Polymeric coatings are commonly applied to impart functionality and colloidal stability to engineered nanoparticles. In natural environments, transformations of the coating can modify the particle transport behavior, but the mechanisms and outcomes of these transformations have not yet been thoroughly evaluated. This study investigates the photo-transformations of polyvinylpyrrolidone (PVP) coatings on gold nanoparticles (AuNPs) under ultraviolet (UV) irradiation, representing light exposure in surface waters or other sunlit environments, and the impact on the AuNP colloidal stability. Multiple orthogonal characterization methods were applied to interrogate UV-induced transformations and their consequences. Rapid oxidation of the PVP coating occurred upon UV exposure. The transformed PVP largely persisted on the AuNP surface, albeit in a collapsed polymer layer around the AuNP surface. This transformation resulted in drastically diminished colloidal stability of the AuNPs, consistent with loss of steric stabilization. While the residual coating modified the interaction of the AuNPs with calcium counterions, it did not prevent subsequent stabilization by humic acid. This study demonstrates the importance of both chemical and physical coating transformations on nanoparticles, and hence the need for orthogonal and complementary characterization methods to fully characterize the coating transformations. Finally, the specific transformations of the PVP-coated AuNPs investigated here are discussed more broadly with respect to generalizability to other polymer-coated NPs and the implications for their fate in sunlit or other reactive environments.

中文翻译：

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金纳米粒子上聚乙烯吡咯烷酮（PVP）涂层的紫外光氧化

聚合物涂层通常用于赋予工程纳米颗粒以功能性和胶体稳定性。在自然环境中，涂层的转变可以改变颗粒的传输行为，但是这些转变的机制和结果尚未得到充分评估。这项研究调查了在紫外线（UV）照射下金纳米颗粒（AuNPs）上聚乙烯吡咯烷酮（PVP）涂层的光变，这表示在地表水或其他阳光照射的环境中的光暴露，以及对AuNP胶体稳定性的影响。多种正交表征方法被应用于询问UV诱导的转变及其后果。紫外线暴露后，PVP涂层迅速氧化。转化后的PVP大部分保留在AuNP表面上，尽管在AuNP表面周围有塌陷的聚合物层。这种转化导致AuNPs的胶体稳定性大大降低，这与空间稳定性的丧失相一致。尽管残留的涂层改变了AuNPs与钙抗衡离子的相互作用，但它并不能阻止腐殖酸随后的稳定作用。这项研究证明了纳米颗粒化学和物理涂层转化的重要性，因此需要正交和互补的表征方法来完全表征涂层转化。最后，本文讨论了PVP包覆的AuNPs的具体转化，涉及对其他聚合物包覆的NP的通用性及其在阳光或其他反应性环境中的命运的含义。