Hydrogenated black-TiOx: A facile and scalable synthesis for environmental water purification

In the last few years, intense efforts have been devoted to the development of new photoactive materials for solar-driven water purification. In particular, the black-TiOx has attracted growing interest demonstrating the required capabilities. We report on the synthesis, characterization and application of hydrogenated-black titanium oxide films for photocatalytic water treatment. Moreover, we compared different experimental conditions in order to maximise the photocatalytic activity of the material while maintaining an industrially compatible and green synthesis approach. The scalability and robustness of the procedure is further demonstrated by using different lasers: a 1064 nm laser, a 532 nm laser at low repetition rate and a 532 nm high repetition rate laser at different scan speeds. The morphology of the irradiated surfaces depends on the laser wavelength, while light adsorption in both UV and visible range is higher than 85% in every case. Amorphous and highly hydrogenated phases were found to be the most abundant although sub-stoichiometric crystalline oxides (TiO and Ti2O3) are also found depending on the laser used. Owing to the presence of a metallic Ti support, a monolithic photochemical diode is realised by depositing a film of Pt nanoparticles on the back-side of the samples. Photocatalytic activity tests reported high degradation rates for methylene blue dye with a maximum quantum efficiency of 0.054% observed on the sample irradiated with the 532 nm laser. Short and long-term photo-stability was investigated resulting in a good reliability of the manufactured diode.