Synergistic effect of microwave rapid heating and weak mineralizer on silica-stabilized tetragonal zirconia nanoparticles for enhanced photoactivity of Bisphenol A

Silica-doped tetragonal mesoporous zirconia nanoparticles (SZ) were successfully synthesized with various concentrations of ammonia solution(NH4OH) using microwave-assisted method for photodegradation of Bisphenol A (BPA). The phase of SZ catalyst was pure mesoporous tetragonal ZrO2 with nano in size (5-10 nm). The increasing concentration of NH4OH solution enhanced the hydrolysis and condensation process, as confirmed by formation of additional Zr-O-Zr, Si-O-Si and Si-O-Zr bonds. The formation of oxygen vacancy (V-o) and Zr3+ surface defects (ZSD) also increased proportionally with the concentration of NH4OH solution. Both properties and the Si-O-Zr bond are supposed to play important roles in stabilizing the tetragonal phase of ZrO2. The V-o and ZSD also lowered the band-gap energy (from 4.35 eV to 3.05 eV) and act as electron acceptors. Catalytic testing showed that 8-SZ gave the highest initial rate (0372 x 10(-3) mM min(-1)) of 10 mg L-1 BPA at pH 7 using 0.5 g L-1 catalyst within 4 h while under similar conditions, 5-SZ, 3-SZ, 0-SZ, ZrO2 and TiO2 only gave 0.263 x 10(-3), 0.211 x 10(-3), 0.145x 10(-3), 0.026x 10(-3) and 0305 x 10(-3) mM min(-1), respectively. These results demonstrate that higher numbers of Si-O-Zr, V-o, and ZSD seemed to be the main factors in the high photoactivity of SZ prepared in 8 M NH4OH solution (8-SZ). A kinetic study demonstrated that the photodegradation followed the pseudo-first-order Langmuir-Hinshelwood model. The mechanism study using scavenging agents proved that photogenerated hole was the main active species, thus led more hydroxyl radicals formed to degrade the BPA. The 8-SZ also exhibited a great potential on degradation of various phenols and dyes in wastewater. (C) 2018 Elsevier B.V. All rights reserved.