Visible-light-driven efficient photocatalytic abatement of recalcitrant pollutants by centimeter-length MoO3/SiO2 monoliths with long service life

Abstract

The alarming challenge of water-pollution can be effectively dealt with by using easy-to-recover monolithic-photocatalysts. Herein, MoO3/SiO2 monoliths have been prepared by wet-impregnation route. The crystallinity of the catalyst and oxidation-state of elements were revealed by XRD and XPS analyses, while EDS and color-mapping confirmed the uniform dispersal of elements in the catalyst. FESEM and HRTEM analyses revealed the highly porous surface of monolith and small particle size whereas BET-analysis revealed its pore-size (~15.05 nm) and excellent surface-area (~202m2/g). The optical properties disclosed that MoO3/SiO2 monoliths were visible-light-active having band-gap ~2.58 eV and a low recombination-rate. The photoactivity of the catalyst was checked through photodegradation of model dye rhodamine-B (Rh-B) and antibiotic metronidazole (MZ). The effects of catalyst-concentration, pH, pollutant-concentration, and illumination-area were investigated. Under visible-light-irradiation, and at natural-pH, excellent efficiency was obtained for Rh-B (88.6%; 0.0129min−1) and MZ-degradation (67.4%; 0.0054min−1). Similar experiments in sunlight manifested better efficiency. High reusability of catalyst (~9%-reduction in efficiency after 4-runs) was justified by post-photocatalytic characterization-results. The trapping-experiments displayed that holes had primary involvement in the degradation. The intermediate products of MZ after photodegradation were identified by GC–MS analysis. The photocatalytic treatment of real wastewater (without physicochemical-treatment) showed ~64% COD-removal and 57% TOC-removal. The current study along with a comparison with literature demonstrates the potential of the MoO3/SiO2 monoliths for the eradication of recalcitrant-contaminants from a real-world-perspective.