Properties and photocatalytic applications of black TiO2 produced by thermal or plasma hydrogenation

TiO₂ nanomaterial photocatalysts for energy and environmental applications have attracted the interest of researchers in recent decades. The broad bandgap (3–3.2 eV), which limits the quantity of light absorption, and the relatively high charge-carrier recombination, which limits photocatalytic activity, are the key bottlenecks. The discovery of black TiO₂ in 2011 sparked global research attention and renewed optimism for solving this challenge. The presence of defects such as Ti³⁺ species and oxygen vacancies at the surface of black TiO₂ nanostructures – so called due to the color assumed by the oxide following a reduction process - is responsible for enhancing the optical absorption of UV to visible light. This review focuses on recent advancements in the development of black TiO₂ nanomaterials, including description of the synthesis processes, focused on plasma and thermal methods to convert TiO₂ to black TiO₂, discussion of black TiO₂ properties, and diverse applications of black TiO₂, and concludes by addressing some essential concerns that must be tackled to unleash the desired future developments, particularly for solar energy production and pollutants decomposition.