In situ synthesis of g-C3N4/TiO2 heterojunction nanocomposites as a highly active photocatalyst for the degradation of Orange II under visible light irradiation.

As a highly active photocatalyst, g-C3N4/TiO2 heterojunction nanocomposites were in situ synthesized by simple ultrasonic mixing and calcination by using TiO2 and melamine as precursors. The morphology and structure of the prepared photocatalysts were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, UV-Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of g-C3N4/TiO2 nanocomposites to degrade Orange II (AO7) under visible light irradiation were evaluated. Results showed that the photocatalytic rate of the prepared g-C3N4/TiO2 photocatalyst to degrade AO7 was about three times than that of pristine TiO2 and g-C3N4. The g-C3N4/TiO2 composite with a ratio of 1:4 had the highest degradation efficiency for AO7 solution. Its degradation efficiency under acidic conditions was significantly higher than that under alkaline conditions. The enhancement of photocatalytic activity can be attributed to the formation of heterojunctions between g-C3N4 and TiO2, which leads to rapid charge transfer and the efficient separation of photogenerated electron-hole pairs. The recycling experiment indicated that the photocatalyst of g-C3N4/TiO2 nanocomposites still maintained good photochemical stability and recyclability after five cycles; this finding was important for its practical applications. A series of free radical trapping experiments showed that •O2- played a crucial role in the degradation of AO7. Graphical Abstract ᅟ.