Green and sustainable synthesis of mesoporous silica from agricultural biowaste and functionalized with TiO2 nanoparticles for highly photoactive performance

Rice husk (RH) is a bio-based material and can be a valuable source of bioenergy. Burning RH to produce thermal energy results in the generation of RH ash (RHA). RHA contains abundant silica. This study prepared mesostructured RH–SBA-15 by using RHA as a silicon source. A nanosized TiO2 photocatalyst was then synthesized using RH–SBA-15 as the support material. XRD and TEM confirmed that TiO2 nanoparticles with mainly anatase structures were adequately dispersed in the hexagonal mesopores of the RH–SBA-15 sample. The TiO2 particles had crystalline sizes of 6.5–7.9 nm and band gap energies of 3.45–3.47 eV. FTIR and XPS spectra verified that TiO2 had been successfully combined with the SiO2 material. The composite catalysts had surface areas of 248–383 m2/g, pore volumes of 0.425–0.575 cm3/g, and pore sizes of 6.12–6.35 nm. Calcination temperature, a parameter in the catalyst production process, strongly influenced the surface characteristics and pore structures of the composite catalysts. We also investigated the photodegradation of reaction blue 4 (RB4) with the composite catalysts. The catalyst's photoactivity was affected by adsorbent type, RB4 concentration, agitation speed, and calcination temperature. In addition, this study explored the photodegradation kinetics and mechanism. Converting RHA into SBA-15-based catalyst composites not only eliminates the disposal problem of agricultural waste, but also provides valuable information on wastewater purification.