Thiol-functionalized Cu-MOF@biochar composite for high-efficiency removal of Pb2+ and Cd2+ from aqueous solutions: Unraveling competitive adsorption mechanisms.

The escalating prevalence of heavy metal pollution from lead (Pb2+) and cadmium (Cd2+) threatens ecological security and public health, necessitating advanced multifunctional adsorbents. Herein, a thiol-functionalized Cu-MOF@biochar composite (SH-MOF@BC) was innovatively synthesized via hydrothermal method. Characterization (SEM-EDS, BET, XRD, FTIR) confirmed a multi-level pore architecture with ultrahigh surface area (379.05 m2/g), an average pore size of 2.2205 nm, and multi-elemental composition (C, O, P, Cu, S). Multi-active sites (-SH, -COOH, -OH, C=O) synergistically enhanced heavy metal sequestration. In batch adsorption tests, the material achieved High uptake of 262.72 (Pb2+) and 57.24 (Cd2+) mg/g in single-component systems, surpassing most advanced composites. Notably, in binary systems, Cd2+ coexistence enhanced Pb2+ uptake due to ion-specific binding, while the composite retained >81% capacity after five regeneration cycles. Langmuir and pseudo-second-order models indicate covalent-driven monolayer chemisorption.Thermodynamic analysis further indicated that the binding was spontaneous (ΔG0 < 0) and endothermic (ΔH0 > 0).XPS analysis identified sulfhydryl groups (-SH) as primary sites, forming stable metal-sulfide complexes (Pb-S, Cd-S). This work provides a scalable green strategy for multi-pollutant wastewater remediation aligned with sustainable chemistry principles.