Tailoring the Silica Amount in Stabilizing the Tetragonal Phase of Zirconia for Enhanced Photodegradation of 2-Chlorophenol

A simple microwave method was employed to prepare silica-doped mesoporous zirconia nanoparticles, SiO₂/ZrO₂ (SiZr) catalysts under various Si amount and then characterized by X-ray diffraction, nitrogen adsorption–desorption analyses, Fourier-transform infrared, electron spin resonance, ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence analyses. The lower amount of Si fully stabilized the ZrO₂ in the tetragonal phase (t-ZrO₂), but the higher amount of Si occupied oxygen vacancies (OV) in the SiZr lattice to disrupt the catalysts with introduce low content of monoclinic phase. The catalyst activity towards on photodegradation of 2-chlorophenol (2-CP) was ranked in the following order: 1SiZr (92%) > TiO₂ (73%) > 2SiZr (67%) > 3SiZr (64%) > 4SiZr (56%) > ZrO₂ (51%). This result demonstrated that 1SiZr gave the highest degradation percentage of 10 mg L⁻¹ 2-CP at pH 5 using 0.375 g L⁻¹ catalyst under visible light irradation within 4 h. The highest photoactivity of 1SiZr is due to the larger surface area and crystallite size, which resulted in a good surface contact with light and thus accelerated the photocatalytic activity. Additionally, the highest amount of OV possesed by 1 SiZr effectively suppressed the electron–hole recombination by acting as an electron acceptors, which consequently affected the t-ZrO₂ stabilization as well as the catalytic activity. The kinetics of photocatalytic degradation of 2-CP correlated with pseudo-first order model, with the surface reaction as the controlling step. The photogenerated hole was the most active species as confirmed by effect of scavenger study. The 1SiZr maintained the photocatalytic activities after five runs and has a great capability in degrading of various phenols derivatives, indicating its potential use in the phenol-based wastewater treatment.