MoO₃ altered ZnO: A suitable choice for the photocatalytic removal of chloro-acetic acids in natural sunlight exposure

The MoO₃ coated ZnO photocatalysts were synthesized for the optimum harvesting of the absorbed ultraviolet sunlight photons by initially permeating Mo⁶⁺ ions at the surface of pre-synthesized ZnO and finally transformed to MoO₃ by thermal treatment in the air. The absorption spectra of the synthesized powders revealed the extension of the absorption edge in the visible region whereas, the photoluminescence spectroscopy established the supporting role of the MoO₃ coating in gradually plummeting the excitons recombination. The growth of additional peaks in Raman as well as X-ray photoelectron spectra and the appearance of the corresponding low-intensity reflection substantiated the surface prevalence of MoO₃. The absence of the individual particles of MoO₃ in FESEM and the verification of coated layer by HRTEM images validated the authenticity of the adopted synthetic route. The electrochemical evaluation of the synthesized powders under illumination revealed the complete elimination of photocorrosion and the synergic role of the MoO₃ layer for improved trap and transfer of charge carriers. The evaluation of the flat-band potentials of the coated powders by Mott-Schottky analysis revealed the suitability of the conduction band edges for the generation of superoxide anion radicals. The photocatalytic activity of the synthesized powders was assessed for the removal of chloro derivatives (mono-, di-, trichloroacetic acids) in comparison to pure acetic acid. A significant effect of the stability, polarity and stereochemical structure of the substrate on the photocatalytic removal process was observed and discussed. The experimental evidences from the time-scale chemical analysis were interpreted for the identification of the reactive oxygen species (ROS) involved in the degradation/mineralization process. The validation of the Langmuir-Hinshelwood kinetic model was also examined. Efforts were made to estimate the plausible route of the degradation/mineralization process.