Adsorption And Catalytic Persulfate Removal Of Dyes In Water With Magnetic Graphene Oxide

In recent years,numerous natural and synthetic dyes have been widely used in industrial production.However,the production and use of dyes could produce a large amount of dye wastewater,which if being discharged directly without effective treatment,could be extremely harmful to the environment and even to human health.In this study,based on the excellent properties of graphene oxide(GO),magnetic graphene oxide(MGO)was prepared by coprecipitation method with GO as the substrate material for the removal of dyes in water.MGO retained the adsorption properties of GO,while the introduction of ferric tetroxide(Fe3O4)solved the separation problem and also made MGO had catalytic properties,which can activate peroxymonosulfate(PMS)for the oxidative degradation of pollutants.Therefore,methylene blue(MB)and coomassie brilliant blue(CBB)were selected as the target pollutants for the adsorption and catalytic degradation in this study.The adsorption and catalytic properties of MGO and its mechanism of removing pollutants were discussed and analyzed.The main research results include the following aspects:(1)Study on MGO adsorption removal of MB in waterA series of MGO with different iron contents(MGO1-MGO4)were prepared by controlling the initial feed ratio and then employed for the adsorptive removal of MB in water.The characterization results of GO and MGO showed that Fe3O4 nanoparticles had been successfully loaded on the surface of GO and the prepared MGO had excellent magnetic separation property.In addition,partial reduction of GO occurred during the preparation of MGO.The results of adsorption experiments indicated that the adsorption capacity of decreased gradually from MGO1 to MGO4 with the increase of iron content in MGO.Water environment and ions in solution had a great effect on the adsorption process.The results of the adsorption kinetic model fitting revealed that the adsorption processes were well described by the pseudosecond order kinetics model.The results of adsorption isotherm model fitting revealed that Langmuir model and Freundlich model both could fit the adsorption processes adequately.According to the calculation,the maximum saturated adsorption capacity of MB by MGO under the optimal conditions was between 37.5-108 mg/L.The results of the adsorption thermodynamic calculations showed that the adsorption processes were all spontaneous endothermic reactions.Based on the above results,it could be inferred that the adsorption mechanism of MGO to MB mainly resulted from electrostatic interactions,hydrophobic interactions,and electron donor-acceptor interactions.The regeneration of MGO was by acid washing method and PMS oxidation method.It was found that the PMS oxidation method had better regeneration ability and less amount of washing water used.Finally,the reaction mechanism of the PMS oxidation was analyzed based on the catalytic experiments of MGO on MB,quenching texts and in-situ open circuit potential(OCP)measurements,which revealed that the strong adsorption capacity of MGO promoted the degradation reaction.The ·OH and1O2 are the main oxidizing species involved in the degradation of MB,and there was no electron-transfer pathway in the system.(2)Study on MGO catalytic removal of CBB in waterIn the catalytic experiments,MGO1 with the best adsorption capacity was selected as the catalyst to degrade CBB by activating PMS.The results of catalytic experiments showed that acidic and weakly alkaline conditions were more favorable to the removal of CBB in MGO1/PMS system.Under the conditions of the dosage of MGO1 and PMS were 0.5 g/L and2 m M with p H no adjusted,the removal of 50 mg/L CBB and TOC was 99.6% and 50.9% in 5h.The influence of Cl--,HCO-3 and HPO2-4 on MGO1/PMS system was related to the concentration in the system.In various water conditions and dye systems,MGO1/PMS system had good removal effect on CBB.The regeneration of MGO1 was by water washing method,which indicated that the MGO1 still had the catalytic ability after five consecutive runs and the CBB removal could reach 90.3%.The characterization of the MGO1 before and after the catalytic reaction revealed that the oxidation intermediates of CBB were presented on the surface of MGO1 after the reaction and the oxidation intermediates could not be completely removed by water washing method.Finally,the reaction mechanism of CBB removal by the MGO1/PMS system was analyzed based on quenching texts and OCP measurements,which proved that ·SO4—,·OH and Fe(IV)were the main oxide species for CBB degradation.The results of OCP showed that the metastable MGO1-PMS* complex was formed but did not participate in the degradation of CBB.In conclusion,MGO has excellent stability and good removal ability for both MB and CBB.The magnetic separation property also makes it easier to recycle and reuse,effectively preventing secondary pollution.As the catalyst,MGO also shows strong universality and can be adapted to a variety of water conditions and dye systems.It is a material with more potential for environmental application.