Nanoparticulate zero valent iron interaction with dissolved organic matter impacts iron transformation and organic carbon stability

Although there is an increasing use of nanoparticulate zero-valent iron (nZVI) in the remediation of contaminated soil and water environments, there is still little understanding of the mechanisms of interaction between nZVI and dissolved organic matter (DOM), including the resulting effects on the fate and functions of both nZVI and DOM. Using a manifold analytical design, the adsorption of DOM (humic acid and fulvic acid) by nZVI (two kinds of naked nZVIs of different sizes and one kind of carboxymethyl cellulose (CMC)-coated nZVI) was investigated. In addition, the effects of this sorption on DOM chemical stability and on nZVI transformation were systematically investigated. The CMC coating on nZVI limited the adsorption of DOM. DOM fractions of moderate and high molecular weights (MW, >3 kDa) had a relatively high affinity to bare nZVI surfaces, whereas the low MW fractions such as quinone-like and protein-like fluorophores preferentially remained in the aqueous phase. Interaction with DOM accelerated the oxidation of the core Fe(0)of nZVI due to the strong iron chelating action of aqueous DOM and potential electron transfer mediating action of the limitedly adsorbed quinone-like DOM fractions. Compared with pristine DOM, the DOM fraction with nZVI was much more stable, while the residual DOM fraction in the aqueous phase after the nZVI adsorption had lower photochemical/chemical stability as indicated by the greater reduction capability, mineralization percentage, and photodegradation percentage. These findings increase our understanding of the effects of nZVI interaction with DOM and have implications on the carbon cycle and on the large scale use of nZVI.