State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; Institute of Environment and Health, Jianghan University, Wuhan 430056, China.
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; Institute of Resources and Environment, Henan Polytechnic University, Jiaozuo 454000, China.
Environ Pollut. 2017 Jun;225:66-73. doi: 10.1016/j.envpol.2017.03.048. Epub 2017 Mar 26.
Photo-reduction of Ag to silver nanoparticle (AgNPs) by dissolved organic matter (DOM) is a possible source of naturally occurring AgNPs. However, how this photo-reduction process is influenced by ubiquitous metal ions is still not well understood. In addition, in previous studies, the formation of AgNPs in DOM solution was usually monitored by UV-Vis spectroscopy, and there is still lack of quantitative analysis for the formed AgNPs. In the present study, the role of Fe/Fe at environmental concentration level on this photochemical process was investigated, and the enhanced formation of AgNPs by Fe/Fe was probed and quantified by using UV-Vis spectroscopy, transmission electron microscopy, and liquid chromatography-inductively coupled plasma mass spectrometry. It was demonstrated that while Fe can oxidize AgNPs to release Ag, Fe can reduce Ag into AgNPs. However, the DOM-induced reduction of Fe makes iron an effective electron shuttle between DOM and Ag, and both Fe and Fe enhanced AgNP formation. The impacts of environmentally relevant factors, including DOM concentration and solution pH, on this process were studied comprehensively, which showed that the catalytic role of iron was more significant at higher DOM concentration and lower pH. This iron-enhanced formation of AgNPs in photo-irradiated Ag-DOM solution have great environmental implications on the formation of natural AgNPs and the transformation of engineered AgNPs in acidic surface water with high iron content.
溶解态有机质（DOM）将银还原为银纳米颗粒（AgNPs）的光还原作用可能是天然 AgNPs 的一个来源。然而，普遍存在的金属离子如何影响这一光还原过程仍不清楚。此外，在以前的研究中，通常通过紫外-可见光谱监测 DOM 溶液中 AgNPs 的形成，而对于形成的 AgNPs 仍缺乏定量分析。在本研究中，研究了环境浓度水平的 Fe/Fe 对这一光化学过程的作用，并通过紫外-可见光谱、透射电子显微镜和液相色谱-电感耦合等离子体质谱对 Fe/Fe 增强 AgNPs 的形成进行了探测和定量分析。结果表明，虽然 Fe 可以将 AgNPs 氧化为 Ag 释放出来，但 Fe 也可以将 Ag 还原为 AgNPs。然而，DOM 诱导的 Fe 还原使得铁成为 DOM 和 Ag 之间有效的电子穿梭体，Fe 和 Fe 都增强了 AgNP 的形成。全面研究了环境相关因素，包括 DOM 浓度和溶液 pH 值对这一过程的影响，结果表明，在较高的 DOM 浓度和较低的 pH 值下，铁的催化作用更为显著。在高铁含量的酸性地表水，光辐照下 Ag-DOM 溶液中这种铁增强的 AgNPs 形成，对天然 AgNPs 的形成和工程 AgNPs 的转化具有重要的环境意义。
