Background Hydrogen gas (H-2) has been identified as a potential energy source to reduce the dependence on fossil fuels. Titanium dioxide (TiO2) semiconductor has been widely used in photocatalysis. Doping of different semiconductor oxides into TiO2 has been documented to enhance its photocatalytic activity. In the present work, beta-Ga2O3/TiO2 (TG) photocatalysts for H-2 production by water/methanol mixture decomposition have been synthesized by the sol-gel method varying the beta-Ga2O3 content (3%, 5% and 10% w/w). The catalysts were characterized by X-ray diffraction, nitrogen adsorption, ultraviolet (UV)-visible diffuse reflectance, Fourier-transform infrared spectroscopy, scanning electron microscopy and photoluminescence analysis. Results An excellent activity for H-2 production under UV light (I-0 = 2.0 mW cm(-2), lambda = 254 nm) was detected in TG composites. Experimental results indicated that the maximum H-2 production rate was 1217 mu mol g(-1) during 5 h of reaction and the TG5 photocatalyst was observed to have a higher activity for photocatalytic H-2 evolution than pure Ga2O3 and Pt/TiO2 (TPt) test material. Moreover, a possible mechanism of charge separation in the composite under UV light irradiation was proposed. Conclusions The H-2 improved activity of TG5 can be attributed to low charge recombination of the e(-)-h(+) pairs that improves the interfacial charge transfer, which is in agreement with the photoluminescence study. (c) 2019 Society of Chemical Industry