Aggregation And Sedimentation Of Graphene Oxide In Water

With the rapid development of nanotechnology,nanoparticles have been widely used in all aspects of production and life.Graphene,due to its unique optical,mechanical and electrical properties,has become the ideal material for many scientific research and industrial applications at present and in the future.As the demand for graphene continues to increase,it will inevitably enter the water environment through various channels,causing a series of environmental behavior and ecological effects.Graphene oxide（GO）is an important branch of grapheme materials.Because of its high hydrophilicity,it can be stably dispersed in water and is considered as the potential nano-pollutant,which has attracted much attention.Therefore,it is necessary to study the environmental behavior of GO after entering the water environment.Based on the change of particle characteristics of GO nanoparticles in water,the effect of typical hydrochemical conditions such as electrolytes and organics on the aggregation and sedimentation characteristics of GO were investigated.At the same time,DLVO theory was used to simulated the potential energy interaction between nanoparticles and quantitative description of the aggregation and sedimentation behavior of GO nanoparticles in water was carried out through the study of aggregation kinetics and sedimentation dynamics,providing a theoretical basis for revealing the behavior of GO in water environment in an all-round way.The main contents and conclusions of this study are as follows:（1）There were abundant oxygen-containing functional groups on the surface of GO,which showed stable dispersion in aqueous solution.Electrolytes induced the GO aggregation by compressing the electric double layer,and the process were divided into two stages,which were consistent with Derjaguin-Landau-Verwey-Overbeek（DLVO）theory.The calculated values of CCC are 180 mmol/L（Na⁺）,4.5 mmol/L(Mg²⁺)and 1.8 mmol/L(Ca²⁺)respectively,all of which were much higher than their concentrations in natural water.Aggregation was an important factor influencing the settlement,and the sedimentation process was consistant with the two stages of the aggregation process.GO had higher aggregation rate and sedimentation rate constant in Ca²⁺system.And the lower the concentration of GO,the higher the stability in water.（2）The presence of natural organic matter may weaken the aggregation effect of electrolyte on GO.The result showed that the three natural organic matter inhibited the aggregation,and the higher the concentration of natural organic matter,the more obvious the inhibition effect on GO namiparticles.Fulvic acid（FA）and Humic acid（HA）,which were easily adsorbed by GO,showed stronger inhibition on GO aggregation than alginate.Nevertheless,the coordination bridge between Ca²⁺and HA resulted in the formation of larger size products and enhanced aggregation of GO.The presence of PAA could inhibit the aggregation of GO by electrolyte.The larger molecular weight of PAA disperses the GO in water more effectively by enhancing the steric hinfrance between nanoparticles.In the sedimentation system with PAA,as the concentration of PAA increases,GO became more stable.（3）The heteroaggregation between GO and MWNTs nanoparticles was also consistent with the classical DLVO theory.The CCC of GO+MWNTs in three electrolyte were 103.44mmol/L（Na⁺）、4 mmol/L(Mg²⁺)and 1.8 mmol/L(Ca²⁺),respectively,which were higher than that of GO and MWNTs.The addition of MWNTs nanoparticles promoted heteroaggregation with GO.However,the mechanism of heteroaggregation was not clear,which may be associated with the hydrogen bonds and chemical bonds in water.