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

Abstract 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.