A Review of the Single-Step Flame Synthesis of Defective and Heterostructured TiO₂ Nanoparticles for Photocatalytic Applications

Titanium dioxide (TiO₂) is an excellent UV-photocatalytic material that is widely used in various applications, including clean energy production, environmental remediation, and chemical production. However, the use of TiO₂ is limited in the field of visible light photocatalysis due to its large bandgap and fast recombination rate between electron and hole pairs, which generally results in a low photocatalytic reaction. Defect/bandgap engineering by doping and the introduction of heterojunctions has been successfully employed to improve the photocatalytic activities of TiO₂ over a wide wavelength. To apply the unconventional structured TiO₂ with high photocatalytic performance to industries, the development of efficient methods for large-scale production is of high importance. Flame synthesis is a very promising method for the rapid production of nanoparticles. In this article, we summarize the latest reports on the synthesis of defective and heterostructured TiO₂ using the single-step method of flame synthesis. Fundamental understandings of reactor configurations, synthesis conditions, precursor preparation and their physicochemical properties are intensively discussed.