Preparation and Photocatalytic Properties of N-Doped Graphene/TiO2 Composites

N-doped graphene (NG)/TiO2 composites were prepared by a two-step hydrothermal method using HF as the surface etchant and urea as the nitrogen source. The morphology, structure, and bonding conditions of the NG/TiO2 composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and photoluminescence (PL) spectroscopy. The effects of NG on the lifetime of photogenerated electron-hole pairs, adsorption capacity, and photocatalytic activity of the composite photocatalysts were also investigated. The photocatalytic activity was evaluated under ultraviolet light and sunlight irradiation. The recovery testing was completed under ultraviolet light irradiation. The results show that TiO2 was uniformly loaded on the NG surface by chemical bonding. The introduction of NG effectively inhibited the recombination of photogenerated electron-hole pairs and improved both the adsorption capacity and photocatalytic activity of the composites. The 7 wt % NG/TiO2 showed the best adsorption capacity of methyl orange (MO). The best photocatalytic activity occurred for 5 wt % NG/TiO2 composites, and after four recovery tests, the photocatalytic degradation of MO under 60 min ultraviolet light irradiation exceeded 90%.