Photocatalytic Degradation Of Gaseous Toluene By CoCuMnO_x/g-C₃N₄

With the rapid development of China's economy,the pollution of atmospheric volatile organic compounds?VOCs?has gradually aroused people's attention.VOCs are one of precursors to photochemical smog and PM2.5,and aromatic and aldehydic VOCs can seriously endanger human health.Therefore,the research on control technology will be helpful to eliminate air pollution and harm to human health caused by VOCs pollution.Photocatalytic oxidation is a cost-effective oxidation technology for VOCs reduction,and to develop VOCs photocatalysts with good catalytic performance is key to the real application of this technology.Nowadays,it has become a hotspot in the research field of photocatalytic technology.In this study,CoCuMnO_x as one solar energy absorbing material was prepared by precipitation hydrothermal crystallization method,and the single-phase graphite type carbon nitride?g-C₃N₄?was prepared by continuous temperature programming.Based on this,the composite catalyst CoCuMnO_x/g-C₃N₄ was prepared subsequently.The activity of the catalyst on photocatalytic degradation of gaseous toluene was investigated by using a self-made batch reactor under the irradiation of halogen tungsten lamp and sunlight respectively.Both fresh and spent catalysts were characterized by XRD,FT-IR,SEM,UV-vis DRS,XRF and BET separately.Photocatalytic degradation pathways and mechanism of toluene were proposed by the trapping experiments of free radicals and intermediate products that determined by GC-MS.According to experimental work,main achievements are listed as below.?1?CoCuMnO_x,g-C₃N₄ and CoCuMnO_x/g-C₃N₄ composite catalysts all have certain photocatalytic activity under the irradiation of halogen tungsten lamp and sunlight,respectively.Based upon characterization analysis,the amounts of CoCuMnO_x/g-C₃N₄ crystal reached the highest and the average grain size grew to the largest?32.1nm?under calcinated temperature of 400? and composite ratio of 1%.Compared with CoCuMnO_x,the band gap of CoCuMnO_x/g-C₃N₄ reduced from 3.2eV to 2.9eV.?2?The photocatalytic degradation efficiency of toluene with an initial concentration of 384mg/m³ by CoCuMnO_x/g-C₃N₄ was 63% under the irradiation of halogen tungsten lamp,which was 15% higher than that by CoCuMnO_x.The degradation efficiency of toluene decreased to 48% after six cycles.?3?Under sunlight irradiation and initial concentration of 384mg/m³,the removal efficiency of toluene by CoCuMnO_x/g-C₃N₄ reached 31%,which was 3% higher than that by CoCuMnO_x.After 5 times of repeated experiments,the degradation efficiency decreased to 29%.The degradation efficiency reached a maximum value of 34.1% under relative humidity of 59% in the chamber of the reactor,but decreased gradually with the increase of acidity.?4?The addition of free radical trapping agents demonstrated the presence of oxidative species such as ·OH,·O₂^- and h⁺ in the process of photocatalytic oxidation,and ·OH and ·O₂^- played major roles in the oxidation of toluene.According to the intermediate products analysis,toluene decomposition started from the hydrogen on methyl and it is gradually oxidized to benzyl alcohol,benzaldehyde and benzoic acid.Then ·OH attacked the benzene ring to break it into more stable small molecules compounds.Through the above research,it will provide certain theoretical foundation in the photocatalytic degradation of VOCs,and also exhibt a new idea and attempt to the preparation of photocatalysts used in the removal of VOCs both in indoor and outdoor.