BPA和EE2在PA微塑料上竞争吸附的位点能量

为研究微塑料上雌激素共存的吸附行为，以17α-乙炔基雌二醇（EE2）和双酚A （BPA）为目标污染物，微塑料聚酰胺（PA）为吸附剂，通过等温吸附实验研究二者在单溶质和双溶质体系下的吸附性能，基于位点能量分布理论进一步剖析二者在PA微塑料上的的吸附特性.同时，采用X射线光谱（XPS）以及傅里叶变换红外光谱（FTIR）对吸附前后的PA微塑料进行表征，探究其可能存在的吸附机理.等温吸附拟合结果及XPS、FTIR的表征结果表明BPA和EE2及二者混合溶液在PA上的吸附属于非均质吸附，疏水分配及氢键作用为主要的吸附机制.位点能量分布分析结果表明，相同浓度（1～4mg/L）条件下，BPA吸附位点主要分布于高能量区；单溶质体系的EE2吸附位点主要集中于低能量区.双溶质体系下，相同浓度的两种物质位点分布函数均随着位点能量的增大而呈指数降低，BPA下降趋势较为平缓，吸附位点分布更集中.两种体系相比较，BPA平均位点能量和位点能量非均质性分别增加了0.749%和2.483%，吸附位点数量减少了10.852%；双溶质体系下EE2平均位点能量降低0.813%，位点能量非均质性增加1.870%，吸附位点数量增加42.429%.双酚A和EE2在PA微塑料上的竞争吸附中，EE2占优势.

Competitive adsorption characteristics of BPA and EE2 on PA microplastics by site energy distribution theory

Microplastics have been driving extensive attention due to their widespread existence and potential threats. 17α-Ethinyl estradiol (EE2) and bisphenol A(BPA) were used as target pollutants, and microplastic polyamide (PA) was used as adsorbent, to study the adsorption behavior of estrogen coexisting on microplastics. The adsorption isothermal properties of the two in single solute and double solute systems were studied by isothermal adsorption experiments. The adsorption characteristics of the two solvend on PA microplastics were further analyzed based on the site energy distribution theory. We charaterized PA before and after adsorption by X-ray photoelectron spectroscopy(XPS), and Fourier transform infrared spectroscopy(FTIR). We explored likely adsorption mechanisms of PA microplastics on different system(BPA-only, EE2-only, BPA-EE2) adsorption. The results of isothermal adsorption experiments and XPS and FTIR spectra showed heterogeneous adsorption of three adsorption systems on PA and hydrophobic distribution and hydrogen bonding are the main adsorption mechanisms. The results of site energy distribution analysis showed, in the system that contained the same concentration (1~4mg/L) of single contaminants, the adsorption sites of bisphenol A were mainly distributed in the high energy level, whereas the adsorption sites of 17α-acetylenestradiol were mainly concentrated in the low energy level. In the system containing the concentration (1~4mg/L) of dual contaminants, exponential decrease was found for the distribution functions of both substances with the increasing site energy, the decrease trend of bisphenol A was more moderate, and the distribution of adsorption sites was more uniform. The average site energy and site energy heterogeneity of bisphenol A increased by 0.749% and 2.483%, respectively, and the number of adsorption sites was decreased by 10.852%; In the dual-contaminant system, the average site energy of EE2 decreased by 0.813%, the site energy heterogeneity increased by 1.870%, and the number of adsorption sites increased by 42.429%. In the competitive adsorption of bisphenol A and EE2 on PA, microplastics, EE2was dominant. This study has certain reference significance for the competitive adsorption of coexisting organic pollutants.