Synthesis, characteristics and mechanistic insight into the clays and clay minerals-biochar surface interactions for contaminants removal-A review

Abstract Biochar (BC), a low-cost, porous and carbon-rich material, exhibits excellent potential as an adsorbent in the immobilization and removal of environmental contaminants from water and soil. To enhance the surface area, functionalities and adsorption efficiency of BC, various clay and clay mineral-based physical and chemical modification methods have been adopted. Although extensive studies have been conducted to evaluate the removal efficiencies of BC-clays and clay minerals composites, insight into synthesis, characteristics, and mechanistic understanding between adsorbents and contaminants in environmental remediation has not been fully developed. Therefore, this review focuses on production methods of BC composites with different clays and clay minerals, their surface interactions, physicochemical characteristics, and specifically various adsorption mechanisms involved in the removal process of in-/organic contaminants, and explains how the sorption capacity of the BC-clay/mineral composites is altered. Environmental applications of various BC-clay/mineral composites and factors affecting the surface chemical reactions and interactions of BC-clay/mineral composites are also provided comprehensively. Moreover, this article discusses the increasing interest of BC-clay/mineral composites in enhancing the adsorption efficiency of different contaminants through various mechanisms. The combined effects of BC-clay/mineral composites for the adsorption of in-/organic contaminants both in soil and water are critically reviewed. Future challenges and prospects regarding the use of BC-clay/mineral composites in environmental remediation and achieving commercialization of this promising technology are also considered.