Chemical Methods for Processing Nanomaterials

Vidya Nand Singh

• Publisher: CRC Press
• Year: 2021
• eBook ISBN: 9780429662928
• Topic: Physical Sciences
• Subtopic: Biology

This book discusses the latest advancements in the processing of various types of nanomaterials. The main objective of the book is to provide the reader with a comprehensive review of the latest advances in synthesis as well as processing of almost all kinds of nanomaterials using various physical and chemical methods. The book includes chapters on Chemical Methods such as microemulsions, colloidal route, wet chemical method, chemical vapor deposition technique, sol-gel method, electrodeposition for growing different kinds of nanomaterials including Chalcogenides, Metal Oxide nanostructures, perovskite nanocrystals, nano structures on patterned electrode, Low Dimensional Carbon Nanomaterials and applications at Nanoscale.

CHAPTER 1
Chemical Methods for Processing Carbon Nanomaterials

Sehmus Ozden^1,2,3

The discovery of fullerene in 1985 opened a new era that is called nanocarbon, and was followed by the discovery of CNTs and graphene. Carbon nanomaterials can be considered attractive candidates in a broad range of nanotechnology applications, ranging from medicine to aerospace because of their outstanding properties, but these nanomaterials need to be processed and modified during or after their fabrication for the specific applications. This chapter discusses chemical processing of carbon nanomaterials, especially CNTs and graphene, which covers various strategies of their synthesis, functionalization for tuning their properties, and the effect of functionalization on their properties. In addition, the application and current challenges on the integration of these materials into the real-life technologies will be discussed.

1. Introduction

1.1 Carbon Nan omaterials

One of the basic elements which has various allotropes is carbon, and it has the ability to create covalent bonds with other carbon atoms in a range of hybridization states, such as sp, sp², and sp³. The most well-known natural allotropes of carbon are graphite and diamond. Even though these allotropes mainly consist of carbon atoms, they have different physicochemical properties because of the hybridization of carbon atoms. For example, even though diamond, which consists of sp³ carbon hybridization, is transparent, an electrical insulator, and the hardest known material, graphite, which consists of sp² carbon hybridization, is opaque, and a soft material with high electrical conductivity.

Fullerene is the first unusual allotrope of carbon that was discovered in 1985 by Robert Curl, Harold Kroto, and Richard Smalley [1]. The discovery of fullerenes opened a new area for carbon allotropes at the nanoscale. The discovery of fullerenes was followed by carbon nanotubes, the straight tubular carbon structure, in 1991 [2]. In 2004, graphene, the one atom thick hexagonal lattice of carbon, was discovered by Andre Geim and Kostya Novoselov at Manchester University (Figure 1.1) [3]. Although various forms of carbon elements have been discovered, there are still many carbon allotropes that need to be experimentally discovered, such as graphyne sheets and graphyne nanotubes [4].

_______________

¹ Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, NJ 08540 USA.

² Chemical and Biological Engineering, Princeton University, Princeton, NJ 08540 USA.

³ Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540 USA.

Email: [email protected]

Figure 1.1. Timeline for the discovery of carbon nanostructures.

All of these carbon allotropes at nanoscale can be considered as members of the same group because they consist of sp² hybridization of hexagonal carbon lattice network. As a result of this hybridization, their properties, such as electrical conductivity and mechanical properties are similar, although they have significant differences because of their sizes and shapes.

Different classification methods can be used for carbon nanomaterials. The first classification method is based on the hybridization of the carbon element, such as sp² and sp³. Fullerene, carbon nanotubes (CNTs), and graphene can be categorized as sp² hybridization, and nanodiamonds can be counted into sip³ hybridization. The other classification method is based on the structural dimension of carbon element, and in this book we are taking this classification into account. There are zero-dimensional (OD) nanostructures, such as fullerene, one-dimensional (1D) nanostructures, such as nanotubes and nanofibers, graphene-like two-dimensional (2D), and three-dimensional (3D) carbon nanostructures (Figure 1.2).

Carbon nanomaterials can be considered attractive candidates in a broad range of nanotechnology applications, ranging from medicine to aerospace, because of their attractive properties, but these nanomaterials need to be processed and modified during or after their fabrication for the specific application. In this chapter, we will discuss chemical processing and modification of carbon nanomaterials to control their properties for emerging applications.

Figure 1.2. Classification of nanomaterials—zero-dimensional (0D) fullerene, one-dimensional (1D) carbon nanotubes, two-dimensional (2D) graphene, and three-dimensional (3D) carbon nanotubes structures.

2. Carbon Nanotubes

Carbon nanotubes were discovered in 1991 by Iijima, although there are some reports that show tubular structure of CNTs in 1952 and 1976. Ijima et al. and Bethune et al. have reported two separate works about the growth of single-wall carbon nanotubes (SWCNTs). SWCNTs can be described as a rolled-up single-layer graphene. Multi-wall carbon nanotubes (MWCNTs) can be thought as rolling up a multi-layer graphene sheet.

CNTs can be classified based on their wall numbers, such as SWCNTs and MWCNTs, or they can be classified based on their chirality, such as zigzag and armchair. They are semiconductors or metallic based on their chirality. CNTs have extraordinary physical, chemical, and mechanical properties that make them exciting future materials for a broad range of advanced technological applications. For example, their mechanical tensile strength (> 100 GPa) and elastic modulus (~ 1 TPa) are much higher than known materials, such as diamond, with the advantages of low density and flexibility. The thermal conductivity is theoretically reported as 6,600 Wm⁻¹K⁻¹. The electrical conductivity of CNTs is 1000 times higher than copper.

CNTs can be produced using various techniques, as shown in Figure 1.3. CNTs were first produced using high temperature fabrication methods, such as arc-discharge and laser ablation methods, but recently these methods have been replaced by low temperature chemical vapor deposition (CVD) techniques. The CVD method is the most commonly used method for producing CNTs. In this process, nanotubes are obtained by thermal decomposition of a hydrocarbon vapor in the presence of a metal catalyst. The properties of CNTs, such as density, length, and quality can be controlled by CVD technique, etc. Here, we will look into the CVD method in a more detailed manner. These methods mainly require a carbon source, catalyst, temperature, and inert gases.

Figure 1.3. Methods for synthesis of CNTs.

The CVD process involves passing a hydrocarbon vapor using methane, ethylene, acetylene, benzene, xylene, and carbon monoxide as hydrocarbon sources through a reactor with a metal catalyst, such as iron, nickel, and cobalt at a proper temperature (Figure 1.4). The growth of CNTs with CVD method depends on different parameters, such as hydrocarbon source, catalyst, temperature, pressure, gas-flow rate, deposition time, reactor geometry, and the location of substrate inside the reactor. All of these factors not only affect the growth of CNTs, but also their yield, type, and quality.

Although the fundamental mechanism of the growth of CNTs is still not understood well, the widely accepted mechanism is that hydrocarbon sources decompose at high temperature and precipitate on the catalyst. When the decomposed carbon precipitates on the surface of the catalyst, the nucleation of CNT growth starts. If the interactions between metal catalyst and the substrate are weak, the growth continues as tip growth (Figure 1.5a). If the interactions between the metal catalyst and the substrate are strong, decomposed carbon deposits on the catalyst from the lower peripheral surface of metal. In both cases, the growth of CNTs stops when the surface of the catalyst is covered by amorphous carbon. To avoid the catalyst poi...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• Table of Contents
• 1. Chemical Methods for Processing Carbon Nanomaterials
• 2. Synthesis of Nanomaterials and Nanostructures
• 3. Wet Chemical Methods for Nanoparticle Synthesis
• 4. Electrodeposition—A Versatile and Robust Technique for Synthesizing Nanostructured Materials
• 5. Nanostructured Materials Using Microemulsions
• 6. Methods of Manufacturing Composite Materials
• 7. Quantum Dots and Their Synthesis Processes
• 8. Chemical Vapor Deposition (CVD) Technique for Nanomaterials Deposition
• 9. CVD Growth of Transition Metal Dichalcogenides MX2 (M: Mo, W, X: Se, S)
• 10. Metal Oxide/CNT/Graphene Nanostructures for Chemiresistive Gas Sensors
• 11. Chemical Route Synthesis and Properties of CZTS Nanocrystals for Sustainable Photovoltaics
• 12. Surface Modification of Glass Nanofillers and Their Reinforcing Effect in Epoxy-Based Nanocomposites
• 13. Gas Sensor Application of Zinc Oxide
• 14. Titanium Dioxide as A Photo Catalyst Material: A Review
• Index