Hydrothermal synthesis of graphene/Fe3+-doped TiO2 nanowire composites with highly enhanced photocatalytic activity under visible light irradiation

In this study, a hydrothermal method was employed to synthesize Fe3+-doped TiO2 nanowires (Fe-NWs) followed by the fabrication of graphene/Fe3+-doped TiO2 nanowire composites (GR/Fe-NWCs). Graphene oxide (GO) was reduced to reduced graphene oxide (RGO), which was uniformly covered with a large number of anatase Fe-NWs simultaneously. As controls, TiO2 Degussa P25 nanoparticles (NPs) were converted to TiO2 nanowires (NWs) by an alkaline hydrothermal process, and graphene/TiO2 nanoparticle composites (GR/NPCs) and graphene/TiO2 nanowire composites (GR/NWCs) were also synthesized by the hydrothermal method. The obtained samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, electron spin resonance (ESR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results confirmed the graphene nature of RGO in the GR/Fe-NWCs and Fe3+ doping into NWs. Additionally, it was found that Fe3+ doping could improve the response of TiO2 nanowires under visible light irradiation and that Fe-NWs have more uniform dispersion on graphene with less agglomeration in comparison with NPs, resulting in more direct contact between TiO2 and graphene, and hence further improved electron-hole pair separation and transportation. The photocatalytic performance of GR/Fe-NWCs was evaluated for the photodegradation of methylene blue (MB) under visible light. The GR/Fe-NWCs showed the highest photocatalytic activity among the tested photocatalysts, with about a 3-fold increase in photocatalytic efficiency over NPs. The mechanism of high photocatalytic activity was also discussed.