聚氯乙烯微塑料对典型单羟基菲的吸附机制

为丰富微塑料与有机污染物间的相互作用机制相关数据,以3-羟基菲(3-OHP, C₁₄H₁₀O)为菲单羟基衍生物代表污染物,聚氯乙烯(PVC)微塑料为研究对象,研究了PVC微塑料在水环境中对3-OHP的吸附行为,并就相关吸附机制进行了深入探讨。该研究借助扫描电镜(SEM)、X射线衍射仪(XRD)、傅里叶红外光谱(FT-IR)等仪器对PVC微塑料进行表征,利用紫外分光光度计得出目标污染物的紫外吸收光谱标准曲线,标准曲线拟合相关系数(R²)>0.99。为保证紫外吸收光谱的准确性,污染物浓度梯度设置为吸光度(Abs)大于0.438,之后根据标准曲线方程计算其浓度,结合相关吸附模型(吸附动力学、吸附等温线和吸附热力学)并配合密度泛函理论(density functional theory, DFT)探讨了在水环境中PVC微塑料对3-OHP的吸附机制。结果如下:(1)吸附动力学实验结果显示伪二级动力学模型拟合程度最好,吸附动力学拟合系数R²=0.998。因此,PVC吸附3-OHP可能是以表面吸附和外液膜扩散的吸附方式,吸附发生24 h后的平衡吸附量为36.866 μg/g; (2)吸附等温线实验表明Langmuir和Freundlich等温线模型拟合度较高,吸附等温线拟合系数R ²分别为0.956和0.907,更加适合描述PVC对3-OHP的吸附过程,吸附模式主要为单层吸附,也存在小部分多层吸附,PVC对3-OHP的最大吸附量为408 μg/g; (3)吸附热力学结果显示PVC微塑料对3-OHP的吸附效率随着温度升高而降低,这表明PVC对3-OHP的吸附为自发、放热的吸附反应;(4)盐度实验结果表明,盐度对3-OHP在PVC上的吸附效率影响不大;(5)DFT理论计算结果表明PVC对3-OHP结合能相对较低,因此推测PVC对3-OHP的主要吸附机制可能是疏水作用,还可能存在弱氢键作用、卤素键作用以及π-π共轭作用。研究揭示了PVC微塑料与有机物相互作用方式,明确了PVC微塑料对3-OHP的吸附模式,探讨了PVC微塑料对3-OHP的相互作用机制,有助于更好地了解PVC微塑料在水溶液中的环境行为。该研究为科学评价微塑料的环境影响提供数据参考,并进一步补充了微塑料的毒理学机制数据。

To enrich data related to the interaction mechanism between microplastics and organic pollutants, in this study, 3-hydroxy-phenanthrene (3-OHP, C_l4H₁₀O), a phenanthrene derivative, was selected as a representative pollutant, and polyvinyl chloride (PVC) microplastics were chosen as the research objects. We investigated the adsorption behavior of 3-OHP on PVC microplastics in aqueous solutions and explored the adsorption mechanism in detail. The PVC microplastics were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The standard curves of the ultraviolet (UV) absorption spectrum of the target pollutant were obtained using a UV spectrophotometer. The fitting coefficient values of all standard curves were higher than 0. 99 (R² > 0. 99). To ensure the accuracy of the UV absorption spectrum, the pollutant concentration gradient was set according to the absorbance (Abs) values, which were higher than 0.438. The measured concentrations were calculated using a standard curve equation. The adsorption mechanism of 3-OHP on PVC microplastics in an aqueous solution was studied by combining adsorption models (adsorption kinetics model, adsorption isotherm model, and adsorption thermodynamics model) and density functional theory (DFT) calculations. The results are as follows： (1) From the adsorption kinetics experiment, the pseudo-second-order kinetic model had the best fitting degree, and the fitting coefficient of adsorption kinetics was 0. 998 (R² = 0. 998). Hence, 3-OHP adsorption on PVC microplastics may be attributed to surface adsorption and external liquid film diffusion; the equilibrium adsorption amount was 36. 866 μg/g after 24 h. (2) The adsorption isotherm experiment showed that the Langmuir and Freundlich isotherm models were more suitable for describing the adsorption mechanism of 3-OHP adsorption on PVC microplastics because of the satisfactory fitting coefficient (R² = 0. 956 and 0. 907), suggesting that the adsorption mode was mainly single-layer adsorption with a small amount of multilayer adsorption. The maximum adsorption amount of 3-OHP adsorption on PVC microplastics was 408 μg/g; (3) the adsorption thermodynamics results showed that the adsorption efficiency of 3-OHP adsorption on PVC microplastics decreased with increasing temperature, indicating that the adsorption of 3-OHP on PVC microplastics was a spontaneous and exothermic adsorption process； (4) the salinity experiment results showed that salinity had little effect on the adsorption efficiency of 3-OHP on PVC microplastics； (5) DFT calculations showed that PVC had a relatively low binding energy to 3-OHP. Therefore, we suggest that the main adsorption mechanism of 3-OHP on PVC microplastics may be the hydrophobic effect； weak hydrogen bonding, halogen bonding, and π-π conjugate action could also play a role in 3-OHP adsorption on PVC. These results reveal the interaction mechanism between PVC microplastics and organic chemicals, and enhance our understanding of the environmental behavior of PVC microplastics in aqueous solutions. To serve as a reference in scientific evaluations of the environmental impact of microplastics, future studies should focus on obtaining toxicological data for the microplastics.