1 3
Topics in Current Chemistry (2019) 377:27
most representative studies aiming at reporting on the photocatalytic decomposition
of FA. In order to consider the most widely investigated photocatalytic systems studies for the present application, sections on TiO 2 , CdS and C 3 N 4 -based photocatalysts
have been included in this manuscript. These sections cite evidence that, as in the
case of the thermal decomposition of FA, the addition of metal nanoparticles is vital
to accelerate the photocatalytic process. In this context, Mott–Schottky photocatalysts have shown to be a very promising approach to adjust the surface charge density of the active metal phase, while decreasing the recombination of electron–holes
pairs by transferring photogenerated electrons from the semiconductor supports to
the metal active phase. Such electron-rich metal species are, in turn, more active in
boosting hydrogen production from FA. This is particularly important for Pd-based
catalysts. Moreover, it has been observed that the use of alloy nanoparticles further
promotes the formation of electron-rich Pd species. In addition, the incorporation of
agents to control the size and shape of nanoparticles are a useful resource to afford
optimized performances. Particular attention has been paid to those systems containing plasmonic nanoparticles (PdAg and PdAu).
Aside from noble metal-containing photocatalysts, noble-metal-free systems have
also been studied in this application. For instance, the utilization of heterojunction
(i.e., CuO/TiO 2 , CdS/Fe 2 O 3 , MoS 2 /CdS, etc.) or core–shell structures (i.e. CdS@
ZIF-8, CdS–ZnS, etc.) has been shown to afford enhanced performances ascribed to
efficient electron–hole pair separation at the interface. Such systems are also promising from an economic viewpoint. Furthermore, the importance of some other photocatalytic systems (i.e., MOFs, GO, NCQDs, etc.) has also been briefly mentioned.
This review highlights the applicability of photocatalysts in hydrogen production from LOHC. It is expected to provide the reader with an overview of the
most representative approaches used so far for this application at a time when the
research community is encouraged to further explore the exciting and barely investigated photocatalytic decomposition of FA. Although important breakthroughs have
recently been achieved in the photodecomposition of FA, the materials used to date
are far from being as sophisticated as those used for some other traditional photocatalytic applications. It could be envisaged that such important application will
soon deserve new efforts towards the design of efficient photocatalytic systems. A
point to consider in this respect is improvement of the stability of the photocatalysts,
which has been shown to be lacking until now. Such aspects could be enhanced by
engineering the optical properties of the materials used, as well as by controlling the
adsorption of the reaction intermediates, which would eventually block the active
sites. Furthermore, another point to consider is the development of photocatalysts
with higher surface area that are able to provide a higher dispersion of the active
sites. In this line, the combination of the traditionally used photocatalytic materials
(i.e. TiO 2 , CdS, g-C 3 N 4 ) with a second component with a higher developed porosity
(i.e., carbon materials, etc.) could be a resourceful alternative to afford highly efficient systems for the photodecomposition of FA.
Acknowledgments The present work was supported by JST, PRESTO (JPMJPR1544) and by Grants-inAid for Scientific Research (nos. 26220911, 25289289, and 26630409, 26620194) from the Japan Society for the Promotion of Science (JSPS) and MEXT and “Elemental Strategy Initiative to Form Core
217
Reprinted from the journal
Topics in Current Chemistry (2019) 377:27
most representative studies aiming at reporting on the photocatalytic decomposition
of FA. In order to consider the most widely investigated photocatalytic systems studies for the present application, sections on TiO 2 , CdS and C 3 N 4 -based photocatalysts
have been included in this manuscript. These sections cite evidence that, as in the
case of the thermal decomposition of FA, the addition of metal nanoparticles is vital
to accelerate the photocatalytic process. In this context, Mott–Schottky photocatalysts have shown to be a very promising approach to adjust the surface charge density of the active metal phase, while decreasing the recombination of electron–holes
pairs by transferring photogenerated electrons from the semiconductor supports to
the metal active phase. Such electron-rich metal species are, in turn, more active in
boosting hydrogen production from FA. This is particularly important for Pd-based
catalysts. Moreover, it has been observed that the use of alloy nanoparticles further
promotes the formation of electron-rich Pd species. In addition, the incorporation of
agents to control the size and shape of nanoparticles are a useful resource to afford
optimized performances. Particular attention has been paid to those systems containing plasmonic nanoparticles (PdAg and PdAu).
Aside from noble metal-containing photocatalysts, noble-metal-free systems have
also been studied in this application. For instance, the utilization of heterojunction
(i.e., CuO/TiO 2 , CdS/Fe 2 O 3 , MoS 2 /CdS, etc.) or core–shell structures (i.e. CdS@
ZIF-8, CdS–ZnS, etc.) has been shown to afford enhanced performances ascribed to
efficient electron–hole pair separation at the interface. Such systems are also promising from an economic viewpoint. Furthermore, the importance of some other photocatalytic systems (i.e., MOFs, GO, NCQDs, etc.) has also been briefly mentioned.
This review highlights the applicability of photocatalysts in hydrogen production from LOHC. It is expected to provide the reader with an overview of the
most representative approaches used so far for this application at a time when the
research community is encouraged to further explore the exciting and barely investigated photocatalytic decomposition of FA. Although important breakthroughs have
recently been achieved in the photodecomposition of FA, the materials used to date
are far from being as sophisticated as those used for some other traditional photocatalytic applications. It could be envisaged that such important application will
soon deserve new efforts towards the design of efficient photocatalytic systems. A
point to consider in this respect is improvement of the stability of the photocatalysts,
which has been shown to be lacking until now. Such aspects could be enhanced by
engineering the optical properties of the materials used, as well as by controlling the
adsorption of the reaction intermediates, which would eventually block the active
sites. Furthermore, another point to consider is the development of photocatalysts
with higher surface area that are able to provide a higher dispersion of the active
sites. In this line, the combination of the traditionally used photocatalytic materials
(i.e. TiO 2 , CdS, g-C 3 N 4 ) with a second component with a higher developed porosity
(i.e., carbon materials, etc.) could be a resourceful alternative to afford highly efficient systems for the photodecomposition of FA.
Acknowledgments The present work was supported by JST, PRESTO (JPMJPR1544) and by Grants-inAid for Scientific Research (nos. 26220911, 25289289, and 26630409, 26620194) from the Japan Society for the Promotion of Science (JSPS) and MEXT and “Elemental Strategy Initiative to Form Core
217
Reprinted from the journal