Preparation And Photocatalytic Properties Of Modified TiO₂/Graphene Composites

With the development of modern industrialized society, a variety of organic pollutants has been produced, which causes serious environmental pollution. Ti O2 is one of the most widely investigated semiconducting photocatalyst and is used in a wide range of applications. However, with its 3.2 e V electronic band gap, Ti O2 is only sensitive to the light wavelengths below 387 nm which belong to the UV range, less than 5% of the total energy of sunlight. Besides, the photogenerated electron-hole pairs, which are mainly responsible for the photocatalytic activity, have faster recombination rates, reducing the photocatalytic efficiency greatly. At the same time, the adsorption capacity for pollutants of the catalytic is also an important factor to effect photocatalytic activity of the catalyst in the photocatalytic process. Therefore, to improve the adsorption capacity of the catalyst is beneficial for improving the photocatalytic activity of the catalyst. Thus, in order to overcome the limitations of traditional Ti O2 photocatalyst, preparation and photocatalytic properties of modified Ti O2/graphene composites were carried out in this paper. Details are as follows:1. Synthesis and Photocatalytic Activity of Graphene/S-Doped Ti O2 Composites. Firstly, S-doped Ti O2(S-Ti O2) was synthesized by the hydrothermal method, and graphite oxide was synthesized from natural flake graphite by a modified Hummer’s method. Then graphene/S-doped Ti O2 Composites(GR/S-Ti O2) were prepared by hydrothermal reaction of graphene oxide(GO) and S-Ti O2. The obtained samples were characterized by scanning electron microscope(SEM), X-ray diffraction(XRD), Raman, FTIR and Photoluminescence(PL) spectrum, and the photocatalytic performance of the samples was evaluated for the photodegradation of methylene blue(MB) under visible light. Compared with S-Ti O2, GR/S-Ti O2 showed higher adsorption capacity for the contaminants and lower recombination rates of photogenerated electron-hole pairs. And the photocatalytic efficiency of GR/S-Ti O2 in degrading methylene blue is about once higher than that of S-Ti O2.2. Synthesis and Photocatalytic Activity of Graphene/Fe3+-Doped Ti O2 Nanowire Composites. The hydrothermal method was employed to synthesize Fe3+-doped nanowires(Fe-NWs) and then fabricate graphene/Fe3+-doped Ti O2 nanowire composites(GR/Fe-NWCs). Graphene oxide(GO) was reduced to the graphene nature of reduced graphene oxide(RGO), which was uniformly covered with a large number of anatase Fe-NWs simultaneously. As controls, Ti O2 Degussa P25 nanoparticles(NPs) were converted to Ti O2 nanowires(NWs) by an alkaline hydrothermal process, graphene/Ti O2 nanoparticle composites(GR/NPCs) and graphene/Ti O2 nanowire composites(GR/NWCs) were also synthesized by the hydrothermal method. The obtained samples were characterized by scanning electron microscope(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), Raman, Fourier Transform Infrared(FTIR), UV-vis diffuse reflectance spectroscopy(DRS), Photoluminescence(PL) spectra, electron spin resonant(ESR) spectra and X-ray photoelectron spectroscopy(XPS). According to the results, we 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 Ti O2 nanowire 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 Ti O2 and graphene, and hence further improve 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 tested photocatalysts, with about 3-fold enhancement in photocatalytic efficiency over NPs. The mechanism of high photocatalytic activity was also discussed.