Coordination-directed Au(III) capture from acidic multi-component wastewater by a 4,6-diaminoresorcinol-chitosan...

Efficient recovery of Au(III) from acidic multiionic aqueous solutions remains a practical challenge, as adsorbents must possess high adsorption capacity, high selectivity, acid stability, and a clear structure-performance relationship. This paper reports a cross-linked chitosan network, CS-DMRN, constructed by introducing 4,6-diaminoresorcinol (DMRN) groups into chitosan, first through formaldehyde co-crosslinking followed by glutaraldehyde crosslinking. Comprehensive characterization (SEM/EDS, FT-IR, XRD, XPS, N₂ adsorption (BET), and TGA) confirmed its robust nitrogen/oxygen-rich framework and mesoporous structure conducive to mass transfer. Batch experiments showed that Au(III) adsorption was endothermic and heterogeneous; within the studied concentration range, the adsorption capacity q_e tended to plateau at higher C₀ values, with plateau adsorption capacities ranging from 1009.58 to 1077.26 mg/g (298 K), 1402.70-1520.95 mg/g (308 K), and 1771.15-1840.87 mg/g (318 K). CS-DMRN maintained excellent performance in acidic media and exhibited preferential adsorption of Au(III) in the presence of competing cations (Li⁺, K⁺, Mg²⁺, Ni²⁺, Zn²⁺). CS-DMRN demonstrates good reusability in repeated adsorption-desorption cycles. Density functional theory (DFT) calculations of the CS-DMRN/AuCl₄^- complex, combined with density of states (DOS), COHP, ELF, and IGMH analyses, indicate that the adsorption process is primarily driven by coordination at N/O donor sites, with electrostatic interactions promoting adsorption. These results collectively demonstrate that CS-DMRN is a high-capacity, highly selective, and recyclable adsorbent suitable for recovering Au(III) from complex acidic solutions, and provide molecular-level insights for further material optimization.