Topics in Current Chemistry (2020) 378:6
1 3
charge carrier lifetime thanks to efficient semiconductor/semiconductor interfacial
charge transfers and/or (2) to use the ferrite semiconductor as a solid visible light
absorption/harvesting system for the photosensitization of wider-bandgap semiconductors (i.e. TiO 2 ).
The reader can refer to the critical reviews by Low et al. [62] and Jang et al. [63]
that extensively depicted and systematically discussed the basic principles of various heterojunction photocatalysts, namely conventional heterojunctions of type I–III
depending on the relative positions of both bandgaps, p–n heterojunctions, direct
Z-scheme heterojunctions (including solid-state Z-scheme) as well as graphenebased heterojunctions.
The elaboration of metal–ferrite semiconductor junctions is another strategy followed by different research groups reported in the next sections of this review. The
supported metals consist usually in nanoscale metal islands on the semiconductor.
The junction forms an electric field that facilitates the separation the photo-generated electrons and holes [64, 65], together with the formation of local space–charge
separation zones at the interphase. Beside their role in enhancing the lifetime of the
charge carries, the supported metallic nanoparticles also act as co-catalyst in different innovative ferrite-based systems used as photocatalysts or photoelectrodes for
hydrogen production and CO 2 reduction (see “Ferrite-Based Photocatalysts and Photoelectrodes for EnergyApplications: Hydrogen Production and CO 2 Reduction”).
The association of ferrites nanoparticles with adsorbent materials such as montmorillonite or palygorskite clays is also reported in the field of environmental remediation for trying to take advantage of the synergistic effect of adsorption and catalysis (see “Ferrite Photocatalysts for Environmental Applications: WaterDetoxification
and Air Depollution”).
Finally, the cationic doping of ferrite—usually depicted as partially substituted ferrites—is a very promising approach investigated by many research groups
for improving the efficiency of the ferrite photocatalysts and photoelectrodes, and
reported in the next sections. Indeed, whatever the crystallographic structures of the
catalysts, the compositional versatility of the ferrites—e.g. as A 1–x A′ x B 1–y B′ y O 3±δ
or A 1–x A′ x B 2–y B′ y O 4±δ in the case of orthoferrites or spinel ferrites, respectively—is
a great advantage for modifying many bulk and surface physico-chemical properties of the ferrites, including their textural, structural or electronic properties, and
as a result for tuning the redox and catalytic ability of the ferrites through A- and/or
B-site cationic partial substitution.
The objective of improving the efficiency of the ferrite-based photocatalysts and
photoelectrodes requires investigating charge trapping and recombination as well
as understanding the factors affecting the related processes. Furthermore, deeper
understanding of the relationship between the physico-chemical properties of the
ferrite-based systems and the catalytic behaviour and efficiency indicators under visible or solar light is absolutely necessary. In particular, understanding the physicochemical phenomena taking place in the bulk, and at the surface and the interfaces
of the multicomponent systems, is of high interest, as well as understanding the catalytic mechanism(s) taking place in such systems, and how the material design can
orientate the efficiency indicators.
120
Reprinted from the journal
1 3
charge carrier lifetime thanks to efficient semiconductor/semiconductor interfacial
charge transfers and/or (2) to use the ferrite semiconductor as a solid visible light
absorption/harvesting system for the photosensitization of wider-bandgap semiconductors (i.e. TiO 2 ).
The reader can refer to the critical reviews by Low et al. [62] and Jang et al. [63]
that extensively depicted and systematically discussed the basic principles of various heterojunction photocatalysts, namely conventional heterojunctions of type I–III
depending on the relative positions of both bandgaps, p–n heterojunctions, direct
Z-scheme heterojunctions (including solid-state Z-scheme) as well as graphenebased heterojunctions.
The elaboration of metal–ferrite semiconductor junctions is another strategy followed by different research groups reported in the next sections of this review. The
supported metals consist usually in nanoscale metal islands on the semiconductor.
The junction forms an electric field that facilitates the separation the photo-generated electrons and holes [64, 65], together with the formation of local space–charge
separation zones at the interphase. Beside their role in enhancing the lifetime of the
charge carries, the supported metallic nanoparticles also act as co-catalyst in different innovative ferrite-based systems used as photocatalysts or photoelectrodes for
hydrogen production and CO 2 reduction (see “Ferrite-Based Photocatalysts and Photoelectrodes for EnergyApplications: Hydrogen Production and CO 2 Reduction”).
The association of ferrites nanoparticles with adsorbent materials such as montmorillonite or palygorskite clays is also reported in the field of environmental remediation for trying to take advantage of the synergistic effect of adsorption and catalysis (see “Ferrite Photocatalysts for Environmental Applications: WaterDetoxification
and Air Depollution”).
Finally, the cationic doping of ferrite—usually depicted as partially substituted ferrites—is a very promising approach investigated by many research groups
for improving the efficiency of the ferrite photocatalysts and photoelectrodes, and
reported in the next sections. Indeed, whatever the crystallographic structures of the
catalysts, the compositional versatility of the ferrites—e.g. as A 1–x A′ x B 1–y B′ y O 3±δ
or A 1–x A′ x B 2–y B′ y O 4±δ in the case of orthoferrites or spinel ferrites, respectively—is
a great advantage for modifying many bulk and surface physico-chemical properties of the ferrites, including their textural, structural or electronic properties, and
as a result for tuning the redox and catalytic ability of the ferrites through A- and/or
B-site cationic partial substitution.
The objective of improving the efficiency of the ferrite-based photocatalysts and
photoelectrodes requires investigating charge trapping and recombination as well
as understanding the factors affecting the related processes. Furthermore, deeper
understanding of the relationship between the physico-chemical properties of the
ferrite-based systems and the catalytic behaviour and efficiency indicators under visible or solar light is absolutely necessary. In particular, understanding the physicochemical phenomena taking place in the bulk, and at the surface and the interfaces
of the multicomponent systems, is of high interest, as well as understanding the catalytic mechanism(s) taking place in such systems, and how the material design can
orientate the efficiency indicators.
120
Reprinted from the journal