Synthesis of a nitrogen-doped titanium dioxide–reduced graphene oxide nanocomposite for photocatalysis under visible light irradiation

Abstract

A nitrogen-doped titanium dioxide–reduced graphene oxide (N-TiO2–RGO) nanocomposite has been synthesized by the combination of a hydrothermal method and a thermal treatment under a NH3/N2 atmosphere. The resulting composites are characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, diffuse reflectance absorption spectroscopy, energy-dispersive X-ray spectroscopy, and Raman characterization techniques. The sequence of the thermal treatment and hydrothermal treatment processes is shown to influence the photocatalytic activity of nitrogen-doped composites. The composites synthesized by using this method show better photocatalytic activities toward the degradation of acetaldehyde under visible light irradiation compared with P25, N-TiO2, and TiO2–RGO. By applying the thermal treatment process after the hydrothermal process, nitrogen atoms can be simultaneously doped in the lattice of TiO2 nanoparticles and on the surface of reduced graphene oxide sheets. The conversion of acetaldehyde, as the model molecule of volatile organic compounds, is measured in a continuous stirred-tank reactor until the steady state condition is reached. The conversion of 50ppm acetaldehyde, in an air flow under illumination from an 80W Hg lamp with a UV cut-off filter, reaches 62% after a 1-h reaction using a 0.07g N-TiO2–RGO sample with an optimum loading of 2wt% graphene oxide. In comparison, the photocatalytic activity of P25 for the degradation of acetaldehyde under visible light irradiation is only 8% under the same reaction conditions. The reaction rates for acetaldehyde degradation are calculated and predicted with pseudo-first-order reaction kinetics, and the activity result of the best N-TiO2–RGO sample is 12.3 times higher than for P25.