The core-shell nature of nanoscale zero-valent iron (nZVI) offers the nanoparticles with fascinating reactivity towards numerous organic pollutants and toxic heavy metals. This unique nanostructure and activity relationship is investigated from the reactions with As(V), which are mapped at sub-nanometer scale with the spherical aberration-corrected scanning transmission electron microscopy (STEM) integrated with electron energy loss spectroscopy (EELS) and X-ray energy dispersive spectroscopy (XEDS). Atomically resolved EELS at the oxygen K-edge unfold that the Fe species in nZVI are well stratified from Fe(III) oxides in the outermost periphery, to a mixed Fe (III)/Fe(II) interlayer, then Fe(II) oxide and the pure Fe(0) phase. This suggests that a well-structured local redox gradient within the shell layer and a favorable conduit for electron transfer from the iron core to the surface-bound As(V). High-resolution X-ray photoelectron spectroscopy with ion sputtering discovers that arsenic species shift from As(V), As(III)/As(V) to As(V)/As(III)/As(0) from the nZVI/water interface to the Fe(0) core. Results reinforce previous work on the efficacy of nZVI for arsenic removal and remediation while the methods of analytical TEM are also applicable to the study of environmental interfaces and surface chemistry.

Core–shell nature of nanoscale zero-valent iron (nZVI) for arsenate removal: A case of structure-activity relationship

2019 Spring National Meeting

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