Elsevier

Chinese Journal of Catalysis

Volume 42, Issue 11, November 2021, Pages 1944-1975
Chinese Journal of Catalysis

Review
Layered double hydroxide photocatalysts for solar fuel production

https://doi.org/10.1016/S1872-2067(21)63861-5Get rights and content

Abstract

Splitting water or reducing CO2 via semiconductor photocatalysis to produce H2 or hydrocarbon fuels through the direct utilization of solar energy is a promising approach to mitigating the current fossil fuel energy crisis and environmental challenges. It enables not only the realization of clean, renewable, and high-heating-value solar fuels, but also the reduction of CO2 emissions. Layered double hydroxides (LDHs) are a type of two-dimensional anionic clay with a brucite-like structure, and are characterized by a unique, delaminable, multidimensional, layered structure; tunable intralayer metal cations; and exchangeable interlayer guest anions. Therefore, it has been widely investigated in the fields of CO2 reduction, photoelectrocatalytic water oxidation, and water photolysis to produce H2. However, the low carrier mobility and poor quantum efficiency of pure LDH limit its application. An increasing number of scholars are exploring methods to obtain LDH-based photocatalysts with high energy conversion efficiency, such as assembling photoactive components into LDH laminates, designing multidimensional structures, or coupling different types of semiconductors to construct heterojunctions. This review first summarizes the main characteristics of LDH, i.e., metal-cation tunability, intercalated guest-anion substitutability, thermal decomposability, memory effect, multidimensionality, and delaminability. Second, LDHs, LDH-based composites (metal sulfide-LDH composites, metal oxide-LDH composites, graphite phase carbon nitride-LDH composites), ternary LDH-based composites, and mixed-metal oxides for splitting water to produce H2 are reviewed. Third, graphite phase carbon nitride-LDH composites, MgAl-LDH composites, CuZn-LDH composites, and other semiconductor-LDH composites for CO2 reduction are introduced. Although the field of LDH-based photocatalysts has advanced considerably, the photocatalytic mechanism of LDHs has not been thoroughly elucidated; moreover, the photocatalytic active sites, the synergy between different components, and the interfacial reaction mechanism of LDH-based photocatalysts require further investigation. Therefore, LDH composite materials for photocatalysis could be developed through structural regulation and function-oriented design to investigate the effects of different components and interface reactions, the influence of photogenerated carriers, and the impact of material composition on the physical and chemical properties of the LDH-based photocatalyst.

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.

  1. Download : Download high-res image (155KB)
  2. Download : Download full-size image

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)

  • N. Kannan et al.

    Renew. Sustain. Energ. Rev.

    (2016)
  • E. Kabir et al.

    Renew. Sust. Energ. Rev.

    (2018)
  • Y. Shi et al.

    Coord. Chem. Rev.

    (2019)
  • J. Wang et al.

    Carbon

    (2019)
  • R.F. Qian et al.

    Catal. Today

    (2019)
  • S.B. Patil et al.

    Int. J. Hydrogen Energy

    (2019)
  • B.H. Wang et al.

    Colloids Surf. A

    (2006)
  • S.L. Bai et al.

    Appl. Surf. Sci.

    (2015)
  • A.Y. Meng et al.

    Appl. Surf. Sci.

    (2017)
  • S. Obregón et al.

    Appl. Catal. B

    (2015)
  • S. Sakthivel et al.

    Water Res.

    (2004)
  • X.L. Hu et al.

    Appl. Catal. B

    (2019)
  • H. Yan et al.

    J. Alloys Compd.

    (2011)
  • S.A. Rawool et al.

    Appl. Catal. B

    (2018)
  • M.A. Khan et al.

    Int. J. Hydrogen Energy

    (2008)
  • H. Yan et al.

    J. Alloys Compd.

    (2011)
  • M.Q. Chen et al.

    Int. J. Hydrogen Energy

    (2018)
  • S. Ye et al.

    Appl. Surf. Sci.

    (2015)
  • J.Q. Liu et al.

    J. Inorg. Mater.

    (2015)
  • X.Q. Chen et al.

    Nanoscale. Res. Lett.

    (2017)
  • K.Z. Qi et al.

    J. Alloys Compd.

    (2017)
  • L.Q. Wang et al.

    Prog. Nat. Sci-Mater. Int.

    (2014)
  • X.X. Yu et al.

    J. Photochem. Photobiol. A

    (2018)
  • Y. Wu et al.

    Int. J. Hydrogen Energy

    (2018)
  • Z.F. Yang et al.

    Int. J. Hydrogen Energy

    (2020)
  • Z. Li et al.

    J. Photochem. Photobiol. C

    (2018)
  • N. Dewangan et al.

    Catal. Today

    (2020)
  • Z.Z. Yang et al.

    Coord. Chem. Rev.

    (2019)
  • S. Anantharaj et al.

    Mater. Today Energy

    (2017)
  • F. Mohamed et al.

    Sci. Total Environ.

    (2018)
  • S.P. Paredes et al.

    J. Phys. Chem. Solids

    (2011)
  • S. Kumar et al.

    Appl. Catal. B

    (2017)
  • X.Y. Xiong et al.

    Sci. Bull.

    (2020)
  • N. Hirata et al.

    Mater. Res. Bull.

    (2015)
  • H.L. Zhou et al.

    Int. J. Hydrogen Energy

    (2018)
  • A.H. Yan et al.

    Appl. Catal. B

    (2019)
  • Q. Huang et al.

    J. Mater. Chem. A

    (2015)
  • J. Liu et al.

    Chem. Eng. J.

    (2020)
  • X. Li et al.

    J. Mater. Chem. A

    (2015)
  • Z. Wang et al.

    Chem. Soc. Rev.

    (2019)
  • J. Gong et al.

    Chem. Soc. Rev.

    (2019)
  • T. Hisatomi et al.

    Chem. Soc. Rev.

    (2014)
  • X.L. Cai et al.

    Chin. J. Chem. Phys.

    (2015)
  • J.L. White et al.

    Chem. Rev.

    (2015)
  • S.R. Lingampalli et al.

    ACS Omega

    (2017)
  • K. Zhang et al.

    Adv. Energy Mater.

    (2016)
  • M.R. Hoffmann et al.

    Chem. Rev.

    (1995)
  • M. Amenomori et al.

    Astrophys. J.

    (2002)
  • C.M. Gao et al.

    Adv. Mater.

    (2019)
  • B. Liu et al.

    Chin. J. Appl. Chem.

    (2019)
  • Cited by (44)

    View all citing articles on Scopus

    This work was supported by the National Natural Science Foundation of China (51774259).

    Available online 20 August 2021

    View full text