Recovery of Au(III) from electronic waste using solid phase extraction based on a magetic nanobiocomposite, OCBS@Fe3O4 @UiO-66-SH

This study created a zirconium-based MOF (UiO-66-NH ₂ ) with thiol groups attached to its magnetic corn surface for adsorption and extraction of Au(III) from electronic waste. Characterization of the composite was verified using FTIR, XRD, FESEM, TGA and BET techniques. The temperature, adsorption period, and pH on Au(III) adsorption were investigated. The pH of solutions significantly impacts Au(III) adsorption, with pH 6.0 being the optimal value. The optimum Au(III) adsorption conditions were 50 ◦C, 40 min, and 10 mg of adsorbent. Moreover, functionalized oxidized magnetic corncobs with thiol (OCBS@Fe ₃ O ₄ @UiO-66-SH) showed a notable ability to adsorb Au(III) with a 1587 mg/g capacity. With mass ratios of Au(III) to competing ions (Mg, Mn, Cu, Zn, Co, Cd, and Ni) fixed at 1:1 or extended to 1:5, this adsorbent prefers Au(III) ions while showing negligible adsorption to other ions. The study validated a technique for extracting Au(III) from various electronic waste samples, achieving high recovery rates (95.30–104.75%), demonstrating its effectiveness and lack of matrix interference. Langmuir, Freundlich, and Temkin isotherm models were used to describe the adsorption process. Comparing models, the Langmuir model with the most excellent R ² value is best for interpreting experimental adsorption data. Among three kinetic models, pseudo-first-order (PFO), pseudo-second-order (PSO) kinetic, and interparticle diffusion (ID) models, PFO model exhibited a high R ² value (0.9976). Thermodynamic calculations reveal a positive Δ H °, indicating the endothermic process, and negative Δ G ° values representing spontaneous adsorption at 298–323 K. The positive Δ S ° shows that the adsorbed molecules are more uniformly dispersed on the surface, potentially enhancing the adsorption capacity.