| Bisphenol A(BPA)and bisphenol S(BPS)are typical environmental endocrine disruptors that have been reported to be detected in a large number of aquatic and soil environments,showed that they pose various threats to ecological safety.Iron oxides are widely distributed in the soil environment,with abundant hydroxyl groups and large specific surface area,and have good adsorption properties for BPA and BPS.In this study,batch adsorption experiments,FT-IR and XPS were used to investigate the adsorption behavior and mechanism of action of BPA and BPS on the surface of goethite,hematite and ferrihydrite.The results of the study contribute to the understanding of the environmental behavior of BPA and BPS in soil,and are of guidance for scientific assessment and management of environmental risks.The following main conclusions are obtained:(1)The equilibrium adsorption amounts of ferrihydrite,goethite and hematite were12.26,11.59 and 8.94 mg/g for BPA and 13.61,5.60 and 2.32 mg/g for BPS,respectively.The equilibrium time for the adsorption of BPA and BPS by the three iron oxides was within 12 h,and no desorption occurred within 36 h after the equilibrium was reached,and the adsorption amounts were relatively stable.The specific surface areas of ferrihydrite,goethite and hematite were 288.5,78.6 and 51.8 m~2/g,respectively,as measured by BET.The adsorption amounts of BPA and BPS by the three iron oxides were positively correlated with the specific surface area.(2)The adsorption kinetic curves of goethite and hematite for BPA and BPS were more consistent with the PFO kinetic model,while the PSO kinetic model could better fitted the adsorption kinetic curves of ferrihydrite for BPA and BPS.The fitted lines of the W-M model for all three iron oxides do not pass through the origin,indicating that the adsorption rates of BPA and BPS are controlled by a combination of intraparticle diffusion and surface adsorption.The Langmuir model can better fitted the isothermal adsorption lines of the three iron oxides,indicating that BPA and BPS are adsorbed on the iron oxide surface as a single molecular layer.(3)The adsorption thermodynamic parameters indicated that the adsorption of BPA and BPS on goethite,hematite and ferrihydrite are spontaneous,entropy-decreasing exothermic reactions.The Gibbs free energy changeΔG for the adsorption of BPA and BPS on the three iron oxides is within-21.22 to-24.12 k J/mol,indicating that the adsorption of BPA and BPS on iron oxides is caused by a combination of different physicochemical interactions.(4)The effect of solution pH on the adsorption of goethite,hematite and ferrihydrite was mainly attributed to electrostatic interaction.The adsorption of BPA by the three iron oxides did not change much under the solution p H of acidic and neutral conditions,while it decreased significantly under alkaline conditions.The adsorption of BPS on the three iron oxides showed a trend of increasing and then decreasing with the increase of the solution p H,and reached the maximum at p H 6-8.With increasing ionic strength,the adsorption of BPA and BPS by goethite slightly increased,while the adsorption of hematite and ferrihydrite decreased,which was the result of multiple effects of salt precipitation effect,electrostatic effect and competitive adsorption.The adsorption of all three iron oxides was inhibited by Cd(Ⅱ)and Ca(Ⅱ),and the inhibitory effect of Cd(Ⅱ)was stronger than that of Ca(Ⅱ).In the two-solute system,BPA and BPS were competitively adsorbed,and the competitive adsorption capacity of BPS was stronger than that of BPA.(5)FT-IR results showed that hydrogen bonds were formed during the adsorption of BPA and BPS by all three iron oxides,and there was a clear chemisorption process for the adsorption of BPA and BPS by ferrihydrite.XPS results showed that the hydrogen bonds were mainly formed by the hydroxyl H on the surface of iron oxides with hydroxyl O in BPA and BPS and sulfonyl O in BPS;the hydroxyl oxygen peak areas of iron oxides all showed a decreasing trend,which indicated the involvement of Fe-OH in the adsorption reaction and the surface complexation of BPA and BPS by using the surface hydroxyl groups of iron oxides as binding sites.The main mechanisms of BPA adsorption by goethite,hematite,and ferrihydrite include hydrophobic interaction,hydrogen bonding and surface complexation;the main mechanisms of BPS adsorption include electrostatic interaction,hydrogen bonding and surface complexation. |
