Temperature effects on VO2thin films deposited by RF sputtering for the degradation by photocatalysis of methylene blue and naproxen

Abstract

The temperature effect on VO2thin films synthesized by RF sputtering on theirmorphological, optical, electrical properties and their activity in the photocatalytic degradation of methylene blue and naproxen was studied. Characterization results presented microcrystallinity for VO2films treated at 50 and 100 °C. Nevertheless, the untreated films and films treated at 200 °C revealed characteristic peaks of monoclinic and tetragonal phases. SEM micrographs with elemental mapping of VO2films showed granularmorphology and a good oxygen dispersion along the film surface, possibly due to a restructuring on the film occasioned by particle coalescence and vanadium oxide island conformation. The electronic transmittance spectra showed the d-d transition characteristic for the square-pyramidal stereochemistry of vanadium (IV) ion, where the optical band interval was high for films treated at 50 °C. Raman spectroscopy results presented an increment in the V = O/V-O ratio as a function of temperature, probably related to superficial vanadium species formation. X-ray spectroscopy results showed the Onon-lattice/Olattice ratio values higher for films treated at 50 °C than the other films, related to an oxide character. The V 2p fit results presented V4+, V5+ regions and satellites for VO2films thermal treated at 50 °C. The electrical resistivity on the VO2films decreased as a function of temperature. Finally, the VO2films thermal treated at 50 °C had higher photocatalytic activity in the degradation of methylene blue and naproxen compared to the other VO2films, possibly associated with high electron mobility between the surface and the bulk, where the oxygen vacancies act as recombination sites for the e-/h+ pairs during photocatalytic degradation.