Effects Of Typical Clay Minerals On The Mobility Of Graphene Oxide In Aquifer Media

As carbonaceous nanomaterials with good application prospect,graphene oxide(GO)is widely used in various fields of production and life due to its excellent physicochemical properties,and the mass production and use of GO will inevitably lead to its release into the environment,posing certain ecological and health risks.As clay minerals are common components in aquifer media,GO entering the environment will inevitably come into contact with clay minerals and interact with them,resulting in changes in GO environmental behavior and fate.In this paper,the effects of different types and forms of clay minerals on the mobility and deposition behavior ability of GO and its derivatives and their dominant mechanisms of action were investigated through photochemical experiments,column migration experiments,combined with various characterization tools and extended Derjaguin-Landau-Verwey-Overbeek(XDLVO)theoretical model calculations.The main findings of the study are as follows:(1)The phototransformation of GO was simulated under experimental conditions,and it was found that phototransformation has a large effect on the morphology,hydrophobicity,surface charge,and the number and distribution of oxygen-containing functional groups of GO.Light can lead to the exfoliation of oxygen-containing functional groups on the GO surface,the increase of C/O ratio,the generation of more folded structures on the surface,the decrease of electronegativity and hydrophilicity,the deterioration of dispersion in the aqueous environment,and the formation of agglomerates more easily.Combined with different water chemistry conditions,it was found that phototransformation also significantly affected the mobility and deposition behavior of GO.The reduced graphene oxide(RGO)produced by phototransformation is more likely to be deposited in aquifer media due to its reduced electronegativity and hydrophilicity,especially under high ionic strength and acidic conditions.(2)The effect of clay minerals as doping media on the mobility and deposition ability of(R)GO was investigated.It was found that the doping of clay minerals in aquifer media significantly inhibited(R)GO migration due to the presence of tiny particles that largely reduced the pore volume of the sand column and trapped(R)GO nanoparticles by physical strain and pore filling;meanwhile,three clay minerals with different roughness and electrochemical characteristics caused the mobility of(R)GO to be obviously inhibited by removing the energy potential barrier and providing additional deposition sites.The mobile behavior of(R)GO is suppressed following the order of kaolinite > montmorillonite > illite.Compared with GO,RGO with small electronegativity and hydrophobicity after phototransformation has a more significant inhibition effect on clay mineral reference media through interception and hydrophobic adsorption.(3)The effect of clay mineral colloids on the mobile ability of(R)GO when co-transported with(R)GO nanoparticles was investigated.It was found that montmorillonite colloids with better dispersion and stability promoted the mobile ability of(R)GO through carrier transport and facilitated dispersion,while kaolinite and illite colloids with poor mobility and stability inhibited the transport of(R)GO nanoparticles by providing additional deposition sites and forming heterogeneous agglomerates with(R)GO to increase pore filling,and the degree of inhibition showed a pattern of illite > kaolinite.Compared with GO,the phototransformation product RGO is more sensitive to the response of coexisting clay colloid due to its lower electronegativity.In summary,the presence of clay minerals affects the mobility and deposition ability of GO.Specifically,the physicochemical properties of GO can be changed under irradiation,which in turn makes the response of clay minerals to its transport behavior more significant.The findings of this paper are of great scientific significance for investigating the occurrence,behavior and fate of carbonaceous microparticulate pollutants in environmental media,and provide a scientific basis for predicting and assessing the environmental risk of carbonaceous microparticulate pollutants and developing pollution control technologies.