Recent progress on ZnIn₂S₄-based composite photocatalysts for photocatalytic hydrogen production coupling organic synthesis

Abstract

Compared with sacrificial-agent-dependent half-reactions in photocatalytic water-splitting hydrogen production, coupling photocatalytic organic synthesis with hydrogen production markedly boosts electron–hole utilization efficiency and cuts reaction costs. In recent years, hexagonal ZnIn₂S₄ has been widely applied in the field of photocatalytic hydrogen production coupled with organic synthesis due to its advantages such as narrow band gap, high hydrogen evolution efficiency, good chemical stability, non-toxicity, and low cost. Herein, we present a comprehensive review of the latest progress in ZnIn₂S₄-based photocatalysts. We first summarize the preparation methods of ZnIn₂S₄ and the strategies to improve its performance, including metal doping, morphological engineering, heterostructure construction and defect engineering. Subsequently, we focus on the research progress of ZnIn₂S₄-based photocatalysts in hydrogen production coupling organic synthesis, including the selective conversion of alcohols, oxidative coupling of amines, thiol dehydrogenation, and biomass oxidation. Finally, the challenges and opportunities that ZnIn₂S₄ faces in practical application are discussed. It is expected that this review will offer insightful guidance for the rational design of semiconductor-based dual-functional photoredox reaction systems, thereby injecting impetus into the research on harvesting environmentally solar fuel production as well as the high-value-added fine chemicals.

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1. Introduction

Hydrogen (H₂) has emerged as a subject of extensive research interest globally, primarily attributed to its high energy density and environmentally benign nature.^1,2 While the conventional industrial process for H₂ production hinges on catalytic reforming, this approach is encumbered by inordinately high energy intensity and substantial environmental contamination.^3,4 Solar-driven H₂ production offers a promising sustainable path for photocatalytic technology.^5,6 Nevertheless, the H₂ generation rate is often limited by sluggish hole reaction kinetics.^7,8 A common solution involves adding sacrificial agents to enhance hole reactivity, but this process is economically inefficient: sacrificial agents are costly, and their oxidation products have low added value. These drawbacks can be ingeniously addressed by substituting the sacrificial agent with a low-value organic compound that is amenable to oxidation, which not only eliminates the use of expensive traditional catalysts, but also enables the production of more valuable oxidized organic products. Therefore, manufacturing desired organic products coupling hydrogen production is a strategy that kills two birds with one stone.

Among numerous photocatalysts, ZnIn₂S₄ has been widely employed in the field of photocatalysis due to its facile synthesis, broad light absorption range, and excellent photocatalytic performance.^9–12 Its primary applications in energy conversion include visible-light-driven photocatalytic water splitting for H₂ production and photocatalytic CO₂ reduction.^13–17 As illustrated in Fig. 1, the ZnIn₂S₄-based photocatalyst has been extensively employed in the field of photocatalysis in recent years, with an increasing trend over successive years. ZnIn₂S₄ possesses suitable band positions and a unique layered structure, endowing ZnIn₂S₄-based photocatalysts with remarkable photocatalytic activity in H₂ production coupling organic synthesis.^18–20 To date, various strategies have been developed to design ZnIn₂S₄-based photocatalysts, including element doping, morphology control, cocatalyst modification, and heterostructure construction.^21,22 These strategies effectively enhance the charge carrier separation efficiency and light absorption capacity of ZnIn₂S₄-based photocatalysts, thereby improving their performance in photocatalytic H₂ production coupling organic synthesis. However, there persists an absence of a comprehensive review that systematically summarizes the applications of ZnIn₂S₄ in photocatalytic hydrogen production coupled with various organic synthesis reactions.

Fig. 1 The illustration shows the number of papers published each year on the topic “photocatalysts, & ZnIn₂S₄” since 2018.

Therefore, this review comprehensively summarizes the structure of ZnIn₂S₄ and introduces several common synthetic methods for ZnIn₂S₄-based photocatalysts. Additionally, we emphasize the modification and optimization of ZnIn₂S₄-based composites and summarize their applications in photocatalytic H₂ production coupling organic value added. Finally, we discuss the current challenges faced by ZnIn₂S₄-based composites in coupling reactions and propose core issues that need to be addressed in the future. We anticipate that this review will deepen the understanding of photocatalytic H₂ production coupling organic synthesis and facilitate the design and development of advanced photocatalysts.

2. Structure and synthesis of ZnIn₂S₄-based photocatalysts

2.1 Structure

As early as 2006, the production scheme of ZnIn₂S₄ in a controllable form was proposed by Gou et al.²³ They successfully synthesized ZnIn₂S₄ nanowires, nanotubes, nanoribbons, and nanospheres through simple solvothermal and hydrothermal pathways. Due to the influence of the three ions, the crystal structure of ZnIn₂S₄ is inherently diverse. The common ZnIn₂S₄ structure is arranged in the atomic layer of S–Zn–S–In–S–In–S, and there are abundant active sites exposed in the edge layer.²⁴ ZnIn₂S₄ has three different forms (cubic, hexagonal, and triangular), and the hexagonal phase is the most stable, the most catalytic efficient, and the most valuable form for research.^25,26 Through certain morphological adjustments, the specific surface area of ZnIn₂S₄ can be increased, its light capture ability can be promoted, more active sites can be exposed, and the migration distance of photogenerated carriers can be shortened, thereby significantly improving the photocatalytic performance of ZnIn₂S₄. Moreover, the successful exploration of the synthesis of more morphologies of ZnIn₂S₄, such as nanoflowers and nanorods, has also expanded the photocatalytic applications of ZnIn₂S₄.^27,28

2.2 Synthesis

Recently, the ZnIn₂S₄-based catalysts with various morphological structures have been developed by scientific researchers.^29–31 Commonly used hydrothermal, solvent thermal and microwave-assisted methods are constantly being improved and optimized. While making the synthesis route simple and convenient, it also gives the catalyst more advantages. In this section, we mainly focus on these several commonly used synthesis methods. Meanwhile, several other synthesis methods are also summarized.

2.2.1 Hydrothermal method. The hydrothermal method has become the most extensively used method for the synthesis of various nanomaterials due to its simplicity, easy control and industrial feasibility. Researchers change the nanostructure of ZnIn₂S₄ by changing the reaction temperature, preparing precursors, and adding modifiers.^32–34 Gou et al. synthesized the regulated ZnIn₂S₄ under the action of different surfactants and proposed the relevant mechanism, which opened up a direction for regulating the structure of ternary sulfide. In 2012, Chen et al.²⁴ synthesized ZnIn₂S₄ in two different crystal phases of hexagonal and cubic phases by employing different precursors. Comparing the difference in photocatalytic activities, they reported that hexagonal ZnIn₂S₄ not only has certain advantages in the degradation of pollutants, but also has good thermal stability. In 2025, Zheng et al.³⁵ constructed a unique g-C₃N₄@ZnIn₂S₄ nanocomposite photocatalyst by growing 1D g-C₃N₄ nanorods in situ on hydrothermally synthesized 2D ZnIn₂S₄ nanosheets (Fig. 2a). As illustrated in Fig. 2b, Zhang et al.³⁶ prepared Co doped MoS₂ nanoplate cocatalysts (Co-MoS₂) with a thick and flat surface by a hydrothermal approach, followed by in situ growth of ZnIn₂S₄ nanosheets on their surface to obtain the 2D/2D structure of Co-MoS₂/ZnIn₂S₄.

Fig. 2 (a) Synthesis of CN@ZnIn₂S₄. Reproduced with permission from ref. 35, copyright 2025, Elsevier. (b) Schematic diagram of the fabrication of Co-MoS₂/ZnIn₂S₄. Reproduced with permission from ref. 36, copyright 2025, Elsevier.

2.2.2 Solvent thermal method. Similar to the hydrothermal method, the solvent thermal synthesis method is relatively simple to operate. Therefore, solvent thermal method is also widely used to prepare ZnIn₂S₄ nanostructures.^37,38 Under different temperature, solvent and coordination conditions, the final product will show different morphologies and crystal structures. Gou et al. prepared hexagonal ZnIn₂S₄ with pyridine as the solvent, and prepared different morphologies such as ZnIn₂S₄ microspheres, nanoribbons, nanotubes and nanowires by changing the template agent and reaction temperature. In addition to the reaction temperature, the solvent types have equally important effects on the synthetic microstructure of ZnIn₂S₄.^39,40 The effect of the solvent on the morphology of the prepared ZnIn₂S₄ was systematically studied by Su et al.⁴¹ In the experiment, zinc nitrate and indium nitrate were dissolved in three different solvents such as water, methanol according to the stoichiometric ratio (1 : 2) and twice the amount of thiourea in water, methanol and ethylene glycol, and thermos-reacted at 140 °C in the solvent for 72 h. Different solvents resulted in different morphologies. Aqueous solvent corresponds to the nanosheet structure, methanol solvent corresponds to the nanoporous structure, and ethylene glycol corresponds to random nanoparticles without a specific morphology.

In 2024, Wang et al.⁴² synthesized ZnIn₂S₄ with sulfur vacancies (ZnIn₂S₄-V_s) by solvothermal binding annealing (Fig. 3a). Workers obtain uniformly assembled ZnIn₂S₄ ultrathin nanosheets at low temperatures and short reaction times through a simple and safe water bath reaction. Then, ZnIn₂S₄ with S vacancies is obtained by annealing ZnIn₂S₄. As illustrated in Fig. 3b, Wang et al.⁴³ prepared a ZnIn₂S₄@Ni(OH)₂/NiO Z-scheme heterostructure photocatalyst with defects by using hydrothermal synthesis combined with low temperature roasting. In 2025, Li et al.⁴⁴ synthesized NiCo₂O₄@ZnIn₂S₄ composites in a two-step process (Fig. 3c). First, NiCo₂O₄ hollow nanoprisms were prepared by co-precipitation and the Kirkendall effect. This is then incorporated into the steps of conventional solvothermal synthesis of ZnIn₂S₄.

Fig. 3 (a) Fabrication process of V_s-ZnIn₂S₄. Reproduced with permission from ref. 42, copyright 2024, Wiley-VCH. (b) The schematic illustration of the synthesis process of ZnIn₂S₄, ZnIn₂S₄@NOH and ZnIn₂S₄@NOH/NO photocatalysts. Reproduced with permission from ref. 43, copyright 2024, Elsevier. (c) Schematic illustration for the fabrication of NiCo₂O₄@ZnIn₂S₄. Reproduced with permission from ref. 44, copyright 2025, Elsevier.

2.2.3 Microwave-assisted method. Microwave-assisted synthesis is a rapid synthesis method of new materials. Compared with the heat conduction process, microwave radiative heating is the direct heating of molecules in a substance through microwave energy, which can provide a faster heating rate and a more uniform temperature distribution, leading to a faster reaction time and higher efficiency. Therefore, as a non-traditional heating method, microwave radiation can effectively replace the heat source in the traditional hydrothermal reaction or solvothermal reaction, and is always used as an auxiliary method to improve traditional synthesis methods. For example, Xia et al.⁴⁵ rapidly synthesized ZnIn₂S₄ nanoflower-like microspheres in a few minutes by using microwave-assisted hydrothermal synthesis. Furthermore, the graded ZnIn₂S₄ microspheres were successfully prepared with the microwave-assisted solvent thermal method, which was conducted using ethylene glycol as solvent by Hu et al.⁴⁶ This is due to the good microwave absorption performance of ethylene glycol, so it can quickly heat up the reaction system. At the same time, the effect of microwave radiation in the local area favors the acceleration of crystal growth and the self-assembly of materials, which leads to the rapid formation of ZnIn₂S₄ with a hierarchical structure. In addition, Naik et al.⁴⁷ successfully synthesized ZnIn₂S₄ nanoparticles using a microwave-assisted method and studied how changes in microwave power affect the light response properties of these particles and their performance in photoelectric applications.

2.2.4 Other methods. In addition to the above methods, other methods can be used for the preparation of ZnIn₂S₄-based composite photocatalysts, such as the co-precipitation method, in situ growth and the impregnation method.^48–51 Yuan et al.⁵² dispersed the prepared ZnIn₂S₄ in NaOH aqueous solution, continuously dropped a certain volume of Ni(NO₃)₂ aqueous solution under stirring, and obtained Ni/ZnIn₂S₄ after continuous stirring and centrifugation. This also revealed the double charge receptor action of Ni(OH)₂ deposited on ZnIn₂S₄. Peng et al.⁵³ dispersed polypyrrole (PPy) in dilute HCl solution and efficiently transferred into glass bottles using the method of in situ growth. Glycerin is firstly added to the solution with stirring, followed by the successive addition of In(NO₃)₃·xH₂O, Zn(NO₃)₂·6H₂O, and thioacetamide (TAA). The mixture is then stirred, subjected to oil bath treatment, and centrifuged to obtain the ZnIn₂S₄/PPy composite catalyst. There are also some ZnIn₂S₄-based composite photocatalysts fabricated by combining different methods. For instance, Chen et al.⁵⁴ prepared MoS₂/ZnIn₂S₄ composite photocatalysts via solvothermal and photodeposition methods. The catalyst showed excellent activity in the activity test of photocatalytic hydrogen production coupling benzyl alcohol (BA) oxidation.

3. Strategies to improve photocatalytic performance

The primitive ZnIn₂S₄ material exhibits unsatisfactory photocatalytic performance, mainly due to its insufficient light absorption capacity and the rapid recombination speed of charge carriers.^55,56 This unfavorable property can be effectively improved by adjusting the band structure of ZnIn₂S₄ and improving its surface and microstructure properties. To address these challenges, scientists have taken a variety of measures to improve the photocatalytic efficiency of ZnIn₂S₄.^57–59 In this chapter, we summarize various methods which could improve the photocatalytic capacity of ZnIn₂S₄ in recent years. Each of the ZnIn₂S₄ optimization strategies outlined below exhibits distinct advantages alongside inherent limitations. Only through their rational integration can the positive effects on catalyst performance be maximized.

3.1 Metal doping

To solve the problem of inefficient photocatalytic capacity of the ZnIn₂S₄ photocatalyst, it is necessary to capture as many incident photons as possible and reduce the recombination of electrons and holes on the surface of the photocatalyst. Deposition of metals on the surface of ZnIn₂S₄ is considered as an effective strategy, which is attributed to the superior charge conduction properties of metals.^60–63 Generally, metal plays two pivotal roles in photocatalysts, including the localized surface plasmon resonance (SPR) effect and formation of Schottky barriers. On account of the low Fermi level of precious metals, many noble metals can be used to trap more free electrons and enhance the separation efficiency of electrons and holes. As early as 2019, Zhu et al.⁶⁴ prepared ZnIn₂S₄ by the solvent method and doped Au on ZnIn₂S₄ nanosheets to prepare Au/ZnIn₂S₄ composite photocatalysts. The composite catalyst can not only produce more hole electron pairs, but also effectively prolong the lifetime of photogenerated electrons. Furthermore, it has lower electron–hole recombination rates, which improves the activity of photocatalysis. For instance, Song et al.⁶⁵ induced SPR effects via silver doping in ZnIn₂S₄, which remarkably enhanced its photocatalytic performance (Fig. 4a). This improvement is closely associated with the SPR-amplified light-harvesting capability and the promoted separation efficiency of photoexcited charge carriers. In addition, Liu et al.⁶⁶ constructed a ZnIn₂S₄-based composite with Ag-Pd bimetallic nanoparticles, where an optimal Schottky barrier was formed at the heterointerfaces (Fig. 4b). By regulating the charge transfer dynamics, the recombination of electron–hole pairs was effectively suppressed, leading to a prolonged lifetime of charge carriers and thus a significant boost in photocatalytic activity.

Fig. 4 (a) Photocatalytic degradation mechanism for pollutants over CoS_x/Ag/Ag₂S/ZnIn₂S₄ composites under visible light. Reproduced with permission from ref. 65, copyright 2022, Elsevier. (b) Schematic illustration of charge transfer and the H₂ evolution mechanism for the Ag-Pd/ZnIn₂S₄ photocatalyst. Reproduced with permission from ref. 66, copyright 2023, Elsevier. (c) The schematic of the reaction mechanism of ZnIn₂S₄ and 2-Ni/ZnIn₂S₄ for H₂ evolution. Reproduced with permission from ref. 68, copyright 2022, Elsevier. (d) Schematic diagram of the photocatalytic mechanism for Bi-Bi₂MoO₆/ZnIn₂S₄ under visible light illumination and (e) photocatalytic H₂ producing performance of the prepared samples. Reproduced with permission from ref. 69, copyright 2023, Elsevier.

Due to the high cost of precious metals and the scarcity of resources, their practical application is somewhat limited, so workers began to engage in the adulteration of non-noble metals. Lin et al.⁶⁷ prepared the Ni/ZnIn₂S₄ composite photocatalyst by doping with non-noble metal Ni, and proved that Ni doping effectively inhibits electron–hole recombination. Therefore, the activity of the composite photocatalyst Ni/ZnIn₂S₄ in the reaction of hydrogen production coupled with BA oxidation was significantly improved. Meanwhile, Chen et al.⁶⁸ employed an in situ photodeposition strategy to anchor Ni clusters on the ZnIn₂S₄ surface, which yielded a 10.6-fold enhancement in hydrogen evolution activity. The underlying reaction mechanism is schematically illustrated in Fig. 4c. Ni-doped photocatalysts have not only overcome the disadvantages of expensive precious metals in the past, but also provide inspiration for the doping of other monometals and their complexes. Furthermore, Geng et al.⁶⁹ utilized Bi as a noble metal substitute to enhance the active sites of ZnIn₂S₄ and induce SPR effects (Fig. 4d). As shown in Fig. 4e, this composite catalyst exhibited superior photocatalytic activity in hydrogen production compared to its Pt-doped ZnIn₂S₄ counterparts.

3.2 Morphology regulation

The catalyst with a hierarchical structure has an abundant specific surface area.^70,71 This is why that accurate regulation and control of the morphology of semiconductor photocatalysts is essential to improve their physicochemical properties and the overall efficiency of the photocatalytic system. With reference to structural regulation, trisodium citrate is known for its ability to precisely manipulate size and morphology in the preparation of advanced materials. Using a simple one-pot solution method, Sheng et al.⁷² prepared multifunctional porous ultra-thin ZnIn₂S₄ nanosheets by carefully adjusting the sodium citrate solution concentration in the synthetic medium. Notably, compared to traditional nanoflower structures (with a specific surface area of 60.18 m² g⁻¹), the as-prepared ultra-thin nanosheets exhibited a remarkable increase in specific surface area, reaching 132.36 m² g⁻¹. This enhanced surface area, coupled with the densely distributed nanopores, not only provides abundant redox active sites for reactions but also ultimately results in a higher density of active sites than that of conventional nanoflower structures.

Moreover, Liu et al.⁷³ reported a spatial decoupling strategy assembly with the cryogenic solvent method forming a high-quality tight heterojunction structure CoP-ZnIn₂S₄ composite photocatalyst (Fig. 5a). As shown in Fig. 5b–d, the CoP-ZnIn₂S₄ composite photocatalyst was used as a model to construct unique CoP coaxial nanorods. CoP as the core is the active site for hydrogen production, and ZnIn₂S₄ as the shell is the oxidative coupling site of amine to imine. This structure has a larger areal density, which provides more reaction sites, and effectively ensures the effective isolation of the active sites of H₂ and imine, and improves its product yield and selectivity. Fig. 5e illustrates the synthesis of ZnIn₂S₄ nanosheets grown by in situ confinement on a porous hollow carbon sphere (PHCS) backbone through the hydrothermal method.⁷⁴ SEM images of the carbon spheres show a diameter of approximately 250 nm and also show a hollow structure and numerous micropores (Fig. 5f). After the hydrothermal treatment, the ZnIn₂S₄/C heterostructure composites retained the original morphology of the carbon framework, and a small number of ZnIn₂S₄ nanosheets were grown inside/outside the frame (Fig. 5g), and the high-resolution TEM images showed the interfacial composition of the composites (Fig. 5h). It is the exploration of the morphology of ZnIn₂S₄ that has led to the emergence of more excellent ZnIn₂S₄ composites with outstanding structural and catalytic properties.

Fig. 5 (a) Schematic illustration for the synthetic process of CoP@ZnIn₂S₄, (b) TEM, (c) SEM, and (d) high-resolution TEM images of CoP@ZnIn₂S₄. Reproduced with permission from ref. 73, copyright 2023, American Chemical Society. (e) Fabrication scheme of the hierarchical hollow structural ZnIn₂S₄/C composite, (f) SEM image of PHCSs, and (g) TEM image and (h) HRTEM images of ZnIn₂S₄/C. Reproduced with permission from ref. 74, copyright 2025, Elsevier.

3.3 Constructing heterojunctions

In addition, due to the differences in the band structure of different semiconductors, it is possible to create a more well-targeted and high-performance photocatalytic system through coupling ZnIn₂S₄ with other semiconductors to construct heterostructures. The formation of heterojunctions can promote the migration of light excited electrons in semiconductors and realize the spatial separation of electrons and holes efficiently. Moreover, heterojunction construction has become a mainstream approach for alleviating ZnIn₂S₄ photo-corrosion. The core mechanism lies in the fact that photogenerated holes (h⁺), with strong oxidizing ability, readily oxidize sulfur ions (S²⁻) in ZnIn₂S₄ to S⁰ or SO₄²⁻; however, heterojunctions facilitate efficient e⁻–h⁺ separation, which mitigates h⁺ accumulation and thus suppresses ZnIn₂S₄ photo-corrosion. By forming heterojunctions and applying diverse semiconductor materials, the constructed heterostructures could effectively enhance the efficiency of photocatalysis.^75–77 Therefore, the construction of rational ZnIn₂S₄-based heterojunction structures is important for the activity of photocatalytic hydrogen production coupling organic synthesis. According to the arrangement of the band structure, heterojunction photocatalysts can be divided into five types: a Type I heterostructure, Type II heterostructure, Z-scheme heterostructure, p–n junction and Schottky junction.

For example, Fig. 6a shows a bifunctional 2D/2D ZnIn₂S₄/CeO₂ photocatalyst with a stepped heterojunction which was successfully synthesized by Zhang et al.⁷⁸ Jiang et al.⁷⁹ also synthesized the CeO₂/ZnIn₂S₄ layer hybrids by the in situ solvothermal method. Given that the chemical properties of the sulfur (S) atom are similar to those of the oxygen (O) atom, the S²⁻ is able to fill the oxygen vacancies in CeO₂. And a novel bifunctional 2D/2D CeO₂/ZnIn₂S₄ photocatalyst was successfully developed. The catalyst has a step-like heterostructure and can simultaneously utilize the electron–hole pair generated by photoexcitation to efficiently produce H₂ and oxidize furfural in a single photooxidation–reduction reaction system. Furthermore, in the EPR spectroscopic analysis, ZnIn₂S₄ nanospheres and CeO₂/ZnIn₂S₄ show an obvious DMPO-˙O₂⁻ signal, and show weaker signals compared with the EPR spectra of cerium oxide nanorods (Fig. 6b). From another perspective, CeO₂ and CeO₂/ZnIn₂S₄ composites exhibit more pronounced significant DMPO-˙OH signals in the EPR spectra, characterized by a typical peak intensity ratio of 1 : 2 : 2 : 1, whereas no such peaks are observed for ZnIn₂S₄ nanospheres (Fig. 6c). In addition, the results of band structure and EPR spectra indicate that the CeO₂/ZnIn₂S₄ system successfully constructs a Z-type structure (Fig. 6d). Li et al.⁸⁰ synthesized the WO₃/ZnIn₂S₄ heterojunction structure and proposed a reasonable photoredox catalytic reaction mechanism (Fig. 6e).

Fig. 6 (a) A reasonable catalytic mechanism for the cooperative photoredox reaction including H₂ production and FOL conversion over the 2D/2D ZnIn₂S₄/CeO₂ heterojunction. Reproduced with permission from ref. 78, copyright 2023, Elsevier. (b) EPR spectra of DMPO-˙O₂⁻ and (c) DMPO-˙OH over CeO₂, (d) ZnIn₂S₄ and CeO₂/ZnIn₂S₄ under solar exposure, and charge carrier flow mechanisms over type II and direct Z-scheme heterojunctions for the CeO₂/ZnIn₂S₄ composite. Reproduced with permission from ref. 79, copyright 2020, Elsevier. (e) Probable mechanism for photoredox-catalyzed integrated reactions including BA oxidation and H₂ generation over WO₃/ZnIn₂S₄ under UV-vis light illumination. Reproduced with permission from ref. 80, copyright 2022, American Chemical Society.

3.4 Defect engineering

From the perspective of the design of the constituent materials, defect engineering is another effective method that is considered to improve the efficiency of photocatalysis. The presence of defects helps to adjust the band structure of nanomaterials to broaden the range of light absorption, and they can act as trapping centers to enhance the separation efficiency of electrons from holes, while acting as catalytically active sites by changing the arrangement of surface atoms.^81–83 The photocatalytic performance of ZnIn₂S₄ was optimized by introducing different types of vacancy defects, such as sulfur vacancies and zinc vacancies. For example, Xia et al.⁸⁴ prepared a Lewis acid-base nano-catalyst (Ni/ZnIn₂S₄) by photodeposition using Zn deficient ZnIn₂S₄ nanosheets as the forerunner. Due to the existence of Zn vacancies, Ni can be selectively deposited in the ZnIn₂S₄ body, so that the double active sites adjacent to Lewis acid Ni and Lewis base S can be co-exposed. The electron-rich S site and the electron-deficient Ni site could serve as the hydrogen production site and organic value-added site of the coupling reaction, respectively, which effectively improved the activity of the photoreaction in the modified system.

Recently, Yang et al.⁸⁵ successfully synthesized ZnIn₂S₄ nanosheets with sulfur vacancies by tuning the concentration of TAA (Fig. 7a). Notably, this strategy not only enabled precise modulation of the ZnIn₂S₄ band structure but also markedly augmented its piezoelectric effect, thereby laying a structural foundation for enhanced photocatalytic performance. Furthermore, Yue et al.⁸⁶ engineered a built-in strong electric field by introducing S vacancies into ZnIn₂S₄ and integrating with NiSe. This electrostatic field effectively mitigated the coulombic attraction between electron–hole pairs to suppress their recombination, thereby achieving highly active photocatalytic hydrogen evolution. The corresponding synthesis route is illustrated in Fig. 7b. The functionality of this built-in electric field is directly validated by the electrostatic potential distributions presented in Fig. 7c and d, where a significant enhancement in the potential difference was observed after the introduction of S vacancies. Fig. 7e depicts the DFT-calculated crystal structure model of ZnIn₂S₄-S_v along the [001] direction.

Fig. 7 (a) The schematic illustrates the synthesis of S-vacancy-engineered ZnIn₂S₄ nanosheets. Reproduced with permission from ref. 85, copyright 2025, Wiley-VCH. (b) Schematic illustration of the synthetic process for the ZnIn₂S₄-NiSe, and NiSe/ZnIn₂S₄-S_v samples, (c) DFT calculations yielded the electrostatic potential diagrams along the [001] direction for ZnIn₂S₄ and (d) ZnIn₂S₄-S_v, and (e) the crystal structure diagram along the [001] direction for ZnIn₂S₄-S_v. Reproduced with permission from ref. 86, copyright 2024, Wiley-VCH.

4. Applications

In photocatalytic systems integrating hydrogen production with organic substrate valorization, the reduction of protons to H₂ occurs at the conduction band (CB) with sufficient reducing potential. Meanwhile, the valence band (VB) energy required for organic matter oxidation often serves as the critical factor determining the reaction feasibility. This energy matching between CB reduction potential and VB oxidation capability is essential for achieving efficient charge carrier utilization and simultaneously driving both hydrogen evolution and organic transformation. The conduction band of ZnIn₂S₄ is situated at −0.9 V and the valence band is at 1.48 V, which not only provides sufficient driving force for proton reduction to hydrogen in the system but also creates favorable conditions for the oxidation of certain organic compounds.

4.1 Selective conversion of alcohols

Selective conversion of alcohols is an important organic chemical transformation process in both laboratory and industrial fields, because the carbonyl compounds (i.e., aldehydes and ketones) and C–C or C–O coupling products generated have important application value as multifunctional structural units for the synthesis of drug intermediates and fine chemicals.^87,88 Traditionally, non-catalytic alcohol oxidation processes often use toxic and corrosive heavy metal oxides such as K₂Cr₂O₇ and KMnO₄, and these processes require harsh conditions.⁸⁹ Meanwhile, solar-powered alcohol oxidation technologies have gained increasing attention due to their environmental friendliness and renewable energy utilization, offering new possibilities for greener, more sustainable development. However, these technologies are limited by the low activity, poor selectivity, and insufficient stability of existing photocatalysts. Thus, developing high-performance ones—capable of efficient solar utilization, rapid charge separation, and precise reaction regulation—is key. ZnIn₂S₄, a visible-light-responsive semiconductor with a suitable band gap and layered structure, has great photocatalytic oxidation potential; modifying it into composites (via heterojunction construction, co-catalyst loading, or metal doping) optimizes performance, making it promising for efficient, selective solar-driven alcohol oxidation. In the following section, we will show the excellent performance of some ZnIn₂S₄-based composite photocatalysts in the field of selective oxidation of alcohols, and explore the mechanism of their photocatalytic coupling reactions and the comparison of their modified properties.

In the design of ZnIn₂S₄-based composite photocatalysts, the introduction of appropriate co-catalysts is of great significance for enhancing charge separation efficiency and activating reaction sites—two core factors that determine the performance of selective alcohol oxidation. Recently, Peng et al.⁵³ described the PPy@ZnIn₂S₄ composite materials which involve the direct growth of ultra-thin ZnIn₂S₄ nanosheets on PPy nanotubes (Fig. 8a). This composite material exhibits excellent photocatalytic activity capable of generating H₂ through the photocatalytic reduction reaction of water and producing 1,4-phenylacetaldehyde (PAD) through the selective oxidation reaction of 1,4-benzenedimethanol (BDM). And the introduction of PPy is mainly to improve the activity of the photoreaction by increasing the sulfur vacancies of ZnIn₂S₄. As shown in the figures, the Gibbs free energies of all possible reactions during the BDM oxidation reaction were calculated for ZnIn₂S₄ and ZnIn₂S₄-S_v (Fig. 8b and c). At the same time, path 4 in the free energy diagram is identified as the best reaction path of BDM oxidation. As shown in Fig. 8d, the BDM oxidation reaction on the ZnIn₂S₄-S_v has a lower free energy than that on ZnIn₂S₄ (0.94 eV and 1.06 eV, respectively), indicating that ZnIn₂S₄-S_v exhibits superior catalytic activity in this oxidation reaction. Therefore, the introduction of PPy can improve the catalytic effect of the BDM oxidation reaction. As shown in Fig. 8e, it is proved that the introduction of PPy into ZnIn₂S₄ can also improve the hydrogen production activity. According to the above analysis, the introduction of PPy into ZnIn₂S₄ can significantly improve the performance of the BDM oxidation reaction and HER process.

Fig. 8 (a) Schematic preparation of PPy@ZnIn₂S₄, (b) the free energy diagrams of 4 pathways in ZnIn₂S₄ and (c) ZnIn₂S₄-S_v, (d) the free energy profiles with the lowest energy barrier of ZnIn₂S₄ and ZnIn₂S₄-S_v are presented by blue and red lines, respectively, and (e) the free energy profiles for hydrogen adsorption at different active sites of ZnIn₂S₄ and ZnIn₂S₄-S_v. Reproduced with permission from ref. 53, copyright 2022, Elsevier. (f) Schematic illustration of the Z-scheme transfer path of photogenerated carriers between HPM and ZnIn₂S₄ heterojunctions. HPB refers to the reduction state of an HPM derived from the formation of a built-in electric field. Reproduced with permission from ref. 90, copyright 2022, Elsevier.

Moreover, for ZnIn₂S₄-based photocatalytic systems, constructing heterojunctions is also a crucial performance optimization strategy—this structure not only facilitates the efficient separation of photogenerated electron–hole pairs (a core bottleneck in photocatalysis) but also regulates the reaction path to precisely match the redox potential requirements of alcohol oxidation coupling with H₂ evolution. Huang et al.⁹⁰ reported an efficient aromatic alcohol oxidation with simultaneous H₂ evolution under aqueous conditions, achieved in a polyoxometalate (POM)-incorporated ZnIn₂S₄ dual-functional photocatalytic system. And the schematic illustration of the Z-scheme path between HPM and ZnIn₂S₄ heterojunctions is shown in Fig. 8f.

For ZnIn₂S₄-based photocatalysts, atomic-level doping modification has emerged as a powerful strategy to overcome performance bottlenecks—it not only constructs well-defined atomic active sites to strengthen the adsorption and activation of reactants but also regulates electronic effects to optimize the dynamics of photogenerated charge transfer, thereby synergistically enhancing catalytic activity for coupled reactions such as H₂ evolution coupling with aromatic alcohol oxidation. In 2025, Zhou et al.⁹¹ employed an approach by doping non-magnetic molybdenum (Mo) into ZnIn₂S₄ materials, while the spin polarization effect is realized and S₂²⁻–Mo–S–In active sites are formed at the atomic level. The synergistic coupling of spin polarization and atomic active sites is the key driving force for the significant enhancement of catalytic performance. As shown in Fig. 9g and h, the optimized Mo/ZnIn₂S₄ showed a catalytic activity of 172.26 mmol g⁻¹ h⁻¹ and 161.46 mmol g⁻¹ h⁻¹ in the production of hydrogen and benzaldehyde, respectively, which was nearly 10 times higher than that of ZnIn₂S₄. Moreover, further improvements in hydrogen and BAD production can be achieved by the external magnetic field generated by the permanent magnet without any additional energy input. Furthermore, the microscopic coordination environment of the photocatalyst was characterized by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy techniques (Fig. 9a–f). It was confirmed that Zn exists mainly in the form of Zn-S coordination and Mo is mainly coordinated with S atoms.

Fig. 9 (a) XANES spectra of the Zn K-edge for Zn foil, ZnO, ZnIn₂S₄ and Mo/ZnIn₂S₄, (b) the Fourier transform of k²⁻ weighted EXAFS spectra at the Zn k-edge of Zn foil, ZnO, ZnIn₂S₄ and 2Mo/ZnIn₂S₄, (d) XANES spectra of the Mo K-edge for Mo foil, MoS₂ and Mo/ZnIn₂S₄, (e) the Fourier transform of k²⁻ weighted EXAFS spectra at the Mo K-edge of Mo foil, MoS₂ and Mo/ZnIn₂S₄, (c) wavelet transform analysis of the k²⁻ weighted Mo K-edge EXAFS signals of Mo foil, MoS₂ and (f) Mo/ZnIn₂S₄. Reproduced with permission from ref. 91, copyright 2025, Elsevier.

Meanwhile, Jia et al.⁹² put forward a new type of 2D/3D ZnIn₂S₄@Ni₁/UiO-66-NH₂ heterojunction, and the spatial separation and ordered distribution of oxidation–reduction sites were realized for photocatalytic H₂ production and BA value addition. The spatial separation and directional electron transfer of redox sites were fully realized. EXAFS spectroscopy analysis illustrates the local environment of Ni to detect the geometrical and electronic structure of the Ni site. Fig. 10a shows a composite diagram of ZnIn₂S₄@Ni₁/UiO-66-NH₂. In addition, Fig. 10b proves that Ni exists in the form of Ni²⁺. The wavelet transform of the composites shows that this verifies the ligation environment of Ni-O and the single-atom properties of Ni (Fig. 10c). The Fourier transform-EXAFS spectra showed that there were no peaks associated with Ni–Ni bonds, indicating that the Ni²⁺ sites were all dispersed (Fig. 10d). The curve fitting of the EXAFS data also indicates that the Ni²⁺ site has a coordinated environment. As shown in Fig. 10e, the best fitting results of the first shell show that Ni is mainly coordinated with oxygen atoms.

Fig. 10 (a) Schematic illustration of the synthetic process of ZnIn₂S₄@Ni₁/UN nanocomposites, (b–d) Ni K-edge XANES and FT-EXAFS spectra of Ni₁/UN-6, Ni foil, and Ni-Pc, and (e) EXAFS fitting of Ni₁/UN-6 (inset: supposed structure of a Ni single-atom anchored on a Zr₆-oxo cluster). Reproduced with permission from ref. 92, copyright 2024, Elsevier.

To gain insights into the research progress of alcohols being selectively converted to aldehydes along with hydrogen production using ZnIn₂S₄-based photocatalysts, Table 1 summarizes recent relevant studies. It presents details such as the specific photocatalyst, synthesis method, target product, light source employed, and key performance indicators.

Table 1 Summary of recent studies of alcohols selectively converted to aldehydes and hydrogen production by ZnIn₂S₄-based photocatalysts^a

Photocatalyst	Synthesis method	Product	Light source	Efficiency (mmol g^−1 h^−1) or selectivity	Ref.
a The E and S in the table represent the yield and selectivity of the corresponding organic compounds.
POM/ZIS	Solvothermal	Benzaldehyde	Xenon lamp (λ ≥ 420 nm 5 h)	H2: 10.60	90
				S: 100%
PPy/ZIS	Solvothermal	1,4-Phenyldicarboxaldehyde	Xenon lamp (λ ≥ 420 nm 6 h)	H2: 0.73	53
				S: 98.90%
Bi/ZIS	One-pot	Benzaldehyde	Xenon lamp (λ ≥ 420 nm 6 h)	H2: 3.66	93
				E: 1.02
P-MoS2-ZIS	Solvothermal	Benzaldehyde	Sunlight (λ: 320–780 nm)	H2: 31.30	94
				E: 31.40
CeO2/ZIS	One-pot	Benzaldehyde	Xenon lamp (AM 1.5 3 h)	H2: 1.50	79
				E: 0.66
Au/ZIS	Solvothermal& in suit deposition	Benzaldehyde	Xenon lamp (λ ≥ 420 nm 4 h)	H2: 0.33	64
				E: 0.35
ZIS NS	One-pot	Benzaldehyde	Xenon lamp (AM 1.5 4 h)	H2: 22.20	72
				E: 0.33
CoP/ZIS	Hydrothermal & solvothermal	Pyruvic acid	Xenon lamp (λ ≥ 420 nm 3 h)	H2: 0.23	95
				S: 93.90%
MoS2/ZIS	Solvothermal & photodeposition	Benzaldehyde	Xenon lamp (λ ≥ 420 nm 5 h)	H2: 3.88	54
				E: 3.69
Ni/V ZIS	In situ photodeposition	Benzaldehyde	Xenon lamp (λ: 400–800 nm 2 h)	H2: 0.82	85
				E: 0.74
NiP/ZIS	Solvothermal	Pyruvic acid	Xenon lamp (λ: 345–385 nm 3 h)	H2: 0.38	20
				S: 97.80%
CoCuP/ZIS	Grinding sintering	Acetone	Xenon lamp (λ: 345 nm, 420 nm, 500 nm 3 h)	H2: 26.80	96
				E: 17.80
CdS/ZIS	Solvothermal	Benzaldehyde	Xenon lamp (λ: 400 nm 6 h)	H2: 12.20	97
				E: 12.10

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4.2 Oxidative coupling of amines

Due to the wide application of C–N conjugation products, the selective oxidation of aniline C–N conjugation has led to the expansion of the field of photocatalysis. This field not only emphasizes the synthesis of high-value C–N coupling products but also pursues the co-production of clean energy under sacrificial-agent-free conditions, which has become a key direction to achieve sustainable photocatalytic reactions. In 2018, the method of photocatalytic preparation of H₂ and selective oxidation of aniline on MOFs by a sacrificial-free Pt cocatalyst was reported for the first time, which attracted widespread attention.⁹⁸ As an excellent visible-light-responsive photocatalyst, ZnIn₂S₄ has shown great application potential in the selective oxidation of aniline C–N conjugates coupling H₂ production. For example, She et al.⁹⁹ reported a hollow Pd@TiO₂@ZnIn₂S₄ nanocassette with a sandwich morphology, which was synthesized by selecting microporous zeolite with subnanoscale Pd nanoparticles embedded as sacrificial templates (Fig. 11a). The composite catalyst exhibited an excellent PHE rate (5.35 mmol g⁻¹ h⁻¹) and aniline oxidative conversion (>99%), due to the enhanced light capture capability of the hollow structure and the improved charge separation efficiency of the miniature size Pd nanoparticles.

Fig. 11 (a) Illustration of the preparation of a sandwich-like hollowed Pd@TiO₂@ZnIn₂S₄ nanobox catalyst. Reproduced with permission from ref. 99, copyright 2022, Wiley-VCH. (b) The calculated energy profile for hydrogen production on BaTiO₃, ZnIn₂S₄ and BaTiO₃-ZnIn₂S₄. Reproduced with permission from ref. 100, copyright 2023, Elsevier. (c) Schematic illustration of the dual-functional photocatalytic reaction mechanism for hydrogen evolution and BA oxidation over Pt@UiO-66-NH₂@ZnIn₂S₄. Reproduced with permission from ref. 101, copyright 2023, Royal Society of Chemistry.

Furthermore, to enhance both stability and activity, ZnIn₂S₄ was simultaneously engineered on two fronts: hetero-atom doping was used to re-tune its band structure, and a chemically inert oxide over-layer provided robust surface shielding. The two tactics operate in concert, efficiently suppressing photo-corrosion and locking the lattice integrity over prolonged illumination. Building on this stabilised matrix, Wang et al. further assembled a layered Z-scheme BaTiO₃@ZnIn₂S₄ heterojunction that integrates piezo-electricity with photochemistry. Under mechanical vibration the built-in piezo-field triggers a “domino” displacement of charges, accelerating Z-path carrier separation and delivering photogenerated electrons and holes to their respective reaction sites with minimal recombination. Exploiting this synergy of piezo-potential and Z-scheme architecture, the composite co-produces 5.59 mmol g⁻¹ of C–N coupled products and 8.04 mmol g⁻¹ of H₂ in a single run, demonstrating that mechanical energy can be seamlessly married to solar energy to boost photocatalytic efficiency. Mechanistic investigation further unveiled a consecutive dehydrogenation C–N coupling sequence for benzylamine, clarifying how the dual-energy input governs reaction selectivity as shown in Fig. 11b.

Similarly, the integration of heterojunction construction and morphological optimization has also been proven to exert a positive effect on promoting the photocatalytic C–N coupling reaction with synchronous H₂ evolution—a trend consistent with the aforementioned performance enhancement strategies for ZnIn₂S₄-based systems. The Pt@UiO-66-NH₂@ZnIn₂S₄ heterojunction with an egg yolk–shell structure was successfully prepared and used as a bifunctional photocatalyst for the C–N coupling reaction with H₂ production by Hou et al.¹⁰¹ In this coupling system, ZnIn₂S₄ acts as a hole collector, and is able to capture and release holes from Pt@UiO-66-NH₂, thereby accelerating the C–N coupling of benzylamine, while Pt acts as an electron collector and is also the active site for the reduction of protons to H₂. The composite photocatalysts show 4 and 16 times higher catalytic activities than that of pure ZnIn₂S₄ and UiO-66-NH₂, respectively. In addition, the well-designed and fabricated layered Pt@UiO-66-NH₂@ZnIn₂S₄ heterostructure enables the simultaneous generation of H₂ and C–N coupling reaction without the use of sacrificial agents. For the first time, the active site separation of Pt and ZnIn₂S₄ was successfully achieved in the interior and surface of UiO-66-NH₂, which significantly enhanced the separation efficiency and extended the lifetime of the charges. A bifunctional photocatalytic reaction mechanism shown in Fig. 11c involving the oxidative coupling of aromatic amines generated by H₂ binding on Pt@UiO-66-NH₂@ZnIn₂S₄ is proposed.

In addition, the sulfur–vacancy (S_v) density in ZnIn₂S₄ can be precisely tuned by synergistic rare-earth-ion doping and in situ cocatalyst decoration, a strategy that concurrently accelerates H₂ evolution, promotes C–N coupling, and steers the selectivity toward imines. Xie et al.¹⁰² synthesized a nanoflower-like ZnIn₂S₄ by dissolution heat synthesis. The S_v generated during the synthesis of ZnIn₂S₄ was doped with rare earth ion Er, and the NiS cocatalyst was grown on the S_V by in situ photodeposition. EPR tests were performed on all three samples to study sulfur vacancies. As shown in Fig. 12d, the ZnIn₂S₄, 2% Er³⁺–ZnIn₂S₄, and 2% Er³⁺–ZnIn₂S₄/NiS (0.5%) samples exhibit a pattern of EPR characteristic signals at g = 2.001. This demonstrates that the number of S vacancies decreases with the increase in Er³⁺ doping and cocatalyst loading. Subsequently, the complex structures of ZnIn₂S₄, 2% Er³⁺–ZnIn₂S₄, and 2% Er³⁺–ZnIn₂S₄/NiS (0.5%) were investigated using Vienna ab initio simulation package-based density functional theory calculations (Fig. 12a and c). Since In is more electronegative than Zn, bond cleavage mainly occurs in zinc–sulfur bonds, which allows Er to replace Zn sites, thus forming Er–S bonds and reducing sulfur vacancies. After the cocatalyst NiS was loaded, the cocatalyst NiS was grown on the S vacancy on the surface of ZnIn₂S₄ by in situ photodeposition, which further reduced the S_v and made the cocatalyst load more stable. The obtained Er³⁺–ZnIn₂S₄/NiS photocatalyst significantly increased the hydrogen generation and C–N coupling productivity of 11.8 mmol g⁻¹ h⁻¹ and 10.2 mmol g⁻¹ h⁻¹, respectively, while the hydrogen generation rate of the original ZnIn₂S₄ was 1.2 mmol g⁻¹ h⁻¹ and the benzylamine coupling activity was 0.7 mmol g⁻¹ h⁻¹. Moreover, the Electron Localization Function (ELF) also indirectly confirmed the reduction of S_v, which stabilized the composite structure and further promoted the improvement of activity (Fig. 12e). In the 2% Er³⁺–ZnIn₂S₄/NiS (0.5%) system, imine was the main product, indicating that the C–C coupling reaction was significantly inhibited, thereby improving the selectivity of imine. This improvement may be attributed to the high efficiency of the NiS-assisted process. The 2% Er³⁺–ZnIn₂S₄/NiS (0.5%) system significantly inhibited the C–C coupling reaction, and the selectivity of imine was improved and became the main reaction product. This optimization may be due to the efficient synergistic effect of NiS.

Fig. 12 (a) Crystal structure model of ZnIn₂S₄, (b) Er³⁺–ZnIn₂S₄ and (c) 2% Er³⁺–ZnIn₂S₄/NiS (0.5%), (d) the EPR spectra of ZnIn₂S₄, 2% Er³⁺–ZnIn₂S₄ and 2% Er³⁺–ZnIn₂S₄/NiS (0.5%), and (e) ELF spectra of ZnIn₂S₄, 2% Er³⁺–ZnIn₂S₄ and 2% Er³⁺–ZnIn₂S₄/NiS (0.5%). Reproduced with permission from ref. 102, copyright 2025, Elsevier. (f) Time-yield plots of NBI and DBA, and NBI selectivity of ZnIn₂S₄ and (g) CoP@ZnIn₂S₄. Reproduced with permission from ref. 73, copyright 2023, American Chemical Society.

In contrast, CoP@ZnIn₂S₄ composites were more selective for C–C coupling products, with the NBI selectivity decreasing to 20% after a 5 hour reaction on the original ZnIn₂S₄ (Fig. 12f).⁷³ In contrast, the NBI generation process on CoP@ZnIn₂S₄ coaxial nanorods was efficient and stable, and the selectivity of NBI was maintained at about 100% (Fig. 12g). It is evident that the main products of ZnIn₂S₄ and CoP@ZnIn₂S₄ are DBA and NBI, respectively. This also provides researchers with more ideas for screening different coupling products of BA.

To gain insights into the research progress of oxidative coupling of amines and hydrogen production via ZnIn₂S₄-based photocatalysts, Table 2 summarizes recent relevant studies. It presents details such as the specific photocatalyst, synthesis method, target product, light source employed, and key performance indicators.

Table 2 Summary of recent studies of oxidative coupling of amines and hydrogen production by ZnIn₂S₄-based photocatalysts^a

Photocatalyst	Synthesis method	Product	Light source	Efficiency (mmol g^−1 h^−1) or selectivity	Ref.
a The E and S in the table represent the yield and selectivity of the corresponding organic compounds.
BaTiO3/ZIS	Solvothermal	N-benzylbenzylamine	Sunlight (λ: 320 nm-780 nm)	H2: 8.04	100
				E: 5.59
Pd/ZIS	in situ icing assisted photo-reduction	N-benzylidenebenzylamine	Xenon lamp (λ ≥ 420 nm 2 h)	H2: 11.10	103
				E: 10.20
CuS & RuS/ZIS	in situ deposition	N-benzylbenzaldimine	Xenon lamp (λ ≥ 420 nm 6 h)	H2: 0.081	104
				S: 99.90%
CoP/ZIS	Self-assembly	N-benzylbenzaldimine	Xenon lamp (λ ≥ 400 nm 5 h)	H2: 3.84	73
				E: 3.82
DZIS	Hydrothermal	N-benzylbenzaldimine	Xenon lamp (λ ≥ 420 nm 2 h)	H2: 4.65	105
				E: 7.39
Pt/UiO-66-NH2/ZIS	Solvothermal	N-benzylbenzaldimine	Xenon lamp (λ ≥ 420 nm 8 h)	H2: 0.85	101
				S: 78.00%
Er^3+-ZnIn2S4/NiS	Hydrothermal	N-benzylbenzaldimine	Xenon lamp (λ ≥ 420 nm 2 h)	H2: 11.80	102
				E: 11.20

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4.3 Thiol dehydrogenation

Due to the indispensable role played by disulfides in many key synthetic, biochemical, and industrial applications, their synthesis methods have received much attention. Traditional disulfide synthesis methods are often accompanied by many by-products, dangerous production steps, and high energy consumption. Photocatalysis has the characteristics of green, energy saving and safety, which provides a new synthesis method of disulfide. Moreover, photocatalysis is also synchronized with disulfide preparation by reducing thiols. Therefore, photocatalytic hydrogen production-coupled thiol reduction applications are promising.

Specific cocatalyst modification strategies can significantly optimize the photocatalytic performance of semiconductor materials in thiol dehydrogenation-coupled reactions, solving the problem of low efficiency caused by carrier recombination. For example, Li et al.¹⁰⁶ successfully synthesized the ZnIn₂S₄ photocatalyst decorated with PdS by hydrothermal and in situ deposition for coupling thiol dehydrogenation to high value-added disulfide and green hydrogen energy (Fig. 13a). They report the synthesis of a PdS modified ZnIn₂S₄ (PdS-ZnIn₂S₄) composite material and its application of photocatalytic thiol coupling to disulfides and hydrogen evolution under visible light. The blank ZnIn₂S₄ catalyst exhibited low yields of bis(4-methoxyphenyl) disulfide (5.4 μmol) and H₂ (4.2 μmol), with a 4-methoxythiophenol conversion rate of only 11.1%, due to rapid carrier recombination. After modification with a PdS cocatalyst, the catalytic performance improved significantly: bis(4-methoxyphenyl) disulfide yield reached 45.6 μmol (8.4-fold increase), H₂ yield 44.9 μmol (10.7-fold increase), and 4-methoxythiophenol conversion rate increased to 91.6%. The sulfur-central radical is a significant reaction intermediate in this coupling reaction. Furthermore, the PdS-ZnIn₂S₄ composites have been demonstrated to effectively catalyze various sulfhydryl compounds with different substituents to generate the corresponding S–S conjugates. As shown in Fig. 13b, a built-in electric field is formed between PdS and ZnIn₂S₄. When irradiated with visible light, the photogenerated holes in the VB of ZnIn₂S₄ migrate rapidly to PdS under the action of the built-in electric field. Moreover, under visible light irradiation, the following possible mechanism has been proposed to explain the coupling process of photocatalytic dehydrogenation of 4-methylthiophenol and precipitation of H₂ from PdS-ZnIn₂S₄ composites (Fig. 13c).

Fig. 13 (a) Systematic illustration of the synthetic procedure of the PdS decorated ZnIn₂S₄ composites, (b) schematic diagram of the internal electric field formed between ZnIn₂S₄ and PdS, and (c) systematic illustration of the photoredox catalyzed mechanism for dehydrogenation coupling of 4-methoxythiophenol (4-MTP) with bis(4-methoxyphenyl) disulfide (4-MPD) and H₂ evolution over the PdS-ZnIn₂S₄ photocatalyst. Reproduced with permission from ref. 106, copyright 2023, Elsevier. (d) UV-vis spectra of ZnIn₂S₄ and different wt% PtS/ZnIn₂S₄ and (e) proposed mechanism for photocatalytic splitting of thiols to produce disulfides and hydrogen over PtS/ZnIn₂S₄ under visible light irradiation. Reproduced with permission from ref. 107, copyright 2018, Elsevier.

In addition, in-depth exploration of the catalytic universality and reaction mechanism of modified ZnIn₂S₄ composites is crucial for promoting the practical application of photocatalytic thiol conversion systems, and multi-case studies can provide comprehensive theoretical support. Zhang et al.¹⁰⁷ reported the formation of small Pt nanoparticles with surface deposition by photoreduction [PtCl₆]^2– on hexagonal ZnIn₂S₄. The resulting Pt/ZnIn₂S₄ nanocomposites exhibit excellent photocatalytic thiol lysis to generate disulfide and hydrogen production under visible light. Isotope labeling was used to prove that the main source of hydrogen is thiols rather than water. As shown in Fig. 13d, the UV-vis diffuse reflectance spectroscopy of the PtS/ZnIn₂S₄ nanocomposites shows that although the loading of PtS does not change the bandgap width of ZnIn₂S₄, the composites show significantly enhanced light absorption in the visible region from 420 to 620 nm. Furthermore, a possible photocatalytic reaction mechanism was proposed to explain the process of thiol cleavage to disulfide on PtS/ZnIn₂S₄ nanocomposites (Fig. 13e).

4.4 Biomass oxidation

Abundant biomass and its derivatives produced by plants through natural photosynthesis is a high-quality organic substrate that can be converted into valuable chemical intermediates. Among them, furfural generated by furfuryl alcohol (FFA) oxidation is a significantly basic material for the chemical industry, and is widely used in rubber synthesis, pharmaceutical manufacturing, pesticide production and other fields.^108–110 Therefore, the combination of efficient photocatalytic hydrogen evolution with FFA oxidation is an innovative and practical strategy that can achieve two benefits with one stone. For example, Hu et al.¹¹¹ reported a ReS₂/ZnIn₂S₄-S_v heterojunction with a novel 3D/3D honeycomb layered structure, which was ingeniously designed for the first time to efficiently catalyze H₂ evolution in combination with biomass oxidation (Fig. 14a). In addition, when NH₂OH·HCl is present, the in situ growth of ReS₂ is accompanied by the generation of S_v in ZnIn₂S₄. This work highlights the idea of simultaneously constructing reasonable heterojunctions and introducing defects to design high-performance catalysts. And as expected, this photocatalyst shows high efficiency in the coupling system, which can well achieve H₂ and furfural generation rates of 1.08 and 0.71 mmol g⁻¹ h⁻¹, respectively. Furthermore, Fig. 14b illustrates the reaction mechanism of the catalyst when it undergoes a synergistic reaction.

Fig. 14 (a) Schematic illustration of the synthetic route of the ReS₂/ZnIn₂S₄-S_v heterojunction for a photo-redox dual reaction system and (b) photocatalytic reaction mechanism of the ReS₂/ZnIn₂S₄-S_v heterojunction under visible light irradiation. Reproduced with permission from ref. 111, copyright 2023, Elsevier. (c) DFF and H₂ production rates and DFF selectivity over different samples and (d) the calculated adsorption free energy of H (ΔGH*) on different atoms of the Ni₁/ZnIn₂S₄ photocatalyst. Reproduced with permission from ref. 112, copyright 2024, American Chemical Society.

In addition, the construction of atomically dispersed active sites is also the core regulation method to improve the selectivity and efficiency of ZnIn₂S₄-based photocatalysts in biomass conversion coupling hydrogen production. Si et al.¹¹² rationally constructed the structure of atomically dispersed Ni on ZnIn₂S₄ nanosheets (Ni₁/ZnIn₂S₄), and the active site that can achieve efficient photocatalytic oxidation of 5-hydroxymethylfurfural (HMF) accompanied by H₂ generation was revealed. Under visible light irradiation, Ni₁/ZnIn₂S₄ was significantly superior to its original ZnIn₂S₄ form, and could catalyze the formation of 2,5-diformylfuran (DFF) with high selectivity (>97%), and achieve high yields of DFF generation (0.39 mmol g⁻¹ h⁻¹) and H₂ generation (0.34 mmol g⁻¹ h⁻¹). The selective oxidation and H₂ generation performance of HMF were also compared with those of other reported photocatalysts (Fig. 14c). This work provides new insights into the development of artificial photosynthesis for the upscaling of value-added chemicals from biomass through the rational construction of atomic dispersion active sites. As shown in Fig. 14d, a photocatalytic mechanism based on the selective oxidation of HMF dominated by photogenerated holes and •OH to generate DFF accompanied by H₂ release was proposed.

Furthermore, to investigate the effect of adding a noble metal catalyst on the reaction, Wang et al.¹¹³ reported that a ZnIn₂S₄/Nb₂O₅ Z-type heterostructure photocatalyst was constructed by growing Nb₂O₅ nanospheres on the petals of ZnIn₂S₄ microspheres. Moreover, by comparing whether there was a Pt source added in the reaction process, the optimal conditions of the reaction were explored. As shown in Fig. 15a, the yield of H₂ was 1.29 μmol g⁻¹ h⁻¹ and the conversion rate of HMF was 21.6% when Pt was used as a cocatalyst. However, in the absence of Pt, the release of H₂ decreased to 50 μmol g⁻¹ h⁻¹, and the conversion rate of HMF was only 1.5%. Therefore, Pt can be used as an effective cocatalyst in bifunctional catalytic systems. The schematic diagram is shown in Fig. 15b.

Fig. 15 (a) Comparison of H₂ evolution of ZnIn₂S₄/NbO-8 from HMF solution and pure water, and photo-conversion of HMF in the meantime and (b) schematic illustration of photo-generated H₂ release from water accompanied by the photocatalytic oxidation of HMF on ZnIn₂S₄/NbO-8 under simulated solar light. Reproduced with permission from ref. 113, copyright 2020, American Chemical Society. (c) Possible mechanism for photocatalytic oxidation of HMF to DFF upon ZnIn₂S₄-5 with abundant dual Zn and In vacancies. Reproduced with permission from ref. 114, copyright 2025, American Chemical Society.

In the rational design of the catalyst for the conversion of hydrogen production coupled DFF to HMF, Zhao et al.¹¹⁴ also provided some ideas for the exploration of ZnIn₂S₄. In 2025, this team successfully created double Zn and In defects in ZnIn₂S₄ by a simple cetyltrimethylammonium chloride-assisted hydrothermal method. The yield (92.0%) of DFF was 3.6-fold (25.8%) higher than that of the original ZnIn₂S₄ when the obtained ZnIn₂S₄-5 was rich in cationic vacancies, and the yield of DFF was 3.6-fold higher (25.8%) than that of the original ZnIn₂S₄ when it was photooxidized by visible light. In particular, ZnIn₂S₄-5 achieved a DFF productivity of up to 1.60 mmol g⁻¹ h⁻¹, significantly exceeding that of the previously reported catalyst (0.075–0.95 mmol g⁻¹ h⁻¹) for the photooxidation of HMF in air. In addition, a mechanism is proposed whereby flower-like ZnIn₂S₄-5 produces photoexcited electrons and holes under visible light irradiation (Fig. 15c), in which the generation and transfer of photogenerated carriers are significantly enhanced by the double Zn and In defects. Subsequently, the O₂ molecules in air are adsorbed and activated at the In site of the catalyst. At the same time, the hydroxymethyl group of HMF tends to adsorb on the Zn site of the catalyst. However, the VB energy of ZnIn₂S₄-5 is only 1.13 V, which is lower than the oxidation potential required for the conversion of HMF to DFF (HMF/DFF = 1.67 V vs. NHE). Therefore, the photogenerated h⁺ in the catalyst cannot directly oxidize HMF to DFF. In this regard, the O₂ adsorbed on the surface of ZnIn₂S₄-5 captures the photoexcited e⁻ and generates active ˙O₂⁻ species. Subsequently, the HMF molecule was under ˙O₂⁻ attack, forming alkoxide anions and ˙OOH intermediates. These alkoxide anions are then attacked by H⁺, producing alkoxide anion radicals. Finally, the α–H bond in the anionic radical was replaced by ˙OOH and is deprotonated to generate DFF and hydrogen peroxide. In the other case, the resulting ˙O₂⁻ species can be oxidized by h to ¹O₂ species. After that, the formed ¹O₂ species reacted with HMF to generate alkoxide anion radicals and ˙OOH. Eventually, through the reaction of ˙OOH with alkoxide anion radicals DFF and hydrogen peroxide are obtained.

To gain insights into the research progress of biomass oxidation coupling hydrogen production via ZnIn₂S₄-based photocatalysts, Table 3 summarizes recent relevant studies. It presents details such as the specific photocatalyst, synthesis method, target product, light source employed, and key performance indicators.

Table 3 Summary of recent studies of biomass oxidation and hydrogen production by ZnIn₂S₄-based photocatalysts^a

Photocatalyst	Synthesis method	Product	Light source	Efficiency (mmol g^−1 h^−1) or selectivity	Ref.
a The E and S in the table represent the yield and selectivity of the corresponding organic compounds respectively.
Mo2C/ZIS	Solvothermal	Furfuraldehyde	Xenon lamp (λ ≥ 420 nm 4 h)	H2: 2.80	115
				E: 11.33
Ni(OH)2/ZIS	in situ impregnation	Furfuraldehyde	Xenon lamp (λ ≥ 420 nm 4 h)	H2: 0.69	52
				E: 0.58
ReS2/ZIS	in situ growing	Furfuraldehyde	Xenon lamp (λ ≥ 420 nm 5 h)	H2: 3.09	116
				E: 2.98
Nb2O5/ZIS	Hydrothermal	2, 5-diformylfuran	Xenon lamp (λ ≥ 420 nm 4 h)	H2: 1.53	114
				S: 88.30%
O-ZIS	in situ topological transformation	2, 5-diformylfuran	Xenon lamp (λ ≥ 420 nm 2.5 h)	H2: 1.52	117
				E: 1.62
CoSe2/ZIS	Hydrothermal & photodeposition	Furfuraldehyde	Xenon lamp (λ ≥ 420 nm 5 h)	H2: 46.60	118
				E: 0.85
CeO2/ZIS	Solvothermal	Furfuraldehyde	Xenon lamp (λ ≥ 400 nm 5 h)	H2: 1.24	21
				E: 1.34
ReS2/ZIS-Sv	Hydrothermal	Furfuraldehyde	Xenon lamp (λ ≥ 400 nm 2 h)	H2: 1.08	111
				E: 0.71

---

5. Conclusion and outlook

This paper systematically reviews various synthesis methods for ZnIn₂S₄-based photocatalysts, which can effectively regulate the morphology and crystalline structures of ZnIn₂S₄, thereby establishing a robust structural basis for enhancing photocatalytic efficiency. In addition, it specifically elaborates on the strategies to improve the performance of ZnIn₂S₄-based photocatalysts: metal doping broadens the light-responsive range by introducing impurity energy levels, while morphological modification utilizes high specific surface area to expose more active sites. Constructing heterostructures leverages interfacial charge separation effects to suppress carrier recombination, whereas defect engineering enhances reactant adsorption and activation through multiple vacancy states. These synergistic strategies comprehensively overcome the photocatalytic performance bottlenecks of ZnIn₂S₄ by addressing three critical aspects: enhancing light absorption efficiency, optimizing photogenerated electron–hole pair separation efficiency, and accelerating surface catalytic reaction kinetics. Notably, this paper discusses the applications of such catalysts in hydrogen production coupled with different organic synthesis reactions, such as the selective oxidation of alcohols, oxidative coupling of amines, dehydrogenation of thiols, and oxidation of biomass. These practical applications fully validate the high efficiency and applicability of ZnIn₂S₄-based photocatalysts in selective oxidation reactions, paving the way for industrial applications in energy conversion and fine chemical industries. However, ZnIn₂S₄-based photocatalysts still face many challenges:

First, in terms of material stability, ZnIn₂S₄-based matrix composites may suffer from photocorrosion under prolonged periods of light irradiation, and sulfur ions on the surface are inevitably oxidized by light and oxygen into sulfur or sulfate ions in this process. This process not only damages the integrity of the crystal structure but also leads to continuous loss of active sites. From the perspective of photocatalytic reaction mechanisms, the irrational migration of photogenerated carriers is the key factor exacerbating photo-corrosion. When photogenerated holes cannot promptly participate in surface oxidation reactions, they preferentially attack sulfur ions within the lattice. Therefore, how to fundamentally suppress the oxidation kinetics of sulfur ions by regulating carrier separation efficiency and migration pathways has become the core direction for enhancing stability. In light-corrosion-resistant design, a dual-function system integrating “carrier regulation and structural protection” should be established. By incorporating energy-matched band-structured cocatalysts, the system effectively traps photogenerated electrons while reducing sulfur ion attacks from photogenerated holes. Moreover, an ultra-thin protective layer can be formed on the surface of the catalyst by atomic layer deposition technology. This approach not only prevents direct contact between oxygen and sulfur ions but also preserves carrier transport efficiency and reactant diffusion pathways.

Second, ZnIn₂S₄-based photocatalysts exhibit spectral responses confined to the visible light region, with negligible utilization efficiency for near-infrared light—accounting for 43% of the solar spectrum, which severely limits their practical energy conversion performance. To achieve full-spectrum absorption and utilization, there is an urgent need to develop superior ZnIn₂S₄-based materials. Current research indicates that phosphorus doping and sulfur vacancy engineering can partially extend the spectral response range, though their effectiveness remains limited. From the perspective of photocatalytic material design, how to achieve efficient capture of the whole spectrum by precisely regulating the band structure or introducing the plasma resonance effect is the key to break through the bottleneck of light energy utilization. In optimizing full-spectrum response, a synergistic strategy of “defect engineering and heterojunction design” can be developed. By precisely regulating sulfur vacancy concentration, defect energy levels are introduced into the bandgap to expand the visible light response. Simultaneously, stepwise heterojunctions with narrow-bandgap semiconductors are constructed to utilize their near-infrared absorption capability, enabling photon capture across the entire spectrum. Furthermore, piezoelectric composite structures are incorporated, where mechanically induced vibrations generate built-in electric fields that enhance carrier separation, thereby indirectly improving low-light utilization efficiency.

Third, ZnIn₂S₄-based catalysts are still in the experimental exploration phase for hydrogen production coupling organic synthesis, particularly regarding the selective control mechanisms in complex systems (such as multi-component biomass conversion). The core advantage of photocatalytic coupling lies in utilizing photogenerated electron–hole pairs to simultaneously drive hydrogen production and organic synthesis half-reactions. However, most current research focuses solely on single reaction pathways, lacking strategies for synergistic regulation of electron transfer efficiency and reaction selectivity in coupled systems. In expanding application scenarios, the focus should be on achieving “atomic economy” and “process greening” in coupled reactions. For complex systems like biomass conversion, surface modification (such as grafting specific functional groups) can enhance catalysts' selective adsorption of target substrates. Combined with theoretical calculations (e.g., DFT simulations) to predict reaction pathways, this approach enables directed conversion from biomass to high-value chemicals. In addition, developing novel photocatalytic reactors (e.g., microchannel reactors) can not only improve mass transfer efficiency and light utilization rates, but also lay the foundation for industrial applications.

Fourth, the hydrogen production coupling organic value-added technology based on ZnIn₂S₄ confronts critical mechanistic challenges: the ambiguous electron distribution between hydrogen evolution sites and organic synthesis centers constrains precise control over product selectivity. The interaction mechanisms among interfacial charge migration, organic intermediates, and heterojunction energy barriers remain unclarified. And due to insufficient real-time data, the dynamic regulatory mechanisms governing hydrogen generation and organic synthesis selectivity have not been fully elucidated. To address these issues, future research should focus on the following directions. To tackle these issues, future research should concentrate on the following directions: developing integrated in situ EPR/Raman platforms to monitor electron and intermediate dynamics, thereby establishing comprehensive correlation models; employing density functional theory calculations to dissect interfacial synergistic effects, simulate electron migration barriers, and optimize cocatalyst loading and conformational configurations; and monitoring element concentration modulation strategies at active sites via in situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques. Such endeavors will propel ZnIn₂S₄-based coupling technology from empirical optimization toward precision design, providing robust theoretical underpinnings for its practical applications. In addition, endeavors such as applying density functional theory calculations to dissect interfacial synergistic effects, simulate electron migration barriers, and optimize cocatalyst loading and conformational configurations will propel ZnIn₂S₄-based coupling technology from empirical optimization toward precision design, furnishing robust theoretical underpinnings for its practical applications.

Author contributions

Jung Wang: writing – original draft. Yu Wei: software. Bo-Hao Zhang: investigation. Kai Yang: validation. Wei-Ya Huang: resources. Kang-Qiang Lu: funding acquisition, investigation, resources, supervision.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 22462010, 22366018, and 5236005), the Jiangxi Provincial Natural Science Foundation (No. 20212BAB213016, 20224BAB203018, 20224ACB213010, 20232BAB213050, 20232ACB203022, and 20252BAC220013), and the Jiangxi Province “Double Thousand Plan” (No. jxsq2023102143, jxsq2023102142, jxsq2023201086, jxsq2023102141, and jxsq2019102053).

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