Understanding the mechanisms of gold(III) adsorption onto additively manufactured polyamide adsorbent, AM-N12

The focus of this paper is to study the adsorption behavior and mechanisms of gold(III) onto additively manufactured polyamide adsorbent, AM-N12 from synthetic multimetal leached solutions. Study of the effect of pH revealed that pH 0 was the optimum condition for reaching maximum gold(III) adsorption. In competitive mixtures containing Au(III) and other metal ions, i.e., Pt, Pd, Cu, Al, Fe, Pb, Sn, Ni, and Zn, extremely high selectivity towards Au ions was observed. Fitting of the adsorption isotherm data showed the order of Freundlich < Langmuir < Sips model, depicting likely monolayer adsorption process. Moreover, the kinetics data fitted well to the pseudo-first-order and pseudo-second-order models. Density Functional Theory (DFT) molecular modelling suggested anion–anion interaction, electrostatic attraction, and hydrogen bonding as possible adsorption mechanisms of gold(III). Furthermore, characterization and X-ray photoelectron spectroscopy (XPS) analysis indicated that after adsorption, portions of Au(III) were reduced to Au(I) and some portions were further reduced to Au(0), thus signifying reduction reaction. Finally, approximately 50 % of the adsorbed gold(III) was desorbed in 24h which was appro and the adsorbent regenerated using a mixture of 0.5 M thiourea and 1 M HCl.