Activated carbon is composed of graphite microcrystals, a single planar mesh carbon and amorphous carbon three parts, among which graphite microcrystals is the main part of activated carbon. The microcrystalline structure of activated carbon is different from that of graphite, and the layer spacing of the microcrystalline structure is between 0.34 nm and 0.35nm, with a large gap. Even if the temperature is as high as 2000 ℃, it is difficult to convert into graphite. This kind of microcrystalline structure is called non-graphite microcrystalline. The majority of activated carbon belongs to non-graphite structure. The graphite-type structure has a regular arrangement of microcrystals and can be converted into graphite after treatment. The non-graphite-like microcrystalline structure gives activated carbon a well-developed pore structure, which can be characterized by pore size distribution. The pore size distribution of activated carbon ranges from less than 1nm to thousands of nm. Some scholars proposed to divide the pore size of activated carbon into three categories: micropore with a pore size smaller than 2nm, mesoporous with a pore size between 2-50nm, and macroporous with a pore size larger than 50nm.

The micropore specific surface area of 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 mesoporous specific surface area accounts for about 5% of the specific surface area of activated carbon, which is the adsorption site of larger molecules that cannot enter the micropore, resulting in capillary condensation under high relative pressure. The specific surface area of macropores is generally no more than 0.5m2/g, and it is only a channel for adsorbent molecules to reach micropores and mesoporous pores, which has little influence on the adsorption process.