Understanding photocatalytic activity and mechanism of nickel-modified niobium mesoporous nanomaterials

ABSTRACT To better understand the photocatalysis oxidation mechanism of different types of coupled semiconductors, mesoporous niobium(V) oxides (n-type) with relatively high surface areas (140 m2 g-1) were synthesized by Evaporation Induced Self-Assemble method and modified with different amounts of NiO (p-type). The materials are polycrystalline nanostructures, with mesoporous of approximately 12 nm and bandgap values in the UVA range of the spectrum (344 – 356 nm). The materials showed remarkable photocatalytic activity and the addition of nickel oxide increased the reducibility of the Nb5+ species and improved the charge transfer in the materials. Studies with indigo carmine dye have shown that the niobium-based materials are able to decolorize a 40 ppm solution in 20 and 60 minutes (1.0% NiO material) in photo-Fenton like reaction, and photocatalysis reactions, respectively, without the strong adsorption of the molecule to the material surface. In addition, in the presence of a radical scavenger the photocatalytic reactions half-life time showed an increase of up to 11 times, which indicates that the indirect oxidation mechanism, with the formation of radicals, is predominant. The formation of hydroxyl radicals during irradiation was confirmed by EPR analysis with the spin trapping method.