Zirconium-based Metal-Organic Frameworks for highly efficient solar light-driven photoelectrocatalytic disinfection

Two synthesized zirconium-based Metal-Organic Frameworks (Zr-MOFs), using 2,6-naphthalenedicarboxylic acid (NDC) and amino-functionalized NDC (4,8-diaminonaphthalene-2,6-dicarboxylic acid, NDC-2NH2) as linkers, have been studied in photoelectrocatalytic disinfection processes. The Zr-based MOFs were deposited onto graphite paper and were deeply analysed to unravel their behaviour in electrocatalytic (EC), photocatalytic (PC) and photoelectrocatalytic (PEC) configurations under solar (Xe-arc lamp), visible (Xe-arc lamp + 400 nm cut-off filter) and 365 nm UV-LED irradiation. TPC results showed reproducible photocurrent response upon repeated on–off cycles and bandgaps were calculated to be 3.13 and 2.11 eV for Zr-NDC and Zr-NDC-2NH2, respectively. The highest photocurrent was obtained for 365 nm UVA in Zr-NDC and was similar for both UVA and solar irradiation in the case of Zr-NDC-2NH2. The Zr-MOFs catalytic electrodes were evaluated for their disinfection activity using a strain of Staphylococcus aureus and performance tracked by measuring colony forming units (CFU). The disinfection efficiency was higher in PEC than PC studies (>2-log reduction or 99 % CFU inhibition) under 365 nm UVA irradiation, suggesting that the anodic bias potential effectively minimized the recombination of the photogenerated electron-hole pairs. A complete disinfection was reached after 60 and 20 min under irradiation of full Xe-arc (solar) spectrum in PC and PEC runs, respectively, for both Zr-MOFs. The high disinfection capacity under solar irradiation was attributed to the transfer of photoexcited electrons from ligand to cluster by high energy photons.