Computational Simulation Of Adsorption Mechanism At Typical Organic Pollutant-mineral Interfaces

The interactions between soil solid phase components and organic contaminants determine the transport,transformation,and bioavailability of contaminants in soils.Minerals are the major solid-phase components of soils,and their microscopic interactions with pollutants,such as adsorption configurations,sites,forces,and group contributions,play a crucial role in understanding the interfacial molecular mechanisms of organic pollutants.However,in the current studies of organic pollutant-mineral micro-interface interactions,it is difficult to fully resolve and quantify the adsorption conformation,sites,forces,and reactive groups contributions at the molecular level by experimental instrumental analysis alone due to the limitations such as impurity interference,instrumental detection limits,and insufficient resolution capabilities,which sometimes present in experimental studies.Density functional theory(DFT)and molecular dynamics(MD)methods are emerging and growing theoretical research tools.They can study the interactions between organic pollutants and mineral micro-interfaces at the molecular level and compensate for the molecular,atomic,and electronic micro-interaction information that existing experimental means are more difficult to provide.To this end,this study uses typical clay minerals(kaolinite,montmorillonite),metal sulfide minerals(Fe S,Zn S),and several typical organic pollutants(bisphenol A,bisphenol S,glyphosate,and methylmercury)as research objects.The microscopic mechanism of the interaction between different typical organic pollutants and minerals was deeply explored with the help of DFT calculations and MD simulations.The main results obtained are as follows.(1)The group reactivity of bisphenol A(BPA)and bisphenol S(BPS)and the molecular binding mechanism of BPA and BPS on the(001)surface and interlayer of montmorillonite were clarified.BPA is more strongly adsorbed on the(001)surface and the interlayer of montmorillonite than BPA.BPA and BPS are more stably adsorbed onto the interlayer of montmorillonite than the(001)surface of montmorillonite.BPA and BPS are more stably adsorbed onto the interlayer of montmorillonite than the(001)surface of montmorillonite.(2)The adsorption configuration and group contribution of the interaction between glyphosate(PMG)and kaolinite/kaolinite-humic acid complex were revealed.The kaolinite-humic acid complex has stronger adsorption of PMG than kaolinite.PMG can be adsorbed on the surface of the kaolinite and kaolinite-humic acid complex in parallel by hydrogen bonds.The carboxyl and hydroxyl groups of humic acid can form H-bond networks network with the phosphonyl and amino groups of PMG,which enhances PMG adsorption stability on the kaolinite-humic-humic acid complex.(3)The crystal surface dependence of methylmercury(Me Hg)adsorption on the surface of mackinawite(Fe S)was revealed.And the reactivity and difference of the Fe site and the S site on the mineral surface were quantified.The preferential binding order of Me Hg on different surfaces of Fe S is(011)surface>(111)surface>(001)surface,and increasing the exposure of Fe S(011)crystal face can improve the adsorption performance of minerals on Me Hg.Me Hg tends to form monodentate complexes through Hg-S and FeHg bonds on Fe S(001)and Fe S(011)surfaces,respectively.While Me Hg prefers to form bidentate Fe-Hg-Fe complexes on the Fe S(111)surface.Me Hg adsorbed at the Fe site of the Fe S surface forms stronger covalent bonds than the S site,with more charge transfer occurring.The Fe sites on the Fe S surface tended to adsorb Me Hg more than the S sites.(4)The crystal surface dependence of Me Hg adsorption on sphalerite(Zn S)surface was found,and the effects and mechanisms of Fe doping and Se doping of Zn S on Me Hg adsorption were investigated.The preferential binding order of Me Hg on different surfaces of Zn S is(311)surface>(110)surface>(111)surface.Me Hg can form Hg-S,Hg-Se,and Hg-Fe bonds on Zn S surfaces,Se doped Zn S,and Fe doped Zn S,respectively,which their covalent bond strength the charge transfer from minerals to Me Hg increases sequentially.Increasing the crystal surface exposure of Zn S(311)surface and Fe atom doping can improve the adsorption performance of sphalerite to Me Hg.