Degradation Mechanism Of Volatile Organic Pollutants By Carbon Nitride Supported Nanoscale Zero-valent Iron And Application Reserach

Volatile organic compounds(VOCs)can causea serious harm to the ecological environment and human health due to strong migration ability and greater toxicity.Nanoscale Zero-valent Iron(nZVI)has been used to degrade VOCs due to its better reduction,adsorption and catalytic abilities.However,in pratical application,nZVI has some problmes such as agglomeration and passivation.Therefore,nZVI supported on polymeric graphitic carbon nitride composite(nZVI@CN)was synthesized via liquid phase reduction method,the reduction and dechlorination ability of nZVI@CN materials on Volatile Chlorinated Hydrocarbons(VCHs)was investigated,and the abilty of activating peroxymonosulfate(PMS)to degradate BETX was studied.The nZVI@CN material was applied to Permeable Reactive Barrier(PRB)technology,and through hydraulic control,the in-situ remediation ability of VOCs contaminated groundwater was investigated.The main results are as follows:(1)The structure,composition,and morphology of nZVI@CN were characterized,the results showed that the nZVI particles were uniformly dispersed on the surface of nZVI@CN,and the particle size was about 50 nm.Compared with nZVI,nZVI@CN has larger specific surface area and total pore volume,and nZVI@CN has good magnetic properties.The reduction and dechlorination experiment results showed that the removal efficiency of trichloroethylene(TCE)(20 mg/L)can reach 87.6%in 3 h with a certain dosage of nZVI@CN(2 g/L).Increasing nZVI@CN dosage,decreasing ion concentration(CaCl2)and solution pH value can promote the removal of TCE,and the dissolved oxygen(DO)concentration has no significant effect on the degradation of TCE.(2)In the experiment of activating PMS to degradate BTEX,the removal efficiency of paraxylene(PX)was 90.9%within 30 min treatment with the optimal reaction conditions(1 mmol/L PMS,0.1 g/L nZVI@CN,20 mg/L PX and pH 6.86),and the mineralization rate measured by the removal of total organic carbon had reached 82.6%.In the nZVI@CN/PMS system,the increase of catalyst dosage and PMS concentration was conductive to the degradation of PX,while the increase of PX concentration and solution pH value may inhibite the degradation of PX,and nZVI@CN showed good stability and reusability for PMS activation in the degradation of PX.Radical quenching and Electron paramagnetic resonance detection confirmed that sulfate and hydroxyl radicals generated by PMS activation were responsible for the degradation of PX,and sulfate radicals were the dominant active species.(3)The nZVI@CN material was used as active filler to construct continuous reaction wall,and through the peristaltic pump to strengthen hydraulic control,the migration of TCE and PX in aquifers and the in-situ remediation ability of TCE and PX contaminated groundwater were investigated.The results showed that when the pumping flow rate achieved 10 mL/min,the hydraulic gradient reached 10%,whch sfrengthens the migration ability of pollutants in the aquifer.In the TCE and PX removal experiment,by injecting a mixed solution of pollutants and PMS,after 12 hours of continuous operation,the removal rate of TCE and PX remained around 85% and 90%,respectively.