Structural engineering of clay minerals for heavy metal remediation: Molecular mechanisms, performance enhancement, and sustainable applications

The acceleration of global urbanization and industrial expansion has precipitated severe contamination of aquatic systems through toxic heavy metal discharges (Cr, As, Cd, Hg, Cu, Pb), creating substantial threats to ecological integrity and public health. Amidst diverse remediation strategies, adsorption emerges as a particularly promising solution due to its operational efficiency and cost-effectiveness, with adsorbent development constituting the primary technological hurdle. Naturally occurring clay minerals (kaolinite, montmorillonite, and palygorskite, etc.) have emerged as superior candidates for water purification applications, leveraging their inherent advantages of geological abundance, structural diversity, modifiable surface chemistry, and exceptional adsorption capabilities. This review systematically synthesizes recent years of scientific advancements in heavy metal sequestration using clay-based materials, with focused analysis on crystallographic properties, molecular-level adsorption mechanisms (electrostatic interaction, ion exchange, surface complexation, hydrogen bond), and critical operational parameters (pH, temperature, ionic strength). A dedicated evaluation of clay composites demonstrates remarkable performance enhancements through chemical modification (surfactant intercalation, functional group grafting) and nanoscale engineering, achieving significant capacity improvements compared to pristine counterparts. By establishing structure-function relationships and optimizing modification protocols, this analysis provides crucial guidance for developing next-generation clay adsorbents, charting a sustainable pathway for addressing anthropogenic pollution challenges through geologically-sourced remediation technologies.