctua-tion in height on the layer surface measured by atomic force microscopy(AFM)was less than 25 pm.By peeling graphite bonded onto

296、 borosilicate glass,thin flakes with a large area consisting of a single layer or a few layers were obtained on the substrate 18.Using sonication of exfoliated graphite for a long time in an alcohol-water mixture,it was possible to cleave the material into flakes as thin as 52 nm thick 19,20.Dis-per

297、sion of sieved graphite powder in N-methylpyrrolidone at a concentration of about 0.01 mg/cm3 gave a grey supernatant after sonication and mild centrifugation,from which thin flakes consisting of less than five layers were recovered by pipetting and atom-1eV-1103/Normalized conductancePotential E /e

298、VN(E)Gate voltage /VFIGURE 3.3 Electric-field-dependent Electric Conductance on the Flakes with Different Thicknesses Prepared by PeelingFrom 103.2 Preparation through the exfoliation of graphite45then filtration 21.The yield of monolayer graphene was about 1 mass%and reported to be improved up to 1

299、2 mass%by repetition of the cleaving process.Other solvents,N,N-dimethylacetamide,-butyrolactone,and 1,3-dimethyl-2-imidazolidinone could be used for the dispersion of thin flakes.The dispersion of sieved graphite in an aque-ous solution of 5-10 mg/cm3 with sodium dodecylbenzene sulfonate gave a sup

300、ernatant after mild sonication,which contained about 3%monolayer graphene 22.Simple sonication of graphite flakes in benzylamine in Ar atmosphere gave a suspension of flakes of few layers at a concentration of 0.5 mg/cm3 23.Thin flakes with an average thickness of 1.18 nm have been prepared from gra

301、phite by sonication in cetyltrimethyl-ammonium bromide solution in glacial acetic acid and used to prepare a composite film by a simple solution blending with poly(vinyl chloride)(PVC)24,25.It has to be pointed out that perfect two-dimensional atomic crystals cannot be obtained even through the clea

302、vage of high crystalline graphite,unless in a limited size or containing many crystal defects.On the thin flakes obtained,scrolling and folding at the edges are impossible to be avoided.3.2 Preparation through the exfoliation of graphiteSynthesis of graphite oxide(GO),a covalent-type intercalation c

303、ompound,and its thermal exfoliation to thin flakes have been used on a large scale in industry to pre-pare flexible graphite sheets,of which the fundamental process is the synthesis of GO by strong oxidation,exfoliation at high temperature,and forming into thin sheets via compressing and rolling 26.

304、Attempts to prepare graphene through GO have been reported since 1962 in a number of papers via procedures similar to those for flexible graphite sheets,even though the word“graphene”was not used.The prepa-ration of graphene through ionic-type intercalation compounds with H2SO4,HNO3,also and potassi

305、um has also been reported.The procedures for the preparation of flexible graphite sheets and thin graphene-like flakes are compared in Figure 3.4.For graphene preparation,both thermal and chemical exfoliation are employed,and also reduction is essential in order to have high electrical conductivity.

306、Thermal exfolia-tion at high temperature,where exfoliation and partial reduction are thought to occur,is used for flexible graphite sheet preparation mainly because it allows production on a large-scale.By starting from intercalation compounds,excluding graphite oxides,a chemical exfoliation is empl

307、oyed for graphene preparation,and reduction is not necessary,because no chemical bonding with oxygen is expected in the intercalation compounds.3.2.1 Preparation using graphite oxidesIn most studies on the preparation of graphene,natural graphite with various particle sizes was selected as starting

308、material,but no information on their detailed crystal-line structure(crystallinity)was presented.In some papers,so-called artificial graph-ite and graphite electrodes were used without a detailed characterization of their CHAPTER 3 Graphene:Synthesis and Preparation46structure,although their structu

309、re and properties are known to depend strongly on the precursor and preparation conditions.GO has been synthesized by the so-called Hummers method 27,which was derived from the method of Staudenmaier 28,consisting of the oxidation of graph-ite in concentrated H2SO4 with NaNO3 and KMnO4,the exclusion

310、 of excess KMnO4 by reducing to water-soluble MnSO4 with H2O2,and then washing by methanol.The Brodie method 29 has also been used,where the oxidation of graphite is carried out in fuming HNO3 with KClO3.To synthesize GO,the electrochemical oxidation of graphite can be applied to natural graphite 30

311、,reactor-grade graphite 31,and various carbon fibers 32,33 in either H2SO4 or HNO3,and also to natural graphite in an ammonia solution 34.The GO synthesized can have a wide range of chemical compositions,such as C8O3.5-4.3H2.5-2.9 35,C8O3.785.05H2.9-4.4 36,C8O2.54H3.91,and C8O4.61H6.70 37,due to the

312、 presence of different oxygen-containing functional groups in different amounts.Exfoliation of GO at a high temperature of around 1000 C for a short time has often been used.During this high-temperature exfoliation,some of the functional groups on the surface of the GO were removed and the thin flak

313、es tended to coalesce.The structural change from GO to graphene by thermal exfoliation by rapid heating to 1050 C has been discussed on graphite particles of about 45 m 38.Thermal exfoliation of GO after being spray-dried with air at 300 C was performed at 1050 C for 30 s,and reported to give a high

314、 concentration of monolayer graphene,up to 80%39.Thin GO flakes were recovered from the supernatant of a dispersion,Intercalation(synthesis of intercalation compounds)GraphiteGraphite intercalation compounds(GICs)Graphite oxide(yfp)H2SO4-,HNO3-,K-Either graphite oxides or H2SO4-GIC(GO)Washing by wat

315、erGICsThermal or chemical exfoliationExpandable graphiteChemical exfoliationRapid heating to a high temperatureExfoliated graphiteReduction by H2gasor chemicalsCompression and rollingFlexible graphite sheetsThin graphene-like flakesSOFIGURE 3.4 Processes for the Preparation of Flexible Graphite Shee

316、t and Graphene Via Intercalation Compounds3.2 Preparation through the exfoliation of graphite47which was prepared in 103 mol/L NaCl aqueous solution by sonication,followed by centrifugation at 3000 rpm 40.The resultant GO dispersion remained stable for several months.A process of reduction of GO aft

317、er exfoliation has usually been included in order to produce thinner flakes,and has been carried out by different methods.By heat treatment in a mixture of Ar and H2 at 500 C for 2 days,monolayer graphene with a thickness of 0.37 nm was obtained 41.A GO film deposited on a SiO2 substrate by spray-co

318、ating was reduced in an air flow containing hydrazine at 80 C 42.Reduc-tion of GO has also been performed in liquid hydrazine,resulting in a stable dispersion of thin flakes due to the stabilization of negatively charged carbon layers surrounded by counter-ion N2H4+43.An aqueous suspension of thin f

319、lakes was obtained by adding either NaOH or KOH(8 mol/L)at 5090 C under mild sonication 47.The treatment of GO flakes by phenyl-isocyanate was also reported to be effective for producing a colloidal suspension of GO flakes with a thickness of about 1 nm 48,because of the formation of hydrophobic che

320、mical groups on the GO surface to keep the flakes separated 49.These isocyanate-treated GO flakes were reduced by hydra-zine,the resultant flakes giving a relatively high electrical conductivity after being used to make a composite with styrene:1 vol%mixing giving about 0.1 S/m and 2.5 vol%mixing ab

321、out 1 S/m 47.The reduction of GO by using either NaBH4 at a steam-bath temperature or hydroquinone under refluxing was reported to give different stacking regularities to the products after reduction,the former resulting in turbostratic but the latter in crystalline stacking of graphite layers 50.A

322、stable aqueous dispersion of thin flakes was obtained after the exfoliation and reduction of GO in the presence of poly(sodium 4-styrensulfonate)45.The reduction of GO was done in a mixed solu-tion of N,N-dimethylacetamide(DMF)and water under microwave irradiation 51.The photocatalytic reduction of

323、GO has also been carried out by suspending GO with the photocatalyst TiO2 in ethanol,but a complete reduction was not achieved 52.It has been experimentally shown that the size and crystallinity of the starting graphite have a marked influence on the thickness of the flakes 53.GO flakes were prepare

324、d through a modified Hummers method from different graphite materi-als and their thermal exfoliation,followed by reduction in a flow of H2 at 450 C,and dispersion in N-methylpyrrolidone by sonication.Figure 3.5 shows a histo-gram of the thickness distribution of 100 flakes recovered from a supernata

325、nt of the suspended solution for five kinds of starting graphite.A narrow distribution of thickness was obtained from artificial graphite,about 80%of the flakes being less than 2 nm,but a broad distribution from 4 to more than 10 layers was obtained from HOPG.This experimental result suggests that t

326、he smaller the lateral size and the lower the crystallinity of the starting graphite,the fewer the number of layers stacked in the flakes.The monolayer graphene prepared from the artificial graphite exhibited a high electrical conductivity of about 1103 S/cm.Conductive and transparent films with thi

327、cknesses of 1486 nm have been pre-pared from GO by exfoliation under sonication and reduction with hydrazine in a water dispersion,followed by making films on a quartz surface and annealing up to 1100 C 54,as shown in Figure 3.6.The optical transparency of the film with 14 nm CHAPTER 3 Graphene:Synt

328、hesis and Preparation48thickness was well over 80%in the wavelength range of 1100 to 3000 nm,and its electrical conductivity was over 200 S/cm.Hydrogen-arc discharge on GO particles has been reported to result simultane-ously in efficient exfoliation,considerable elimination of oxygen-containing fun

329、c-tional groups,and structural annealing 55.The sheet prepared in this way showed a high electrical conductivity of about 2103 S/cm,much higher than the sheet prepared by argon arc-discharge exfoliation(about 2102 S/cm)and also than that by conventional thermal exfoliation(about 80 S/cm).A hydrosol

330、of GO flakes prepared from natural graphite powder gave a thin mem-brane(0.5-20 m thick)at the liquid/air interface by warming to 353 K,which was Highly oriented pyrolytic graphiteNatural flaky graphiteKish graphiteFlaky graphite powderNumber of flakesArtificial graphiteThickness /nm2010302010302010

331、302030102010002468101214161820FIGURE 3.5 Distribution Histogram of Thickness of Flakes Prepared From Various Graphite SamplesCourtesy of Prof.H.-M.Cheng of the Institute of Metal Research,China.86 nm thick22 nm thick14 nm thickFIGURE 3.6 Thin Sheets Prepared in Different Thicknesses from Graphite Ox

332、ide Through Exfoliation,Reduction and Annealing at 1100 CFrom 54.3.2 Preparation through the exfoliation of graphite49flexible and self-standing 56.It was shown that GO sheets could be deposited at any place defined by a molecular template,owing to the electrostatic attraction between the negatively

333、 charged GO flake and the positively charged template 57.The patterned GO deposits were reduced by exposure to hydrazine vapor.Spontaneous exfoliation of graphite in chlorosulfonic acid(HSO3Cl)gave dispersion with a relatively high concen-tration of thin flakes of about 2 mg/cm3,of which 70%were identified as monolayer 58.Exfoliated graphite prepared through the conventional process(Figure 3.4)was