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摘要:
由于塑料制品大量使用和不当处置，环境中微塑料(尤其是纳米塑料)的地球化学行为已成为全球关注的热点问题。团聚效应是控制纳米塑料地球化学行为的重要因素。自然界中纳米塑料大小不一，然而已有的研究结果对于纳米塑料尺寸与团聚效应的关联性还存在一定矛盾。为揭示不同尺寸纳米塑料的团聚行为及影响作用机制，本文以50nm、100nm、200nm聚苯乙烯纳米塑料(PS50、PS100、PS200)为研究对象，利用动态光散射技术实时监测不同pH(3.0～10.0)及NaCl溶液(浓度0～800mmol/L)中纳米塑料的Zeta电位(ζ 电位)和水动力直径，并通过理论计算得到三种粒径纳米塑料的临界团聚浓度(CCC)和总相互作用能。PS50、PS100和PS200去离子水中的初始ζ电位分别为−35.2mV、−35.1mV和−38.2mV，高的表面负电荷使其在水中保持分散。离子强度增加引起的电荷屏蔽效应促进了纳米塑料的团聚，PS50、PS100、PS200在NaCl溶液中CCC值分别为325mmol/L、296mmol/L、264mmol/L，表明初始ζ电位值接近时，粒径越小的纳米塑料越稳定，能够在环境中较长时间地迁移。随着pH从酸性增加至碱性，纳米塑料表面酸性官能团发生去质子化，负电荷增多，导致其团聚行为受到抑制。当pH=7时，即使是在较高离子强度下(400mmol/L NaCl)，PS100 和 PS200基本恢复稳定，但 PS50 仍发生快速团聚，可能因为在此条 件下 PS50 的 ζ 电位仍较小(−19.3mV)。通过回归分析可知，三种尺寸纳米塑料的团聚行为与ζ电位密切相关(r2为0.70～0.88)。因此在实际应用中，需要综合考虑溶液pH、离子强度以及纳米塑料自身尺寸等容易影响ζ电位的因素，以更精准地预测和评估纳米塑料在自然环境中的地球化学行为。
Abstract:The geochemical behavior of microplastics (MPs) and nanoplastics (NPs) in the environment has become a global hot topic. Aggregation effect is an important factor controlling the geochemical behavior of NPs, yet there is conflicting evidence regarding the dependence of aggregation on NPs size. Investigating the general patterns and dominant mechanisms governing the aggregation behavior of different-sized NPs under various environmental conditions, will provide help in understanding and predicting the fate of NPs with different sizes. The study has shown that NPs with the same chemical composition but different sizes have different stability and mobility under the same conditions. The critical coagulation concentration (CCC) for NPs increases with the decrease in particle size at a fixed surface ζ potential (CCC=325mmol/L, 296mmol/L, 264mmol/L for 50nm, 100nm, and 200nm, respectively); indicating smaller NPs may transport longer distances. As the pH increased from 5.5 to 7, the negative surface charge of 100 and 200nm NPs allowed them to remain stable even at higher ionic strength. However, 50 nm NPs underwent rapid aggregation because of its smaller ζ potential. Therefore, the effects of pH, ionic strength and NPs sizes should be considered comprehensively in predicting and evaluating the geochemical behavior of NPs in the natural environment. The BRIEF REPORT is available for this paper at
http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202305020058 . -
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图 1 不同尺寸PSNPs的表征：a～c分别为PS50、PS100和PS200的TEM图像；d～f分别为与之对应DLS测量的平均水动力直径；g～i为三种PSNPs的 ζ 电位值随pH值的变化情况
Figure 1.
图 4 在不同pH条件下(pH=3、7、10)PS50 (a，d)、PS100 (b，e)、PS200 (c，f)在400mmol/L 氯化钠溶液中的团聚动力学和ζ电位值
Figure 4.
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