Adsorption of contaminants from aqueous solutions by modified biochar: a review

Environmental context As a low-cost adsorption material with good biocompatibility and high adsorption efficiency, biochar is widely used to treat contaminants in water and soil environments. However, due to its low adsorption capacity and narrow adsorption range, it is necessary to modify biochar to improve its adsorption performance. This review describes the three major biochar modification methods and reviews their adsorption effects on different contaminants, then makes recommendations and suggestions for future development of biochar. Abstract As an adsorption material with low cost, good biocompatibility and high adsorption efficiency, biochar is widely used to treat contaminants in water. By modifying biochar, its physiochemical properties can be effectively improved, thereby improving its directional adsorption capacity for target contaminants. Many studies have been conducted to improve the adsorption capacity of modified biochar for contaminants and to explore the adsorption mechanism. However, there is currently no systematic analysis and summary of various modification methods and their adsorption effects on different contaminants. This review combines all recent papers on the adsorption of contaminants by modified biochar. In addition, this review summarises and specifically divides biochar modification methods into physical modification, chemical modification and compound modification. Physical modification can mainly improve the specific surface area and other physical characteristics of biochar, while chemical modification can form more functional groups in biochar. Compound modification can effectively combine the advantages of different types of adsorption materials to improve the adsorption capacity for contaminants. The adsorption effects of these three types of modification methods on heavy metals, inorganic salts and organic pollutants were compared, and their adsorption mechanisms were systematically reviewed for different types of contaminants. Finally, recommendations and suggestions are put forward for the future development of biochar. In summary, biochar has broad application prospects as a popular adsorption material for the adsorption and removal of contaminants. According to different types of contaminants, a specific modification method can be selected for biochar to achieve the best effect of removing target contaminants.