Highly selective recovery of Au(III) from wastewater by thioctic acid modified Zr-MOF: Experiment and DFT calculation

A novel adsorbent (UiO-66-TA) was presented by modifying metal-organic framework composites with thioctic acid. UiO-66-TA were characterized by fourier transform infrared (FT-IR), field emission scanning electron microscopy (FESEM), thermogravimetric (TG), Brunner-Emment-Teller (BET) measurement and X-ray photoelectron spectroscopy (XPS), which indicating that it had excellent morphology and specific surface area. The adsorption performances of UiO-66-TA for Au(III) were studied. The results showed that UiO-66-TA had a strong adsorption capacity under acidic conditions and the optimal pH was 2.0. Isotherm and kinetic adsorption were also conducted and found that the experimental values correspond to Langmuir model and pseudo-second-order isotherm model, indicating that the mechanism is mainly chemical adsorption on a uniform surface. Wastewater experiment showed that UiO-66-TA can be used for highly selective recovery Au(III) in actual life. The regeneration and thermodynamic experiments indicated that UiO-66-TA can be reused and were a spontaneous endothermic process. XPS analysis and the zeta potential proved that the main adsorption mechanisms were ion exchange and chelation. DFT calculation found that there are two ways to combine Au with S on UiO-66-TA and their distances are 2.38 Å and 2.39 Å, indicating that the gold and sulfur play a major role in chelation. In summary, UiO-66-TA was a hopeful adsorbent and could be used to collect gold ions from wastewater in a sustainability perspective.