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Effective Functionalization of Disordered Oxide Lattices on Iron Particle Surfaces Using Mechanochemical Reactions
journal contribution
posted on 2013-05-16, 00:00 authored by Satoshi Motozuka, Motohiro Tagaya, Hiroshi Nishiyama, Masami Nishikawa, Toshiyuki Ikoma, Tomohiko Yoshioka, Sadaki Samitsu, Junzo TanakaThe
mechanochemical surface functionalization of iron oxides with
disordered lattices on bare iron (Fe) particles was investigated using
simple milling processes to clarify the formation mechanism of the
oxide layer and investigate the near-surface models with different
states. The homogeneous α-Fe particles at the milling equilibrium
were first prepared under an argon atmosphere. After the subsequent
milling reaction of the particles with oxygen molecules, the surface
analyses by X-ray diffraction and Raman and X-ray photoelectron spectroscopies
revealed that the near-surface layers consisted of two iron oxide
phases (α-Fe2O3 and Fe3O4) through oxygen atom diffusion, and the α-Fe2O3 was dominantly grown on the near surface. During the
initial reaction, the signals from an electron spin resonance suggested
the dangling bond formation on α-Fe2O3. The oxygen atoms effectively induce disordered lattices in the
local area to form oxidized Fe3+ clusters, and the geometric
distortion formed the dangling bonds, which were theoretically supported
by a molecular orbital calculation to elucidate the increase in the
unpaired electron sites on the α-Fe2O3. Therefore, the defective Fe3+ ions induced by the lattice
mismatching between the clusters and bare α-Fe are found to
form the disordered lattice that contains the oxygen atoms with unpaired
electrons, which are successfully induced by the near-surface strain
based on the simple mechanochemical reactions. The patterns of surface
activation of the Fe particle surfaces by oxidization will be capable
of novel chemical reactions by selective oxygen insertion as well
as deep oxidation.