Visible Light-Responsive N-Doped TiO2 Photocatalysis: Synthesis, Characterizations, and Applications

Photocatalysis based on semiconductors has recently been receiving considerable research interest because of its extensive applications in environmental remediation and renewable energy generation. Various semiconductor-based materials that are vital to solar energy utilization have been extensively investigated, among which titanium oxide (TiO2) has attracted considerable attention because of its exceptional physicochemical characteristics. However, the sluggish responsiveness to visible light in the solar spectrum and the inefficient separation of photoinduced electron–hole pairs hamper the practical application of TiO2 materials. To overcome the aforementioned serious drawbacks of TiO2, numerous strategies, such as doping with foreign atoms, particularly nitrogen (N), have been improved in the past few decades. This review aims to provide a comprehensive update and description of the recent developments of N-doped TiO2 materials for visible light-responsive photocatalysis, such as (1) the preparation of N-doped/co-doped TiO2 photocatalysts and (2) mechanistic studies on the reasons for visible light response. Furthermore, the most recent and significant advances in the field of solar energy applications of modified N-doped TiO2 are summarized. The analysis indicated the critical need for further development of these types of materials for the solar-to-energy conversion, particularly for water splitting purposes.