Application Of Heterogeneous Catalysis On The Degradation Of Typical Organochloride Compounds

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.