Promotion of phenol photodecomposition and the corresponding decomposition mechanism over g-C3N4/TiO2 nanocomposites

Composite photocatalysts containing TiO2 nanoparticles grown on nanosheet-structured graphitic carbon nitride (g-C3N4) were synthesized using a facile calcination approach. A series of g-C3N4/TiO2 nanocomposites was prepared by varying the amount of the urea precursor from 1 g to 5 g. The as-prepared catalysts were characterized by X-ray diffraction; scanning electron microscopy; N-2 adsorption-desorption isotherm analysis; and Fourier transform infrared, X-ray photoelectron, and UV-Vis spectroscopies. The results revealed that small TiO2 particles were well dispersed on the surface of the g-C3N4 nanosheets. Compared with pure TiO2 nanoparticles, the obtained g-C3N4/TiO2 nanocomposites showed enhanced photocatalytic activity toward the degradation of phenol as a result of improved separation of photogenerated electrons and holes derived from the synergistic interaction of TiO2 and g-C3N4. The g-C3N4/TiO2 composite prepared with 4 g of urea precursor showed the best photocatalytic performance toward phenol decomposition with a degradation rate of 99.4%. It was found that during the degradation process, p-benzoquinone, catechol, and hydroquinone were generated; hydroquinone was identified as the main intermediate product. Furthermore, mechanisms were proposed to explain the electron-hole separation and transport over the g-C3N4/TiO2 photocatalyst as well as phenol degradation under ultraviolet light irradiation.