ReviewLayered double hydroxide photocatalysts for solar fuel production
Graphical Abstract
This review provides a comprehensive summary of recent advances in LDH-based photocatalysts for solar fuel production. In particular, various modification strategies for improving the photocatalytic activity of LDH have been discussed.
Introduction
Accelerated global industrialization is causing serious environmental damage and depleting fossil fuel resources which threaten the sustainable development of human society [1, 2, 3]. Solar energy is a clean and green energy with the potential to mitigate the environmental damage caused by the use of fossil fuels and solve energy shortages [4, 5, 6, 7]. Among various solar energy conversion methods, the photocatalysis of water splitting and CO2 reduction has attracted much attention [8, 9, 10, 11, 12, 13] because the conversion method not only obtains clean, renewable, and high-heating-value H2 and secondary solar fuels, but also effectively reduces CO2 emissions.
Since 1972, TiO2 has become the most popular photocatalyst owing to its excellent chemical and photocorrosion resistance and low cost [14, 15, 16, 17, 18, 19]. However, it has a number of disadvantages, namely a narrow solar-light absorption range, a high rate of recombination of photogenerated electron-hole pairs, and low solar-light utilization [20, 21, 22, 23]. Various strategies, such as noble-metal deposition [24, 25, 26], semiconductor composites [27, 28, 29], and ion doping [30, 31, 32], have been employed to improve its photocatalytic efficiency. In addition to TiO2, viable photocatalysts such as Cu2O [33, 34, 35], CdS [36], CdZnS [37, 38, 39], g-C3N4 [36, 40, 41], and Bi-based compounds [42, 43, 44], have been widely investigated, as shown in Fig. 1. The band edge positions of several semiconductor photocatalysts at pH = 7 in aqueous solution are shown in Fig. 2. However, the widely used metal oxides, metal sulfides, and graphite phase carbon nitride still have limitations, such as low visible-light utilization, poor stability, and a high rate of photogenerated electron-hole recombination [45, 46, 47]. For example, ZnO [48, 49, 50, 51, 52, 53], SrTiO3 [54, 55], ZnIn2S4 [56], ZnS [57, 58, 59], and other wide-bandgap semiconductor materials suffer from poor light absorption ability, while narrow-bandgap semiconductor photocatalysts, such as CoO [60, 61, 62], MoS2 [63, 64, 65], CuFeS2 [66, 67], and In2S3 [68, 69] suffer from slow charge transfer, and a high rate of photogenerated electron-hole recombination; moreover, the physical structures of some materials suffer from poor stability, low high-temperature tolerance, and photocorrosion during reaction processes [70]. Table 1 summarizes the conduction band (CB) and valence band (VB) positions, bandgap, and advantages and disadvantages of general photocatalysts.
In recent years, layered double hydroxides (LDHs), which are two-dimensional (2D) anionic clays with brucite-like structures, have attracted great attention as a novel class of semiconductor photocatalysts because of their unique layered structures, highly dispersed metal components, controllable composition, exchangeable guest anions, high specific surface areas, controllable particle size, low cost, and mass producibility [71, 72, 73, 74, 75, 76, 77]. LDH-based catalysts have appeared in the fields of pollutant degradation [78, 79, 80, 81, 82, 83], CO2 reduction [84, 85, 86, 87, 88], photocatalytic water oxidation [89, 90, 91, 92, 93], and water photolysis for H2 production. It is worth mentioning that research on LDHs for photocatalytic H2 production and CO2 reduction emerged in the last few decades. The purpose of this review is to present recent progress and advances in the research on LDH-based photocatalysts to inform the design of novel and highly efficient LDH-based photocatalysts for solar fuel production.
Section snippets
Properties of LDH
LDH is a type of 2D anionic clay based on a brucite structure, as shown in Fig. 3. The general chemical expression of LDH is M12+M23+(OH)2x+ (An−)x/n·mH2O where M12+ = Zn2+, Ni2+, Mg2+, Co2+, and other divalent metal cations; M23+ = Cr3+, Al3+, Fe3+, Mn3+, and other trivalent metal cations; An− = CO32−, NO3−, Cl−, SO42−, and other interlayer anions; x is the molar ratio of M3+/ (M2+ + M3+), usually ranging from 0.2 to 0.33; and m is the number of interlayer water molecules [101, 102, 103].
Each
Principle of photocatalytic H2 production over LDH-based photocatalysts
The H2 production mechanism of LDH-based photocatalysts is similar to that of traditional photocatalysts. The catalytic H2 production mechanism shown in Fig. 11 involves four main steps: reactant adsorption, carrier generation and separation [180], interfacial transport of photogenerated electrons and holes, and surface catalytic reaction [181].
The first step is reactant adsorption; however, photocatalysts used in photocatalytic H2 production are generally in direct contact with the reactant,
Principle of photocatalytic CO2 reduction over LDH-based photocatalysts
CO2 is a stable chemical compound, in which a C–O bond can be broken and form a new C–H bond after consuming a large amount of energy [244, 245, 246]. Unlike conventional CO2 reduction that requires high temperature and high pressure, photocatalytic CO2 reduction is a mild process and the energy generated by solar light is the only energy input [190, 247, 248].
Photocatalytic CO2 reduction over LDH-based photocatalysts mainly involves five steps: (1) CO2 molecules are adsorbed on the surface or
Conclusions and prospects
In summary, LDHs are a promising type of semiconductor photocatalyst owing to its unique 2D layered structure, highly dispersed metal components, adjustable composition, exchangeable interlayer guest anions, high specific surface area, controllable particle size, low cost, and mass producibility. However, they still have the following limitations: (1) The quantum efficiency of LDHs under solar irradiation is generally poor owing to their low carrier mobility and high electron-hole recombination
References (327)
- et al.
Renew. Sustain. Energ. Rev.
(2016) - et al.
Renew. Sust. Energ. Rev.
(2018) - et al.
Coord. Chem. Rev.
(2019) - et al.
Carbon
(2019) - et al.
Catal. Today
(2019) - et al.
Int. J. Hydrogen Energy
(2019) - et al.
Colloids Surf. A
(2006) - et al.
Appl. Surf. Sci.
(2015) - et al.
Appl. Surf. Sci.
(2017) - et al.
Appl. Catal. B
(2015)
Water Res.
Appl. Catal. B
J. Alloys Compd.
Appl. Catal. B
Int. J. Hydrogen Energy
J. Alloys Compd.
Int. J. Hydrogen Energy
Appl. Surf. Sci.
J. Inorg. Mater.
Nanoscale. Res. Lett.
J. Alloys Compd.
Prog. Nat. Sci-Mater. Int.
J. Photochem. Photobiol. A
Int. J. Hydrogen Energy
Int. J. Hydrogen Energy
J. Photochem. Photobiol. C
Catal. Today
Coord. Chem. Rev.
Mater. Today Energy
Sci. Total Environ.
J. Phys. Chem. Solids
Appl. Catal. B
Sci. Bull.
Mater. Res. Bull.
Int. J. Hydrogen Energy
Appl. Catal. B
J. Mater. Chem. A
Chem. Eng. J.
J. Mater. Chem. A
Chem. Soc. Rev.
Chem. Soc. Rev.
Chem. Soc. Rev.
Chin. J. Chem. Phys.
Chem. Rev.
ACS Omega
Adv. Energy Mater.
Chem. Rev.
Astrophys. J.
Adv. Mater.
Chin. J. Appl. Chem.
Cited by (44)
Layered double hydroxides for air pollution control: Applications, mechanisms and trends
2024, Journal of Cleaner ProductionRecent advance of layered double hydroxides materials: Structure, properties, synthesis, modification and applications of wastewater treatment
2023, Journal of Environmental Chemical Engineering
This work was supported by the National Natural Science Foundation of China (51774259).
Available online 20 August 2021