Chemically Derived Graphene

Functionalization, Properties and Applications

Jintao Zhang

• Publisher: Royal Society of Chemistry
• Year: 2018
• eBook ISBN: 9781788014397
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Chemistry
• Index: Chemistry

The increasing interest in graphene, due to its unique properties and potential applications, is sparking intense research into chemically derived graphene. This book provides a comprehensive overview of the recent and state-of-the-art research on chemically derived graphene materials for different applications.

Starting with a brief introduction on chemically derived graphene, subsequent chapters look at various fascinating applications such as electrode materials for fuel cells, Li/Na-ion batteries, metal–air batteries and Li-S batteries, photocatalysts for degradation of pollutants and solar-to-fuels conversion, biosensing platforms, and anti-corrosion coatings. The emphasis throughout this book is on experimental studies and the unique aspects of chemically derived graphene in these fields, including novel functionalization methods, particular physicochemical properties and consequently enhanced performance.

With contributions from key researchers, the book provides a detailed resource on the latest progress and the future directions of chemically derived graphene for students and researchers across materials science, chemistry, nanoengineering and related fields.

CHAPTER 1

Introduction to Chemically Derived Graphene

QIUJIAN LE^†a, TIAN WANG^†a, YUXIN ZHANG^a AND LILI ZHANG,*^b

^a College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China;

^b Institute of Chemical and Engineering Sciences, A*STAR, 1 Pesek Road, Jurong Island 627833, Singapore
*E-mail: [email protected], [email protected]

1.1 General Background of Graphite and Its Derivatives

Graphite consists of a stack of graphene sheets, making it a three-dimensional carbon allotrope with two-dimensional lattice bonds. In each graphene layer, three of the four outer shell electrons in an individual carbon atom are bound to its three neighboring carbon atoms by strong sp² bonds (or sigma bonds), leaving one electron moving freely to define its conductivity. Relatively weak van der Waals interactions hold the graphene sheets together in the third direction, allowing the easy separation of layers of graphene sheets. Unlike the free electrons in metals, the free electrons, so-called π-electrons, in each graphene layer are able to move freely only on the atomic plane and thus graphene does not conduct in the direction perpendicular to the plane. After oxidization by Hummers,¹ Staudenmaier,² or Brodie’s³ methods, graphite layers are intercalated with water molecules, ions, and oxygen-containing functional groups, i.e., hydroxyl, carboxyl, and carbonyl groups. As a result, the distance between layers is expanded and the van der Waals forces are weakened, facilitating further exfoliation processes. The oxidized product is known as graphite oxide. Monolayer graphite oxide, also known as graphene oxide, can be obtained by ultrasonication or vigorous stirring in the form of water-dispersible suspensions.⁴ Chemically derived graphene (CDG) is finally obtained via reduction with various reducing agents, such as hydrazine,^5–8 sodium borohydride,^9,10 active metal,^11–13 reductive organics,^14–18 and some other methods.^19–23

Graphite and its derivatives, such as graphite oxide, graphene oxide, and graphene, consist all of carbon atoms. However, they differ in terms of their atomic arrangement and chemical composition. Graphite is composed of a number of graphene layers, rendering it an excellent lubricant. Graphite oxide has a similar layered structure to that of graphite, but with a larger interlayer spacing (about two times that of the original graphite) owing to the intercalation of water molecules, functional groups, and ions. Due to the destruction of the conjugated structure in graphite by oxidation processes, graphite oxide exhibits poor electrical conductivity. However, the introduction of foreign molecules and oxygen-containing functional groups increases the hydrophilicity of graphite, facilitating subsequent processes in water-like environments. Graphene oxide refers to monolayer graphite oxide produced through the exfoliation of graphite oxide. It displays unique properties arising from the presence of rich functional groups, such as tunable solubility in a variety of solvents, controllable electrical and optical properties, and compatibility with organic and inorganic compounds to form composites. Graphene possesses much better electrical conductivity than graphene oxide. However, the obtained graphene still differs from the ideal material due to the defects and functional groups introduced during oxidation–reduction–exfoliation processes. Nevertheless, functionalized CDG holds great promise in electrocatalysis, photocatalysis, electrochemical energy storage and conversion, flexible devices, anti-corrosion, water purification, sensors, and many other areas. Perfect graphene refers to a defect-free two-dimensional single atomic layer of graphite. Numerous and excellent properties arise from its sp² hybridization and thin atomic thickness of 0.35 nm, such as a large theoretical specific surface area (2630 m² g⁻¹),²⁴ ultrahigh intrinsic charge carrier mobility of 200000 cm² V⁻¹ s⁻¹,²⁵ good optical transparency (∼97.7%),²⁶ high Young’s modulus (∼1 TPa),²⁷ and excellent thermal conductivity (3000–5000 W m⁻¹ K⁻¹).²⁸ The properties of graphite and its derivatives are summarized and compared in Table 1.1.

Table 1.1 Properties of graphite and its derivatives

Product	Graphite	Graphene	Graphite oxide	Graphene oxide	Chemically derived graphene
Form	Layered structure (>10 layers)	Monolayer carbon atom	Layered structure with expanded interlayer spacing	Monolayer structure with many defects	Monolayer structure with some defects
Powder form	Film	Paste/powder	Suspension/powder	Suspension/powder
Elemental composition	C	C	C, O, H	C, O, H	C, O, H
Density (g cm^−3)	2–2.3	∼0.77 mg m^−2	Depends on defects	Depends on defects	Depends on defects
Electrical conductivity (S m^−1)	2–3 × 10^5 (in-plane)	10^6 (in plane)	Nearly insulator	Nearly insulator	4600–5880
3 × 10^2 (cross-plane)
Thermal conductivity (W m^−1 K^−1)	2000 (in-plane) 20 (cross-plane)	5300 (in-plane)	N/A	1.68–2.21 (in-plane)	61 (in-plane), 0.09 (cross-plane)
Young’s modulus	N/A	1.06 TPa	N/A	290–470 GPa	6.3 GPa
Basic synthesis method	Exists in nature	Micromechanical exfoliation, chemical vapor deposition, epitaxial growth, chemically derived methods	Hummers method, Staudenmaier method, Brodie method	Thermal, chemical, electrochemical, exfoliation of graphite oxide	Chemical oxidation–exfoliation–reduction of graphite, liquid exfoliation, solid exfoliation by ball milling, intercalation–exfoliation
Main applications	Pencils, batteries, refractories, steel making, brake linings	Fundamental research, semiconductor, energy storage, screen, optoelectronic applications	Intermediate product of CDG, biomedicine, catalysis	Intermediate product of CDG, biomedicine, energy storage, catalysis, environmental protection, sensor, optoelectronic applications	Semiconductor, energy storage, catalysis, optoelectronic applications, biomedicine

This book will focus on the most recent and state-of-the-art progress on CDG materials and their applications. General fabrication methods and properties of CDG will be covered in the following sections. Challenges with respect to the technology, economics, and environmental concerns will be presented in the last section of this introductory chapter.

1.2 Preparation Methods and State-of-the-art Research Progress

The main methods to produce CDG include the chemical oxidation–exfoliation–reduction of graphite, liquid exfoliation of graphite, solid exfoliation of graphite, intercalation–exfoliation of graphite, and bottom-up chemical assembly.²⁹Figure 1.1 shows these typical methods for the mass production of CDG.²⁹ These methods differ in terms of the yield, efficiency, cost, properties of the product, and environmental impact. The achievement of uniform product quality with a green and sustainable process at low cost is a universal challenge.

Figure 1.1 Four typical methods for the production of CDG. Reprinted by permission of Macmillan Publishers Ltd: Nature Nanotechnology (^{ref. 29}), Copyright 2014.

1.2.1 Chemical Oxidation–Exfoliation–Reduction of Graphite

This method for the production of CDG involves the oxidation of bulk graphite, exfoliation of graphite oxide, and reduction of graphene oxide. There are three well-known oxidation methods: modified Hummers,¹ Staudenmaier,² and Brodie procedures.³ All three methods involve the use of strong inorganic protonic acids (such as concentrated sulfuric acid, fuming nitric acid, or their mixtures) to intercalate small molecules within the graphite layers, followed by an oxidation reaction using KMnO₄, KClO₄, or other strong oxidants. Exfoliation of graphite oxide through ultrasonication or vigorous stirring results in graphene oxide and few-layer graphite oxide. CDG is finally obtained through a reduction process. Sometimes, exfoliation and reduction can be carried out in a single step.

Chemical, thermal, electrochemical, and hydrothermal reduction processes are the most commonly used reduction methods. In particular, chemical reduction is the most widely applied reduction method due to its simplicity, the possibility of large scale production, and good disparity in various solutions. A variety of organic and inorganic reducing agents have been used to reduce graphene oxide. Stankovich et al.^4,30 reported the successful reduction of graphene oxide with hydrazine monohydrate, providing...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• Contents
• Chapter 1 Introduction to Chemically Derived Graphene
• Chapter 2 Preparation and Characteristics of Edge-functionalized Graphene Nanoplatelets and Their Applications
• Chapter 3 Functionalization of Chemically Derived Graphene as Electrode Materials for Fuel Cells
• Chapter 4 Functionalization of Chemically Derived Graphene for Solar Energy Conversion
• Chapter 5 Functionalization of Chemically Derived Graphene for Photocatalysis
• Chapter 6 Graphene-based Materials as Electrodes for Li/Na-ion Batteries
• Chapter 7 Functionalization of Chemically Derived Graphene as Electrode Materials for Metal–Air Batteries
• Chapter 8 Application of Graphene Derivatives in Lithium–Sulfur Batteries
• Chapter 9 Functionalization of Chemically Derived Graphene for High-performance Supercapacitors
• Chapter 10 Functionalization of Chemically Derived Graphene for Flexible and Wearable Fiber Energy Devices
• Chapter 11 Chemically Derived Graphene for Water Purification and Gas Separation
• Chapter 12 Chemically Derived Graphene for Surface Plasmon Resonance Biosensing
• Chapter 13 Principle, Properties, and Applications of Graphene and Graphene Oxide as Anticorrosion Coating Materials
• Subject Index