Laser irradiation in water for the novel, scalable synthesis of black TiO_x photocatalyst for environmental remediation

Since 1970, TiO₂ photocatalysis has been considered a possible alternative for sustainable water treatment. This is due to its material stability, abundance, nontoxicity and high activity. Unfortunately, its wide band gap (≈3.2 eV) in the UV portion of the spectrum makes it inefficient under solar illumination. Recently, so-called “black TiO₂” has been proposed as a candidate to overcome this issue. However, typical synthesis routes require high hydrogen pressure and long annealing treatments. In this work, we present an industrially scalable synthesis of TiO₂-based material based on laser irradiation. The resulting black TiO_x shows a high activity and adsorbs visible radiation, overcoming the main concerns related to the use of TiO₂ under solar irradiation. We employed a commercial high repetition rate green laser in order to synthesize a black TiO_x layer and we demonstrate the scalability of the present methodology. The photocatalyst is composed of a nanostructured titanate film (TiO_x) synthetized on a titanium foil, directly back-contacted to a layer of Pt nanoparticles (PtNps) deposited on the rear side of the same foil. The result is a monolithic photochemical diode with a stacked, layered structure (TiO_x/Ti/PtNps). The resulting high photo-efficiency is ascribed to both the scavenging of electrons by Pt nanoparticles and the presence of trap surface states for holes in an amorphous hydrogenated TiO_x layer.