Chemically Derived Graphene: Functionalization, Properties and Applications: Volume 46 (Nanoscience & Nanotechnology Series) - Hardcover

Hardcover

ISBN 10: 1788010809 ISBN 13: 9781788010801

Publisher: Royal Society of Chemistry, 2018

Synopsis

A comprehensive overview of the recent and state-of-the-art research on chemically derived graphene materials for different applications.

About this title

From the Back Cover

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.

From the Inside Flap

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.

Excerpt. © Reprinted by permission. All rights reserved.

Chemically Derived Graphene

Functionalization, Properties and Applications

By Jintao Zhang

The Royal Society of Chemistry

Copyright © 2018 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-78801-080-1

Contents

Chapter 1 Introduction to Chemically Derived Graphene Qiujian Le, Tian Wang, Yuxin Zhang and Lili Zhang, 1, 
Chapter 2 Preparation and Characteristics of Edge-functionalized Graphene Nanoplatelets and Their Applications In-Yup Jeon, Sun-Hee Shin, Amal Kumar Mandal and Jong-Beom Baek, 30, 
Chapter 3 Functionalization of Chemically Derived Graphene as Electrode Materials for Fuel Cells Dongsheng Geng, Xiangbo Meng and Yun Zong, 68, 
Chapter 4 Functionalization of Chemically Derived Graphene for Solar Energy Conversion Lutfi Kurnianditia Putri, Wee-Jun Ong, Lling-Lling Tan, Yi-Hao Chew and Siang-Piao Chai, 102, 
Chapter 5 Functionalization of Chemically Derived Graphene for Photocatalysis Han Hu, Songcan Wang and Lianzhou Wang, 128, 
Chapter 6 Graphene-based Materials as Electrodes for Li/Na-ion Batteries Jiantie Xu, Qinghua Fan, Jianmin Ma, Hua-Kun Liu and Shi-Xue Dou, 155, 
Chapter 7 Functionalization of Chemically Derived Graphene as Electrode Materials for Metal-Air Batteries Zhi-Wen Chang andXin-bo Zhang, 199, 
Chapter 8 Application of Graphene Derivatives in Lithium-Sulfur Batteries Alen Vizintin, Bostjan Genorio and Robert Dominko, 222, 
Chapter 9 Functionalization of Chemically Derived Graphene for High-performance Supercapacitors Kang Li, Si Chen and Jintao Zhang, 242, 
Chapter 10 Functionalization of Chemically Derived Graphene for Flexible and Wearable Fiber Energy Devices Huili Li and Tao Chen, 279, 
Chapter 11 Chemically Derived Graphene for Water Purification and Gas Separation Chengzhen Sun and Bofeng Bai, 303, 
Chapter 12 Chemically Derived Graphene for Surface Plasmon Resonance Biosensing Y. V Stebunov, A. V Arsenin and V S. Volkov, 328, 
Chapter 13 Principle, Properties, and Applications of Graphene and Graphene Oxide as Anticorrosion Coating Materials Houyi Ma, Ru Yan, Nan Wang and Hongxiu Dai, 354, 
Subject Index, 384, 

CHAPTER 1

Introduction to Chemically Derived Graphene

QIUJIAN LE, TIAN WANG, YUXIN ZHANG AND LILI ZHANG

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 p-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, Staudenmaier, or Brodie's 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. Chemically derived graphene (CDG) is finally obtained via reduction with various reducing agents, such as hydrazine, sodium borohydride, active metal, reductive organics, and some other methods.

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), ultrahigh intrinsic charge carrier mobility of 200000 cm2 V-1 s-1, good optical transparency (~97.7%), high Young's modulus (~1 TPa), and excellent thermal conductivity (3000–5000 W m-1 K-1). The properties of graphite and its derivatives are summarized and compared in Table 1.1.

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. Figure 1.1 shows these typical methods for the mass production of CDG. 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.

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, Staudenmaier, and Brodie procedures. 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. reported the successful reduction of graphene oxide with hydrazine monohydrate, providing a simple and feasible method for the mass production of CDG materials. However, significant agglomeration occurred upon reduction. To solve the agglomeration problem, Li et al. reduced a graphene oxide aqueous solution using hydrazine hydrate under alkaline (pH = 10) conditions. The residual oxygen-containing functional groups of the reduced graphene oxide were ionized as negative charges under alkaline conditions. Thus, electrostatic repulsion prevents the p–p stacking of graphene sheets, resulting in uniformly dispersed aqueous solutions of CDG. In 2011, Zhou et al. reported a rapid method to reduce graphene oxide with hydroxylamine at 90 °C, obtaining a dispersible CDG solution. Other reducing agents, such as hydroquinone,14 sodium borohydride, strong alkaline solution, and hydroiodic acid, have been explored as effective reagents to remove the oxygen-containing functional groups of graphene oxide.

In a typical thermal reduction process, graphite oxide or graphene oxide is heated rapidly under Ar or N2 atmosphere, taking advantage of the pyrolysis of the oxygen-containing functional groups in the interlayer of graphite or on the surface of graphene oxide, releasing CO and CO2 gases. Such gases force the graphite layers to expand rapidly overcoming the van der Waals forces between the layers, thereby achieving the exfoliation and reduction of graphite oxide in one step. The temperature of the thermal reduction has a great influence on the degree of reduction of graphite oxide. High temperatures of ~1000 °C afford a high degree of reduction. Electrochemical reduction removes the oxygen-containing functional groups from the surface of graphene oxide via an electrochemical process in a given buffer solution at room temperature. A high C/O ratio of 23.9 has been reported using this reduction method. However, the complex preparation procedure for the working electrode and separation of the obtained CDG limit its wide application. Hydrothermal reduction takes place in an enclosed vessel, during which the pressure in the reactor increases with the temperature, and the solution can reach a temperature higher than the boiling point of the solvent. The oxygen-containing functional groups between the graphite oxide sheets are removed, and chemically derived graphene is obtained. Zhou et al. reported that supercritical water cannot only partially remove the oxygencontaining functional groups of graphene oxide but also recover part of the aromatic structure in the carbon lattice. A homogeneous graphene solution can be obtained under alkaline conditions (pH = 11), while agglomeration occurs under acidic conditions (pH = 3). Wang et al. reported that the CDG obtained by hydrothermal reduction with DMF and hydrazine monohydrate as the solvent presented a higher C/O ratio than the one produced by chemical reduction with hydrazine monohydrate at atmospheric pressure.

1.2.2 Liquid Exfoliation

In a typical procedure of direct liquid exfoliation, graphite is firstly dispersed in a solvent or surface active agent, where enough surface energy can be gained to overcome the van der Waals forces between the graphene layers. Subsequently, the mixture is subjected to sonication or ball milling. Monolayer or few-layer graphene platelets are exfoliated from the graphite surface, leading to the production of CDG with good morphology and properties. Liquid exfoliation has advantages over other processes owning to its simple procedure and cheap production cost. Therefore, this method plays an important role in promoting the applications of graphene and its derivatives. According to the medium, liquid exfoliation can be divided into three categories: organic solvent-assisted exfoliation, surfactant-assisted exfoliation, and other exfoliation methods.

Successful exfoliation highly depends on the selection of the solvent. Liquid exfoliated graphene was obtained in organic solvent N-methylpyrrolidone (NMP) for the first time, and the as-prepared graphene presented little defects on the surface. Furthermore, almost all the graphene platelets obtained contained less than six layers. The drawback was that the concentration of the graphene suspension was relatively low, only 0.01 mg mL-1. Ionic liquids have a surface energy close to that of graphene, which is a key prerequisite for the direct exfoliation of graphite in a solvent. The first successful application of ionic liquids in the liquid exfoliation of graphite was achieved with 1-butyl-3-methyl imidazolium salts. The concentration of the as-prepared graphene suspension was 0.95 mg mL-1 (ultrasonication for 1 h), and most graphene platelets were less than five atomic-layer thick. It is worth noting that the concentration of graphene achieved in 1-methyl-3-butylimidazolium hexafluorophosphate was up to 5.3 mg mL-1 with an average thickness of the graphene platelets of 6–7 atomic layers. Despite the low content of monolayer graphene, ionic liquids do produce stable high-concentration CDG suspensions.

The solvents discussed above are not volatile, which cause problems for subsequent processes. This makes it difficult to remove the solvent when fabricating graphene as thin films or composite materials. In general, the presence of residual solvents can significantly affect the performance of the power measurement equipment and thus, complete removal of the solvent is highly required. Therefore, the preparation of CDG in low boiling-point solvents is more promising. So far, liquid-phase exfoliation in low boiling-point solvents has been rarely reported. Coleman et al. described the separation of graphene in low boiling-point solvents such as chloroform, acetone, and isopropanol. Under optimum conditions, the highest concentration of a graphene suspension reached 0.5 mg mL-1. Despite the rapid development of liquid-phase exfoliation in recent years, many obvious problems still exist. Among them, the most important one is the relatively low concentration of the obtained CDG dispersions. Better exfoliation efficiency can be obtained by adding inorganic salts, organic salts, or other auxiliary agents, or by increasing the ultrasonication time. For example, the exfoliation efficiency was significantly improved upon addition of inorganic NaOH in NMP, N,N-dimethylacetamide, and cyclohexanone. The concentration of a graphene suspension in cyclohexanone was 20 times larger after addition of NaOH.

1.2.3 Solid Exfoliation by Ball Milling

Ball milling is a common technology in the powder production industry. For most ball mill equipment, two methods can be used for peeling and grinding. The first one is shear stress, which is considered to be a good mechanical path for exfoliation. This method allows the fabrication of graphene sheets with large size. The second one is the vertical impact of the ball during rolling, which can shatter graphene sheets and sometimes shatter crystalline structures into amorphous or unbalanced phases. Therefore, it is desirable to reduce such vertical impact during the fabrication process in order to obtain high-quality large-size graphene.

At first, ball milling was only used to reduce the size of graphite. This method was not further explored until the first report on the liquid-phase exfoliation of graphite in 2010. Knieke et al. and Zhao et al. improved the ball milling procedure, making it capable of producing graphene materials. Similar to liquid exfoliation, chemically inert inorganic salts are mixed with graphite to weaken the van der Waals forces so as to achieve the exfoliation of monolayer or few-layer graphene platelets from graphite. Leon et al. reported a method to exfoliate graphite based on the interaction of graphite with solid melamine. Jeon et al. described an approach to functionalize the edges of graphene at large scale via solid exfoliation of graphite. Graphite was mixed with hydrogen, carbon dioxide, sulfur trioxide, or a gas mixture containing carbon dioxide and sulfur anhydride, followed by a dry milling process. Under different humidity conditions, a variety of functionalized graphene sheets were obtained. According to another study by Jeon, after grinding the original graphene sheets with dry ice for 48 h, smaller graphite particles (100–500 nm) functionalized with sulfonic groups were successfully obtained, which could be highly dispersed in various solvents and further exfoliated into single-layer or several-layer graphene nanosheets (GNSs) with high quality. Although the ball-milling method is regarded as an effective method for the large-scale preparation of graphene, the decomposition of the ball milling medium still cannot be ignored. On the other hand, ball mill-assisted solid exfoliation requires high energy input and the structure integrity of the resultant CDG may be damaged. Studies have shown that decomposition cannot be completely avoided during the milling process. Thus, fragmentation and defects are unavoidable. However, this could be a double-edged sword in the preparation of CDG. On the one hand, it can be used to functionalize graphene and improve the exfoliation efficiency; on the other hand, the size of CDG can be tailored by such ball milling processes.

(Continues...)

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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2018
• Language: English
• ISBN 10: 1788010809
• ISBN 13: 9781788010801
• Binding: Hardcover
• Number of pages: 408
• Editor: Jintao Zhang