微塑料加速老化及分离过程的实验研究

微塑料自然老化的长期性严重限制了老化微塑料的相关研究. 为了加速微塑料老化，并提高实验室分离效果，以高密度聚乙烯微塑料(high-density polyethylene，HDPE)为试验材料，通过单紫外(UV)和紫外活化过硫酸盐(UV+P)两种方法加速模拟微塑料自然老化，并基于老化过程中微塑料特性的改变，改进分离方法. 将虹吸管插入静置分层后的澄清液面底部，打开真空抽滤机使液体缓缓注入抽滤瓶，一方面分离浮于上部的微塑料，另一方面有效过滤澄清液体中的部分微塑料，以提高样品分离效率；通过扫描电子显微镜(SEM)、傅里叶红外光谱(FTIR)和羰基指数(carbonyl index，CI)分别表征微塑料老化前后的形貌、官能团变化和老化程度. 结果表明:①相比于UV处理的微塑料，UV+P处理的微塑料具有更强的亲水性，表现在分离时长的显著性差异上(P<0.05). ②UV和UV+P两种老化方法产生的小分子有机物，通过4次清洗达到较高的去除率，分别为95.29%、94.71%. ③该分离方法下两种老化微塑料都有较高的样品产率，分别为84.63%(UV)、86.63%(UV+P). ④通过SEM观察到，与原始微塑料相比，老化后的微塑料表面出现明显裂纹、缝隙及小孔，且两种老化方法得到的微塑料其表面形态有所差异. ⑤FTIR图谱下，老化微塑料有异于原始样品的特征峰出现，主要为羰基峰及羟基峰. ⑥CI分析表明，HDPE在5 d内即可达到较高的老化程度，此时CI分别为0.39(UV)、0.49(UV+P). 研究显示:单紫外(UV)和紫外活化过硫酸盐(UV+P)两种老化方法均能获得亲水性、表面形态和官能团有异于原始微塑料的样品；改进的分离方法能够快速、高效地获取样品. 

Laboratory Accelerated Aging and Separation Process of Microplastics

The extremely low weathering rate of microplastics in the environment is a current problem, which greatly restricts the understanding of microplastics and limits their research. To accelerate the aging of microplastics and improve laboratory separation, high-density polyethylene (HDPE) was aged by two methods, namely ultraviolet (UV) radiation and UV-activated persulfate (UV+P) treatments. These methods simulated and accelerate the aging of microplastics. During the aging process, separation methods were improved based on microplastics property changes, which increased the separation efficiency. The specific methods are as follows: Put siphon tube into the bottom of the clarified liquid after resting and layering, and vacuum filter the liquid slowly into the filter bottle through the pipe. This method can separate floated microplastics and effectively filter suspended microplastics from clarified liquids. The surface morphology of HDPE was characterized by scanning electron microscopy (SEM). The functional groups and degree of aging were determined using Fourier infrared spectroscopy (FTIR) and the carbonyl index (CI), respectively. The results showed that the UV+P treated microplastics were more hydrophilic than the UV treated microplastics, as shown by the significant difference in separation time (P<0.05). During the aging process, the removal rates of small organic molecules by four cleanings reached 95.29% and 94.71%. The two aged microplastics had high yields of 84.63% (UV) and 86.63% (UV+P) under this separation method. The SEM images showed that the aged microplastics had a rough surface with many cracks and small holes compared with the original HDPE. The two different aging methods may potentially influence the surface morphology of microplastics. FTIR showed that new peaks, mainly attributed to carbonyl and hydroxyl groups, were detected in aged microplastics but were not present in virgin microplastics. CI showed that microplastics can reach a high degree of aging in 5 days, and the Cis were 0.39 (UV) and 0.49 (UV+P). Overall, the two aging methods (UV and UV+P) can obtain microplastics that differ from the original microplastics in terms of hydrophilicity, surface morphology and functional groups. The improved separation method can obtain samples rapidly and efficiently.