The Aggregation Behavior Of Graphene Oxide In Complex Water Systerms And Its Removal

With the rapid development of nanotechnology,graphene oxide(GO)with unique structure and physical and chemical properties,is used in many fields of life and industry,becoming a bright star among many carbon nanomaterials.It is inevitable that GO will be discharged into the natural environments including atmosphere,lake and soil during the processes of production,transportation,treatment and discharge.GO can be stably dispersed in aqueous solutions due to its large specific surface area and abundant oxygen-containing functional groups,but various factors will affect the aggregation behavior of GO and consequently its fate in the complex natural aquatic system.In this paper,the effects of total nitrogen,total phosphorus and the ratio of total nitrogen to total phosphorus in eutrophic water on the coagulation and sedimentation of GO particles were qualitatively explored through static batch sedimentation experiments.Simultaneously,the interaction between GO particles as well as the aggregation mechanism in simulated eutrophic aquatic systems were quantitatively described through sedimentation kinetics and DLVO theory,which will enrich the theoretical basis of GO aggregation in the complex natural aquatic system.It is reported that GO has certain ecotoxicity,so it has been widely considered as a potential nanomaterial pollutant.Thus,this article investigated the factors affecting the removal of GO by the other man made nanomaterial—nanoscale zero-valent iron(nZVI),which was also of great significance for protecting the ecological environment.The main contents of this study were as follows:(1)The accumulation behavior of GO in simulated eutrophic water was studied.Specifically,ammonium salts and phosphates were applied to simulate the total nitrogen and total phosphorus content in the water.The effects of ion concentration,ion type,and pH on GO stability were investigated.The experimental results show that the aggregation of GO is highly related to the cations in the solution.Specifically,as the electrolyte concentration increases,the degree of aggregation of GO increases.Besides,it can be concluded that GO tended to be dispersed in alkaline eutrophic lake.At the same time,it can be predicted that GO will tends to aggregation under the coexistence impact of total phosphate and nitrogen based on TN/TP influence.Subsequently,the aggregation mechanism of GO was further analyzed based on DLVO theory and microscopic characterization.According to the results,it was found that electrostatic potential energy and gravitational potential energy play an important role in the process of GO aggregation,and there are other possible mechanisms of aggregation.The experimental results are helpful to reveal the aggregation or dispersion behavior of GO in the eutrophic natural lake.(2)The factors affecting the removal of GO by nZVI were investigated by batch experiments.The results of batch experiments indicated that nZVI could promote the aggregation of GO depending on the particle size and concentration of nZVI at pH<5.0 and on the ionic strength and cation type in the whole tested pH values.The pH-and cation-induced homoaggregation of GO and the heteroaggregation of GO with nZVI induced by electrostatic attraction contributed to the removal of GO in the acidic solution;while the removal of GO in the alkaline solution was attributed to the attachment of GO with small size on nZVI,which was independent of pH,nZVI size,and nZVI concentration.These findings some extent could reveal the information not only for the preparation of GO-supported nZVI composites but also for the assessment of the application of nZVI as adsorbent for GO removal and the environmental fate of GO after it came into contact with nZVI.