Engineering Zr–W Mixed Oxide Heterojunctions from UiO-66-Type MOFs Templates: Bridging DFT and Mechanistic Insights into Organic Abatement

Abstract The release of harmful chemicals into the environment is still increasing. This study aims to develop highly efficient and stable hybrid oxide photocatalysts (t/m-ZrO2@WO3-X) through hydrothermally assisted pyrolysis routes, based on (Zr/W)UiO-66-type MOFs template, suitable for the abatement of organic dyes such as methylene blue (MB) and indigo carmine (IC), using a mathematical approach. XRD, TGA, FTIR, XPS, EDX, SEM, photoluminescence, UV–vis DRS, N2 sorption, Raman analysis, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry analyses demonstrated the formation of t-ZrO2, m-ZrO2 and monoclinic WO3 oxides. Under optimal conditions, the degradation yields of IC and MB were found to be 95.11% and 92.82%, respectively, as determined by mathematical modeling with an R2 value of 97.70%. The impact of different types of water (tap, river, and surface) and anions and cations on the degradation efficiency was evaluated. DFT and Monte Carlo studies revealed that the LUMO was distributed between the benzene and pyrrole rings, while the HOMO was oriented toward the pyrrole ring. Analysis of Fukui indices for radicals suggests that N-methylated sites are most susceptible to attack by •O2–, h+ and •OH radicals produced by photolysis. Analysis of radical scavengers suggests that h+, •O2– and •OH species are responsible for dye breakdown. LC-MS analysis reveals dye mineralization through pyrrole ring cleavage, followed by carbonyl group oxidation and intermediate formation. The toxicity of IC and MB was assessed using the fathead minnow LC50 (96 h), oral rat LD50 (mg/kg), Daphnia magna LC50 (48 h), bioaccumulation factor, mutagenicity, and developmental toxicity. The presence of WO3 in the hybrid oxides plays a significant role in photon absorption and the efficient separation of photoinduced electrons. The materials proved to be stable after five cycles of use.