Optimization of toluene removal over W-doped TiO₂ nano-photocatalyst under visible light irradiation

This study outlines the optimization of photocatalytic degradation of toluene by W-doped TiO₂ nanoparticles under visible light irradiation. Experiments were carried out based on the central composite design (CCD) methodology. W-TiO₂ nanoparticles were synthesized with various tungsten contents at different calcination temperatures by the sol-gel method. The nanoparticles' characteristics were determined using appropriate techniques such as field emission scanning electron microscopy, particle size analysis, X-ray diffraction and energy-dispersive spectroscopy. The effect of different operational conditions of coating mass, initial toluene concentration, and exposure time on the toluene removal efficiency was investigated. Result showed that tungsten has a fundamental role in improving the photocatalytic activity of TiO₂ under visible light, as well as improving its photoactivity under UV irradiation by decreasing the rate of electron/hole charge recombination. Analysis of the obtained data on toluene removal with a CCD approach illustrated that the quadratic model can effectively predict the toluene removal with coefficient of determination of R² = 0.862. Tungsten content and exposure time affect the toluene removal efficiency more than other factors. Results showed that maximum toluene removal efficiency slightly depends on the initial concentration of toluene. At the initial toluene concentration of 4000 ppm, the optimum values of the calcination temperature, tungsten content, coating mass, and exposure time were 500°C, 0.52 wt%, 11.7 g/m², and 8 h, respectively, with 59% removal of toluene.