Advances in selective heavy metal removal from water using biochar: A comprehensive review of mechanisms and modifications

Heavy metals are common pollutants in the aquatic environment that are difficult to degrade and harmful. Biochar has emerged as a promising material for heavy metal remediation in water due to its advantages such as high surface area, strong adsorption capacity, and low cost. However, current research primarily focuses on single-pollutant systems, whereas actual water bodies often contain coexisting multiple metal ions. Competitive adsorption among these ions significantly interferes with the selective removal efficiency of biochar. This paper systematically reviews the latest advances in biochar-based selective adsorption materials, and explores the influence of inherent properties such as feedstock type, pore structure, and surface functional groups on adsorption performance. It reveals key mechanisms including surface complexation, ion exchange, and electrostatic attraction, and summarizes the remarkable effects of modification techniques such as acid treatment and metal impregnation. In addition, this paper analyzes the selective adsorption behaviors and mechanisms of biochar toward typical heavy metals such as cadmium, lead, and chromium. Finally, it highlights current research gaps, including uncertainties in biochar production, application, long-term stability, and environmental risks, while also outlining future research directions. This work aims to provide theoretical guidance and technical support for the design and application of biochar materials.