A study on enhanced process and mechanism for toluene remocal by combining Fe-ZSM-5 with vacuum ultraviolet and persulfate
In recent years,the advanced oxidation process of vacuum ultraviolet(VUV)synergistic peroxymonosulfate has been gradually developed for the treatment of low concentration of volatile organic pollutants(VOCs).However,it is urgent to select an appropriate catalyst for coupling with VUV/PMS system to further enhance the degradation efficiency and mineralization efficiency of industrial low-concentration benzene series of VOCs.Therefore,based on the acidity characteristics of ZSM-5,this study aims to fabricate Fe-ZSM-5 catalyst through wet impregnation method,and evaluates the catalytic activity and degradation mechanism of VUV+PMS+Fe-ZSM-5 system on toluene removal under wet condition.The results showed that nearly 100.0％of toluene was degraded within 240 min in VUV+PMS+Fe-ZSM-5 system,and the mineralization rate was as high as 67.0％.Ammonia temperature programmed desorption(NH3-TPD)and pyridine infrared(FTIR)were utilized to analyze the type and amount of acid species of the catalysts.It can be achieved that Fe modification reduces the amount of Brønsted acid in ZSM-5 catalyst,but increases the amount of Lewis acid,which may be beneficial to improve the activity and stability of the reaction.Electron paramagnetic resonance(EPR)spectrum demonstrated that sulfate radicals(SO4-)and hydroxyl radicals(OH)are the main active species in the VUV+PMS+Fe-ZSM-5 for toluene removal.Several intermediate products including benzyl alcohol,benzaldehyde,benzoic acid,acetic acid,propionic acid,2-pentanone were detected during the degradation process by liquid chromatography-mass spectrometry(LC-MS),while no gaseous intermediates were found in the outlet by gas chromatographic(GC),indicating that this process can effectively avoid secondary air pollution and transfer intermediates to the liquid phase for further treatment.The study provides a new idea for low-concentration benzene series of VOCs control by catalyst+VUV/PMS wet process.
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