Preparation And Photocatalytic Property Of Graphene Oxide/Zinc Oxide Based Composites

ZnO has become a potential photocatalyst due to its bandgap similar with that of TiO2, low cost and non-toxic. However, ZnO suffers from two major drawbacks:the high recombination rate of electron-hole pairs and the high band-gap energy, resulting in limiting its application. Graphene, a two-dimensional (2D) one-atom-thick planar sheet of sp2-bonded carbon atoms, has attracted a tremendous amount of attention owing to its extraordinarily high electrical conductivity and large specific surface area, which is considered a promising 2D carrier or a building block for nanocomposites to improve their photocatalytic property. In this paper, we aimed at resolving these problems in the prepared process of GO/ZnO composites catalysts and enhancing the photocatalytic performance of GO/ZnO composites. Three strategies were designed:(1) the size of ZnO nanoparticles were controlled and loaded on graphene by using sodium citrate, resulting in increasing surface area of ZnO nanoparticles; (2) the spectral response range of ZnO were expanded by doping magnesium and modifying the band structure of ZnO; (3) the heterojunction structure between ZnO and Bi2O3 were built, in order to promote the separation of electron-hole pairs and expand the scope of the absorbable wavelength of ZnO. The main investigatory results were as follows:(1) The GO/ZnO composites were prepared by the coprecipitation method with GO and Zn(CH3COO)2 as raw materials, and their structure and morphology were investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), respectively. Furthermore, their photocatalytic property was analyzed. The results showed that sodium citrate had a significant effect on the controllable size of ZnO nanoparticles. When the content of sodium citrate was 0.72 mmol, the size of ZnO coated GO was about 5 nm. The photocatalytic activity of GO/ZnO composite was estimated by degrading methyl orange (MO) under the UV light. It is found that, when the GO content in composite powder was 0.51%, the photocatalytic activity of GO/ZnO composite with 5 nm size of ZnO nanoparticle was the best than that of others, of which the photocatalytic degradation rate for MO came up to about 100% in 120 min.(2) With GO, Zn(CH3COO)2 and Mg(CH3COO)2 as raw materials, C2H5OH as a solvent, C2H2O4 as a precipitant, GO/MgxZn1-xO composites were developed using the coprecipitation method. The structure and morphology of GO/MgxZn1-xO composites were investigated by XRD, X-ray photoelectron spectroscopy (XPS), SEM and TEM, respectively. Moreover, the photocatalytic property was analyzed. The results indicated that the nanoparticles were loaded on GO, and the band gap of ZnO could be changed by doping magnesium from 3.26 eV to 3.44 eV. According to the photocatalytic activity, doping Mg could improve the photo-degradation efficient of GO/ZnO composites significantly, and the Mg content in GO/MgxZn1-xO composites had a little influence on photocatalytic properties. When the content of GO was 1.85%, and the temperature was 600 ℃, the photocatalytic activity of GO/MgxZn1-xO composite had an excellent performance. Methyl orange was degraded completely within 60 min under the UV irradiation.(3) GO/ZnO-Bi2O3 heterojunction catalyst was synthesized by hydrothermal method with Zn(CH3COO)2 and Bi(NO3)3 as raw materials and cetyl trimethyl ammonium bromide (CTAB) as a surfactant. The structure and morphology of GO/ZnO-Bi2O3 heterojunction catalyst were investigated by XRD, SEM and TEM, and the photocatalytic property was evaluated. The results showed GO/ZnO-Bi2O3 catalyst was composed of ZnO and Bi2O3 phases. ZnO and Bi2O3 formed nano lamellar structure on GO sheet. The UV-vis spectrum indicated that the heterojunction was benefited to the red shift of adsorption band. When the content of graphene was 5.4%, bismuth nitrate concentration was 45.9%, pH value was 5 and the temperature is 110 ℃, both of adsorption and degradation ability of resultant samples possessed excellent performances. The absorbed ability of resultant samples for rhodamine B came up to about 74.62% within 30 min, and Rh B was completely degraded in 30 min under UV light. Moreover,90% RhB in solution could be degraded within 100 min under visible light.