WO₃?nH₂O-based photocatalysts: Structural analysis, rational design, and applications in energy conversion and environmental remediation

Photocatalysis is an attractive "green" solution to the energy crisis and environmental pollution; however, its practical application is still thwarted by low efficiency. As the core link of this technology, the continuous development of new photocatalysts is the main idea to improve efficiency. In the past few decades, a large number of semiconductor materials with photocatalytic activity have been synthesized successively, including transition metal oxides, nitrides, sulfides, carbon based materials, and metal organic frameworks. Considering various factors such as catalytic activity, production cost, and environmental safety, metal oxides are the most promising carriers of photocatalytic materials for development among them, such as titanium dioxide (TiO2). Recently, tungsten trioxide (WO3) based photocatalyst, especially tungsten trioxide hydrates (WO3nH(2)O, n = 0.33, 0.5, 1 and 2), has become a new favorite among scholars. Not only due to its wider light response range and higher photocatalytic activity compared to TiO2, but also because the rich hydroxyl groups give it more flexible surface structure regulation possibilities. At present, there are over 200 literatures on WO3nH(2)O-based photocatalysts have published; yet, no review article concluding such materials. To promote the development and provide a reference for colleagues, we present a systematic review of the applications and research progress of WO3nH(2)O-based photocatalysts in the past decade. Starting from structural analysis, this work summarizes the preparation methods and modification strategies. Subsequently, it explores the application status in energy conversion and environmental pollution control, and finally a critical assessment and outlook of technical challenges and research opportunities for future was proposed.