Pore structure of activated carbon

Activated carbon is composed of three parts: graphite microcrystals, single planar network carbon, and amorphous carbon, among which the smaller the particle size, the faster the pore diffusion rate, and the stronger the adsorption capacity of activated carbon.

Activated carbon is composed of three parts: graphite microcrystals, single planar network carbon, and amorphous carbon, among which graphite microcrystals are the main component of activated carbon. The microcrystalline structure of activated carbon is different from that of graphite. The interlayer spacing of its microcrystalline structure is between 0.34 and 0.35nm, with large gaps. Even at temperatures above 2000 ℃, it is difficult to convert into graphite. This microcrystalline structure is called non graphite microcrystals, and the vast majority of activated carbon belongs to non graphite structure. The arrangement of microcrystals in graphite like structures is relatively regular and can be transformed into graphite after treatment. The non graphitic microcrystalline structure gives activated carbon a well-developed pore structure, which can be characterized by pore size distribution. The pore size distribution range of activated carbon is very wide, ranging from less than 1nm to thousands of nm. Scholars have proposed to classify the pore size of activated carbon into three categories: micropores with a pore size less than 2nm, mesopores with a pore size between 2-50nm, and macropores with a 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, which is the adsorption site of larger molecules that cannot enter the micropores, resulting in capillary condensation at higher relative pressures. The specific surface area of macropores generally does not exceed 0.5m2/g, and it is only a channel for adsorbate molecules to reach micropores and mesopores, with little impact on the adsorption process.