Photoreduction and Stabilization Capability of Molecular Weight Fractionated Natural Organic Matter in Transformation of Silver Ion to Metallic Nanoparticle

Abstract

Photoinduced reduction of silver ion (Ag + ) to silver nanoparticles (AgNPs) by dissolved organic matter (DOM) plays a crucial role in the transformation and transport of engineered AgNPs and Ag + in aquatic environments. DOM is a mixture of natural polymers with wide molecular weight (MW) distribution, and the roles of specific components of DOM in the photoreduction of Ag + to AgNPs are still not understood. In this study, MW fractionated natural organic matter (M f -NOM) were investigated for their roles on the photoreduction process and stabilization of the formed AgNPs. This photoinduced reduction process depends highly on pH, concentration of Ag + and NOM, light quality, and the MW of M f -NOM. Monochromatic radiation and light attenuation correction suggested that the difference of M f -NOM on reduction was mainly ascribed to the differential light attenuation of M f -NOM rather than the "real" reductive ability. More importantly, compared with low MW fractions, the high MW M f -NOMs exhibit drastically higher capability in stabilizing the photosynthesized AgNPs against Ca 2+ -induced aggregation. This finding is important for a better understanding of the differential roles of M f -NOM in the transformation and transport of Ag + and engineered AgNPs in DOMrich surface water.

Particle Coating-Dependent Interaction of Molecular Weight Fractionated Natural Organic Matter: Impacts on the Aggregation of Silver Nanoparticles

“…The MW distribution, UV−vis spectroscopy and fluorescence excitation−emission spectroscopy of M f -NOMs prepared by ultrafiltration was characterized in our previous study. 20 Generally, the molar absorptivity at 280 nm increased with the increasing of MW, indicating the abundances of aromatic moiety in higher MW M f -NOMs. In addition, the maximum intensity of fluorescence peaks (in the range of 350/ 452−370/468 nm) increased as the MW of M f -NOM decreased, suggesting the abundances of carboxylic moiety in lower MW M f -NOMs.…”

“…19 In our previous study, we observed that high MW Suwannee River NOM plays more significant role in stabilizing NOM-reduced AgNPs in the presence of Ca 2+ than low MW NOM. 20 These findings further highlighted the importance of the distinguishing roles of different NOM fractions in the transport and subsequent chemical transformation and toxicity of engineered AgNPs. However, in commercial AgNPs products, AgNPs are often modified with various capping agents or coatings, which make the interaction between AgNPs and NOM more complicated.…”

Source and Pathway of Silver Nanoparticles to the Environment

“…In addition, as DOM is a mixture with wide molecular weight (MW) distribution, the exact roles of specific components of DOM in the photoreduction of Ag + to AgNPs are still not well understood. In a recent study [28], we found that the difference of MW fractionated natural organic matter (M f -NOM) on photoreduction of Ag + was mainly ascribed to the differential light attenuation of M f -NOM, rather than the "real" reductive ability. More importantly, compared with low MW fractions, high MW M f -NOMs showed drastically higher capability in stabilizing the photosynthesized AgNPs against Ca 2+ -induced aggregation.…”

Superoxide-Mediated Extracellular Biosynthesis of Silver Nanoparticles by the Fungus Fusarium oxysporum

“…This red-shift was also observed for AgNPs in the presence of Cu 2+ , which should be ascribed to the divalent metal ion-induced aggregation and fusion of AgNPs. 32,33 Then, SOD, a specific superoxide scavenger, 34,35 was added to the growing cultures to further validate the role of superoxide in AgNP formation. Figure 3B shows that SOD can partially abolish the formation of AgNPs by F. oxysporum, demonstrating the critical role of superoxide in the reduction of silver.…”

“…The different peak shape of spectra indicated the different sizes or aggregation states of AgNPs, 33 which may be associated with the experimental batchdependent composition and concentration of extracellular polymeric substances that play an important role in stabilizing AgNPs. 36 Activity of Enzymes Responsible for Superoxide Production.…”