Using rice husk ash as a SiO₂ source in the preparation of SiO₂/Nb₂O₅ and SiO₂/ZnS heterostructures for photocatalytic application

This work presents the synthesis of SiO₂/Nb₂O₅ and SiO₂/ZnS heterostructures using the microwave-assisted hydrothermal (MAH) method, which is fast and has low temperature. The silica used in the synthesis was obtained by burning the rice husk without any pre- or post-treatments. The obtained samples were characterized using various techniques such as X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and UV-visible. The obtained silica was found to be amorphous, and the materials used for modification showed characteristic of the type of synthesis used. SEM images showed that Nb₂O₅ and ZnS interacted with the SiO₂ surface, filling the voids. In the photocatalytic process, the heterostructures showed enhanced decolorization efficiency for dyes such as rhodamine B (RhB) and methylene blue (MB) compared to SiO₂. For RhB, the silica decolorized approximately 24%, and for MB, it discolored approximately 27%; SiO₂/Nb₂O₅ showed 91.24% decolorization efficiency for RhB and 72.77% MB, while SiO₂/ZnS showed approximately 96% for RhB and 100% for MB. All samples were tested under the same conditions. This demonstrates that the use of rice husk residue not only improves the photocatalytic activity of heterostructures but also promotes the utilization of improperly discarded residues.