Hollow Spherical Hierarchical MoO 3 /SiO 2 –TiO 2 Structures for Photocatalytic Decomposition of Organic Pollutant in Water

Abstract

MoO3/TiO2–SiO2 layered spherical composites with hierarchical structures have been synthesized via a template and sol-gel methods in which TOKEM-320Y anion exchanger was used as template. The properties of MoO3/TiO2–SiO2 spherical composites were characterized by X-ray diffraction, Scanning electron microscopy, Energy-dispersive X-ray spectroscopy, 3D X-ray microtomography, N2 sorption, Infrared and Raman spectroscopies and ultraviolet spectrophotometry. The photocatalytic activity of MoO3/TiO2–SiO2 composites was evaluated by photocatalytic degradation of methylene blue (MB) aqueous solution under irradiated with an I2 excilamp (λmax = 312 nm) and its photoabsorption energy properties are related to the interaction between TiO2–SiO2 and MoO3 which occurs through oxygen in Ti-O-Mo and Si-O-Mo. The layered hierarchical structure results in lower oxygen vacancy concentrations in composites (0.0425) and a reduced bandgap width (2.58 eV in compare to 3.18 eV for MoO3 spheres), which increases the composite's absorption of light in the visible light regime (λ absorption edge is 480.5 nm). Photocatalytic degradation of the MB dye followed the pseudo-first-order-kinetics. Degradation product analysis was done using the HPLC-MS technique. The dye degradation is initiated by demethylation of the molecule and lead to formation of azure A, B and C and thionin. The results showed that MoO3/TiO2–SiO2 composites exhibited a much higher photocatalytic activity (rate constant is 0.0645 min‒1) than that of MoO3 spheres and other MoO3 samples in the literature. This investigation demonstrates that MoO3/TiO2–SiO2 layered spherical composites is a promising candidate material for photocatalytic decomposition of organic dyes in textile waste water which are considered as one of the greatest threats to the environment.