A complete review on the surface functional groups in pyrolyzed biochar and its interaction mechanism with heavy metal in water

Heavy metal pollution in water has become a major environmental issue. Among the various methods for heavy metal treatment, pyrolyzed biochar is widely used due to its high adsorption rate and diverse physicochemical properties. The effectiveness of biochar in removing heavy metals is closely related to the types and characteristics of its surface functional groups. This article systematically reviews the classification and characteristics of surface functional groups on pyrolyzed biochar, with a focus on the types of oxygen, nitrogen, and sulfur functional groups and their mechanisms of action in the adsorption of heavy metals. The article analyzes the impact of pyrolysis conditions and raw materials on the formation of these functional groups and points out that surface functional groups enhance the removal efficiency of heavy metals by biochar through charge interactions, coordination complexation, and physical adsorption, among other mechanisms. The article also provides a detailed summary of methods and effects for regulating surface functional groups and offers suggestions for future research, including the development of pollution-free functional group introduction techniques and the exploration of potential applications of biochar in other fields.