Study On The Preparation And Photocatalytic Activity Of BiOX/g-C₃N₄

The bismuth oxyhalide（BiOX,X=Cl,Br,I）,as a new semiconductor photocatalyst,has become one of the research hotspots in recent years due to its unique layered structure.However,the photocatalytic performance of pure Bi OX is poor due to its limited light absorption,unsuitable band gap,and low separation efficiency of photogenerated carriers.Therefore,in the thesis,Bi OBr was used as the research object to improve the photocatalytic performance by constructing heterojunction with graphite carbon nitride（g-C₃N₄）and Bi OI.The main results are as follows:A series of graphitic carbon nitrides（g-C₃N₄）were prepared by thermal polymerization method through adjusting the ratio of urea and melamine（10:0,8:2,6:4,5:5,4:6,0:10）,and the calcination temperature（550°C,575°C,600°C,625°C）.The structure and morphology of the samples were investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,and BET specific surface area analyzer（BET）.The results showed that g-C₃N₄ materials with periodic arrangement of heptaazine rings were prepared under the above conditions.The yield of g-C₃N₄ prepared at 575℃was the highest when the used precursor was pure urea,and its degradation rate reaches 30.91%to 15 mg/L methyl orange（MO）.By exploring the photocatalytic degradation mechanism,it could be seen that OH is the main active species during the process of g-C₃N₄ sample degradating MO.Pure BiOBr was prepared by precipitation method using tetra-propyl ammonium bromide as bromine source.And the binary composite Bi OBr/x%g-C₃N₄（Bi OBr/x%CN,x=0.05,0.1,1 or 3）heterojunction was prepared by in situ compositing g-C₃N₄.The successful preparation of the composite was proved by XRD,FT-IR,XPS,EDS and other characterization methods.The morphology of the sample was observed by SEM and TEM methods,which showed nanometer sheets structure.The photocatalytic activity of the catalysts was evaluated by selecting 20 mg/L of MO as the target pollutant.The results showed that the photocatalytic activity of Bi OBr/0.1%CN is better,its degradation rate was41.06%higher than that of pure Bi OBr,and h⁺plays an important role in the degradation process.Furthermore,the photocatalytic nitrogen fixation performance of Bi OBr/0.1%CN was studied,which was 39.74%higher than that of pure Bi OBr.The improvement of photocatalytic performance of Bi OBr/0.1%CN heterojunctions was mainly due to the fact that the construction of S-scheme heterojunctions reduced the recombination rate of the photo-generated electron-hole and accelerated the transport rate of carriers.Using sodium iodide as iodine source,the ternary composites Bi OBr/Bi OI/0.1%CN and Bi OBr/Bi OI/0.1%CNH heterojunction were prepared by in situ compositing Bi OBr,Bi OI and g-C₃N₄（CN）or HNO₃ modified g-C₃N₄（CNH）by precipitation method.The characterization of structure and morphology showed that the ternary composites were successfully prepared and showed nanosheets-assembled flower-like structure.Different pollutants（MO,rhodamine B（Rh B）,risamine rhodamine B（LRB）,methylene blue（MB）,Cr（VI））were used as simulated pollutants.The photocatalytic activity of Bi OBr/Bi OI/0.1%CN was better than that of Bi OBr/0.1%CN under visible light towards the above-selected pollutants.The reason was that the absorption range of ternary composite towards visible light was wider than that of binary composite and the separation and transport efficiency of photogenerated electron-hole was higher.And the photocatalytic performance of Bi OBr/Bi OI/0.1%CN was more excellent than that of similar materials reported recently...