Study On Photocatalytic Degradation Performance Of Metal Organic Frame And Composite Materials For Odor Gases In Livestock And Poultry Farming

With the optimization of China’s agricultural industry structure and the improvement of residents’living standards,the large-scale livestock and poultry farming industry has developed rapidly.The complaint problem brought by odor pollution has become one of the main bottlenecks in the development of livestock and poultry farming industry in China.Due to the characteristics of low concentration,large gas volume,complex composition,and rapid spatial and temporal changes,the economic and efficient treatment of odor gases has become a serious challenge for livestock and poultry breeding.Traditional odor gas treatment technologies include physical,chemical and biological methods,which have disadvantages such as high operation cost and poor treatment effect,making it difficult to meet the demand of livestock farming odor gas treatment.Advanced oxidation technology,including photocatalysis,has the advantages of good catalytic activity,high stability and low price,and has broad application prospects in the treatment of odor gases from livestock and poultry breeding.Based on the advantages of metal-organic framework（MOF）,such as large specific surface area,high porosity,multiple functional sites,designable structure and adjustable function,this study took the odor gas from livestock and poultry farming as the target pollutant,and designed new composite materials,analyzed the physicochemical and photoelectric properties,evaluated the photocatalytic performance,recycling performance and renewable performance,explored the photocatalytic mechanism,and realized the efficient photocatalytic degradation of odor gas,which was of great significance for solving the problem of odor gas treatment in livestock and poultry farming.The main research contents are as follows.（1）Aiming at the problems of small specific surface area and easy compounding of photogenerated electron-hole pairs of conventional titanium dioxide,the mixed-crystal phase Ti O₂ photocatalyst was synthesized by MIL-125 high-temperature pyrolysis to achieve efficient photocatalytic degradation of typical odor gases from livestock and poultry farming under UV light irradiation.Benefiting from the fact that the pyrolysis-derived Ti O₂ material can retain the advantages of large specific surface area and adjustable function of the precursor MOF,the degradation efficiency of the prepared improved photocatalyst for most odor gas components reached more than 80%,and its deodorization effect was significantly improved compared with that of commercial P25.In the photocatalytic degradation of mixed manure,most of the odor gas concentrations were reduced to below the odor threshold,indicating that MIL-125-derived Ti O₂has a good application prospects.The effect of environmental humidity on the photocatalytic effect was explored,and it was found that the optimal degradation effect of typical odor gases from livestock farming was achieved at 30 wt%,while the photocatalytic effect of odor gases under high humidity conditions performed poorly.In addition,the key components of odor gases in the actual livestock farming environment were further analyzed,and it was found that hydrogen sulfide and methyl mercaptan had the highest odor contribution but the worst deodorization effect.Therefore,the development of photocatalysts suitable for efficient sulfide degradation should be considered.（2）Aiming at the problems of low photocatalytic degradation efficiency of reduced sulfides and great influence of environmental humidity on photocatalysts,Ui O-66@Ti O₂composite were synthesized by solvothermal method,which provided an effective strategy for efficient photocatalytic degradation of methyl sulfide under UV irradiation conditions.Thanks to the advantages of large specific surface area and high adsorption capacity for sulfide of Ui O-66,the degradation efficiency of Ui O-66@Ti O₂ for methyl sulfide is 7.1 times higher than that of Ti O₂,indicating that the catalyst has excellent photodegradation performance.In addition,the effects of photocatalyst dosage,initial concentration of methyl sulfide and relative humidity on the photodegradation effect were investigated,and the optimal degradation conditions of methyl sulfide were determined to realize the efficient and stable operation of Ui O-66@Ti O₂ under high humidity environment.The photocatalytic mechanism and methylsulfide degradation pathway of the composite system was investigated,which provided theoretical support for the development of the Ti O₂ and MOF composite system suitable for the efficient degradation of reduced sulfide.（3）Aiming at the problems of poor visible light utilization and low photogenerated carrier migration efficiency of common titanium dioxide-based photocatalysts,Bi VO₄/graphene/Ui O-66-NH₂ composites were synthesized by a combination of solvent thermal method and solvent filtration method,which provided a new idea for efficient photocatalytic degradation of reduced sulfur compounds under visible light irradiation conditions.The prepared Bi VO₄/graphene/Ui O-66-NH₂ materials combine the advantages of high visible light utilization,strong redox ability and fast carrier migration rate,and show excellent photocatalytic activity with removal rates higher than 78%for all the reduced sulfides（hydrogen sulfide,ethyl mercaptan,propanethiol,methyl sulfide,ethyl sulfide and dimethyl sulfide）.The new composite photocatalyst with large specific surface area is beneficial to slow down the interference of sediments to on its catalytic process,thus improving the cycle times of the photocatalyst.By analyzing the energy band structure and catalytic active groups,the degradation mechanism of the composite Z-type photocatalytic system was revealed,which provides a new green and efficient method for the catalytic degradation of reduced sulfides.（4）Aiming at the problems of poor efficiency of hydrogen sulfide photocatalytic degradation and easy deactivation of catalyst,Ti O₂/Cu S/MIL-125-NH₂ composites were successfully synthesized by in situ solvothermal method,which provides a useful strategy for efficient photocatalytic degradation of hydrogen sulfide under visible light irradiation conditions.The results show that the highly dispersed encapsulation of Cu ions enables the composite to exhibit high adsorption performance on hydrogen sulfide,and the formed local high concentration region can promote the degradation of H₂S while further oxidizing the by-product SO₂,effectively preventing secondary pollution.Meanwhile,the tight heterogeneous structure of Ti O₂/Cu S/MIL-125-NH₂composite can effectively promote the photogenerated electron-hole pair separation and improve its photocatalytic activity,which can maintain the degradation efficiency of hydrogen sulfide above 97%,indicating that the composite system combining adsorption and photocatalytic properties has excellent performance.Further study shows that the prepared Ti O₂/Cu S/MIL-125-NH₂ photocatalyst can be regenerated efficiently by simple and economical deionized water washing,providing a green solution for the economical and efficient degradation of hydrogen sulfide.