Mechanisms Of Polycyclic Aromatic Hydrocarbons Sorption By Diesel Soot And Elemental Carbon Of Diesel Soot

Soot is a kind of black carbon produced by incomplete combustion of biomass and fossil fuels,which releases into the environment by dry and wet atmospheric deposition.Soot has strong sorption for organic contaminants,which could control the transfer,transformation of organic contaminants in the environment.Thus,exploring the sorption behaviors and mechanisms of organic contaminants by soot is helpful for predicting and assessing the environmental health risks of organic contaminants.Sorption of organic contaminants by soot is suggested to be combination of nonlinear and competitive adsorption on elemental carbon of soot and linear and noncompetitive partition in authigenic organic matter of soot.The nonlinear isotherms of organic contaminants by soot could change to be linear under competition.In previous study,the linear isotherms of organic contaminants by soot under competition were attributed to linear partition in the authigenic organic matter of soot alone,ignoring that they might be attributed to linear and nondisplaceable adsorption on the elemental carbon of soot dominated by external surface.In addition,the sorption behaviors of organic contaminants by soot and elemental carbon of soot need to be further studied.Therefore,in this study,elemental carbon（EC-Soot）of a diesel soot（D-Soot）was obtained by removing authigenic organic matter（OM-Soot）through organic-solvent extraction.Sorption of polycyclic aromatic carbons（PAHs）by D-Soot,EC-Soot and OM-Soot were investigated,respectively.Main conclusions of this study are as follows:（1）The isotherms of naphthalene with phenanthrene/p-nitrophenol by D-Soot and EC-Soot changed from nonlinear to linear with the decrease of sorption capacity.The isotherms of naphthalene in OM-Soot with or without phenanthrene/p-nitrophenol were all linear and noncompetitive.The competition on the surface of EC-Soot dominated by external surface（i.e.,the surface of mesopore/macropore and other external surface）was different from that of activated carbon dominated by micropore surface,i.e.,complete displacement of naphthalene by p-nitrophenol could occur for the micropore surface of activated carbon,but not for the external surface of soot.The residual linear isotherms of naphthalene on EC-Soot under competition should be attributed to surface adsorption,while the linear isotherms of naphthalene in OM-Soot should be attributed to linear partition.Due to D-Soot was composed of EC-Soot and OM-Soot,the linear isotherms of naphthalene by D-Soot under competition should be attributed to not only the linear partition in OM-Soot,but also the residual linear adsorption on EC-Soot.（2）The sorption capacity of 6 PAHs on EC-Soot was negatively correlated with melting point but not the molecular sizes of organic contaminants,suggesting that the sorption of PAHs on EC-Soot was dominated by external surface adsorption but not pore-filling.Sorption coefficient（logK_d）of PAHs in OM-Soot was positively correlated with octanol-water distribution coefficient(logK_ow).Sorption capacity of PAHs in OM-Soot was positively correlated with water solubility(logS_w),verifying that the sorption of PAHs in OM-Soot was dominated by partition.The partition contribution of PAHs in OM-Soot to the total sorption of D-Soot could increase with the water solubility of PAHs increased.