Removal Of Two Typical Chlorinated Organics From Water By Zero-valent Iron Supported On Modified Graphene

China has always been a country with large demand for the production and consumption of chlorinated organic products.Because most chlorinated organic compounds are highly toxic,difficult to be biodegraded and can exist in the ecological environment for a long time,they have seriously threatened the sustainable development of the ecological environment.Therefore,it is still an important task to develop effective remediation methods and remediation technologies.Among them,nanoscale zero-valent iron(nZVI)technology has attracted widespread attention because of its advantages of low cost,simple preparation method and no secondary pollution,and however,the oxidation reaction on the surface of nZVI particles and the agglomeration between nZVI particles also limit the application of nZVI technology.In this study,two nano-solid catalytic materials(i.e.,PdFe@r-GO and nZVI@SN-rGO)were prepared by reductive coprecipitation and hydrothermal synthesis,carbon tetrachloride(CT)and 2,4-dichlorophenoxyacetic acid(2,4-D)were used as target pollutants which were dechlorinated in three different reaction systems.The effects of removal efficiency of target pollutant and reactive conditions under different reaction systems were investigated.In addition,the kinetic characteristics and degradation reaction mechanism of target pollutant were analyzed,and the possible degradation pathways were discussed.In order to solve the defect of nanometer zero-valent iron particles,the following achievements have been obtained:1.The agglomeration of Pd/Fe bimetallic nanoparticles or zero-valent iron nanoparticles could be avoided by using reductive graphene oxide and S/N doped graphene as carriers,respectively.And compared with the case without carriers,the specific surface area could be increased several times to expose more surface active sites.2.Ultrasound cavitation could effectively disintegrate and remove the passivation layer on the surface of nZVI particles,so as to solve the problem that the passivation layer formed on the surface of nZVI particles in the process of degradation of chlorinated organic compounds,which would block the contact between the target pollutants and the reactive sites.Consequently,the sustained high reactivity of nZVI particles can be obtained.3.When hydrogen peroxide was added to bulk solution,homogeneous Fenton reaction system could be transformed into heterogeneous Fenton-like reaction system by using nanoscale zero-valent iron instead of ferrous ions.Compared with traditional Fenton reaction,it could realize rapid separation of iron components and reduce the amount of precipitatesafter reaction.4.By adding transition metal palladium as hydrogenation catalyst,combining the reduction of nZVI with catalytic hydrogenation,the activation energy of carbon tetrachloride degradation reaction could be significantly reduced,and the associated active hydrogen atoms could significantly improve the reactivity of nZVI particles.5.The transformation products of CT and 2,4-D during the degradation were identified using high performance liquid chromatography(HPLC),ion chromatograph(IC),gas chromatography(GC)and gas chromatography mass spectrometry(GC-MS),and the possible reaction pathways were proposed based on the measured results.