Activated carbon modification refers to the treatment of activated carbon using certain methods to change its surface functional group properties and quantities. Different treatment methods can result in different modified activated carbons (5-7). After being modified with O3 and NaOH, the activated carbon surface contains significantly more oxygen functional groups, especially phenolic and carboxylic acid groups. On the other hand, the use of nitric acid oxidation can significantly increase the content of acidic functional groups on the surface. In practical applications, the method of surface modification of activated carbon should be determined according to the water quality of the water to be treated. If concentrated nitric acid is used for oxidation, the acidic functional groups on the activated carbon surface will increase, making it more hydrophilic, which is not conducive to the adsorption of organic substances such as phenol, aniline, humic acid, and chloroform in the water.

Therefore, the research direction for activated carbon surface modification to remove organic pollutants should be to reduce the content of oxygen functional groups such as lactones and carboxylic acids, and increase the hydrophobicity of the activated carbon surface. Bai Shulin and others found in their study on the adsorption of Cr(III) in aqueous solution using modified activated carbon that when the activated carbon modified with HNO3 was heat-treated at 300-400°C, a large number of acidic functional groups were produced on the surface, resulting in a high cation exchange capacity and good adsorption exchange capacity for heavy metal ions Cr(III) (11). However, if the oxidized activated carbon is heated at high temperatures (above 800°C), a large number of basic functional groups will be produced on the surface, resulting in a high anion exchange capacity and strong adsorption exchange capacity for anions.