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

• TiO2 promotes melon to form at 400 °C, whereas it forms at 500 °C for only melamine.
• The highest photocatalytic activity was achieved when calcination was performed at 400 °C.
• Coordinated NTiN bonds were formed in MA/TiO2 (400) and disappeared at high temperature.
• The surface area decreased and the pore size increased with increasing of temperature.
• Only MA/TiO2 (400) has a narrower band gap than pure g-C3N4.

A composite of graphitic carbon nitride and TiO2 (g-C3N4/TiO2) with enhanced photocatalytic hydrogen evolution capacity was achieved by calcining melamine and TiO2 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 TiO2 precursor can promote the formation of melon at a low temperature. The highest photocatalytic activity of g-C3N4/TiO2(400) was achieved when the calcination was performed at 400 °C, exhibiting H2 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-C3N4/TiO2(400) can be attributed to: (1) the strong UV–vis light absorption due to the narrow bandgap caused by synergic effect of TiO2 and g-C3N4, (2) high surface area and porosity, (3) the effective separation of photo-generated electron-holes owing to the favorable heterojunction between TiO2 and g-C3N4.

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