Study On The Interaction Between Carbon Nanotubes And Nature Organic Matter

The rapid development of nano technology and industry linked nanomaterials to human life.Therefore,more and more attention has been paid to the potential harm of nanomaterials to the environment and human health.As the final destination of nanomaterials,the migration and transformation of nanomaterials in the water environment are of great significance for the scientific assessment and management of the ecological risks of nanomaterials.When nanomaterials released into the aqueous environment,their environmental behavior was greatly affected by their own physicochemical properties and water environment factors.In this study,multi-wall carbon nanotubes(MWNTs)with different out-diameters and different surface functional groups were selected as the research object,and the effects of solution p H,humic acid(HA)and other physical and chemical factors on the adsorption,suspension/precipitation behavior of MWNTs with different physical and chemical properties were studied by adsorption isotherm and adsorption kinetics.The changes of MWNTs before and after HA adsorption were characterized by means of transmission electron microscopy,Raman spectroscopy,Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS),and the influence of HA on the adsorption and aggregation behavior of MWNTs was tried to explain in the mechanism.Finally,we try to use the interdisciplinary method Density Functional Theory(DFT)to simulate the adsorption behavior of HA on the surfaces of multi-walled carbon nanotubes and hydroxylation multi-walled carbon nanotubes.The main results of this study are as follows:(1)The p H of the solution significantly affects the adsorption of HA on the surface of MWNTs with different out-diameters and surface functional groups,and the adsorption amount decreases with the increase of p H.The adsorption isotherms ofHA on the surface of carbon nanotubes with different functional groups and different diameters were consistent with Langmuir and Freundlich equations.The specific surface area of MWNTs significantly affects the adsorption capacity of HA.The adsorption capacity of HA on different surface functional groups of MWNTs decreases with the increase of pipe diameter.With the same diameter,surface hydroxylation and carboxylation reduced the maximum adsorption capacity of MWNTs on HA.The adsorption kinetics study showed the adsorption capacity of MWNTs increased rapidly in the first 24 hours,then gradually slowed down.The adsorption rate of HA on the surface of unmodified MWNTs is faster.(2)In the aquatic environment,the physical and chemical properties of MWNTs have a significant influence on its suspension/sedimentation behavior.The suspension of hydroxylated and carboxylated MWNTs was higher than that of unmodified MWNTs under the same pipe diameter.When the surface functional groups are the same,MWNTs with smaller diameter and larger specific surface area are more likely to agglomerate and settle.In the presence of HA,for MWNTs with different surface functional groups,HA adsorption can enhance the suspension performance of MWNTs in aqueous solution.The adsorption capacity of HA determines its influence on the suspension/settling behavior of MWNTs.The influence of HA is relatively weakened by surface hydroxylation and carboxylation.(3)The results of Raman spectroscopy showed that the MWNTs with smaller diameter and larger specific surface area had disordered carbon accumulation microstructure and many defects,and the adsorption of part of HA would cover the defects on the MWNTs surface.The results of FTIR characterization showed that the overall structure of MWNTs was not damaged to a large extent after adsorption of HA,and the adsorption of HA and the hydroxyl group and carboxyl group on the surface of MWNTs reacted,reducing the content of hydroxyl group and carboxyl group.X-ray photoelectron spectroscopy was used to characterize C-MWNTs,and the results showed that the surface carboxyl substituted carbon nanotubes contained hydroxyl,ether,aldehyde,quinone,ketone and carboxyl groups.The calculated results of DFTshow that compared with O-MWNTs,HA is more easily adsorbed on the surface of P-MWNTs and the adsorption is more stable.This study helps to better grasp the different appearance,surface functional groups of MWNTs in the actual adsorption in the aquatic environment,suspension and settlement,such as environmental behavior,for the scientific assessment of MWNTs in water environment of the migration,transformation,tending towards to provide theoretical basis for the scientific assessment and management of production and application of nanomaterials and their potential ecological harm has important scientific significance.