activated carbonIt is composed of three parts: graphite microcrystals, single planar network carbon, and amorphous carbon, with graphite microcrystals being the main component of activated carbon. The microcrystalline structure of activated carbon is different from that of graphite, with interlayer spacing ranging from 0.34 to 0.35 nm and large gaps. Even at temperatures above 2000 ℃, it is difficult to convert into graphite, and this microcrystalline structure is called non graphite microcrystals. The vast majority of activated carbon belongs to non graphite structures. The microcrystalline arrangement of graphite structure is relatively regular and can be transformed into graphite after treatment. The non graphitic microcrystalline structure gives activated carbon a developed pore structure, which can be characterized by pore size distribution. The pore size distribution range of activated carbon is very wide, from less than 1nm to several thousand nm. Some scholars have proposed to divide the pore size of activated carbon into three categories: micropores with pore size less than 2nm, mesopores with pore size between 2-50nm, and macropores with pore size greater than 50nm.

The specific surface area of micropores in activated carbon accounts for more than 95% of the specific surface area of activated carbon, which largely determines the adsorption capacity of activated carbon. The specific surface area of mesopores accounts for about 5% of the specific surface area of activated carbon, and they are adsorption sites for larger molecules that cannot enter micropores, resulting in capillary condensation at higher relative pressures. The specific surface area of macropores generally does not exceed 0.5m2/g, and they are only channels for adsorbate molecules to reach micropores and mesopores, with little impact on the adsorption process.

Usually, it is a porous amorphous carbon with strong adsorption capacity in powder or granular form. Obtained by carbonizing solid carbonaceous materials (such as coal, wood, hard fruit shells, fruit cores, resins, etc.) at high temperatures of 600-900 ℃ under isolated air conditions, and then oxidizing and activating them with air, carbon dioxide, water vapor, or a mixture of the three gases at 400-900 ℃.

Carbonization causes substances other than carbon to evaporate, and oxidation activation can further remove residual volatile substances, generate new and expand existing pores, improve microporous structure, and increase activity. Low temperature (400 ℃) activated carbon is called L-Carbon, and high temperature (900 ℃) activated carbon is called H-Carbon. H-carbon must be cooled in an inert atmosphere, otherwise it will transform into L-Carbon. The adsorption performance of activated carbon is related to factors such as the chemical properties and concentration of the gas during oxidation activation, activation temperature, activation degree, and the composition and content of inorganic substances in activated carbon. It mainly depends on the properties and activation temperature of the activated gas.

The carbon content, specific surface area, ash content, and pH value of the aqueous suspension of activated carbon all increase with the increase of activation temperature. The higher the activation temperature, the more complete the volatilization of residual volatile substances, the more developed the microporous structure, and the larger the specific surface area and adsorption activity.

The ash composition and content in activated carbon have a significant impact on its adsorption activity. Ash content is mainly composed of K2O, Na2O, CaO, MgO, Fe2O3, Al2O3, P2O5, SO3, Cl -, etc. The ash content is related to the raw materials used to produce activated carbon, and increases with the removal of volatile compounds in the carbon.

By 2007, the annual output of activated carbon had reached 900 kt, of which coal based (quality) activated carbon accounted for more than 2/3 of the total output;