Effect Of Typical Carbon Nanomateirals On Environmental Behavior Of Organic Contaminants

On the basis of the conclusion of carbon nano-materials’ adsorption properties oforganic contaminants and the analysis of the limitations of current studies in whichattention was not paid to the heterocyclic compounds and adsorption properties ofcolloidal carbon nano-materials, we selected two typical systems to lead researcheson the adsorption mechanisms of organic contaminants to carbon nano-materials inorder to see the effects of nanomaterials on the environmental behavior and fate ofthese contaminants. In the first system, we studied the adsorption mechanisms of awidespread kind of organic chemicals—heterocyclics, which were neglected byresearchers, on two kinds of single-walled carbon nanotubes. Heterocyclics arerelatively hydrophilic and ready to transport in the environment. The adsorption tonanomaterials may reduce their environmental mobility. In the other system, weconducted research of adsorption and transport experiments of carbon nano-colloidalform (nC60), which was seldom discussed but was of great importance. Strongadsorptive and mobile abilities of nC60may enhance the mobility of highlyhydrophobic apolar organics so that their behavior and fate could be altered.In order to complete the knowledge on adsorption property of carbonnanomaterials and extend their application, we focused on the carbon nanotubeadsorption phenomena and machanisms of heterocyclic organic chemicals.Adsorption of single-ringed N-and S-heterocyclic aromatics on single-walled carbonnanotubes (SWCNTs) was examined to explore the potential effects that carbonnanotubes (CNTs) might have on environmental contaminants. Adsorbates includedpyrimidine,2-aminopyrimidine,4,6-diaminopyrimidine, thiophene, benzene andaniline while adsorbents included pristine SWCNTs, oxidized SWCNTs, andnonporous graphite. The results showed that besides hydrophobic effect, adsorptionof heterocyclic aromatics was significantly enhanced by non-hydrophobic interactionssuch as π–π coupling and π electron donor–acceptor (EDA) interactions.Particularly, the–NH2-substituted compounds exhibited much stronger adsorptionaffinities to oxidized SWCNTs than benzene, even though they are much lesshydrophobic. The lone-pair electrons of the N heteroatoms and the–NH2group canenable n–π EDA interactions with SWCNT surfaces. Lewis acid–base interaction isanother significant adsorption-enhancement mechanism for the–NH2-substitutedcompounds (and possibly for pyrimidine) on SWCNTs. For the N-heterocyclicaromatics, due to the reaction of both adsorbates’ and SWCNTs’ surface functionalgroups, adsorption affinity is highly dependent on the O-functionality of the SWCNT surface and solution pH. It indicated that selective adsorption of N-heterocyclicaromatics could be possibly achieved by adjusting the surface functionality of CNTsand solution chemistry. On the other hand, the adsorption of nanomaterials mayalter the partition of heterocyclics between soil and aqueous phase and reduce themobility of heterocyclics in the environment.There is seldom any research carried out on carbon nano-colloid as adsorbents orconsidered their environmental influences on transport and fate of hydrophobicorganic compounds in the environment. In this part, we examined the effect ofnano-C60on transport of persistent hydrophobic contaminants in porous mediamacroscopicly. We examined the enhanced transport of PCB in saturated sandy soilcolumns by a variety of nC60samples, including nC60samples prepared under naturalorganic matter (NOM) or surfactant or second organic solvent conditions as well asnC60samples by typical solvent exchange method, all of which were prepared byphase-transferring C60from toluene to aqueous phase. While the modified nC60samples have similar mobility as the unmodified nC60, their contaminant-mobilizingcapabilities are significantly different. We also conducted batch adsorptionexperiments to see the adsorption affinity of PCB to different nC60samples as well asdesorption kinetics to examine the extent of desorption hysteresis. And we foundthat significantly enhanced contaminant-mobilizing capabilities of the modified nC60are likely due to a combined effect of increased adsorption affinities and increasedtendency of desorption non-equilibrium, which likely caused by the changes of nC60aggregation properties induced by the presence of NOM/surfactant or the secondorganic solvent. Findings in this study indicated that formation conditions andsolvent constituents in nC60preparation might have vastly different effects on theirinfluence on the fate and transport of organic contaminants and that stable colloidalsuspension of nC60in aqueous environments can significantly affect the fate andtransport of hydrophobic organic contaminants by serving as contaminant carrier.The information is of great importance to ecological assessment of bothnanomaterials and organic contaminants.