Highly active WO₃@anatase-SiO₂ aerogel for solar-light-driven phenanthrene degradation: Mechanism insight and...

The global energy crisis and water pollution drive the researchers to develop highly effective and less energy intensive water purification technologies. In this study, a highly active WO₃@TiO₂-SiO₂ nanocomposite was synthesized and used for photocatalytic degradation of persistent organic pollutants under simulated solar light. The optimum WO₃@TiO₂-SiO₂ prepared with 2 wt% WO₃ loading and calcination at 800 °C exhibited higher photocatalytic activity, as the rate constant (k₁) for phenanthrene degradation was ∼7.1 times of that for the commercial TiO₂ (P25). The extremely large specific surface area (>400 m²/g) of WO₃@TiO₂-SiO₂ afforded it with enlarged pollutants adsorption performance and abundant active surface sites. The heterojunction of anatase with SiO₂ as well as loading of WO₃ decreased the band gap energy (E_g) of TiO₂, which extended the utilization spectrum of TiO₂ to visible region. Formation of Ti-O-Si band indicated the excess charges can cause Brønsted acidity due to the absorption of protons to compensate the charges. Moreover, the migration of photo-excited electrons from the conduction band of anatase to WO₃ and holes in the opposite direction restrained the electron-hole recombination. The photocatalytic degradation mechanism and pathway for phenanthrene degradation were proposed based on experimental analysis and density functional theory (DFT) calculation, and the toxicities of the degradation intermediates were evaluated by quantitative structure-activity relationship (QSAR) analysis. WO₃@TiO₂-SiO₂ also showed good separation (settling) performance and high stability. Our work is expected to offer new insight into the photocatalytic mechanism for WO₃, TiO₂ and SiO₂ based heterojunctions, and rational design and synthesis of highly efficient photocatalysts for environmental application.