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A REVIEW OF THE SURFACE CHEMISTRY OF ACTIVATED CARBON

 Giddys Jossy |  Feb 02, 2019 |  10:51 am |  101
CHAPTER ONE

1.0 INTRODUCTION
1.1 Background to the Study
Activated Carbon (AC) is a family of microporous materials used in a myriad of commercial applications as adsorbents for the removal of gaseous and liquid pollutants as well as many other applications. Activated carbon is the generic term used to describe a family of carbonaceous adsorbents with a highly amorphous structure and an extensively developed internal pore structure. AC is produced from a variety of carbonaceous rich materials such as wood, coal, lignin and coconut shell (Vivekanand Gaur and P. A. Shankar, 2012).
The adsorption phenomenon of AC results from its large microporous surface area. This large surface area relative to the size of the actual carbon particle makes it easy to remove large amounts of impurities in a relatively small enclosed space. The adsorptive structure in AC is comprised of ordered carbon atoms of aromatic planes. These graphitic planes form crystallites; i.e., the turbostratic layer stacks, similar to graphite. However, the angular orientations of the planes in the ACs are random to each other, whereas in the graphite they are well ordered. AC is invariably associated with appreciable amounts of heteroatoms such as oxygen, hydrogen, sulfur and nitrogen, that exist in the form of functional groups and/or atoms chemically bonded to the structure. In the carbon matrix, oxygen is the predominant heteroatom present in the form of functional groups, including carboxyl, carbonyl, phenols, lactones, quinones and others. The unique adsorption properties of AC can be significantly influenced by these functional groups. The surface oxygen complexes of AC are mainly created by two major oxidation methods, namely dry and wet. The former is a method involving reactions with oxidizing gases (steam, CO2, air, etc.) at high temperatures (> 600° C), while wet oxidation involves reactions between AC surfaces and oxidizing solutions such as aqueous nitric, sulfuric and ortho-phosphoric acids and hydrogen peroxide at low/reflux temperatures (100° C) (Vivekanand Gaur and P. A. Shankar, 2012).
Activated carbons (ACs) are used as adsorbents extensively. The usage of ACs for removing surfactants from industrial process streams is increasing (Wu and Pendleton, 2001). Surfactant removal processes involved in large-scale continuous industrial processes consume a large quantity of ACs. For example, the expected usage of ACs in one aluminium plant in West Australia is up to 4 — 5 ton per day (Alcoa, 1998). With such large amounts consumed, choosing an appropriate type of AC for the adsorption process becomes very important from the perspective of improving the adsorption process efficiency and reducing the overall cost of materials. Many industrial processes are developed empirically. A large number of ACs are available from commercial suppliers, hence, it is difficult for industrial researchers to identify and select an appropriate AC with the intention of achieving a highly efficient surfactant removal without knowing the proper parameters of ACs. By proper we imply a selection based on knowledge of adsorbent-adsorbate interaction and an understanding of the physical and chemical system properties controlling their interactions. Wong (1998) has shown that knowledge of ACs adsorption capacity and the adsorbent's physical and chemical properties are factors influencing the amount adsorbed by an AC. Despite the existence of a vast literature on the basic physical properties of ACs, additional information on ACs surface chemistry and its behaviour in the selected suspension medium is critical for selecting and applying ACs with confidence in large-scale and continuous industrial processes. It is well know that the physical properties of AC influence adsorption both from gas and from liquid phases (Bansal et al., 1988). Within the AC manufacturing industry, the specific surface area and the pore volume are regarded as the principal contributors to the adsorption process.
1.2 Aim and Objectives
The aim of this work is to investigate the optimal conditions for the preparation of activated carbon from coconut shell by surface chemistry with the following objectives. The objectives of this work are to:
Produce and characterize activated carbon from coconut shell by employing the carbonization process, porosity determination, surface acidity determination and so on.  
1.3 Problem Statement
Optimizing the process parameters for the preparation of activated carbon for an effective waste water treatment would curtail the problem of environmental issues as a results of discharged of untreated wastewater into water bodies and the immediate environment would pose serious threat both human and aquatic life. In this study coconut shell has been chosen as raw material for preparation of AC because it is considered superior to those obtained from other sources mainly due to small macrospores structure which renders it more effective for the adsorption of gas/vapour and for the removal of colour and odour of compounds. And it has high fixed carbon and low ash content. The adsorption behaviour of activated carbon is determined not only by their porous structures but also by the chemical nature of its surface. 
Adsorption capacity is determined by porosity, and the functional group present on the surface, is getting affected by polar and non polar structure of the adsorbate. In adsorption process surface chemistry and porosity plays an important role, so activated carbons are investigated by different characterization method.
1.4 Justification
Consumables such as water, beverages, pharmaceuticals, viable gases, chemicals, etc, are only fit for consumptions when they have been purified of contaminants like odours, tastes, or colours. The commonly used adsorbent (commercial activated carbon), which is often scarce and costly, thus posing limiting to households and industrial usages. Agricultural materials particularly those containing cellulose, shows potential adsorption capacity for various pollutants, but some of these agricultural materials are either scarce or have very small adsorption capacity. Coconut shell was found to be a suitable material for the preparation of activated carbon owing to its high carbon content and low ash content, ecofriendly and availability (renewable in nature).
1.5 Limitation
This study is limited to produce activated carbon from coconut shells with varying concentrations of activating agents employing surface chemistry route and to explore its potentiality for acidity treatment.
1.6 Scope of the Study
The scope of the work includes:
The production of activated carbon from agricultural waste (coconut shell).
The optimization of the effective parameters such as sodium hydroxide, potassium hydroxide concentration as activating agents, variable activation temperature and variable activation time on the effects of the preparation of activated carbons by chemical activation method.
Characterization of the resulting activated carbons for its specific surface area, adsorptive capacity, morphology of the AC using Scanning Electron Microscope (SEM), isotherm study and Fourier Transform Infrared (FTIR) spectroscope. 
 of the data obtained from the batch adsorption experiment via Langmuir and Freundlich isotherms.

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