The strong cross-linking between crystallites makes the non-graphitizing carbons tough, and they exhibit a well-developed microporous structure. Because of the weak cross-linking between the nearby microcrystallites and the underdeveloped porous structure, the carbon produced is sensitive. There are several graphene layers in the graphitizing carbon that are positioned parallel to one another. ACs are divided into graphitizing and non-graphitizing varieties based on their ability to form graphite. The interlayer spacing is 0.34 to 0.35 nm in AC, while it is 0.33 nm in graphite. The structure of AC differs from that of graphite in terms of the distance between layers. The layers of fused hexagons that make up the graphite crystal are kept unified by weak van der Waals forces. AC and pure graphite have fundamental chemical structures that are very similar. The structure of AC has a significant impact on its ability to absorb substances. The relationship between a compound's concentration and solubility is what drives adsorption. The molecules move from the bulk phase and get adsorbed in the pores in a semi-liquid state. An adsorbate layer is formed on the adsorbent's surface as a result of this action. (c) Liquid-phase adsorption: the adhesion of ions, molecules, or atoms from a liquid to a surface is known as liquid-phase adsorption. The ratio of the compound's partial pressure to vapour pressure controls the adsorption process. This condensation process causes the bulk-phase molecules to condense in the pores of the AC. When gas is exposed to an adsorbent, it draws molecules to its surface where they concentrate and are drawn away from the gas phase. (b) Gas-phase adsorption: air, natural gas, chemicals, and petrochemicals are typically purified or separated on a large scale using gas-phase adsorption. Due to the short-range and cumulative nature of these forces, AC has the strongest physical adsorption forces among substances known to mankind. Additionally, they are additive, which means that the adsorption force is the sum of all atomic interactions. (a) London dispersion forces: these have an extremely small range and are sensitive to the distance between the adsorbate molecule and the surface of the carbon. Descriptions of the forces that occur between molecules are as follows: Adsorption of molecules is reinforced on AC by London dispersion forces (van der Waals forces), gas-phase adsorption and liquid-phase adsorption. Gas adsorption analysis suggests that one gram of AC has more than 3000 m 2 surface area because of its high level of microporosity that can deliver a high activation level for practical application. Before activation, charcoal has a specific surface area of 2.0 to 5.0 m 2 g −1, which increases to 1000 m 2 g −1 once activated. Small, low-volume pores that are present in AC enhance the surface area that is accessible for chemical reactions such as adsorption (which is different from absorption). Because of its significant surface area, AC is frequently utilized for a variety of purposes, including removing impurities from air and water. It has a wide spectrum of pores of varying sizes, from obvious fractures and fissures to molecular dimensions. 1.1 IntroductionĪctivated carbon (AC), also known as activated charcoal, is a rough, imperfectly structured kind of graphite. The classification, characteristics, and usage of AC are the main topics of this chapter. ACs are also cost-effective adsorbents for a variety of sectors, including water purification, food-grade goods, cosmetics, automotive applications, industrial gas purification, petroleum, and precious metal recovery, mostly for gold. Since the removal of contaminants requires carbonaceous materials with a high degree of porosity, well-developed surface area, and distinct functional groups, use of ACs is one of the finest methods for eliminating pollutants from aqueous solution and the atmosphere. It may be used to clean, dechlorinate, deodorize, and decolourize both liquid and vapour applications because of its large surface area, pore structure, and high degree of surface reactivity. Anthracite and bituminous coals have been the main sources of AC until recently, although AC may be made from any carbonaceous material. Coconut shells, coal, and wood are the basic sources of ACs.
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