Hollow Spherical Hierarchical MoO3/SiO2–TiO2 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 (λ_max = 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.