Mechanismof Heterogeneous Fenton Reaction KineticsEnhancement under Nanoscale Spatial Confinement
2020
Nanoscale
catalysts that can enable Fenton-like chemistry and produce
reactive radicals from hydrogen peroxide activation have been extensively
studied in order to overcome the limitations of homogeneous Fenton
processes. Despite several advantageous features, limitation in mass
transfer of short-lived radical species is an inherent drawback of
the heterogeneous system. Here, we present a mechanistic foundation
for the way spatial confinement of Fenton chemistry at the nanoscale
can significantly enhance the kinetics of radical-mediated oxidation
reactionspollutant degradation in particular. We synthesized
a series of Fe3O4-functionalized nanoreactors
with precise pore dimensions, based on an anodized aluminum oxide
template, to enable quantitative analysis of nanoconfinement effects.
Combined with computational simulation of spatial distribution of
radicals, we found that hydroxyl radical concentration was strongly
dependent on the distance from the surface of Fenton catalysts. This
distance dependency significantly influences the gross reaction kinetics
and accounts for the observed nanoconfinement effects. We further
found that a length scale below 25 nm is critical to avoid the limitation
of short-lived species diffusion and achieve kinetics that are orders
of magnitude faster than those obtained in a batch suspension of heterogeneous
catalysts. These findings suggest a new strategy to develop an innovative
heterogeneous catalytic system with the most effective use of hydroxyl
radicals in oxidation treatment scenarios.
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