Inter-transformation between silver nanoparticles and Ag + induced by humic acid under light or dark conditions
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Inter-transformation between silver nanoparticles and Ag+ induced by humic acid under light or dark conditions Yujia Liu1,2 Chao Li1 Si Luo2 Xi Wang2 Qingmei Zhang3 Haiyong Wu1 ●
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Accepted: 29 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The fate and toxicity of silver nanoparticles (AgNPs) and ions in water bodies is largely determined by the natural organic matter (NOM)-mediated redox cycling. However, the process of NOM-mediated redox cycling in the day/night cycles remains elusive. In this study, the inter-transformation between AgNPs and Ag+ ion caused by humic acid (HA) was investigated under controlled light and dark conditions. It was shown that HA induced the reduction of Ag+ into AgNPs in simulated sunlight, and also oxidize AgNPs to release Ag+ in darkness. Kinetics data demonstrated that the rates of AgNPs formation and dissolution increased along with the increment of HA concentrations. Along with the pH increase, the reduction of Ag+ accelerated, but the oxidative dissolution of AgNPs was inhibited. In day-night cycles, the AgNPs and Ag+ concentrations exhibited similar waveshaped change curves. The peaks of AgNPs and Ag+ ion appeared at 7 p.m. and 7 a.m., respectively. The toxicity of AgNPs/ Ag+ to Escherichia coli was determined primarily by the concentration of dissolved Ag+, but also affected by the particlespecific toxicity. The dual role of HA implied that previous reports about the photo-reduction of Ag+ to AgNPs by NOM should be reconsidered, and the oxidizability of HA in darkness strongly affect the transformation and toxicity of AgNPs in water. Keywords AgNPs Reduction Oxidation Natural organic matter Sunlight ●
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Introduction Silver nanoparticles (AgNPs) and various silver compounds are increasingly used in an wide range of applications, including bactericides, medical, toys, electrical produces, and etcetera (Chao et al. 2011; Li et al. 2015).
Supplementary information The online version of this article (https:// doi.org/10.1007/s10646-020-02284-3) contains supplementary material, which is available to authorized users. * Qingmei Zhang [email protected] * Haiyong Wu [email protected] 1
Soil and Fertilizer Institute of Hunan Province, Hunan Academy of Agricultural Sciences, 401125 Changsha, China
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College of Resources and Environment, Hunan Agricultural University, 410128 Changsha, China
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Hunan Provincial Environmental Protection Air Compound Pollution Prevention Engineering Technology Center, Hunan Research Academy of Environmental Science, 410004 Changsha, China
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The AgNPs and silver ions (Ag+) are inevitably released into the aquatic environment by human activities, e.g., laundering and skin cleaning, which is believed to be the major resource of AgNPs in the wastewater (Benn and Westerhoff 2008; Kaegi et al. 2011). Previous study demonstrated high removal efficiency of AgNPs in municipal sewage plant (Li et al. 2013), however, AgNPs discharged from manufacturing and disposal of co
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