Effects of calcining temperature on photocatalysis of g-C3N4/TiO2 composites for hydrogen evolution from water

A composite of graphitic carbon nitride and TiO 2 (g-C 3 N 4 /TiO 2 ) with enhanced photocatalytic hydrogen evolution capacity was achieved by calcining melamine and TiO 2 sol-gel precursor. Characterization results reveal that heating temperature had a great influence on the structure, surface area and properties of the composites. Compared with the polycondensation of pure melamine, the presence of TiO 2 precursor can promote the formation of melon at a low temperature. The highest photocatalytic activity of g-C 3 N 4 /TiO 2 (400) was achieved when the calcination was performed at 400   °C, exhibiting H 2 production rate of 76.25   μmol/h under UV–vis light irradiation (λ   >   320   nm) and 35.44   μmol/h under visible light irradiation (λ   >   420   nm). The highest photocatalytic performance of g-C 3 N 4 /TiO 2 (400) can be attributed to: (1) the strong UV–vis light absorption due to the narrow bandgap caused by synergic effect of TiO 2 and g-C 3 N 4 , (2) high surface area and porosity, (3) the effective separation of photo-generated electron-holes owing to the favorable heterojunction between TiO 2 and g-C 3 N 4 .