Competitive Adsorption Of Multicomponent Aromatic Compounds On Porous Polymeric Resins: Behaviors And Mechanisms

Aromatic organic compounds in water pose a threat to human life because of their high toxicity and difficult degradation,so they have been continuously concerned by researchers.The composition of pollutants in environmental water is complex,and many kinds of pollutants usually coexist.The study on the competitive adsorption behavior and mechanism of organic pollutants on polymer adsorbents can provide an important theoretical basis for the practical application of this kind of wastewater treatment.In this paper,the Polanyi adsorption potential energy equation is redefined by the adsorption phase transformation method,based on which the typical Dubinin-Ashtakhov?D-A?adsorption model is modified and applied to the multi-solute adsorption systems to quantitatively analyze the interactions between organic compounds and adsorbents during competition.The parameter E₀defined on the basis of?₀ in the original D-A model represents the characteristic energy,but the quantitative comparison of the interactions between adsorbates and adsorbents by E₀values is not accurate,while the parameters Ea and E_Hvalues in the modified D-A model represent the energy contribution of all interactions between adsorbates and adsorbents and the energy contributions of specific interactions between adsorbents and adsorbents,respectively.In this study,MN200?polystyrene-divinylbenzene skeleton?and XAD-7?polymethacrylate skeleton?were selected as the research objects to carry out a series of single-component and multi-component adsorption experiments.The contents and results are as follows:Firstly,the adsorption isotherms of several typical phenols and amine compounds at room temperature?25??were obtained in a single static adsorption experiment.The original adsorption isotherms were transformed into gas phase and n-hexadecane phase?HD phase?by adsorption phase transformation,and fitted by D-A model.The results show that nitro substituents enhance the adsorption of phenolic compounds and amines on MN200.In the converted gas phase adsorption isotherms,phenolic compounds and amines containing nitrogroups show the largest equilibrium adsorption capacity,p-nitrophenol has the largest Ea and E_Hfitted values,and larger Ea and E_Hvalues usually have a larger equilibrium adsorption capacity.Compared with the fitting Ea and E_Hvalues of p-nitrophenol,p-chlorophenol and p-methylphenol,the order of substitution effect for Ea and E_His nitro>chloro>methyl.In addition,the equilibrium adsorption capacity of m-nitrophenol is smaller than that of p-nitrophenol.And it is due to the additional resonance effect of p-nitrophenol,which enhances the electron attraction and adsorption capacity of p-nitrophenol.Aniline and nitrobenzene have a large maximum fitting adsorption capacity because aniline and nitrobenzene are liquid at normal temperature,and the solute will form a pure solute state when adsorbed to the resin micropores.Therefore,liquid aniline and nitrobenzene are easier to be adsorbed into the resin micropores.The equilibrium adsorption capacity of all adsorbates on MN200 resin is larger than that of XAD-7,which is mainly due to the difference of their specific surface area?MN200:1021 m²/g;XAD-7:495 m²/g?and the rich micropore structure of MN200.The fitting results show that the Ea and E_Hvalues of MN200 are higher than those of XAD-7,respectively,indicating that the interactions between MN200 and phenolics or amines is stronger than that between XAD-7 and organic compounds.In the multi-component competitive adsorption experiment,the energy parameters of the respective adsorption isotherms were fitted by the original D-A model and the modified D-A model,and corresponding with the structural properties of each adsorbate.It is found that in the equal molar concentration competitive adsorption of phenol and four substances?aniline,p-nitrophenol,p-chlorophenol and p-nitroaniline?on MN200resin,the competition of phenolic organic compounds for phenol is stronger than that of amine organic compounds,which is due to the fact that amine organic compounds can form multi-layer adsorption with phenol through hydrogen bonding,thus reducing the competition for effective adsorption sites.And nitro-substituted phenols and amines,namely p-nitrophenol and p-nitroaniline,tend to have larger Ea and E_Hvalues which are larger than those of p-chlorophenol,and have larger adsorption capacity.This is due to the fact that nitro groups change the polarity and acidity of organic molecules,thus enhancing the adsorption.Then,the fitted Ea and E_Hin the modified D-A model are compared,and the magnitude of the non-specific interaction in the binary solute system is quantitatively analyzed.It is concluded that the non-specific interaction of solute in the competitive system changes little compared with the single solute adsorption.However,different solutes show different competitive ability,and the solutes with strong specific interaction are more competitive in the binary solute system,indicating that the specific force between adsorbents and adsorbates is the main factor affecting competitive adsorption behavior.This result is consistent with that of ternary solute system.Similarly,the nitro-substituted organic compounds on XAD-7 show a large equilibrium adsorption capacity.The fitting E₀and b values of organic compounds on MN200 resin are higher than those on XAD-7,respectively.