Ferrate(VI)-Induced Arsenite and Arsenate Removal
by In Situ Structural Incorporation into Magnetic Iron(III) Oxide
Nanoparticles
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Abstract
We
report the first example of arsenite and arsenate removal from
water by incorporation of arsenic into the structure of nanocrystalline
iron(III) oxide. Specifically, we show the capability to trap arsenic
into the crystal structure of γ-Fe<sub>2</sub>O<sub>3</sub> nanoparticles
that are in situ formed during treatment of arsenic-bearing water
with ferrate(VI). In water, decomposition of potassium ferrate(VI)
yields nanoparticles having core–shell nanoarchitecture with
a γ-Fe<sub>2</sub>O<sub>3</sub> core and a γ-FeOOH shell.
High-resolution X-ray photoelectron spectroscopy and in-field <sup>57</sup>Fe Mössbauer spectroscopy give unambiguous evidence
that a significant portion of arsenic is embedded in the tetrahedral
sites of the γ-Fe<sub>2</sub>O<sub>3</sub> spinel structure.
Microscopic observations also demonstrate the principal effect of
As doping on crystal growth as reflected by considerably reduced average
particle size and narrower size distribution of the “in-situ”
sample with the embedded arsenic compared to the “ex-situ”
sample with arsenic exclusively sorbed on the iron oxide nanoparticle
surface. Generally, presented results highlight ferrate(VI) as one
of the most promising candidates for advanced technologies of arsenic
treatment mainly due to its environmentally friendly character, in
situ applicability for treatment of both arsenites and arsenates,
and contrary to all known competitive technologies, firmly bound part
of arsenic preventing its leaching back to the environment. Moreover,
As-containing γ-Fe<sub>2</sub>O<sub>3</sub> nanoparticles are
strongly magnetic allowing their separation from the environment by
application of an external magnet
