Effective Recovery of Pt(IV) from Acidic Solution by a Defective Metal-Organic Frameworks Using Central Composite Design for Synthesis

Recovery of precious metal ions such as Pt(IV) from acidic media is very important owing to their increasing supply risks and environmental threats; nonetheless, it is still a challenging task. Metal-organic frameworks (MOFs) as a class of porous nanomaterials have attracted extensive attention for their sustainable and environmental applications. Here, MOFs of UiO-66 was synthesized by central composite experimental design to effectively recover Pt(IV) anions (PtCl ₆ ^2- ) in strongly acidic solutions. The synthesized UiO-66s were evaluated for adsorption kinetics and uptake capacities, and the UiO-66 synthesized under the optimal conditions showed very fast precious metal adsorption rate and high uptake capacity. The optimally synthesized UiO-66 was verified to have a defective structure with large amount of incompletely coordinated Zr atoms. The incompletely coordinated Zr, supposedly the adsorption site for PtCl ₆ ^2- through electrostatic attraction or ion exchange, was confirmed by X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy. Furthermore, the binding energy (E _bind ) of PtCl ₆ ^2- in the synthesized UiO-66 materials were calculated following the density functional theory method, in which a much greater E _bind for PtCl ₆ ^2- bound with incompletely coordinated Zr was observed in the optimally synthesized UiO-66 compared with those bound with complete-coordinated Zr in other synthesized UiO-66 materials.