| Photocatalysis based on semiconductor catalysts is a new way to efficiently utilize solar energy. It`s a technolygy with wide application prospect in many field, including water splitting and pollutant degradation. As the photocatalysts studied originally were most of wide band semicondutors which could only use ultraviolet light, researchers pay more attention on visible-light-induced semiconductor materials in these years. Graphite carbon nitride(g-C3N4) is one of the important visible-light-induced photocataysts. It has been widely studied due to its excellent performances such as appropriate band edge potentials, stable molecule structure and performances, nontoxicity. However, like many ohther single semiconductor materials, g-C3N4 also has high recombination efficiency of photogenerated electron-hole pairs, which could reduce the photoactivity dramatically. On the other hand, the low specific surface area resulting in the low adsorption capacity could also limite the applications of g-C3N4.Forming heterojunctions with other materials is an efficient way to broaden the absorption region in sunlight energy spectrum and suppress the recombination of photo-generated carriers of g-C3N4. In this study, we fabricated g-C3N4 by directly heating melamin in middle temperature. The microstructure, morphology and optical properties of the synthesized g-C3N4 based hybrid catalysts were characterized using X-ray diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), infrared spectroscopy(FT-IR), UV–Vis diffuse reflection spectroscopy(DRS) and photoluminescence(PL) emission spectroscopy. The photoactivity of the g-C3N4 based hybrid catalysts was evaluated by photodegradation of Rhodamine B(Rh B) and some other dyes from water as a model toxic contaminant under visible light irradiation. We discussed the influence of g-C3N4 content on the photodegradation efficiency and determine the optimum parameter.The main results and conclusions in this study are summarized as following:(1) The g-C3N4/Bi OX(X=Cl, Br, I) composite catalysts were fabricated by hydrolysis. g-C3N4 could improve the photo-activity of Bi OCl efficiently and the g-C3N4/Bi OCl composite photocatalyst has a degradation rate 1.3-folder than Bi OCl. However, for the narrow bandgap semiconductor Bi OBr and Bi OI, g-C3N4 based composite catalysts didn’t have an enhancement in photoactivit y.(2) We studied the photo-degradation kinetics of the g-C3N4/Bi OCl hybrid catalysts with different g-C3N4 content. The optimal g-C3N4 content is 0.2 and the hybrid g-C3N4/Bi OCl(x=0.2) sample could degrade 90% Rh B molecules in 20 min. The ARR is 1.3-folder than pure Bi OCl and g-C3N4. Reslults also showed that the LUMO energy of dye has an effect on the degradation rate of the hybrid catalysts. Higher LUMO energy of dye could help the catalyst have a faster photo-degradation rate.(3) The g-C3N4/Bi OClxBr1-x hybrid catalysts were prepared by hydrolysis. The doping ratio of Cl could affect the band gap of Bi OClxBr1-x solid solution. When x value is lower than 0.8, the solid solution has a wide band gap and the photo-activity of the hybrid catalyst has more enhancement. Bi OCl0.8Br0.2 has a narrow band gap, which could make the sample absorb visible light. The g-C3N4/Bi OCl0.8Br0.2(w=0.2) composite catalysts has the best photocatalytic activity with a ARR of about 1.322 μmol min-1 g-1.(4) The WO3/g-C3N4 composite catalysts were prepared by directly heating H2WO4/g-C3N4 mixed powders. When using Rh B as the model contaminate, the optimal ratio of WO3 is 0.1. The WO3/g-C3N4-0.1 has a degradation rate of 0.0108min-1, 3.4 and 2.2-folder of g-C3N4 and WO3 respectively. In addition, WO3/g-C3N4-0.1 hybrid catalyst has a better photocatalytic performance than some traditional photocatalysts. |
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