Study On Degradation Of Organic Pollutants By Water Falling Film Dielectric Barrier Discharge Combined With Metal Oxyhydroxides

Discharge plasma can produce high-energy electrons,excited molecules,free radicals and other active substances,which are able to react with organic compounds in water,and finally achieve the purpose of degradation of organic pollutants.Compared with other organic pollutant treatment technologies,discharge plasma is fast,efficient and no secondary pollution,simple operation and so on.However,this technology needs high energy to achieve efficient degradation of pollutants.How to reduce energy consumption has become a hot issue in the research and applicationof discharge plasma technology.The introduction of catalyst in the discharge plasma can increase the strong oxidizing ·OH production,and then improve the pollutant treatment effect and energy efficiency.Metal oxides are the most commonly used plasma catalyst.Metal oxyhydroxides are a special form of metal oxides,and it has been found that metal oxyhydroxides have higher catalytic activity than traditional metal oxides in a variety of advanced oxidation technologies,and are widely distributed in nature,making the cost of mining is low.In this study,discharge plasma and metal oxyhydroxides was combined to increase the yield of ·OH and improve the degradation effect and energy efficiency for pollutants by using the rich catalytic active sites on the surface of metal oxyhydroxides.The main work and research results are as follows:(1)A coaxial water falling film dielectric barrier discharge(DBD)device was established.The effect of experimental parameters on the degradation of trans ferulic acid(FA)was investigated,and the formation and evolution of active substances in the reactor were studied.The experimental results showed that the FA degradation efficiency increased with the increase of discharge voltage,the increase of medium thickness was not conducive to the FA degradation the degradation efficiency of FA increased at first and then decreases with the increase of ventilation flow rates,and the weak alkali condition was beneficial to the degradation of FA.The peroxone reaction between ozone and hydrogen peroxide formed by DBD in solution could promote the formation of ·OH and FA degradation(2)Cobalt oxyhydroxides(CoOOH)was prepared.The physicochemical properties of the catalysts were characterized,and the catalytic performance and mechanism of CoOOH in DBD were studied.The results showed that the degradationefficiency of FA was increased by 23.8%to 98.2%by adding 0.5g CoOOH for 10 min when the discharge voltage was 11.2 kV,and the energy efficiency was 2.9 times higher than that of DBD alone.The results of catalytic mechanism study showed that the oxygen vacancy and Lewis acidic sites on the surface of CoOOH were the active sites.H2O2 and O3 were decomposed into peroxide-like speices on these active sites and then converted into·OH.(3)Ce and Mn doped CoOOH were used to enhance the catalytic activity.The results showed that the degradation efficiency of caffeic acid(CA)treated with 0.5g/L CoOOH and DBD for 8 min was 86.1%,and the energy efficiency was 1.39 g/kWh.When DBD combined with Cei/Co9OOH and Mn0.5/Co9.5OOH for 8 min,the degradation efficiency of CA was 96.9%and 100%,respectively,and the energy efficiency increased to 2.03 g/kWh and 2.35 g/kWh.Active sites analysis show that the doping of Ce and Mn increased the content of oxygen vacancies and Lewis acidic sites in CoOOH,thus improving the conversion efficiency of ozone and hydrogen peroxide to·OH.(4)Increasing the amount of wastewater treatment,and loading Mn/CoOOH catalyst on activated carbon fiber(ACF)to improve the recyclability of the catalyst.The results showed that when DBD treated 20 L FA and CA mixed wastewater for 100 min,the degradation efficiency of FA and CA were 64.7%and 76.6%,respectively.ACF was adsorptive,and the degradation efficiency of FA and CA by 15 g ACF and DBD were 74.3%and 84.4%,respectively,with 100 min treatment,while adding 15 g Mn/CoOOH/ACF could increase the degradation efficiency to 81.6%and 94.2%under the same treatment time.Mn/CoOOH/ACF can significantly enhance-OH concentration in DBD process to increase degradation efficiency of pollutants.Compared with fresh CoOOH,86.6%of the Mn/CoOOH was still on the ACF after being reused three times,indicating ACF can improve the recoverability Mn/CoOOH.