Rational design and fabrication of TiO2 nano heterostructure with multi-junctions for efficient photocatalysis

In addition to the extended light absorption, the effective spatial charge separation is a crucial factor for highly efficient metal-oxide semiconductor-based photocatalysts. Herein, a rational design of metal-semiconductor-metal nano heterostructure for enhancing photocatalytic performance is proposed. The semiconductor nanoparticles are integrated with two metals in one single nano heterostructure. The disordered layers are induced on the surface of TiO2 to promote the light absorption capacity. More importantly, the n-n(+) junction is fabricated at the contact region between crystalline TiO2 (n-TiO2) and disordered layers (n(+)-TiO2). Besides, the Schottky diode and Ohmic contact are formed on n-TiO2 and n(+)-TiO2, respectively. As a result, the existence of multi-junctions leads to the formation of multiple continuous built-in electric fields, thus remarkably accelerating the spatial separation of charge carriers. The resulting nano heterostructure with multi-junctions (Pt-TiO2-H-Ag) exhibits remarkably promoted photocatalytic performance. The maximum hydrogen generation rate of Pt-TiO2-H-Ag under solar illumination (18001.0 mu mol/h/g) is 8.3, 9.3, and 1.5 times superior to that of Pt-loaded P25 (Pt-P25), Pt loaded TiO2 (Pt-TiO2), and hydrogenated Pt-TiO2 (Pt-TiO2-H), respectively. Moreover, the photocatalytic performance under visible illumination is significantly enhanced by Pt-TiO2-H-Ag. Specifically, the H-2 generation rate of Pt-TiO2-H-Ag (2382.7 mu mol/h/g) is about 15.1, 17.2, and 1.4 times higher than that of Pt-P25, Pt-TiO2, and Pt-TiO2-H, respectively. The corresponding apparent quantum efficiency of Pt-TiO2-H-Ag is 15.8% (420 nm). The nano heterostructure with multi-junctions also exhibits excellent stability after five cycles, remaining hydrogen evolution rates of 15581.5 and 2211.4 mu mol/h/g under solar and visible illumination, respectively. This effective and controllable manufacturing strategy could provide new opportunities to simultaneously extend optical absorption and facilitate the spatial charge separation and transport of wide-bandgap metal-oxide semiconductors. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.