New insight into sequential of silica-zirconia precursors in stabilizing silica-doped tetragonal zirconia nanoparticles for enhanced photoactivity

Silica-doped tetragonal zirconia nanoparticles (SiO₂-ZrO₂) catalysts were synthesized with the addition of ZrO₂ prior to SiO₂ by the microwave-assisted method and compared with a different sequence of ZrO₂ and SiO₂ (ZrO₂-SiO₂). The catalysts were characterized by X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, Fourier-transform infrared, electron spin resonance, ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence analyses. The catalyst phase was pure tetragonal ZrO₂ (t-ZrO₂) with nano in size (9–10 nm). The sequential of SiO₂ and ZrO₂ precursors significantly affected the catalyst framework and led to a different number of pore volume and defect sites, including oxygen vacancies (OV), metal defects site (MDS) and Si-O-Zr bonds, which altered their behaviour towards t-ZrO₂ stabilization and applications. It was found that the synergistic effect between nanocrystals and the appropriate amount of defect sites influenced the stabilization of t-ZrO₂. The catalytic activity towards photodegradation of 2-chlorophenol (2-CP) are in the following order: SiO₂-ZrO₂ (92%) > ZrO₂-SiO₂ (59%) > ZrO₂ (50%) > SiO₂ (20%). The highest photoactivity of SiO₂-ZrO₂ is due to the large pore volume, which offered good surface contact with light. Besides, the higher crystallinity, Si-O-Zr bonds, and OV and MDS also could contribute to the excellent performance in 2-CP degradation. The abovementioned properties provided good electron-hole pair mobility and electron trapping for enhanced photoactivity.