Journal
JOURNAL OF CONTAMINANT HYDROLOGY
Volume 118, Issue 3-4, Pages 96-104Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jconhyd.2010.09.003
Keywords
Zero-valent iron; Nanoparticles; Core-shell model; Hydrogen sulfide; Heavy metals; Mercury; Zinc
Funding
- NASA
- Pennsylvania Infrastructure Technology Alliance (PITA)
- US Environmental Protection Agency (EPA) [R829625, GR832225]
- EPA [R829625, 1099896, GR832225, 909038] Funding Source: Federal RePORTER
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Aspects of the core-shell model of nanoscale zero-valent iron (nZVI) and their environmental implications were examined in this work. The structure and elemental distribution of nZVI were characterized by X-ray energy-dispersive spectroscopy (XEDS) with nanometer-scale spatial resolution in an aberration-corrected scanning transmission electron microscope (STEM). The analysis provides unequivocal evidence of a layered structure of nZVI consisting of a metallic iron core encapsulated by a thin amorphous oxide shell. Three aqueous environmental contaminants, namely Hg(II), Zn(II) and hydrogen sulfide, were studied to probe the reactive properties and the surface chemistry of nZVI. High-resolution X-ray photoelectron spectroscopy (HR-XPS) analysis of the reacted particles indicated that Hg(II) was sequestrated via chemical reduction to elemental mercury. On the other hand, Zn(II) removal was achieved via sorption to the iron oxide shell followed by zinc hydroxide precipitation. Hydrogen sulfide was immobilized on the nZVI surface as disulfide (S-2(2-)) and monosulfide (S2-) species. Their relative abundance in the final products suggests that the retention of hydrogen sulfide occurs via reactions with the oxide shell to form iron sulfide (FeS) and subsequent conversion to iron disulfide (FeS2). The results presented herein highlight the multiple reactive pathways permissible with nZVI owing to its two functional constituents. The core-shell structure imparts nZVI with manifold functional properties previously unexamined and grants the material with potentially new applications. (C) 2010 Elsevier B.V. All rights reserved.
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