Freezing Facilitates Formation of Silver Nanoparticles under Natural and Simulated Sunlight Conditions.
Freezing Facilitates Formation of Silver Nanoparticles under Natural and Simulated Sunlight Conditions.
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DOI：
10.1021/acs.est.9b05926
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发表时间：
2019-11
影响因子：
11.4
通讯作者：
Zhiqiang Tan;Xiaoru Guo;Yongguang Yin;Bowen Wang;Qingsheng Bai;Xia Li;Jing-fu Liu;G. Jiang
中科院分区：
文献类型：
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作者：
Zhiqiang Tan;Xiaoru Guo;Yongguang Yin;Bowen Wang;Qingsheng Bai;Xia Li;Jing-fu Liu;G. Jiang
在光介导的有机污染物转化过程中，冷冻是必不可少的。然而，冷冻过程对天然有机物(NOM)还原Ag+的影响尚不清楚，这给自然形成纳米银(AgNPs)带来了很大的不确定性。本研究研究了在自然和受控冷冻条件下，NOM对Ag+的太阳光诱导还原作用。自然(室外)冻结实验表明，在自然阳光照射下，AgNPs在三种水介质(包括一种天然溶液和两种河水)中有强烈的聚集和沉淀。室内模拟日光照射和受控冻结实验表明，在-20℃和反复冻融循环(-20°C~4℃)下，与在4℃下保持相比，极大地促进了AgNPs的形成和生长。最后，在自然冻结过程中，商业AgNPs可能通过降低溶解速度和与新形成的AgNP在河水样品中形成均一聚集体来影响Ag+的氧化还原还原。此外，在与环境有关的浓度水平上，特别是在光照条件下，当Ag+和AgNPs同时存在时，冷冻对AgNPs的形成具有促进作用。这项工作强调了冷冻过程对AgNPs自然形成的重要性。
Freezing is essential in the light-mediated transformation of organic pollutants. However, the effects of the freezing process on the reduction of Ag+ by natural organic matter (NOM) remains unclear, causing significant uncertainties in the natural formation of silver nanoparticles (AgNPs). This study investigated the sunlight-induced reduction of Ag+ by NOM under natural or controlled freezing processes. Natural (outdoor) freezing experiments demonstrated intense aggregation and precipitation of AgNPs in three aqueous media including a NOM solution and two river waters, under natural sunlight irradiation. Indoor experiments under simulated sunlight irradiation and controlled freezing processes showed that freezing at -20 °C and repeated freeze-thaw cycles (-20 °C to 4 °C) drastically accelerated the formation and growth of AgNPs compared to maintenance at 4 °C. Finally, under the natural freezing process, commercial AgNPs were found to influence the redox reduction of Ag+ probably through a reduction in dissolution rates and homoaggregation with AgNP newly formed in the river water samples. Additionally, the enhancement effect of freezing on AgNPs formation was confirmed in the presence of Ag+ and AgNPs both at environmentally relevant concentration levels, especially upon light irradiation. This work emphasizes the importance of freezing processes on the natural formation of AgNPs.