Colloidal Stability Of Carbon Nanotubes In Aqueous Environment And Their Adsorption Of Typical Perfluorinated Compounds

Carbon nanotube（CNT）,as a typical engineering nanomaterial,has been widely used in chemistry,electronics,energy and construction industries due to its unique structure and physical and chemical properties.Perfluorinated compounds（PFCs）are a kind of synthetic organic compounds with high surface activity,high thermal stability and high chemical stability.They are widely used in textiles,product coatings,packaging materials,petrochemical and other products or consumer products related to life and production.The production and application of CNT and PFCs inevitably lead to their release into the water environment,which creates the possibility of the coexistence of the two in environmental media and also causes certain environmental health risks.In this paper,the common disinfectants H₂O₂ and O₃ in sewage treatment plants were used to oxidize CNT,and the influence of environmental transformation process on CNT surface functional groups,electrochemical properties,hydrophobicity,morphology and other physical and chemical properties were explored.The real-time dynamic light scattering method was used to explore the agglomeration behavior characteristics of CNT and their derivatives under different water chemical conditions,and the derivation of Hamaker constant and DLVO model fitting are used to quantitatively evaluate the suspension stability of CNT in different water environments.Experiments and model fitting methods are used to study the adsorption behavior and mechanism of CNT and their derivatives on perfluoroalkyl carboxylic acids（PFCAs）,and to explore the influence of water chemical conditions on the adsorption of PFCAs by CNT.The main research conclusions are as follows:（1）CNT can be oxidized by H₂O₂ and O₃ under mild environmental conditions,and the oxidation ability of O₃ is higher than that of H₂O₂.Oxidation treatment can significantly increase the content of oxygen-containing functional groups on the surface of CNT,increase surface electronegativity,reduce hydrophobicity,and make the morphology of CNT rougher.（2）In the background electrolyte of monovalent cations（such as Na⁺and K⁺）and divalent cations(such as Mg²⁺)with strong hydration capacity,the suspension stability of CNT is directly proportional to the degree of oxidation（O/C ratio）,and the oxidized CNT are more easily dispersed in the water environment due to the introduction of hydrophilic oxygen-containing functional groups.However,in the Ca²⁺background electrolyte,the suspension stability of O₃-CNT with the highest degree of oxidation is the worst.This is because the ozone treatment increases the hydroxyl and carboxyl functional groups,And Ca²⁺has a strong complexing ability,which can produce bonding and bridging between functional groups,thereby promoting mutual contact and collision between particles,and making oxidized CNT easier to agglomerate.When Na⁺is the background electrolyte,the agglomeration degree of the original CNT and O₃-CNT both decrease with the increase of p H value.However,when Ca²⁺is the background electrolyte,the increase in p H value leads to the enhancement of the suspension stability of the original CNT,but has no obvious effect on the suspension stability of the O₃-CNT.This is also due to the bonding and bridging of Ca²⁺between the degraded CNT particles.（3）PFCAs with longer carbon chains showed stronger adsorption affinity for（O-）CNT adsorbents.For the same PFCA,the adsorption capacity of the original CNT was better than that of the O-CNT.Hydrophobic interaction and electrostatic interaction are the dominant mechanisms for carbon nanotubes to adsorb PFCAs.As the p H value increases,the functional groups on the surface of the（O-）CNT adsorbent deprotonate,the surface electronegativity increases,and the electrostatic repulsion with PFOA（representative PFCAs）increases,and the adsorption was inhibited.The increase of ionic strength on the one hand reduces the surface negative charge of the（O-）CNT adsorbent,and on the other hand promotes the agglomeration of（O-）CNT colloid to generate additional adsorption sites,thus enhancing the adsorption of PFOA.With the increase of Na⁺concentration,CNT is more likely to agglomerate than O-CNT,and has stronger adsorption capacity for PFOA.With the increase of Ca²⁺concentration,the aggregation trend of O-CNT with abundant functional groups was enhanced,and the adsorption affinity between O-CNT and PFOA was greater than that of the original CNT.Carbon nanotube materials can be oxidized under mild environmental conditions,and their suspension stability and surface properties in the water environment change,which affects the behavior and fate of perfluorinated compounds in the environment.It provides a basis for predicting and evaluating the potential environmental health risks of carbon nanotubes and perfluorinated compounds,and provides theoretical support for comprehensively revealing the environmental behavior and fate of carbon nanotubes.