Dual functionalization of UiO-66-NH2 for efficient and selective Au(iii) adsorption: the synergistic effect of electrostatic and coordination interactions

Abstract

This study describes a dual-functionalized metal–organic framework (MOF), UiO-66-AVIM-TSC, for efficient and selective Au(III) adsorption from aqueous solutions. Prepared via in situ polymerization of an amino-functionalized imidazolium ionic liquid (AVIM) on UiO-66-NH₂ and subsequent modification with thiosemicarbazide (TSC), the obtained UiO-66-AVIM-TSC is characterized by Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), zeta potential measurements, and X-ray diffraction, confirming the successful functionalization and structural integrity. Adsorption experiment results reveal that UiO-66-AVIM-TSC exhibits a maximum adsorption capacity of 220.26 mg g⁻¹ at room temperature under an optimal adsorption pH of 3.0, outperforming UiO-66-NH₂ and UiO-66-AVIM. The adsorption isotherm and kinetic data align with the Langmuir model and pseudo-second-order isotherm model, suggesting that the adsorption mechanism is primarily chemical adsorption on a homogeneous surface. Thermodynamic analysis indicates that the adsorption is an endothermic (ΔH° = 64.736 kJ mol⁻¹) and spontaneous (ΔG° < 0) process. The adsorbent UiO-66-AVIM-TSC also shows high Au(III) selectivity over coexisting ions (Zn²⁺, Cu²⁺, etc.) and retains >85% efficiency after four rounds of recycling. It is found that the adsorption is mainly dominated by ion exchange and coordination, and the reduction of Au(III) into Au(I) and Au(0) is also involved in the adsorption process.