| Non-thermal plasma has a wide range of application in water treatment due to the high efficiency,easy to operation and environmental friendliness.Air is usually used as the background discharge gas for non-thermal plasma technology in practical application.Nitrogen form air can be excited by discharge to generate a high density of N atoms and produce reactive N-based species（RNS）,such as NO·,NO2·,etc.and its derivatives formed with water,including nitrites（NO2-）,nitrates（NO3-）and peroxynitrites.These reactive nitrogen species can participate in the degradation process of organic matter to produce nitrated and nitrosation products,which cause new secondary pollution to the water environment.However,much effort has been devoted to optimizing the reaction system,improving energy efficiency and organic matter removal efficiency,the influence of RNS eg nitrate is still ingnored.Based on the above problems,the introduction of metal-doped Ti O2 into discharge system could not only degraded organic pollutant but also reduced nitrate from discharge,resulting in high removal efficiency of organice pollutant.In this study,Fe/Ti O2,Ag/Ti O2and Ag-Cu/Ti O2 photocatalysts were prepared by the sol-gel method,and the effects of these catalyst on organic pollutant degradation and nitrate reduction in Dielectric Barrier Discharge（DBD）plasma system were systematically studied using phenol as a probe molecule.In this study,the mechanism of excited charge carrier transfer of different photocatalysts in DBD plasma system is analyzed in detail,and the degradation mechanism of phenol and reduction pathway of nitrate in the combination of DBD photocatalyst system are discussed.The main research work and conclusions are as follows:1.Building the surface dielectric barrier discharge system,and using 8.5 k V as the discharge voltage to observe the phenol degradation rate and nitrate reduction effect of Fe/Ti O2.The results show that Fe/Ti O2 can effectively improve the phenol degradation efficiency by 10%,but it does not show a promotion effect on the reduction efficiency of nitrate generated by discharge.Through analysis methods such as UPS,PL,XPS,and trapping free radicals,it is found that the Fe3+loaded can form the Fe impurity energy band below the conduction band of Ti O2,and the reduction of the work function promotes the photo-generated electron transfer of Fe/Ti O2.At the same time,Fe-doped Ti O2 produces more oxygen vacancies,which is conducive to the reaction of photogenerated electrons with surface O2,OH-or H2O molecules,and promotes the production of strong oxidizing species·OH,which enhances the degradation of phenol.However,the concentration of formic acid generated after adding Fe/Ti O2 is slightly lower than that when adding TiO2,which hinders the conversion of formic acid to a strong reducing substance·CO2-,and Fe/Ti O2 produces a large amount of·OH,which obviously inhibits the reduction of nitrate radicals.2.The phenol degradation rate and nitrate reduction effect of Ag/Ti O2 were studied.The results show that Ag/Ti O2 exhibits catalytic performance different from that of Fe/Ti O2under the discharge voltage of 8.5 k V in the surface DBD plasma.In the photocatalytic treatment of phenol wastewater by DBD,the reduction effect of Ag/Ti O2 on nitrate is better than that of Fe/Ti O2 and Ti O2.However,the degradation effect of Ag/Ti O2 on phenol is not as good as that of Fe/Ti O2 and Ti O2,and even shows inhibition.The H+capture and irradiation hydrogen evolution experiments confirmed that the addition of Ag/Ti O2 electrons is beneficial to the reduction of H+to H2,and the reduction reaction of H2 and NO3-occurs.However,Ag/Ti O2 produces the reaction of photogenerated electrons and H+,which inhibits the reaction of photogenerated electrons and O2,reduces the generation of strong oxidizing substances·OH,and causes the degradation rate of phenol to decrease;3.To study the effect of bimetal Ag-Cu supported Ti O2 catalyst on phenol degradation rate and nitrate reduction rate.The results show that Ag-Cu/Ti O2 is added into the surface dielectric barrier plasma,with 8.5 k V as the discharge voltage,the catalysts loaded with Ag and Cu have better oxidative degradation performance of phenol than Ti O2 and single metal-doped catalyst Ag/Ti O2.Moreover,the reduction performance of Ag-Cu/Ti O2 to nitrate is better than that of Ti O2.It was confirmed by XPS characterization that Ag and Cu were successfully supported on Ti O2.Analysis of PL and UV-vis DRS and active material capture experimental results speculate that the excellent redox catalytic activity of Ag-Cu/Ti O2 is due to the localized surface plasmon resonance effect of Ag metal nanoparticles absorbing light energy,which excites hot electrons from metal nanoparticles.The loading of Cu is beneficial to the migration of hot electrons,promotes the utilization of hot carriers,produces more strong redox substances,and improves the degradation rate of phenol and the reduction rate of nitrate. |
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