The inside of activated carbon has crystal structure and pore structure, and the surface of activated carbon also has certain chemical structure. The adsorption performance of activated carbon depends not only on the physical (pore) structure of activated carbon, but also on the chemical structure of activated carbon surface. During the preparation of activated carbon, the edge chemical bond of aromatic sheet formed in the carbonization stage breaks to form edge carbon atom with unpaired electrons. These edge carbon atoms have unsaturated chemical bonds, can react with heterocyclic atoms such as oxygen, hydrogen, nitrogen and sulfur to form different surface groups, the existence of these surface groups undoubtedly affect the adsorption performance of activated carbon. X-ray studies have shown that these heterocyclic atoms combine with carbon atoms at the edges of the aromatic sheet to produce surface compounds containing oxygen, hydrogen and nitrogen. When these edges become the main adsorption surfaces, these surface compounds change the surface characteristics and surface properties of activated carbon. Activated carbon surface groups are divided into acidic, alkaline and neutral 3 kinds. Acidic surface functional groups include carbonyl, carboxyl, lactone, hydroxyl, ether, phenol, etc., which can promote the adsorption of alkaline substances on activated carbon. The basic surface functional groups are mainly pyranone (cycloketone) and its derivatives, which can promote the adsorption of acidic substances on activated carbon.

The surface of activated carbon prepared by acid activators such as phosphoric acid is mainly acidic groups, which can adsorb alkaline substances well. The surface of activated carbon prepared by KOH, K2CO3 and other alkaline activators is mainly alkaline groups, which is suitable for adsorption of acidic substances; The surface functional groups of activated carbon prepared by physical activation methods such as CO2 and H2O are generally neutral.