Carbon Meta-Nanotubes E-Book

Marc Monthioux

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 903

Veröffentlichungsjahr: 2011

Beschreibung

Meta-Nanotubes are a new generation of carbon nanotubes (CNTs) which result from the chemical transformation of regular CNTs and their subsequent combination with foreign materials (atoms, molecules, chemical groups, nanocrystals) by various ways such as functionalisation, doping, filling, and substitution. These new nanomaterials exhibit enhanced or new properties, such as reactivity, solubility, and magnetism, which pristine CNTs do not possess. Their many applications include electronic and optoelectronic devices, chemical and biosensors, solar cells, drug delivery, and reinforced glasses and ceramics. Carbon Meta-Nanotubes: Synthesis, Properties and Applications discusses these third generation carbon nanotubes and the unique characteristics they possess. Beginning with a general overview of the subject, this book covers the five main categories of meta-nanotubes, namely: * Doped Carbon Nanotubes * Functionalised Carbon Nanotubes * Decorated or Coated Carbon Nanotubes * Filled Carbon Nanotubes * Heterogeneous Nanotubes Providing unparalleled coverage of these third generation or meta-nanotubes, and possibilities for future development, this book is essential for anyone working on carbon nanotubes.

Leseprobe

Contents

About the Editor

Dedication

List of Contributors

Foreword

Acknowledgements

List of Abbreviations

Introduction to the Meta-Nanotube Book

1 Time for a Third-Generation of Carbon Nanotubes

2 Introducing Meta-Nanotubes

3 Introducing the Meta-Nanotube Book

1 Introduction to Carbon Nanotubes

1.1 Introduction

1.2 One Word about Synthesizing Carbon Nanotubes

1.3 SWCNTs: The Perfect Structure

1.4 MWCNTs: The Amazing (Nano)Textural Variety

1.5 Electronic Structure

1.6 Some Properties of Carbon Nanotubes

1.7 Conclusion

2 Doped Carbon Nanotubes: (X:CNTs)

2.1 Introduction

2.2 n-Doping of Nanotubes

2.3 p-Doping of Carbon Nanotubes

2.4 Practical Applications of Doped Nanotubes

2.5 Conclusions, Perspectives

3 Functionalized Carbon Nanotubes: (X-CNTs)

3.1 Introduction

3.2 Functionalization Routes

3.3 Properties and Applications

3.4 Conclusion

4 Decorated (Coated) Carbon Nanotubes: (X/CNTs)

4.1 Introduction

4.2 Metal-Nanotube Interactions – Theoretical Aspects

4.3 Carbon Nanotube Surface Activation

4.4 Methods for Carbon Nanotube Coating

4.5 Characterization of Decorated Nanotubes

4.6 Applications of Decorated Nanotubes

4.7 Decorated Nanotubes in Biology and Medicine

4.8 Conclusions and Perspectives

5 Filled Carbon Nanotubes

5.1 Presentation of Chapter 5

5a Filled Carbon Nanotubes:

5a.1 Introduction

5a.2 Synthesis of X@CNTs

5a.3 Behaviours and Properties

5a.4 Applications (Demonstrated or Expected)

Acknowledgements

5b Fullerenes inside Carbon Nanotubes: The Peapods

5b.1 Introduction

5b.2 The Discovery of Fullerene Peapods

5b.3 Classification of Peapods

5b.4 Synthesis and Behavior of Fullerene Peapods

5b.5 Properties of Peapods

5b.6 Applications of Peapods

Acknowledgements

Overall Conclusion for Chapter 5

6 Heterogeneous Nanotubes: (X*CNTs, X*BNNTs)

6.1 Overall Introduction

6.2 Pure BN Nanotubes

6.3 BxCyNz Nanotubes and Nanofibers

6.4 B-Substituted or N-Substituted Carbon Nanotubes

6.5 Perspectives and Future Outlook

Acknowledgements

Plates

Index

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Library of Congress Cataloging-in-Publication Data

Carbon meta-nanotubes : synthesis, properties, and applications / [edited by] Marc Monthioux.p. cm.Includes bibliographical references and index.ISBN 978-0-470-51282-11. Nanostructured materials. 2. Nanotubes. 3. Organic compounds–Synthesis. I. Monthioux, Marc.TA418.9.N35C336 2012620.1′17–dc23

2011033599

A catalogue record for this book is available from the British Library.

Print ISBN: 978-0-470-51282-1 (HB)ePDF ISBN: 978-1-119-95473-6oBook ISBN: 978-1-119-95474-3ePub ISBN: 978-1-119-96094-2Mobi: 978-1-119-96095-9

About the Editor

Marc Monthioux has dedicated his scientific life to carbon materials for more than 30 years, with transmission electron microscopy as his main investigation tool. He graduated from the University of Orléans (France), where he also prepared his first two-year Doctorate thesis work (Specialty Thesis) on investigating the carbonization and graphitization mechanisms of heavy petroleum products, with Dr. Agnès Oberlin as his supervisor. He was then recruited by the French National Center for Research (CNRS) in 1982 and worked for five years at the French Institute of Petroleum (IFP, Rueil-Malmaison) while preparing his second five-year thesis (State Thesis) dedicated to experimentally mimicking the natural coalification and petroleum generation processes. After receiving this ultimate academic degree in 1986, he moved to the University of Pau, France along with Agnès Oberlin’s team to work on advanced carbon-containing ceramic fibres and composites and pyrolytic carbons. After Dr. Oberlin retired, he led the laboratory for two years then merged it with a large CNRS laboratory in 1995, the Center of the Preparation of Materials and Structural Studies (CEMES) located at the University of Toulouse, France, renowned worldwide for its pioneering role in the development of transmission electron microscopy. While affiliated to CEMES, he has spent about two years working in the USA at the Dupont Experimental Station, Wilmington, Delaware as a consultant for Dupont de Nemours (carbon fibres) then the Conoco Company (pitch-based cokes), then at the University of Pennsylvania, Philadelphia under a NATO fellowship where he started getting involved in carbon nanoforms with David Luzzi and Jack Fischer. Once back in France, he combined working mainly on carbon nanoforms and pyrolytic carbons at CEMES with working as a consultant for three years for IMRA-Europe (Sophia-Antipolis, France) installing a laboratory and leading a team dedicated to hydrogen storage in carbon materials.

Dr. Monthioux has authored more than 190 papers in international journals and conference proceedings and has contributed to more than 15 books and topical journal special issues. Among his scientific achievements one can note: the demonstration of the existence of a graphitizability continuum between the formerly known ‘hard’ (non-graphitizable) carbons and ‘soft’ (fully graphitizable) carbons; the most complete and successful experimental duplication of the natural coalification processes ever, which has revealed the leading role of the pressurized confinement of the effluents; the discovery of the ability of single-wall carbon nanotubes (SWCNTs) in being filled with molecules, starting with the example of nanopeapods; the fabrication of the world smallest and most sensitive supraconducting quantum interference device (the nanoSQUID) for magnetic measurements, based on a single SWCNT.

He is currently CNRS Research Director at CEMES (Toulouse, France), Editor of Carbon journal (Elsevier), Chairman of the French Carbon Group (GFEC), and Chairman of the European Carbon Association (ECA).

Dedication

While this book was being prepared for publication, the news has hit us that our friend and colleague Jack Fischer had passed away on Tuesday, June 28th, 2011, at the age of 72. Of course, we know that we are all only briefly on this earth. Of course, we know that this will happen to every one of us eventually. Of course, we knew that this probably had to happen sooner for Jack as he had been struggling with complications arising from polycystic kidney disease for a decade. But the death of a dear person, relative or friend, is one of the hardest pieces of news to accept in life, as we subconsciously think of them as immortal. We just refuse to believe they can die.

We are not going to talk extensively about Jack’s scientific skills and his dedication to science in general and carbon more specifically. The importance of Jack’s inputs in carbon science, from graphite intercalation compounds to nanocarbons, has resulted in a highly successful career which accounts for more than 400 papers, more than 20 000 citations, a h-index of 65, 68 supervised PhD students and postdocs … the kind of achievements that all scientists would be proud of, and that most will not get. Detailed summaries about Jack’s scientific path and career, from his first appointment to the University of Pennsylvania in Philadelphia, one of the eight prestigious universities of the so-called US ‘Ivy League’ only six years after graduating with a PhD degree in Nuclear Science and Engineering in 1966, can be found in several obituaries that have been published since then (for instance by P.K. Davies and Y. Gogotsi in Carbon 49 (2011) 4075).

We are proud and happy that this book contains Jack’s last scientific contribution. And therefore, we wish to dedicate this book to him. We are friends grieving, and aside from the scientific merits that will survive him for many years to come, we would also like to state that Jack was not only a brilliant scientist, but that he was also a multicultural person, an oyster lover, a fan of classical music, a faithful friend, and a nice fellow. We will miss him.

Marc MonthiouxOn behalf of the co-authors

List of Contributors

Revathi R. BacsaLaboratoire de Chimie de Coordination – ENSIACET, UPR-8241 CNRS, Université de Toulouse, BP 44362, F-31030 Toulouse, France

Stéphane CampidelliLaboratoire d’Electronique Moléculaire, DSM/IRAMIS/SPEC, CEA Saclay, F-91191 Gif-sur-Yvette, France

John E. FischerDept. of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104-6272, USA

Dmitri GolbergNanoscale Materials Center, National Institute for Materials Science, University of Tsukuba, Ibaraki 305-0044, Japan

Marc MonthiouxCentre d’Elaboration des Matériaux et d’Etudes Structurales (CEMES), UPR-8011 CNRS, Université de Toulouse, BP 94347, F-31055 Toulouse, France

Alain PénicaudCentre de Recherche Paul Pascal (CRPP), UPR-8641 CNRS, Université Bordeaux I, F-33600 Bordeaux, France

Pierre PetitInstitut Charles Sadron, UPR-22 CNRS, Université de Strasbourg, BP 84047, F-67034 Strasbourg, France

Maurizio PratoDipartimento di Scienze Farmaceutiche, Universitá di Trieste, I-34127 Trieste, Italy

Philippe SerpLaboratoire de Chimie de Coordination – ENSIACET, UPR-8241 CNRS, Université de Toulouse, BP 44362, F-31030 Toulouse, France

Jeremy SloanDept. of Physics, University of Warwick, Coventry, CV4 7AL, UK

Ferenc SimonDept. of Physics, Institute of Physics, Budapest University of Technology and Economics, PO Box 91, H 1521 Budapest, Hungary

Mauricio TerronesDept. of Physics, PMB 136, The Pennsylvania State University, University Park, PA 16802, USAResearch Center for Exotic Nanocarbons (JST), Shinshu University, Nagano 380-8553, Japan

Stanislaus S. WongDept. of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USACondensed Matter Physics and Materials Science Dept., Brookhaven National Laboratory, Upton, NY 11973, USA

Foreword

Carbon is a fascinating element and one of the most abundant on Earth. It is still surprising us with all the variety of structures that it produces at the nanoscale. The birth of C60 (or Buckminsterfullerene) in the mid-1980s spawned a revolution in nanoscience and nanotechnology. Soon after the bulk synthesis of C60, a new type of chemistry emerged and these studies resulted in the quest of novel nanocarbon forms such as carbon nanotubes (single-, double-, and multi-walled). Although single- and multi-walled carbon nanotubes were observed in the 1970s by Morinobu Endo, it was not until 1991, when Sumio Iijima reported the concentric tubular structure (nested concentric elongated fullerenes) using electron diffraction of the carbon residues produced in an arc discharge generator used to synthesize C60 soot, that carbon nanotubes became a major focus for nanoscience and nanotechnology.

These novel sp2-like hybridized carbon structures (fullerenes and nanotubes) are unique due to their cage-like morphology. Therefore, it is not only possible to use their outer surface reactivity, but also their inner surface, in order to functionalize or encapsulate molecules or materials that could lead to novel applications. This book tries to emphasize the fact that the available surfaces of nanotubes could be used to obtain modified nanotubes by the adsorption or chemisorption of different materials including molecules, metals, clusters, and so on. These modified tubular carbon materials could be called meta-nanotubes and the objective of this book, the first of its kind, is to review the different approaches able to modify carbon nanotubes (single-, double- and multi-walled), in order to produce carbon-based materials that could be used in more efficient devices during the twenty-first century.

The book is divided into six chapters contributed to by leading scientists around the world. They deal with different ways of modifying the surfaces of carbon nanotubes. The first chapter provides an overview of pristine (pure) carbon nanotubes and how this tubular material (considered as a building block) can then be modified to give rise to meta-nanotubes. The following chapters of this book deal with the different ways of modifying nanotubes by doping, chemical molecule functionalization, cluster decoration, filling of nanotubes, and the synthesis of heteroatomic nanotubes. These chapters review the latest work in the field, pose some unsolved issues and propose new directions along the production of novel meta-nanotubes and their applications. Therefore, this book should be used as a guide to perform novel and innovative research in the area of carbon nanotubes, and some of this work could even be extrapolated to explore other graphene-like systems.

This book is also dedicated to the memory of John E. ‘Jack’ Fischer, an outstanding carbon scientist who passed away on June 28, 2011. He contributed enormously to the fullerene and nanotube fields publishing more than 400 papers in high impact journals. His contributions triggered innovative work and applications, especially in the areas of batteries and energy storage devices. He was a great human being and had a spectacular sense of humour. This is another great loss for the world carbon community, after Richard Smalley (2005) who boosted the research on nanotubes, Adolphe Pacault (2008) who organised the research on carbon in France from the 60’, Peter Eklund (2009) who was a major figure in the world of condensed matter physics and world famous for his experiments on nanotubes, P.L. Walker (2009) who pioneered the research on carbon at Penn State and Sugio Otani (2010) who first introduced and developed pitch as a precursor for carbon fibre. We are fortunate to inherit their scientific legacy.

Harold, W. Kroto (Nobel Laureate, FRS)Florida State UniversityTallahassee, Florida, USA

Acknowledgements

Published with the kind assistance of the Groupe Français pour l’Etude du Carbonehttp://www.gfec.net a member of the European Carbon Association http://www.hpc.susx.ac.uk/ECA

List of Abbreviations

AAC

azide-alkyne cycloaddition

AC

alternating current

AEPA

2-aminoethylphosphonic acid

AES/OES

atomic emission/optical emission spectroscopy

AFM

atomic force microscopy

ALD

atomic layer deposition

APTEOS

aminopropyltriethoxysilane

bcc

body centered cubic

BCS

Bardeen-Cooper-Schrieffer

bct

body-centred tetragonal

BEDT-TTF

bis-ethylenedithiotetrathiafulvalene

BNNT

boron nitride nanotube

BNNW

boron nitride nanowire

BSA

bovine serum albumin

BWF

Breit-Wigner-Fano

CAT

coaxial tube

CB

conduction band

CCVD

catalysed chemical vapour deposition

CESR

conduction electron spin resonance

CNF

carbon nanofibre

h-CNF

herringbone carbon nanofibre

p-CNF

platelet carbon nanofibre

CNT

carbon nanotube

CoPc

cobalt phtalocyanine

CVD

chemical vapour deposition

DC

direct current

DFT

density functional theory

DMF

dimethylformamid

DMSO

dimethylsulfoxide

DMTA

dynamic mechanical thermal analysis

DNA

deoxyribonucleic acid

DOS

density of states

DPP

diphenylporphyrin

DWCNT

double-wall carbon nanotube

EDAC

ethyl dimethylaminopropylcarbodiimide

EELS

electron energy loss spectroscopy

EPR

electron paramagnetic resonance

ESR

electron spin resonance

EXAFS

extended X-ray absorption fine structure

FAD

flavine adenine dinucleotide

fcc

face-centred cubic

FE

field emission

FEB

ferrocene-ethanol-benzylamine

FET

field effect transistor

FITC

fluorescein isothiocyanate

FL

Fermi liquid

FTIR

Fourier transform infrared spectroscopy

GC-MS

gas chromatography mass spectrometry coupling

GIC

graphite intercalation compound

GOx

glucose oxidase

HADF

high-angular dark field

HDP

homogeneous deposition precipitation

HOMO

highest occupied molecular orbital

HOPG

highly oriented pyrolytic graphite

HPLC

high pressure liquid chromatography

HRTEM

high resolution transmission electron microscopy

HV

hexyl-viologen

ICP

inductively coupled plasma

IgG

immunoglobulin G

IR-vis

infrared-visible

ITO

indium tin oxide

IUPAC

International Union of Pure and Applied Chemistry

LDA

local density approximation

LEEPS

low energy electron (point) source microscopy

LPC

lyso-phosphatidylcholine

LUMO

lowest unoccupied molecular orbital

LPG

liquefied petroleum gas

MAO

methylaluminoxane

MD

molecular dynamics

MOCVD

metal organic chemical vapour deposition

MRI

magnetic resonance imaging

MUA

mercaptoundecanoic acid

MS

mass spectrometry

MWCNT

multi-wall carbon nanotube

b-MWCNT

bamboo multi-wall carbon nanotube

c-MWCNT

concentric multi-wall carbon nanotube

h-MWCNT

herringbone multi-wall carbon nanotube

NDT

nonane dithiol

NMR

nuclear magnetic resonance

NMRP

nitroxide mediated radical polymerisation

ONIOM

our own n-layered integrated molecular orbital and molecular mechanics

PAA

polyacrylic acid

PABS

poly(m-aminobenzenesulfonic acid)

PAMAM

polyamidoamine

PDADMAC

poly(diallyldimethylammonium chloride)

PDDA

poly(diallyldimethylammonium)

PE

polyethylene

PEG

polyethyleneglycol

PEI

polyethyleneimine

PEM

proton exchange membrane

PES

photo-electron/photo emission spectroscopy (also named XPS)

PMMA

polymethylmetacrylate

PmPV

poly{(m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}

P3OT

poly-3-octylthiophene

PPM

pentagonal pinch mode

PS

polystyrene

PSA

prostate specific antigen

PSS

poly(sodium styrene-4-sulfonate)

PVA

polyvinylalcohol

PVP

polyvinylpyrollidone

QC

quantum computing

QCM

quartz crystal microbalance

RBM

radial breathing mode

RDF

radial distribution function

RPA

random phase approximation

SA

streptavidin

SDS

sodium dodecyl sulfate

SEM

scanning electron microscopy

SGO

similar graphene orientation

SHE

standard hydrogen electrode

SpA

staphylococcal protein A

SSA

specific surface area

STEM

scanning transmission electron microscopy

STM

scanning tunnelling microscopy

STS

scanning tunnelling spectroscopy

SWBNNT

single-wall boron nitride nanotube

SWCNT

single-wall carbon nanotube

TCE

tetracyanoethylene

TCNQ

tetracyanoquinodimethane

TCNQF4

tetrafluorotetracyanoquinodimethane

TDAE

tetrakis(dimethylamino)ethylene

TEM

transmission electron microscopy

TEP

thermoelectric power

TG

thermal gravimetry

TGA

thermogravimetry analysis

TLL

Tomonaga-Lüttinger liquid

TM

tangential mode

TMTSF

tetramethyl-tetraselenafulvalene

TMTTF

tetramethyltetrathiafulvalene

TTF

tetrathiafulvene

TPD

thermally programmed desorption

TPO

triphenyl phosphine oxide

UV-vis-NIR

ultraviolet-visible-near infrared

VGCF

vapour-grown carbon fibre

vis-NIR

visible-near infrared

XANES

X-ray absorption near-edge structure

XPS

X-photoelectron spectroscopy (also named PES)

XRD

X-ray diffraction

ZnNc

zinc-naphtalocyanine

ZnP

zinc-porphyrin

Introduction to the Meta-Nanotube Book

Marc Monthioux

CEMES, CNRS, University of Toulouse, France

1 Time for a Third-Generation of Carbon Nanotubes

So-called multi-walled carbon nanotubes (MWCNTs) have been known since the 1950s (see [1] and references within, the very first evidence of their occurrence being dated 1952 [2]). Micron-size filamentous carbons (which are now understood as being catalytically-grown MWCNTs subsequently thickened by a catalyst-free chemical vapour deposition or CVD process) have been known from the early twentieth century [3], and even the late nineteenth century [4] where a patent was filed [5] to protect the intellectual property of a CVD-based process aiming to prepare carbon filaments to be used as wires in the just-born electric bulbs invented by Joseph Swan in 1878 (and subsequently improved, or more or less duplicated, by Thomas Edison a few months later). After carbon filaments were replaced in electric bulbs by tungsten wires, they were mostly seen as undesirable by-products to get rid of, for example, in the coke industry [3] where gas exhausts could be obstructed by the abundance of grown carbon filaments (resulting from the thermal cracking of the released gaseous hydrocarbons in presence of iron minerals, that are omnipresent in coal), or in the nuclear industry, where the formation and deposition of carbon filaments could adversely affect the efficiency of metallic-tubed heat exchangers in helium-cooled reactors [6]. Carbon nanotubes with diameters in the ∼3 nm range were even incidentally synthesized as early as 1976 [7] but were merely considered as a material curiosity whose growth mechanisms were worth being elucidated.

Hence, it took decades and the landmark paper by Sumio Iijima in 1991 [8], followed after two years with the discovery of the so-called single-walled carbon nanotubes (SWCNTs) and, more importantly, a way to synthesize them in a reliable and reproducible manner [9,10], for the unique properties of CNTs to be finally figured out and their countless applicative potentialities to be acknowledged and explored. A second generation of carbon nanotubes was thus born, as the flagship of the worldwide activity on nanoscience and nanotechnology which started meanwhile.

Twenty years later, the relevant synthesis processes (i.e. those which are suitable for commercial scale production) are now all defined, most of CNT properties are predicted and demonstrated. Most of the current research efforts are focused on the actual use of CNTs, that is, their integration in devices and incorporation in advanced materials and crafts of practical interest. This is where the natural beauty of CNTs, that is, their structural perfection, which had made them ideal objects to study and had attracted the attention of physicists, caused their limitations. In many instances, CNTs appeared to be difficult to handle, purify, sort, disperse, mix, and so on. On the other hand, in many of the applications envisaged, CNTs were needed to be suitably combined with other phases. In other words, it was time to develop a third-generation of carbon nanotubes modified from the pristine ones by the various means that chemists could think of. That is to say, it was time to consider ‘meta-nanotubes’.

2 Introducing Meta-Nanotubes

Carbon nanotubes can be modified in many ways, generally involving chemical treatments that make use of the polyaromatic nature of their skeleton. Because electronics was among the very first applications that CNTs were considered for, doping their electronic structure was rapidly thought to allow promising developments. The doping was achieved by following various routes, for example, grafting functions or metal nanoparticles, inserting dopants in or between SWCNTs, and/or substituting lattice carbon atoms by heteroatoms. The resulting materials were however often indifferently referred to as ‘doped nanotubes’, although they could be very different from each other from the point of view of materials. Furthermore, modifying CNTs and combining them with foreign components appeared to open many more promising developments than in merely electronics. CNTs had to no longer be considered as such but as starting materials to be used as host, substrate, mould, structural skeleton, and so on. A whole specific field of research was then opened, and it was necessary to find a way to differentiate modified CNTs from pristine ones and to accurately discriminate the various forms of modified CNTs. This is where we created the word ‘meta-nanotubes’ [11,12] (from ancient Greek metá, meaning ‘beyond, after’), defined as modified nanotubes resulting from the transformation of pristine nanotubes by various ways, which leaves the nanotubes being associated with a foreign component X, where X can be atoms or molecules, chemical functions, or phases. Five different kinds of association of X with CNTs were identified and are listed below, tentatively roughly ranked according to the increasing structuration of the component X (from isolated atoms to phases), as well as the increasing intimacy and strength of the X-versus-CNT association.

2.1 Doped Nanotubes (X:CNTs)

These are carbon nanotubes which are associated with electron donor or acceptor elements such as Br2, K, Rb, and so on. These substances (or compounds) more generally can be used to modify the overall electronic structure and behaviour. The association is intimate, that is, it is not merely a matter of coating or grafting the outer surface but does not involve a strong chemical bonding. Both the association mechanisms and the doping processes are related to that of intercalation compounds in graphite (GICs) and the inserted element (e.g. Li, K, etc.) is therefore found in between graphenes in MWCNTs, or in between SWCNTs in SWCNT bundles. The doping material does not make an individual phase, as opposed to the coating or filling phases mentioned next. The preferred techniques to identify the dopant relate to spectroscopy (e.g. EELS, XPS) or chemical analysis methods. The doping process is usually reversible, sometimes spontaneously in some conditions, as for Li-doped CNTs exposed to air for instance.

2.2 Functionalized Nanotubes (X-CNTs)

These are nanotubes at the surface of which various individual chemical functions are grafted, that is, where the foreign component X does not form a phase by itself. X-CNT bonds can be covalent or weaker, for example, through so-called p-stacking. Reversibility, that is, defunctionalization, is easy via either chemical or physical (e.g. thermal) procedures. The preferred ways to characterize the grafted functions are chemical analysis techniques such as FTIR spectroscopy or chemical titrations. It is a quite important topic mostly developed since to address some of the major issues of pristine CNTs such as reactivity, dispersability, solubility, and so on which are compulsory properties for many processes involving CNTs.

2.3 Decorated (Coated) Nanotubes (X/CNTs)

These are nanotubes at the surface of which the foreign component X is a genuine phase, from the point of view of chemistry and structure. It is deliberately bonded to the CNT surface, either as a continuous coating or a discontinuous decoration. They are most often nanoparticles but the category may also include CNTs onto which complex compounds are adsorbed or bonded such as polymers, structured biomolecules (e.g. DNA), and so on. Reversibility is generally easy and made possible via chemical or physical procedures, as for functionalized CNTs. In the related applications, the intrinsic properties of the CNT underneath may be of minor importance since the CNTs may basically be used as a substrate, while the needed properties are brought by the coating material. As the foreign component of those meta-CNTs is a phase, it may be characterized by diffraction techniques (e.g. XRD, electron diffraction), among others. It is worth noting that functionalizing the CNTs so that the nanotube surface attractiveness towards the nanoparticles is enhanced may be a previous step in the preparation of decorated (coated) CNTs.

2.4 Filled Nanotubes (X@CNTs)

These are carbon nanotubes which the inner cavity is fully or partially filled with foreign atoms, molecules, or compounds. They are probably the most versatile of the meta-nanotubes described here, and thereby are likely the ones which open the wider research field, both regarding scientific and technological aspects. As opposed to doping, the filling components generally gather and associate into a phase, enabling their identification by diffraction techniques, in addition to spectroscopic methods. The foreign component X is not chemically bonded to the CNT host, but possibly by van der Waals forces. However, because the encapsulation situation often corresponds to a situation of low free energy, the filling event exhibits a limited reversibility upon solvating methods, yet variable with the diameter of the CNT host cavity (the narrower the cavity, the more stable the contained phase). Removing the filling phases hence can require severe conditions such as decomposition upon high thermal treatments.

2.5 Heterogeneous Nanotubes (X*CNTs)

These are carbon nanotubes whose carbon atoms from the hexagonal graphene lattice are partially or even totally substituted with hetero-atoms, typically nitrogen and/or boron. Obviously, one of the major consequences of such a substitution is the modification of the electronic structure, and thereby the electronic behaviour, of the resulting nanotubes. It also allows the development of a specific side-wall chemistry using the reactivity of the substituting heteroatoms. Yet the amount of foreign component X can be low (e.g. in the range of few percent for the substitution of C by N or B). Hetero-CNTs are the only meta-CNTs for which X is no longer more or less independent from the host. It is integrated to the meta-CNT structure and because of this, the reversibility is not possible.

3 Introducing the Meta-Nanotube Book

Chapter 1 of this book is dedicated to an introduction to pristine carbon nanotubes. Because it is doubtful that any reader of this book would ignore what carbon nanotubes are in the first place, it was wondered whether such a chapter was necessary. We finally decided it was, because the world of carbon nanotubes, and nanocarbons generally speaking, is related to the complex and labyrinthic world of carbon materials, which has kept scientists and engineers busy for more than a century. The high potential and attractiveness of carbon nanotubes in the field of nanosciences and nanotechnology means that many researchers, specifically younger ones, get involved in the field without really knowing what a genuine graphitic material is, for example. Another reason is that official definitions, as stated by IUPAC for instance, of terms related to nanotube science are still lacking and it was necessary to define those terms at least in the context of this book.

Chapters 2 to 6 describe the five kinds of meta-nanotubes in the same order as presented in Section 2 above. Only Chapter 5 is split into two parts, due to the specific place that a peculiar type of filled carbon nanotube, namely the peapod, is taking in the field. Each of the chapters is authored by the pioneering and/or most active scientists in the related field. Hence, although authors have made an overview of their field as far as possible, the content of each chapter reflects in a various extent the field of interest and activity of the related authors. This has meant that some aspects, yet of significance, appear not to be covered. For instance, CNT functionalization aiming to optimize the interaction with the matrix in composites designed for structural (mechanical load transfer), electrical (charge carrier transfer), or thermal (phonon transfer) application was not specifically developed. Also, in spite of the clear discrimination we tentatively made between each meta-CNT categories, we could not prevent some overlapping between chapters.

Indeed, at some point, discriminating between a heavily doped CNT for which the dopant is located inside the CNT cavity and a CNT slightly filled with atoms whose low proportion barely allows a phase to build up could not be obvious. Likewise, functionalized CNTs and coated CNTs were found to meet when the foreign component X to consider was in large quantity and bonded to the CNT surface via van der Waals forces only. For instance, I would personally have categorized DNA-wrapped SWCNTs as coated-CNTs but the authors preferred to consider them functionalized-CNTs and I respected that. Another difficulty was that meta-CNTs may belong to several categories and this actually is an eventuality whose occurrence is going to increase as the field develops. For instance, decorating CNTs with nanoparticles often comes with a preliminary functionalization step to attract and retain the nanoparticles as well as to prevent their further coalescence. Even worse, hetero-CNTs can subsequently be functionalized then decorated, making the resulting materials belong to three out of five categories…

Hence, we beg the reader to be indulgent. This book is the first attempt of its kind. We hope to be given the opportunity to make further, revised editions of it, in which we will try to gradually fix every flaw that will be brought to our attention, thanks to the feedback we will receive from our readership.

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