Porous biomorphic silica@ZnO nanohybrids as the effective photocatalysts under visible light

In this study, zinc oxide nanohybrids based on functionalized bio-silica were synthesized and used for the degradation of Congo red under visible light. Diatom was used as a Si natural source with hierarchical nanostructures to produce porous silica support. Functionalized porous silica is a good candidate for direct immobilization of metal oxide and therefore of interest as the catalyst. Here, six hybrids of functionalized bio-silica and ZnO were synthesized and characterized by FT-IR, XRD, SEM/EDX, BET/BJH, and UV-Vis spectroscopy. Then, the synthesized catalysts were subjected to degradation of different anionic azo dyes (Congo red, methyl orange, and methyl red) under visible light irradiation. The results show the decrease of band gap in bio-silica@ZnO hybrids which enhance the photocatalytic properties of hybrids due to the shifting to visible light adsorption. The best photocatalytic result of SiO₂@ZnO hybrid was obtained from chitosan-based amino-functionalized silica due to the best functionalization, highest loading of ZnO, low band gap, and filling of diatom pores with functional groups.