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. • First-time synthesis and structural confirmation: A novel mixed-valence Ni-MOF-808 was successfully synthesized, and partially replacing Zr 4+ with Ni 2+ at the node level was confirmed by XRD, XPS, and quantitative XPS. • Enhanced physicochemical properties: The modified framework exhibited about 30 % increase in BET surface area (1850 m 2 /g), an enlarged pore size (23 Å), and thermal stability up to 475 °C. Comparative studies indicated lower Ni incorporation in UiO-67 and none in UiO-66, highlighting the defect tolerance of MOF-808. • Optimized adsorption performance: Achieved up to 98.06 % removal of UV filters, following pseudo-first-order kinetics and Langmuir isotherm models, with Plackett–Burman screening and optimization through RSM. • Excellent reusability: Maintained high adsorption efficiency and capacity retention over five adsorption–desorption cycles, demonstrating robust stability and regeneration potential. • Real-world applicability: Verified in real wastewater treatment, achieving ~99 % removal efficiency, marking the first successful application of the novel Ni-MOF-808 structure for UV filter removal.