Multi-mechanism synergistic adsorption of lead and cadmium in water by structure-functionally adapted modified biochar: A review

Abstract

Modified biochar has emerged as an effective and sustainable material for the remediation of Pb2 + and Cd2+-contaminated water. This review provides a comprehensive investigation of the preparation methods, physicochemical properties, and adsorption mechanisms of modified biochar, focusing on its enhanced adsorption performance. Through various modification techniques such as chemical modification, physical activation, metal loading, and other functionalization, biochar's adsorption capacity for Pb2+ (adsorption up to 582.57 mg·g−1) or Cd2+ (219.82 mg·g−1) has been significantly increased. The structural modifications include optimizing surface area, enriching functional groups, and introducing selective adsorption sites. Furthermore, the study highlights the multi-mechanism nature of the adsorption process, including surface complexation, ion exchange, precipitation, and physical filling. Where Pb2+ adsorption predominantly relies on inner layer complexation and precipitation, while Cd2+ is mainly removed through outer layer complexation and electrostatic attraction. The influence of environmental factors and material properties has been quantified, enabling modified biochar to adapt to complex aquatic environments. Future research should focus on developing green modification technologies, improving the understanding of adsorption mechanisms in complex systems, advancing engineering applications for enhanced recyclability, conducting life-cycle assessments, and fostering interdisciplinary research to optimize biochar's potential for global water purification and ecological restoration.

Keywords

• Biochar
• Modification methods
• Lead and cadmium
• Adsorption characteristics
• Removal mechanisms