Aggregation behavior determines the fate and bioavailability of nanoparticles in aquatic environments. This study investigated the effect of UV irradiation and salts (NaCl, Na₂SO₄, CaCl₂, and Na₃PO₄) on the aggregation of three polystyrene nanoparticles (PSNPs) with various surface functional groups. UV irradiation promoted the aggregation of pristine PSNPs in NaCl (>100 mM) and amino-modified PSNPs (PSNPs-NH₂) in NaCl (≥100 mM) or Na₂SO₄ (≥100 mM) solutions. Under UV irradiation, hydroxyl radicals (˙OH) degraded the sulfate groups of PSNPs and amino groups of PSNPs-NH₂ and decreased electrostatic repulsion forces among particles. Carboxyl-modified PSNPs (PSNPs-COOH) were relatively stable in NaCl and Na₂SO₄ solutions because of their high negative surface charge and hydrophilicity even after UV irradiation. Similarly, because the negative surface charge of PSNPs and PSNPs-NH₂ in CaCl₂ (1–50 mM) remained high under UV exposure, the strong electrostatic forces retarded the UV effect on the aggregation of PSNPs and PSNPs-NH₂. However, UV irradiation accelerated PSNPs-COOH aggregation in CaCl₂ (≥20 mM), probably because UV irradiation generated more carboxyl groups, which bind with Ca²⁺ and increase aggregation via a bridging effect. PO₄³⁻ inhibited ˙OH photogeneration and stabilized the three types of PSNPs. Our study reveals the intriguing effects of light irradiation and salts on the aggregation behavior of emerging plastic nanoparticles in aquatic environments.

中文翻译：

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紫外线诱导的聚苯乙烯纳米塑料的聚集：自由基，表面官能团和电解质的影响

聚集行为决定了水生环境中纳米颗粒的命运和生物利用度。这项研究调查了紫外线辐射和盐（NaCl，Na ₂ SO ₄，CaCl ₂和Na ₃ PO ₄）对具有各种表面官能团的三种聚苯乙烯纳米颗粒（PSNP）聚集的影响。紫外线照射促进了NaCl（> 100 mM）中原始PSNPs的聚集和NaCl（≥100mM）或Na ₂ SO ₄（≥100mM）溶液中氨基修饰的PSNPs（PSNPs-NH ₂）的聚集。在紫外线照射下，羟基自由基（˙OH）降解PSNPs的硫酸根和PSNPs-NH _2的氨基并降低了颗粒之间的静电排斥力。羧基修饰的PSNP（PSNPs-COOH）在NaCl和Na ₂ SO ₄溶液中相对稳定，因为即使在UV照射后，它们的负表面电荷和亲水性也很高。同样，由于CaCl ₂中PSNPs和PSNPs-NH ₂的负表面电荷（1-50 mM）在暴露于紫外线下仍然很高，因此强大的静电力阻碍了UV对PSNPs和PSNPs-NH ₂聚集的影响。然而，紫外线辐射加速了CaCl ₂（≥20mM）中PSNPs-COOH的聚集，可能是因为紫外线辐射产生了更多的羧基，这些羧基与Ca ²⁺结合并增加了聚集通过桥接效应。PO ₄ ^3-抑制˙OH的光生并稳定了三种类型的PSNP。我们的研究揭示了光辐射和盐对水生环境中新兴的塑料纳米粒子聚集行为的吸引作用。