Spinel ferrite materials have an electronic band structure that
is well suited for visible light-induced catalysis, however, their
photocatalytic activity remains low due to the daunting
charge-carrier separation process. In this article, we report that
high-surface-area mesoscopic architectures composed of tightly
connected ultrasmall spinel ferrite nanocrystals can efficiently
suppress electron-hole recombination, manifesting an exceptional
activity and magnetic recyclability in photocatalytic reduction of
aqueous Cr(VI). Revealed by electron microscopy, N₂ physisorption,
and X-ray scattering studies, the resulting materials, which were
obtained through a block copolymer-assisted cross-linking
aggregation of colloidal nanoparticles, show a 3D interconnected
nanoporous structure with a large internal surface area (up to
159 m² g⁻¹) and exhibit small grain composition
(ca. 6–8 nm in size). Through a systematic synthesis of various structural
analogues to the spinel ferrite family and optical absorption and
electrochemical impedance spectroscopy analyses, we demonstrate that
the electronic band structure fits the electronic requirements for
both Cr(VI) reduction and water oxidation under UV–vis light
irradiation. Among spinel ferrites, ZnFe₂O₄
presents the highest
activity, readily operating without additional sacrificial reagents
in photocatalytic detoxification of aqueous Cr(VI), which together
with transient gas analysis and fluorescence spectroscopy results
suggest a competitive formation of oxygen and hydroxyl radicals at
the catalyst surface. These findings provide an essential tool for
the delineation of the electronic structure-catalytic property
relationship in spinel ferrite nanostructures offering intriguing
possibilities for designing new photocatalytic systems for efficient
environmental pollution purification and energy conversion.

More information can be found in: Euaggelia Skliri, Jianwei Miao, Jian Xie, Guangfeng Liu, Teddy Salim, Bin Liu, Qichun Zhang, Gerasimos S. Armatas
“Assembly and photochemical properties of mesoporous networks of spinel ferrite nanoparticles for environmental photocatalytic remediation“, Applied Catalysis B: Environmental 227, 330 (2018).