Gallium oxide nanoparticles prepared through solid-state route for efficient photocatalytic overall water splitting
Gallium oxide (Ga2O3) is one of the most efficient photocatalysts for the overall water splitting. Doping with appropriate metal cations substantially boosts the quantum yield to split water into H2 and O2. In this research, Ga2O3 nanoparticles in the β polymorph (β-Ga2O3) are successfully prepared through a solid-state route under heat treatment. The size of the photocatalyst particles is sufficiently small to shorten the migration distance of the photoexcited charge carriers from the bulk to the surface. To beneficially modify the bulk state of β-Ga2O3, doping with various metals including alkaline-earth metals and first row transition metals is performed. The alkaline-earth metal cations generally increase the water splitting activity. On the other hand, the first row transition metal cations decrease the activity, except for Zn. No systematic trend is observed on the water splitting activity of β-Ga2O3 doped with metal cations in the same group or in the same period. The oxidation state of the dopants plays a role in dictating the water splitting activity. Doping with metal cations having oxidation states lower and higher than that of Ga increases and decreases the activity, respectively. In particular, doping with Zn considerably increases the water splitting activity. At a Zn amount of 1 mol% in the presence of Rh0.5Cr1.5O3 (0.5 wt% Rh) co-catalyst, the H2 and O2 evolution rates can reach as high as 400 and 195 μmol h―1, respectively, with a H2/O2 molar ratio of 2 under UV irradiation with an average intensity of 58 mW cm−2 at 254 nm.