Visible-light enhancement of methylene blue photodegradation by graphitic carbon nitride-titania composites

Composites of graphite-like C 3 N 4 (g-C 3 N 4 ) and TiO 2 were synthesized by direct heating of melamine in the presence of different TiO 2 amounts in a semi-closed stainless steel container. The resulting samples were characterized using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (DRS), photoluminescence spectrum (PLS), thermogravimetric analysis , scanning electron microscopy, and transmission electron microscopy techniques. The results reveal that the microstructure and DRS and PLS characteristics of the composites vary with the composition. XPS Ti 2p peaks for the composites exhibit a shift to lower binding energy in comparison to pure TiO 2 . The photocatalytic degradation properties of the composites were evaluated using methylene blue (MB) as a model compound under visible light irradiation (400–600   nm). The results indicate that photocatalytic degradation of MB is higher for g-C 3 N 4 –TiO 2 composites with optimum TiO 2 content (26.4 and 80.0   wt%) than for pure g-C 3 N 4 or TiO 2 . Moreover, the activity of an optimum composite sample was still as high as 91% after use in four consecutive photocatalytic cycles.