Functionalization of Graphene

Vasilios Georgakilas

• Publisher: Wiley-VCH
• Year: 2014
• ISBN:
  9783527672776
• Edition: 1
• Topic: Sciences physiques
• Subtopic: Chimie physique et théorique

All set to become the standard reference on the topic, this book covers the most important procedures for chemical functionalization, making it an indispensable resource for all chemists, physicists, materials scientists and engineers entering or already working in the field. Expert authors share their knowledge on a wide range of different functional groups, including organic functional groups, hydrogen, halogen, nanoparticles and polymers.

Chapter 1

An Introduction to Graphene

Konstantinos Spyrou and Petra Rudolf

1.1 Brief History of Graphite

Carbon takes its name from the latin word carbo meaning charcoal. This element is unique in that its unique electronic structure allows for hybridization to build up sp³, sp², and sp networks and, hence, to form more known stable allotropes than any other element. The most common allotropic form of carbon is graphite which is an abundant natural mineral and together with diamond has been known since antiquity. Graphite consists of sp² hybridized carbon atomic layers which are stacked together by weak van der Waals forces. The single layers of carbon atoms tightly packed into a two-dimensional (2D) honeycomb crystal lattice is called graphene. This name was introduced by Boehm, Setton, and Stumpp in 1994 [1]. Graphite exhibits a remarkable anisotropic behavior with respect to thermal and electrical conductivity. It is highly conductive in the direction parallel to the graphene layers because of the in-plane metallic character, whereas it exhibits poor conductivity in the direction perpendicular to the layers because of the weak van der Waals interactions between them [2]. The carbon atoms in the graphene layer form three σ bonds with neighboring carbon atoms by overlapping of sp² orbitals while the remaining p_z orbitals overlap to form a band of filled π orbitals – the valence band – and a band of empty π* orbitals – the conduction band – which are responsible for the high in-plane conductivity.

The interplanar spacing of graphite amounts to 0.34 nm and is not big enough to host organic molecules/ions or other inorganic species. However several intercalation strategies have been applied to enlarge the interlayer galleries of graphite from 0.34 nm to higher values, which can reach more than 1 nm in some cases, depending on the size of the guest species. Since the first intercalation of potassium in graphite, a plethora of chemical species have been tested to construct what are known as graphite intercalation compounds (GICs). The inserted species are stabilized between the graphene layers through ionic or polar interactions without influencing the graphene structure. Such compounds can be formed not only with lithium, potassium, sodium, and other alkali metals, but also with anions such as nitrate, bisulfate, or halogens.

In other cases the insertion of guest molecules may occur through covalent bonding via chemical grafting reactions within the interlayer space of graphite; this results in structural modifications of the graphene planes because the hybridization of the reacting carbon atoms changes from sp² to sp³. A characteristic example is the insertion of strong acids and oxidizing reagents that creates oxygen functional groups on the surfaces and at the edges of the graphene layers giving rise to graphite oxide. Schafheutl [3] first (1840) and Brodie [4] 19 years later (1859) were the pioneers in the production of graphite oxide. The former prepared graphite oxide with a mixture of sulfuric and nitric acid, while the latter treated natural graphite with potassium chlorate and fuming nitric acid. Staudenmaier [5] proposed a variation of the Brodie method where graphite is oxidized by addition of concentrated sulfuric and nitric acid with potassium chlorate. A century later (1958) Hummers and Offeman [6] reported the oxidation of graphite and the production of graphite oxide on immersing natural graphite in a mixture of H₂SO₄, NaNO₃, and KMnO₄ as a result of the reaction of the anions intercalated between the graphitic layers with carbon atoms, which breaks the aromatic character. The strong oxidative action of these species leads to the formation of anionic groups on graphitic layers, mostly hydroxylates, carboxylates, and epoxy groups. The out of planar C–O covalent bonds increase the distance between the graphene layers from 0.35 nm in graphite to about 0.68 nm in graphite oxide [7]. This increased spacing and the anionic or polar character of the oxygen groups formed impart to graphene oxide (GO) a strongly hydrophilic behavior, which allows water molecules to penetrate between the graphene layers and thereby increase the interlayer distance even further. Thus graphite oxide becomes highly dispersible in water. The formation of sp³ carbon atoms during oxidation disrupts the delocalized π system and consequently electrical conductivity in graphite oxide deteriorates reaching between 10³ and 10⁷ Ω cm depending on the amount of oxygen [2, 8].

1.2 Graphene and Graphene Oxide

For several decades the isolation of graphene monolayer seemed to be impossible on the basis of, among other things, theoretical studies on the thermodynamic stability of two-dimensional crystals [9]. An important step in this direction was made by a research group in Manchester guided by Geim and Novoselov in 2004 [10] who reported a method for the creation of single layer graphene on a silicon oxide sub...

Table of contents

• Cover
• Related Titles
• Titlepage Text
• Copyright
• Preface
• List of Contributors
• Chapter 1: An Introduction to Graphene
• Chapter 2: Covalent Attachment of Organic Functional Groups on Pristine Graphene
• Chapter 3: Addition of Organic Groups through Reactions with Oxygen Species of Graphene Oxide
• Chapter 4: Chemical Functionalization of Graphene for Biomedical Applications
• Chapter 5: Immobilization of Enzymes and other Biomolecules on Graphene
• Chapter 6: Halogenated Graphenes: Emerging Family of Two-Dimensional Materials
• Chapter 7: Noncovalent Functionalization of Graphene
• Chapter 8: Immobilization of Metal and Metal Oxide Nanoparticles on Graphene
• Chapter 9: Functionalization of Graphene by other Carbon Nanostructures
• Chapter 10: Doping of Graphene by Nitrogen, Boron, and Other Elements
• Chapter 11: Layer-by-Layer Assembly of Graphene-Based Hybrid Materials
• Index
• End User License Agreement