Facile in situ synthesis of graphitic carbon nitride (g-C3N4)-N-TiO2 heterojunction as an efficient photocatalyst for the selective photoreduction of CO2 to CO

Abstract A series of composites of graphitic carbon nitride and in situ nitrogen-doped titanium dioxide (g-C 3 N 4 -N-TiO 2 ) were prepared by a simple pyrolysis process of urea and Ti(OH) 4 . The obtained products were characterized by means of X-ray diffraction, FT-IR transmission spectroscopy, electron microscopy, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, etc. Compared with g-C 3 N 4 and commercial P25, the as-prepared photocatalysts exhibit enhanced photocatalytic performance for photoreduction of CO 2 in the presence of water vapor at room temperature. It was found that the mass ratios of urea to Ti(OH) 4 in precursors play a role in formation of the composites, and the high ratios of urea to Ti(OH) 4 result in the composites of g-C 3 N 4 and N-doped TiO 2 , while low ratios only result in N-doped TiO 2 . An interesting selectivity of photocatalytic products displayed that N-doped TiO 2 samples were related to CH 4 and CO generation, while g-C 3 N 4 and N-TiO 2 composites were related to CO generation, and the product selectivity may originate from the formed g-C 3 N 4 . The highest amount of CO (14.73 μmol) was obtained on the optimized photocatalyst under 12 h light irradiation, which is four times of that over commercial P25. Based on these results, a possible mechanism for the enhanced photocatalytic performance was proposed.