Template-free solvothermal synthesis of WO3/WO3·H2O hollow spheres and their enhanced photocatalytic activity from the mixture phase effect

Abstract

Well-defined WO₃·H₂O hollow spheres composed of nanoflakes were successfully synthesized by a template-free solvothermal process with i-PrOH–H₂O mixture solvent. In this process, the tungsten precursor was firstly hydrolyzed to form solid spheres composed of both WO₃·2H₂O and WO₃·H₂O phases. Then, these solid spheres underwent an Ostwald ripening process and the WO₃·2H₂O phase was dehydrated to WO₃·H₂O at the same time to form hollow spheres with a pure WO₃·H₂O phase. With appropriate calcination temperature, hollow spheres with WO₃ (major) and WO₃·H₂O (minor) mixture phases were created. These hollow spheres with WO₃ and WO₃·H₂O mixture phases demonstrated a largely enhanced photocatalytic activity for RhB degradation under visible light irradiation compared with either pure WO₃·H₂O hollow spheres or pure WO₃ hollow spheres which could be attributed to the matched band structure between the WO₃ and WO₃·H₂O phases. Thus, an effective charge carrier separation can occur between the WO₃ and WO₃·H₂O phases of these hollow spheres under visible light irradiation, contributing to the observed largely enhanced photocatalytic performance.