Anisotropy of photocatalytic properties of MoO₃/TiO₂–SiO₂ core–shell polycrystalline composites

In this work, the effect of the preferred orientation of MoO₃ crystals in polycrystalline MoO₃/TiO₂–SiO₂ composites on their optical properties and photocatalytic activities in the decomposition reaction of organic dyes was investigated. The anisotropy of the photocatalytic properties was shown. The MoO₃/TiO₂–SiO₂ core–shell spherical composites were prepared using TOKEM-320Y anion exchange resin as a template by the combined method, including template and sol–gel methods. The XRD, XPS, EDS, SEM, Raman, IR, DRS, N₂ sorption, and PL techniques were used to characterize the elemental and phase compositions, textural and optical properties of the MoO₃/TiO₂–SiO₂ spherical particles. The MoO₃/TiO₂–SiO₂ composites prepared at 600 °C were characterized by the lowest anisotropy coefficient (1.23) of the crystals growth rate in the plane (l00) relative to the crystals growth rate in the plane (lll) and the highest concentration of oxygen vacancies. High temperature treatment of MoO₃/TiO₂–SiO₂ samples up to 700 °C leads to a change in the degree of their texture, which is due to the growth of the anisotropy coefficient up to 1.38 and crystallites in the (l00) plane, which was confirmed by increasing the Lotgering factor. The content of Mo⁵⁺ in the surface and subsurface layers of such composites is the highest. The MoO₃/TiO₂ − SiO₂ composites prepared at 600 °C exhibited a much higher photocatalytic activity (the rate constant is 0.0319 min^-1). This work demonstrates that the predominant orientation of MoO₃ crystals in the (l00) plane negatively affects the oxygen defect (the value decreases to 0.0486) and MoO₃/TiO₂ − SiO₂ polycrystalline composites photocatalytic activity.