Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 51, Issue 4, Pages 2288-2294Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.6b04315
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Funding
- National Natural Science Foundation of China (NSFC) [21677107, 51578398]
- Collaborative Innovation Center for Regional Environmental Quality
- State Key Laboratory for Pollution Control and Resource Reuse
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A nanostructure-based mechanism is presented on the enrichment, separation, and immobilization of arsenic with nanoscale zero-valent iron (nZVI). The As-Fe reactions are studied with spherical aberration corrected scanning transmission electron microscopy (Cs-STEM). Near-atomic resolution (<1 nm(3)) electron tomography discovers a thin continuous layer (23 +/- 3 angstrom) of elemental arsenic sandwiched between the iron oxide shell and the zerovalent iron core. This points to a unique mechanism of nanoencapsulation and proves that the outer layer, especially the Fe(0)-oxide interface, is the edge of the As-Fe reactions. Atomic resolution imaging on the grain boundary provides strong evidence that arsenic atoms diffuse preferably along the nonequilibrium, high-energy, and defective polycrystalline grain boundary of iron oxides. Results also offer direct evidence on the surface sorption or surface complex formation of arsenate on ferric hydroxide (FeOOH). The core-shell structure and unique properties of nZVI clearly underline rapid separation, large capacity, and stability for the treatment of toxic heavy metals such as cadmium, chromium, arsenic, and uranium.
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