(381v) Asparagine Anchored on Mesoporous Silica for Au (III) Capture: Elucidation of Adsorption-Reduction Mechanisms and Their Implications Towards Selective Au (III) Recovery

Gold recovery from industrial wastewater requires effective materials that can selectively collect and separate Au³⁺ from other metal ions. Herein, amino acid asparagine (Asn) was introduced on mesoporous silica (SBA-15) through a sequential functionalization with aminopropylethoxysilane and glutaraldehyde linkers. Results from FTIR, TGA, SEM-EDS, SAXRD, N₂ adsorption/desorption, EA and DLS confirm the successful fabrication of Asn@SBA-15. The material was further probed using TEM-SAED, EDS mapping, WAXD and XPS to elucidate the mechanisms involved in Au³⁺ capture. Results reveal that Au³⁺ (as AuCl₄^-, pH=2) initially binds with the protonated amines of the anchored Asn and residual –NH₂ on the Asn@SBA-15 surface. Once captured, AuCl₄^- is readily reduced to Au⁰ and agglomerates as nano-islets on Asn@SBA-15 surface. The maximum equilibrium Au³⁺ uptake reached 307 mg g^-1, with a rate that follows pseudo-second-order kinetics. The Au³⁺ sequestration process is endothermic and spontaneous that is favoured with temperature increase. In a simulated acidic electronic wastewater, Asn@SBA-15 is highly selective and prefers Au³⁺ by a = 16 – 116,000 times over Al³⁺, Ni²⁺, Cu²⁺, Pb²⁺ and Pd²⁺. Asn@SBA-15 can be employed to repeatedly recover Au³⁺ with consistent performance through adsorption-reduction mechanisms combined with Au⁰ extraction using acidic thiourea.