Efficacy Of Sulfide-modified Nanoscale Zero-valent For The Removal Of Organic Contaminants In Both Reducing And Oxidizing Reaction System

In recent years,nanoscale zero-valent iron（nZVI）has shown great application prospects in environmental pollution remediation engineering,due to its high reactivity and cost-effectiveness.However,there are still some shortages in applying nZVI in practical application.Particularly,nZVI was easily corroded in water and the formation of iron（hydro）oxide passivation layer would greatly inhibit its reactivity and selectivity towards pollutants.The sulfide-modified nZVI is more hydrophobic,and the iron sulfur compounds（Fe S_x）layer covering on the surface of nZVI can alleviate the corrosion reactions in water.In this work,sulfide-modified nZVI（S-nZVI）was synthesized and employed in reduction and oxidation reaction systems for the degradation of contaminants.The main contents and results are as follows:Part one:S-nZVI was applied to remove trichloroethylene（TCE）in the presence of different co-contaminants(Cr⁶⁺,Cd²⁺and NO₃^-).The removal of TCE by S-nZVI in TCE/Cr⁶⁺and TCE/Cd²⁺mixed solution decreased significantly with the increasing concentration of Cr⁶⁺and Cd²⁺.In contrast,the presence of NO₃^-enhanced the TCE removal by S-nZVI.The increasing initial p H from 5.61 to 9 resulted in a slight decrease of TCE removal in all reaction systems,while the increasing p H exerted negligible influence on the dechlorination of TCE.This indicated that the increasing p H only inhibited the adsorption of TCE.Simultaneously,the removal of co-contaminants was examined.S-nZVI had a poor sequestration of Cr⁶⁺,compared with that of Cd²⁺and NO₃^-,which was due to the rapid surface passivation of S-nZVI by the products of Cr⁶⁺reduction.SEM-EDS analysis verified that much more precipitates formed on the S-nZVI surface in the systems with Cr⁶⁺and Cd²⁺and NO₃^-.XPS analyses demonstrated the presence of surface layer of Fe Sx on S-nZVI,and the reactivity loss toward TCE degradation in TCE/Cr⁶⁺and TCE/Cd²⁺mixed solution was associated closely with the formation of Fe/Cr and Fe/Cd precipitates on the surface of S-nZVI.Part two:S-nZVI was employed to activate PS and H₂O₂for the removal of sulfamethazine（SMT）.The removal of SMT in the S-nZVI/PS system increased with the increasing PS concentration,while there was an optimum H₂O₂concentration in the S-nZVI/H₂O₂system.The S-nZVI/H₂O₂system showed much stronger oxidative capacity than the S-nZVI/PS system under the same fitting condition.Moreover,the S-nZVI/PS system was more susceptible to the molar ratio of Fe/S,and a higher SMT removal was achieved under conditions of Fe/S≥40.Nevertheless,the S-nZVI/PS system was efficient over a wide p H range of 3～9,while the efficient p H in the S-nZVI/H₂O₂system was confined to just 3.In addition,the SMT removal by the S-nZVI/PS system was further examined in simulated groundwater and it was found that the influence of groundwater components on the removal of SMT was insignificant over the p H range of 5～8,but a notable negative effect was observed at p H 9.