New Preparation Method Of Bismuth Based Composite Photocatalyst And Its Degradation Of Organic Pollutants

With the excessive exploitation of the earth resources and the rapid expansion of industrial production,environmental pollution and energy crisis have become two key factors restricting human development.Under such situation,sustainable development is imperative.Therefore,the development of pollution control technology should also take green and sustainable as an important premise.Semiconductor photocatalysis,as a potential green and sustainable technology,has been widely studied and rapidly developed.A large number of novel photocatalysts have been prepared and many new applications have been developed.Among them,the preparation of Bi based photocatalyst and its application in the treatment of refractory organic pollutants in water is one of the main directions.A series of classical Bi based photocatalysts such as Bi₂O₃,Bi₂S₃,BIOX（x=Cl,Br,I）,Bi₂WO₆ and Bi VO₄ have been developed.Through various modification methods,the morphology and band structure of these Bi based photocatalysts can be adjusted,or they can be combined with other materials to enhance the photocatalytic ability.It has been applied to the removal of various refractory organic pollutants and achieved fruitful results.However,due to the lack of innovation in synthesis technology,the controllable synthesis of materials is not available.As a result,the capability of the new catalytic materials is uneven,and there is still a big gap from the practical application.Based on the above situation,BiOBr/BiOI heterojunction and Bi/Bi₂O₃/C composite photocatalyst with high performance and practical application potential were prepared through some synthesis technology innovation.The crystal phase,morphology,structure and photoelectric properties of the as prepared materials were characterized a variety of techniques.Antibiotics and fluorescent brighteners were used as target pollutants to evaluate the activity of photocatalyst.By exploring the influence of environmental conditions on the degradation of pollutants,the mineralization degree of pollutants,the reusability and stability of the catalyst,the practical application potential of the catalyst was evaluated.The main research contents and conclusions are as follows:（1）A novel solvothermal reduction-ion exchange method was proposed for the synthesis of flower-like Bi OBr/Bi OI heterojunction.The phase,morphology,element composition and energy band structure of the flower like Bi OBr/Bi OI heterojunction were analyzed by various characterization tests,and the process of its formation was studied.The optimal proportion of Bi OBr/Bi OI heterojunction was screened by degradation of levofloxacin hydrochloride wastewater,and the results showed that the best performance was achieved when the molar ratio of Br and I was 12:1.The degradation efficiency of levofloxacin hydrochloride in simulated wastewater reached 97%under visible light irradiation for 120 min,and the mineralization rate was 75.9%under visible light irradiation for 180 min.The environmental conditions of the whole photocatalytic reaction were optimized,and the optimum catalyst usage and p H was 1 g/L and9.0,respectively.The results of free radical capture experiments showed that the hole played a major role in the whole photocatalytic process.By analyzing the photoelectric properties of the materials and the change of the energy band structure of the materials,it was concluded that the heterostructure formed by the two materials promoted the separation of the photogenerated carriers,which was the main reason for the improvement of the photocatalytic performance of the materials.（2）A Bi based MOF:CAU-17 was synthesized according to the literature.The Bi/Bi₂O₃/C ternary composite photocatalyst was prepared with the aid of atmosphere conversion in the pyrolysis derivatization process,and the proportion of each component of the prepared photocatalyst was controlled by changing the atmosphere conversion temperature.The phase,morphology and other structural properties of material were analyzed by various means to clarify the change rule of component proportion of Bi/Bi₂O₃/C composite photocatalyst with atmosphere conversion temperature.Subsequently,the formation process and performance improvement mechanism of Bi/Bi₂O₃/C composite photocatalyst were discussed.Fluorescent brightener 351 was used as the target pollutant to evaluate the catalytic activity and reusability of the material.The results showed that the best catalytic performance was obtained when the atmosphere conversion temperature was 400℃.After 240 min illumination,the fluorescent whitening agent 351 could be completely removed by Bi/Bi₂O₃/C composite photocatalyst.The adsorption and conduction of carbon components and the plasma resonance effect of elemental Bi were the main mechanisms for the improvement of catalytic activity.The free radical capture experiment showed that the main active substance was hole.The structure of the photocatalyst was stable,and the degradation efficiency was still up to 83%after four cycles.Moreover,the catalytic reaction was stable,almost not affected by the external ions.