Novel transmetalated Zr-MOFs for tailoring porosity and mixed-valence nodes: Efficient removal of hazardous UV filters from wastewater

A novel mixed-valence MOF, designated as NiMOF-808, was synthesized via partial post-synthetic transmetalation of Zr 4+ in MOF-808 and characterized by PXRD, XPS, TGA, SEM, BET, and Zetapotential (ζ) analyses. The new framework exhibits a significantly higher adsorption capacity (445 mg/g (±11)) for polar UV filters than activated carbon and UiO-66, attributed to its large surface area and mixed-valence nodes. PXRD and XPS confirmed the successful incorporation of nickel at the node level, with three Ni species detected. Quantitative XPS showed that Ni species replaced 1.15 of the six Zr 4+ atoms per node. TGA revealed high thermal stability with decomposition at 475 °C. BET analysis revealed a nearly 30 % increase in surface area (1435 to 1850m 2 /g) with a larger pore diameter of 23 Å compared to the parent MOF. Zetapotential measurements showed a reduction from ζ = +30 mV to ζ = +4 mV following Ni incorporation, accompanied by a 1.06 pH-unit shift in PZC, indicative of a lower net positive surface charge. Comparative transmetalation of UiO-67 and UiO-66 resulted in lower or no Ni incorporation, respectively. Adsorption studies targeting ethyl cinnamate and benzophenone, representatives of ordinary UV filters, were conducted, with variable screening using a Plackett–Burman design and process optimization via the RSM method. NiMOF-808 achieved up to 98.06 % (±2.8 %) removal at a concentration of 0.005 g/L using 1 g/L of adsorbent and maintained its efficiency over five reuse cycles. Different sourced wastewater effluents resulted in 88.32(± 5.1) % and ~ 99(± 3.0)% removal of UV filters by NiMOF-808, suggesting the method's practical applicability. Kinetic and isotherm modelling showed pseudo-first-order kinetics and Langmuir behavior.