This study investigated the possible natural formation of silver nanoparticles (AgNPs) in Ag(+)-fulvic acid (FA) solutions under various environmentally relevant conditions (temperature, pH, and UV light). Increase in temperature (24-90 degrees C) and pH (6.1-9.0) of Ag(+)-Suwannee River fulvic acid (SRFA) solutions accelerated the appearance of the characteristic surface plasmon resonance (SPR) of AgNPs. The rate of AgNP formation via reduction of Ag(+) in the presence of different FAs (SRFA, Pahokee Peat fulvic acid, PPFA, Nordic lake fulvic acid, NLFA) and Suwannee River humic acid (SRHA) followed the order NLFA > SRHA > PPFA > SRFA. This order was found to be related to the free radical content of the acids, which was consistent with the proposed mechanism. The same order of AgNP growth was seen upon UV light illumination of Ag(+)-FA and Ag(+)-HA mixtures in moderately hard reconstituted water (MHRW). Stability studies of AgNPs, formed from the interactions of Ag(+)-SRFA, over a period of several months showed that these AgNPs were highly stable with SPR peak reductions of only ~15%. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements revealed bimodal particle size distributions of aged AgNPs. The stable AgNPs formed through the reduction of Ag(+) by fulvic and humic acid fractions of natural organic matter in the environment may be transported over significant distances and might also influence the overall bioavailability and ecotoxicity of AgNPs.

中文翻译：

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Ag +水溶液与黄腐酸的相互作用：银纳米颗粒形成的机理和稳定性的研究。

这项研究调查了在各种环境相关条件（温度，pH值和紫外线）下，Ag（+）-富里酸（FA）溶液中银纳米颗粒（AgNPs）可能的自然形成。Ag（+）-Suwannee河富叶酸（SRFA）溶液的温度（24-90摄氏度）和pH（6.1-9.0）升高，加速了AgNPs的特征性表面等离振子共振（SPR）的出现。通过在不同FAs（SRFA，Pahokee泥炭黄腐酸，PPFA，Nordic湖黄腐酸，NLFA）和Suwannee河腐殖酸（SRHA）存在下还原Ag（+）形成AgNP的速率遵循NLFA> SRHA> PPFA> SRFA。发现该顺序与酸的自由基含量有关，这与所提出的机理是一致的。在中等硬度的再生水中（MHRW）中的Ag（+）-FA和Ag（+）-HA混合物的紫外线照射下，可以看到相同顺序的AgNP生长。由Ag（+）-SRFA相互作用形成的AgNP的稳定性研究历时数月，显示这些AgNP高度稳定，SPR峰降低仅约15％。透射电子显微镜（TEM）和动态光散射（DLS）测量显示了老化AgNPs的双峰粒度分布。通过环境中天然有机物的富里腐酸和腐殖酸级分减少Ag（+）形成的稳定AgNPs可能会迁移很远的距离，并且可能还会影响AgNPs的整体生物利用度和生态毒性。由Ag（+）-SRFA的相互作用形成的，经过几个月的研究表明，这些AgNP高度稳定，SPR峰仅降低了约15％。透射电子显微镜（TEM）和动态光散射（DLS）测量显示了老化AgNPs的双峰粒度分布。通过环境中天然有机物的富里腐酸和腐殖酸级分减少Ag（+）形成的稳定AgNPs可能会迁移很远的距离，并且可能还会影响AgNPs的整体生物利用度和生态毒性。由Ag（+）-SRFA的相互作用形成的，经过数月的研究表明，这些AgNPs高度稳定，SPR峰降低仅约15％。透射电子显微镜（TEM）和动态光散射（DLS）测量显示了老化AgNPs的双峰粒度分布。通过环境中天然有机物的富里腐酸和腐殖酸级分减少Ag（+）形成的稳定AgNPs可能会迁移很远的距离，并且可能还会影响AgNPs的整体生物利用度和生态毒性。