As a kind of bio-refractory,highly toxic compounds,organochloride can enter the environment through volatilization,leakage and some other pathways.Since it has been widely detected in water,these substances will do great harm to ecological environment and human if there is no effective remediation measure.Nano-scale zero-valent iron(nZVI)particles are now attracting more and more research interests for its large specific surface area,high reactivity,small particle size,easy accessibility and low cost.Factors such as the formation of passive shells and agglomeration have,however,restricted the development and application of nZVI.How to improve the performance of nZVI with material modification and method optimization has become a hotspot.In this study,typical organochlorid―carbon tetrachloride and 2,4-D‖were chosen as target pollutants,Fe0@Fe3O4 and Fe0/Pd@Fe3O4 nanoparticles prepared by the optimized reductive coprecipitation method were applied on the degradation of carbon tetrachloride and 2,4-D in the form of Fe0@Fe3O4 synergistic reduction system,Fe0/Pd@Fe3O4 bimetallic reduction system and Fe0@Fe3O4/H2O2heterogeneous Fenton-like system.The effects of different reaction conditions like initial pH values,temperature,catalyst dosage and contaminant concentrations on the removal of target pollutants were evaluated while the possible reaction mechanism and degradation pathway were proposed.The main conclusions are as follows:(1)The introduction of Fe3O4 helped to avoid the agglomeration of nZVI,which,in turn,enlarged the specific surface area of nZVI.It also provided a synergistic effect that promoted the relative rates of mass transfer and chemical reaction at reactive sites.Magnetite may also react with chlorinated organic pollutants by releasing structural ferric and ferrous.(2)Palladium could accelerate the formation of active hydrogen atoms on the surface of the particles,change the electronic properties of iron,promote the electron transfer,enhance the stability of nZVI,and avoid the formation of iron oxides on the surface of catalyst.The Fe/Pd bimetallic system could not only enhance the activity of catalyst,but also can reduce the formation of intermediate products.(3)Compared with traditional Fenton system,Heterogeneous Fenton-like system composed of Fe0@Fe3O4 and hydrogen peroxide could rapidly complete the degradation of pollutants and was convenient for recovery and recycling.(4)Under the optimum condition,more than 90%of target pollutants could be efficiently reduced in Fe0@Fe3O4 synergistic reduction system,Fe0/Pd@Fe3O4bimetallic reduction system and Fe0@Fe3O4/H2O2 heterogeneous Fenton-like system;Concentration of iron ion,chloride ion and degradation products were tested to help to study the degradation pathway and reaction mechanism of target pollutants in different systems. |