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Active Carbon: A Powerful Filter for Water and Air Purification
2023/4/28
Active carbon, also known as activated carbon or activated charcoal, is a form of carbon that has been processed to create millions of tiny pores on its surface. These pores increase the surface area of the carbon, making it very effective at adsorbing (not absorbing) various substances from water and air. Active carbon can remove contaminants such as organic compounds, taste and odor compounds, synthetic chemicals, heavy metals, and microorganisms. In this article, we will explore some of the properties and applications of active carbon.
The main property of active carbon is its high surface area, which can range from 3000 to 2000 m2/g depending on the type and degree of activation. This means that one gram of active carbon can have a surface area equivalent to a football field or more. The high surface area allows active carbon to adsorb a large amount of substances onto its surface by physical or chemical forces.
Another property of active carbon is its pore size distribution, which determines what kind of substances it can adsorb. Active carbon has three types of pores: micropores (less than 2 nm in diameter), mesopores (2-50 nm), and macropores (more than 50 nm). Micropores are responsible for most of the adsorption capacity of active carbon, as they can trap small molecules such as gases and volatile organic compounds. Mesopores and macropores are useful for adsorbing larger molecules such as proteins and bacteria.
A third property of active carbon is its surface chemistry, which affects its affinity for different substances. Active carbon has various functional groups on its surface, such as carboxyl, hydroxyl, carbonyl, and phenolic groups. These groups can interact with the substances to be adsorbed by forming hydrogen bonds, ionic bonds, or covalent bonds. The surface chemistry of active carbon can be modified by various treatments such as acid washing, base washing, impregnation, or oxidation.
Water treatment: Active carbon can remove organic pollutants, chlorine, chloramines, trihalomethanes, pesticides, herbicides, pharmaceuticals, hormones, and other contaminants from drinking water, wastewater, industrial water, and groundwater. Active carbon can also improve the taste, odor, and color of water. Active carbon can be used in different forms such as powder (PAC), granular (GAC), fibrous (ACF), or cloth (ACC). PAC is added directly to the water and removed by filtration or sedimentation. GAC is packed in columns or beds and used for continuous or intermittent flow treatment. ACF and ACC are used as membranes or filters for selective removal of contaminants.
Air purification: Active carbon can remove volatile organic compounds (VOCs), odors, smoke, fumes, gases, and other pollutants from indoor and outdoor air. Active carbon can also protect against biological agents such as bacteria, viruses, spores, and allergens. Active carbon can be used in different forms such as pellets, granules, fibers, cloths, foams, or honeycombs. Pellets and granules are used in fixed-bed or moving-bed reactors for gas-phase treatment. Fibers and cloths are used in filters or masks for personal protection or ventilation systems. Foams and honeycombs are used in catalytic converters or scrubbers for removing nitrogen oxides or sulfur oxides from exhaust gases.
Properties of Active Carbon
Active carbon is derived from various sources such as coal, wood, coconut shells, and other organic materials. The raw materials are subjected to physical or chemical activation processes that involve high temperature, steam, oxygen, or chemicals. These processes open up the pores and create a network of channels within the carbon structure.The main property of active carbon is its high surface area, which can range from 3000 to 2000 m2/g depending on the type and degree of activation. This means that one gram of active carbon can have a surface area equivalent to a football field or more. The high surface area allows active carbon to adsorb a large amount of substances onto its surface by physical or chemical forces.
Another property of active carbon is its pore size distribution, which determines what kind of substances it can adsorb. Active carbon has three types of pores: micropores (less than 2 nm in diameter), mesopores (2-50 nm), and macropores (more than 50 nm). Micropores are responsible for most of the adsorption capacity of active carbon, as they can trap small molecules such as gases and volatile organic compounds. Mesopores and macropores are useful for adsorbing larger molecules such as proteins and bacteria.
A third property of active carbon is its surface chemistry, which affects its affinity for different substances. Active carbon has various functional groups on its surface, such as carboxyl, hydroxyl, carbonyl, and phenolic groups. These groups can interact with the substances to be adsorbed by forming hydrogen bonds, ionic bonds, or covalent bonds. The surface chemistry of active carbon can be modified by various treatments such as acid washing, base washing, impregnation, or oxidation.
Applications of Active Carbon
Active carbon is widely used in various industries and sectors for water and air purification purposes. Some of the common applications are:Water treatment: Active carbon can remove organic pollutants, chlorine, chloramines, trihalomethanes, pesticides, herbicides, pharmaceuticals, hormones, and other contaminants from drinking water, wastewater, industrial water, and groundwater. Active carbon can also improve the taste, odor, and color of water. Active carbon can be used in different forms such as powder (PAC), granular (GAC), fibrous (ACF), or cloth (ACC). PAC is added directly to the water and removed by filtration or sedimentation. GAC is packed in columns or beds and used for continuous or intermittent flow treatment. ACF and ACC are used as membranes or filters for selective removal of contaminants.
Air purification: Active carbon can remove volatile organic compounds (VOCs), odors, smoke, fumes, gases, and other pollutants from indoor and outdoor air. Active carbon can also protect against biological agents such as bacteria, viruses, spores, and allergens. Active carbon can be used in different forms such as pellets, granules, fibers, cloths, foams, or honeycombs. Pellets and granules are used in fixed-bed or moving-bed reactors for gas-phase treatment. Fibers and cloths are used in filters or masks for personal protection or ventilation systems. Foams and honeycombs are used in catalytic converters or scrubbers for removing nitrogen oxides or sulfur oxides from exhaust gases.
