Cobalt monoxide/tungsten trioxide p-n heterojunction boosting charge separation for efficient visible-light-driven gaseous toluene degradation

A novel cobalt monoxide/tungsten trioxide p-n heterojunction was fabricated via a two-step hydrothermal method for improving the photocatalytic activity for gaseous pollutant degradation and oxygen evolution. The TEM characterization results indicated that the CoO nanoparticles with diameter of 30 nm were uniformly distributed on the surface of WO3 nanoplates, which not only increased the light absorption efficiency but also promoted charge separation efficiency owing to a formed internal electric field in p-n junction hybridized system. In all samples, 15 wt% CoO/WO3 displayed the highest photocatalytic activity, where the degradation conversion of toluene achieved to 85.4% in 4 h, which were 2.0- and 20.3-folds higher than that of WO3 and CoO, respectively. Besides, the as-prepared CoO/WO3 composite also exhibited significantly increased photocatalytic oxygen production under visible light irradiation. Moreover, by in-situ infrared spectra, the main intermediate products, including benzyl alcohol, benzaldehyde, benzoic acid and formate or acetate were clearly clarified at the interface over the catalysts. Combined with the ESR, VB-XPS and UPS, a possible mechanism for the photocatalytic process over the CoO/WO3 p-n heterojunctions were proposed and discussed.