1 3
Topics in Current Chemistry (2020) 378:6
bands, mainly comprising strongly mixed e g states of Fe 3d and O 2p states, and
of the t 2g states of Fe 3d, respectively. For instance, LaFeO 3 , one of the most
common and promising perovskite-like ferrite catalysts, is usually reported with
a bandgap between 2.0 and 2.6 eV, depending on the synthesis method and their
resulting physico-chemical properties [37, 82]. Ansari et al. used CoFe 12 O 19 hexaferrites as photocatalyst with a 3-eV bandgap [34]. By contrast Zielinska-Jurek
et al. graphically estimated the bandgap of the BaFe 12 O 19 semiconductors material at 1.0 eV [26].
1.4 Towards More Efficient Ferrite‑Based Photocatalytic Materials
Ferrite semiconductor-based photocatalysis and photoelectrochemistry have
attracted attention because of the ability of the ferrite materials to absorb and consequently use visible light—and therefore to directly convert the solar energy—for
performing surface redox reactions allowing environmental remediation to be implemented and solar fuels to be synthesized. During the photocatalytic process, the
recombination of the photo-generated electron–hole pairs plays a highly negative
role. Thus, similarly to the wide-bandgap semiconductor TiO 2 , considered as the
most frequently used semiconductor photocatalyst under UVA light, the photocatalytic efficiency of the ferrites is usually defined by the abundance and stability of the
photo-generated charges (electron and holes). Therefore, efforts have been devoted
to extending the lifetime of such charge carriers, i.e. to slow down their recombination rate. Many approaches have been investigated for that purpose, including the
modification of the shape of the nanoparticles or of their chemical compositions
through the design and fabrication of semiconductor heterostructures, hybrid nanocomposites, doped-nanostructures or more generally multiphase materials.
The design of semiconductor heterojunctions is a general and very promising strategy for elaborating ferrite-based photocatalysts with improved efficiency,
whether the reactions concern environmental applications (water and air depollution) or the solar fuel field for the energy-related applications (CO 2 conversion or H 2
production). Basically, a heterojunction can in general be schematically described
as the interface between two different semiconductors with unequal band structure,
which can result in band alignments [59, 60]. In recent years, most of the studies were devoted to the creation of controlled heterojunctions with anatase TiO 2
of different morphologies absorbing UVA light, or with the smaller gap graphitic
g-C 3 N 4 semiconductor absorbing visible light, as well as to the design of visiblelight-responsive ferrite/ferrite interface heterojunctions. Whatever the configuration
investigated, the heterojunction strategy was mainly implemented for use as photocatalysts and photoelectrodes for energy applications. Details are given in the further
corresponding sections.
In some cases like for conventional Z-scheme heterojunctions, there is no physical contact between both systems and the charges migrate through donor/acceptor
pairs [61]. Depending on the bandgaps and on the relative position of the valence
and conduction bands of both semiconductors, the engineering of ferrite-based heterojunctions aims (1) to separate spatially the photo-generated charges to extend the
119
Reprinted from the journal
Topics in Current Chemistry (2020) 378:6
bands, mainly comprising strongly mixed e g states of Fe 3d and O 2p states, and
of the t 2g states of Fe 3d, respectively. For instance, LaFeO 3 , one of the most
common and promising perovskite-like ferrite catalysts, is usually reported with
a bandgap between 2.0 and 2.6 eV, depending on the synthesis method and their
resulting physico-chemical properties [37, 82]. Ansari et al. used CoFe 12 O 19 hexaferrites as photocatalyst with a 3-eV bandgap [34]. By contrast Zielinska-Jurek
et al. graphically estimated the bandgap of the BaFe 12 O 19 semiconductors material at 1.0 eV [26].
1.4 Towards More Efficient Ferrite‑Based Photocatalytic Materials
Ferrite semiconductor-based photocatalysis and photoelectrochemistry have
attracted attention because of the ability of the ferrite materials to absorb and consequently use visible light—and therefore to directly convert the solar energy—for
performing surface redox reactions allowing environmental remediation to be implemented and solar fuels to be synthesized. During the photocatalytic process, the
recombination of the photo-generated electron–hole pairs plays a highly negative
role. Thus, similarly to the wide-bandgap semiconductor TiO 2 , considered as the
most frequently used semiconductor photocatalyst under UVA light, the photocatalytic efficiency of the ferrites is usually defined by the abundance and stability of the
photo-generated charges (electron and holes). Therefore, efforts have been devoted
to extending the lifetime of such charge carriers, i.e. to slow down their recombination rate. Many approaches have been investigated for that purpose, including the
modification of the shape of the nanoparticles or of their chemical compositions
through the design and fabrication of semiconductor heterostructures, hybrid nanocomposites, doped-nanostructures or more generally multiphase materials.
The design of semiconductor heterojunctions is a general and very promising strategy for elaborating ferrite-based photocatalysts with improved efficiency,
whether the reactions concern environmental applications (water and air depollution) or the solar fuel field for the energy-related applications (CO 2 conversion or H 2
production). Basically, a heterojunction can in general be schematically described
as the interface between two different semiconductors with unequal band structure,
which can result in band alignments [59, 60]. In recent years, most of the studies were devoted to the creation of controlled heterojunctions with anatase TiO 2
of different morphologies absorbing UVA light, or with the smaller gap graphitic
g-C 3 N 4 semiconductor absorbing visible light, as well as to the design of visiblelight-responsive ferrite/ferrite interface heterojunctions. Whatever the configuration
investigated, the heterojunction strategy was mainly implemented for use as photocatalysts and photoelectrodes for energy applications. Details are given in the further
corresponding sections.
In some cases like for conventional Z-scheme heterojunctions, there is no physical contact between both systems and the charges migrate through donor/acceptor
pairs [61]. Depending on the bandgaps and on the relative position of the valence
and conduction bands of both semiconductors, the engineering of ferrite-based heterojunctions aims (1) to separate spatially the photo-generated charges to extend the
119
Reprinted from the journal