Pd–TiO2–SrIn2O4 heterojunction photocatalyst: enhanced photocatalytic activity for hydrogen generation and degradation of methylene blue

A novel heterojunction photocatalyst of TiO2-SrIn2O4 is found to be active for hydrogen generation from water as well as for the degradation of methylene blue under sunlight type radiation. Photocatalytic activity for hydrogen generation increases with increase in SrIn2O4 concentration and the optimum concentration is found to be 40% (by weight). The presence of a Pd co-catalyst enhances the photocatalytic activity and the catalyst is found to be stable after repeated cycles of photocatalysis experiments. A higher rate of degradation of methylene blue is observed when the composite is used as photocatalyst compared to pure TiO2 and SrIn2O4. Detailed characterization of the composite revealed that TiO2 exists as a dispersed phase on SrIn2O4 and the particle size of TiO2 and TiO2-SrIn2O4 is around 20 nm and 15 nm, respectively. Photocurrent experiments show a relatively higher current output for the composite compared to pure TiO2. The enhanced photocatalytic activity of the composite is attributed to a synergistic effect of the increased lifetime of the charge carriers in the composite and increased surface area of the sample. The dispersion of TiO2 nanoparticles on SrIn2O4 results in the formation of hetero-junctions between TiO2 and SrIn2O4 leading to efficient interfacial transfer of photogenerated electrons from TiO2 to SrIn2O4 and enhancing the lifetime of the charge carriers. The Pd co-catalyst enhances the activity of the composite further by increasing the availability of electrons in it and providing active sites for hydrogen evolution.