Preparation And Photocatalytic Properties Of Bismuth Oxyhalide Matrix Composites

With the rapid development of nuclear chemical industry,electroplating catalysis industry and rinsing and dyeing industry,a large number of pollutants such as radioactive nuclear industrial wastewater,high-concentration heavy metal wastewater,and refractory biochemical waste are accumulated in the human living environment.It not only brings devastating disasters to the natural ecological balance,but also has a significant impact on the living environment of human beings.On the other hand,the utilization rate of resources and energy by human beings is very low,especially the exploitation of non-renewable resources is increasing,but the progress of developing new renewable energy is very slow.If this situation is not improved,human beings will face the double blow of insufficient energy supply and plummeting living environment quality in the future.As far as the water environment is concerned,the problem that we urgently need to solve is to eliminate pollutants in the water environment.Among the water pollution sources,the dye waste exceeds 2 million tons,which has become one of the important pollution sources in the water environment.Starting from bismuth oxyhalide-based nano-semiconductor materials and zeolite-like imidazole framework compounds（ZIF-67）,the following researches were carried out:（1）In order to realize the treatment of organic dye wastewater,experiments were designed to explore the preparation process of BiOX₁/BiOX₂.Firstly,BiOBr and BiOCl nano-semiconductor photocatalysts were prepared by hydrothermal synthesis method under different experimental conditions,and then BiOCl/BiOBr heterojunction composite photocatalysts were prepared by one-pot method and hydrothermal synthesis method.Rhodamine B（Rh B）was selected as the target pollutant for photocatalytic degradation experiments,and the effects of BiOBr and BiOCl material ratio,reaction time,p H,catalyst dosage and pollutant concentration on the photocatalytic reaction were investigated.The results showed that the composite photocatalyst with the BiOCl/BiOBr ratio of 3:7 had the highest degradation efficiency of Rh B within 120 min under the conditions of temperature of25°C,p H of 6.0 and catalyst dosage of 20.0 mg（the degradation efficiency is 88.0%）.（2）In order to further explore the photocatalytic ability of bismuth oxyhalide and overcome the problem of difficult separation of dyes and photocatalysts during sewage treatment,BiOBr/ZIF-67 heterojunction composite photocatalysts were prepared using metal-organic framework materials ZIF-67 and BiOBr as raw materials.It was used to degrade Rhodamine B（Rh B）in wastewater.The loading of ZIF-67 on BiOBr was controlled by changing the molar ratio of Co/Bi.The results showed that the removal rate of Rh B by BiOBr/ZIF-67（30%）was95.2%after 60 min of dark treatment and 120 min of light.The exact loading of ZIF-67 was determined by XRD,FT-IR,SEM and BET,and the photocatalytic mechanism was analyzed by PL,UV-Vis and M-S.The results show that the BiOBr/ZIF-67 composite was successfully prepared and may be a Z-scheme heterojunction composite photocatalyst.In addition,the cycling experiments show that BiOBr/ZIF-67 has good stability and is easy to separate from sewage.The recovered and dried BiOBr/ZIF-67 can be used continuously,and the degradation efficiency is not lower than 80%of the original after 4 cycles of experiments.（3）In order to explore whether the composite of BiOBr,BiOCl and ZIF-67 has better photocatalytic performance,BiOCl/BiOBr（3:7）with the best photocatalytic performance was composited with ZIF-67 to prepare BiOCl/BiOBr/ZIF-67.The preparation method still adopts hydrothermal synthesis method and one-pot method.In order to explore the ability of the catalyst to treat composite dye wastewater,BiOCl/BiOBr/ZIF-67 was used for photocatalytic degradation of the mixed solution of methylene blue（MB）,Congo red（CR）and rhodamine B（Rh B）.Experiments show that the photocatalytic ability of BiOCl/BiOBr/ZIF-67 is significantly improved compared to BiOCl/BiOBr,BiOCl/ZIF-67 and BiOBr/ZIF-67.Therefore,it is feasible to select BiOCl/BiOBr/ZIF-67 as a photocatalyst for organic dye wastewater treatment.