In this study, we demonstrated that
oxalate modification could
promote the Cr(VI) removal performance of zerovalent iron (ZVI) and
increase the removal rate constant by about 20 times. This dramatic
enhancement of Cr(VI) removal was attributed to the binding of oxalate
groups on the surface of ZVI in a monodentate mononuclear configuration.
The surface structure of oxalate-modified zerovalent iron (OA-ZVI)
and the Cr(VI) adsorption behaviors on ZVI and OA-ZVI were carefully
investigated. The theoretical results revealed that this oxalate modification
favored Cr(VI) adsorption on the ZVI surface with a much lower adsorption
energy and also accelerated electrons transfer from the iron core
to the surface, which could produce more surface Fe(II) to easily
reduce Cr(VI) via a single electron transfer pathway, greatly promoting
the reduction removal of Cr(VI). More importantly, OA-ZVI still remained
at a high Cr(VI) removal activity even after six cycles of use for
both simulated and real Cr(VI)-containing wastewaters, revealing its
excellent continuous Cr(VI) removal ability for practical application.
This study provides an environmental-benignity surface modification
method of ZVI and also highlights the importance of surface functional
groups on the Cr(VI) removal property of ZVI.
Microscale zero-valent iron is one of the most important multifunctional environmental remediation materials, yet its passivated iron oxide shell hampers the transportation of inherent electrons. Herein, the authors exert tensile strain onto mZVI by interstitial boron doping that destabilizes lattice FeFe interactions, thereby liberating the electrons trapped in the iron reservoir. Tensile strain also upshifts the equilibrated Fermi level at the iron/iron oxide Ohmic heterojunction, thus populating the oxide shell with abundant electrons for robust heavy metal sequestration. Strained-mZVI exhibits a 62 times faster Cr(VI) removal rate than its unstrained counterpart and can successfully treat industrial wastewater such as landfill leachate, electroplating, and chromium effluents. The excellent property and exceedingly low cost ($2000 ton −1 ) of strained-mZVI results in its great potential to remediate heavy metal-contaminated water and soil.
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