As an emerging pollutant, microplastics (MPs) may interact with dissolved organic matter (DOM) which is prevalent in the aqueous environment. Meanwhile, the aging of MPs in the actual environment increases the uncertainty of their environmental fate. Here, the interaction mechanisms between pristine and aged polypropylene microplastics (PP-MPs) and humic acid (HA) at pH 7.0 were explored. Microstructural changes of HA were examined by fluorescence and Fourier transformation infrared (FT-IR) spectroscopy. Atomic force microscopy coupled with infrared (AFM-IR) and micro-Raman techniques were used to characterize and analyze the interacted PP-MPs. The addition of HA increased the surface roughness of both pristine and aged PP-MPs. Results of AFM-IR and Raman spectra showed that the interaction of PP-MPs with HA accelerated their surface oxidation and enhanced the characteristic signals. XPS spectra showed that the oxygen content ratio of pristine and aged PP-MPs increased by 0.95% and 1.48% after the addition of HA, respectively. PP-MPs after aging interacted more strongly with HA and there was a higher affinity between them. Two-dimensional correlation spectroscopy (2D-COS) combined with FT-IR spectra further elucidated the interaction mechanism at the molecular level. This work will help to evaluate the environmental impact of MPs in ecosystems and understand their interactions with DOM.

作为一种新兴污染物，微塑料 (MPs) 可能与水环境中普遍存在的溶解有机物 (DOM) 相互作用。同时，实际环境中议员的老龄化增加了其环境命运的不确定性。在这里，探索了原始和老化的聚丙烯微塑料 (PP-MPs) 与腐殖酸 (HA) 在 pH 7.0 下的相互作用机制。通过荧光和傅里叶变换红外 (FT-IR) 光谱检查 HA 的微观结构变化。原子力显微镜结合红外 (AFM-IR) 和显微拉曼技术用于表征和分析相互作用的 PP-MP。HA 的添加增加了原始和老化 PP-MP 的表面粗糙度。AFM-IR和拉曼光谱结果表明，PP-MPs与HA的相互作用加速了它们的表面氧化并增强了特征信号。XPS 光谱显示，添加 HA 后，原始和老化 PP-MPs 的氧含量比分别增加了 0.95% 和 1.48%。老化后的PP-MPs与HA的相互作用更强烈，并且它们之间的亲和力更高。二维相关光谱（2D-COS）结合FT-IR光谱进一步阐明了分子水平的相互作用机制。这项工作将有助于评估 MPs 在生态系统中的环境影响，并了解它们与 DOM 的相互作用。老化后的PP-MPs与HA的相互作用更强烈，并且它们之间的亲和力更高。二维相关光谱（2D-COS）结合FT-IR光谱进一步阐明了分子水平的相互作用机制。这项工作将有助于评估 MPs 在生态系统中的环境影响，并了解它们与 DOM 的相互作用。老化后的PP-MPs与HA的相互作用更强烈，并且它们之间的亲和力更高。二维相关光谱（2D-COS）结合FT-IR光谱进一步阐明了分子水平的相互作用机制。这项工作将有助于评估 MPs 在生态系统中的环境影响，并了解它们与 DOM 的相互作用。