Construction of Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture for visible-light-driven hydrogen production

In this paper, a novel Au/g-C₃N₄/ZnIn₂S₄ plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture has been successfully constructed by integrating Au/g-C₃N₄ plasmonic photocatalyst composite with 3D ZnIn₂S₄ nanosheet through a simple hydrothermal process. The Au nanoparticles were firstly anchored on the surface of pristine g-C₃N₄ material to get Au/g-C₃N₄ plasmonic photocatalyst. Ascribing to the surface plasmon resonance of Au nanoparticles, the obtained Au/g-C₃N₄ plasmonic photocatalyst shows a significant improved photocatalytic activity toward hydrogen production from water with visible light response comparing with pristine g-C₃N₄. Further combining Au/g-C₃N₄ plasmonic photocatalyst with 3D ZnIn₂S₄ nanosheet to construct a heterojunction composite. Owing to the synergistic effect of the surface plasmon resonance of Au nanoparticles in Au/g-C₃N₄ and the heterojunction structure in the interface of Au/g-C₃N₄ and ZnIn₂S₄, the prepared Au/g-C₃N₄/ZnIn₂S₄ plasma photocatalyst heterojunction composite shows an excellent photocatalytic activity toward hydrogen production from water with visible light response, which is around 7.0 and 6.3 times higher than that of the pristine C₃N₄ and Znln₂S₄ nanosheet, respectively. The present work might provide some insights for exploring other efficient heterojunction photocatalysts with excellent properties.     

Boosted photogenerated carriers separation in Z-scheme Cu3P/ZnIn2S4 heterojunction photocatalyst for highly efficient H2 evolution under visible light

Developing low-cost, highly efficient and robust photocatalystic hydrogen evolution system is a promising solution to environmental and energy crisis. Herein, a Z-scheme Cu₃P/ZnIn₂S₄ heterojunction photocatalyst was successfully constructed for the first time via a facile solution-phase hybridization method. The optimized Cu₃P/ZIS composite exhibited the highest H₂ production rate of 2561.1 μmol g⁻¹ h⁻¹ under visible light irradiation (>420 nm), which was 5.2 times greater than that of bare ZnIn₂S₄ and even exceeded the photocatalytic performance of Pt/ZIS composite. The apparent quantum yield of 10 wt% Cu₃P/ZnIn₂S₄ can reach 22.3% at 420 nm. The huge boost of photocatalytic hydrogen evolution activity is ascribed to the formation of heterojunction with the built in electric field within Cu₃P/ZnIn₂S₄ and Z-scheme charge carriers transfer pathway, which result in efficient separation and migration of charge carriers. In addition, both experimental and theoretical calculation confirmed that the charge-carriers transfer pathway of Cu₃P/ZnIn₂S₄ photocatalyst follows the Z-scheme mechanism instead of conventional type-Ⅱ heterojunction mechanism. This work is considered helpful for getting a great deal of insight into constructing high-activity and cost-effective transition metal phosphides (TMPs) based photcatalytic hydrogen production system and rationally designing Z-scheme heterojunction photocatalyst.     

Construction of 3D/3D heterojunction between new noble metal free ZnIn2S4 and non-inert metal NiMoO4 for enhanced hydrogen evolution performance under visible light

Promoting the separation of electron and hole plays an important role in photocatalytic hydrogen production. However, single semiconductor materials cannot fully realize their potential due to the rapid recombination of photogenerated carriers. Therefore, in this experiment, a new photocatalyst ZnIn₂S₄/NiMoO₄ was prepared by using an electrostatic self-assembly method, which greatly improved the electron-hole recombination phenomenon. After 5 h reaction under visible light irradiation, ZIS/NMO-3 composite catalyst prepared in ethanol showed the best photocatalytic activity, and the hydrogen evolution capacity reached 173.09 μmol. The hydrogen evolution capacity of ZIS/NMO-3 was 2.47 and 25.83 times that of short rod-like NiMoO₄ and microflower-like spherical ZnIn₂S₄, respectively. Through some physical characterization and electrochemical experiments, it can be seen that NiMoO₄ and ZnIn₂S₄ have good composability. Meanwhile, the composite catalyst ZnIn₂S₄/NiMoO₄-3 has high current response characteristics. It can be seen from the fluorescence emission spectra that the composite catalyst presents the lowest peak value, which indicates that ZIS/NMO-3 can effectively inhibit the recombination of photogenerated electrons and holes. When ZnIn₂S₄ is loaded on NiMoO₄, the separation of photogenerated carrier will be accelerated due to the formation of heterojunction, thus improving the photocatalytic activity. At the same time, the large specific surface area will also provide more abundant active sites for the composite catalyst, which provides a good condition for photocatalytic hydrogen production. This work provides an efficient, uncomplicated and feasible method for the synthesis of ZIS/NMO-3 composite catalyst with excellent properties.     

Direct Z-scheme ZnIn2S4/LaNiO3 nanohybrid with enhanced photocatalytic performance for H2 evolution

The direct Z-scheme ZnIn₂S₄/LaNiO₃ nanohybrid based on ZnIn₂S₄ nanosheets and LaNiO₃ cubes was synthesized by a facile hydrothermal method. The ZnIn₂S₄/LaNiO₃ nanohybrid showed improved photocatalytic H₂ evolution and stability. The photocatalytic H₂ evolution activity of ZnIn₂S₄/LaNiO₃ nanohybrid is 3-fold enhanced than that of bare ZnIn₂S₄. The enhanced performance of ZnIn₂S₄/LaNiO₃ nanohybrid is mainly ascribed to the formation of heterojunction between LaNiO₃ and ZnIn₂S₄. The heterojunction can facilitate charge transport on the interface between LaNiO₃ and ZnIn₂S₄ and suppress the recombination of photo-generated charge carriers over ZnIn₂S₄/LaNiO₃ nanohybrid, which were well demonstrated by photoelectrochemical tests. Moreover, the direct Z-scheme photocatalytic reaction mechanism was proposed to elucidate the improved performance of ZnIn₂S₄/LaNiO₃ nanohybrid photocatalyst. This study may provide some guidance on the construction of direct Z-scheme photocatalytic system for photocatalytic H₂ evolution.     

Integration of ReS2 on ZnIn2S4 for boosting the hydrogen evolution coupled with selective oxidation of biomass intermediate under visible light

Challenge remains to develop a high activity of photocatalyst for large-scale industrial application in photocatalytic selective conversion of biomass alcohols into the value-added chemicals accompany with H₂ evolution in aqueous solution. Herein, ReS₂ as high efficiency co-catalyst is utilized to modify the flower-like ZnIn₂S₄ (ZIS) microspheres to obtain heterojunction composite, result in dramatically enhancements in photocatalytic oxidation of furfural alcohols cooperative with H₂ evolution. Further studies show that the optimal catalyst containing 4.08 wt% ReS₂ (RZIS-3) realize remarkably generation rates of H₂ and furfural at 3092.9 and 2981.1 μmol g^?1 h^?1, respectively, nearly 12 times faster than that of blank ZnIn₂S₄. Mechanism studies verify that the migration of the photogenerated carriers from ZnIn₂S₄ to ReS₂ leading to the remarkably photoactivity of the composite. Moreover, the typical photocatalysis not rely on a single model substrate, and high performance of the composite has been identified for the oxidation of other alcohols biomass intermediate to value-added aldehydes/ketones, providing a new insight for design and fabrication of the novel photocatalytic hydrogen evolution systems.     

ZnIn2S4 modified CaTiO3 nanocubes with enhanced photocatalytic hydrogen performance

Novel ZnIn₂S₄/CaTiO₃ nanocubes were prepared by a two-step method and used as a visible light photocatalyst for efficient hydrogen production. The control of the content of CaTiO₃ could effectively change the photocatalytic H₂ production activity of ZnIn₂S₄/CaTiO₃ nanocubes, and the maximum H₂ evolution amount reached to 133116.43 μmol g⁻¹ in 6 h. The photocatalytic hydrogen production efficiency of ZnIn₂S₄/CaTiO₃ nanocubes was almost 4.5 times higher than that of pure ZnIn₂S₄. The electrochemical impedance spectrum of ZnIn₂S₄/CaTiO₃ exhibited the smallest arc radius, time-resolved PL spectrum showed that the carrier lifetime of ZnIn₂S₄/CaTiO₃ nanocubes was 3.29 ns, and the photocurrent density of ZnIn₂S₄/CaTiO₃ reached to 0.81 μA cm⁻². The prepared ZnIn₂S₄/CaTiO₃ nanocubes increased visible light absorption, improved the separation and transfer of photo-generated electrons and holes, and inhibited the recombination of photo-generated electron-hole pairs. ZnIn₂S₄/CaTiO₃ nanocubes exhibited the enhanced photocatalytic activity and high stability, and could be used as promising photocatalyst for hydrogen production application.     

The ZnIn2S4/CdS hollow core-shell nanoheterostructure towards enhanced visible light photocatalytic H2 evolution via bimetallic synergism

The ZnIn₂S₄/CdS hollow core-shell nanoheterostructure with bimetallic synergism is synthesized via a hybrid chemical method. As revealed, the ZnIn₂S₄/CdS hollow core-shell nanoheterostructure (ZnIn₂S₄/CdS-3) exhibits remarkable visible light photocatalytic hydrogen evolution (～5209.43 μmol·g^?1·h^?1, AQE of ～20.26%) than that of single CdS (～40 folds) and single ZnIn₂S₄ (～12 folds), and achieves decent photocatalytic stability (average HER performance of ～5056.80 μmol·g^?1·h^?1), which is mainly ascribed to that, the formed ZnIn₂S₄/CdS heterostructure with appropriate potential gradient and Zn/In bimetallic synergism can improve carrier transportation, including increasing carrier transportation, prolonging lifetime and decreasing recombination, the hollow core-shell nanostructure can provide abundant active sites and increase solar efficiency, while can maintain a photocatalytic stability.     

An anti-symmetric dual (ASD) Z-scheme photocatalytic system: (ZnIn2S4/Er3+:Y3Al5O12@ZnTiO3/CaIn2S4) for organic pollutants degradation with simultaneous hydrogen evolution

An anti-symmetric dual (ASD) Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst was prepared by isoelectric point and calcination methods. The photocatalytic activity is estimated via degradation of Acid Orange II as a target organic contaminant with simultaneous hydrogen evolution under simulated solar-light irradiation. The prepared ASD Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst has a high photocatalytic activity, which can be assigned to the enlarged photoresponse range, increased reduction surface and enhanced separation efficiency of photo-induced carriers. Furthermore, the cyclic experiment proves that the prepared ASD Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst still maintains a high photocatalytic activity within five repetitive cycles. Moreover, the mechanism on photocatalytic degradation of organic pollutants with simultaneous hydrogen evolution caused by ASD Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst is proposed. It is wished that this study could provide a promising pathway for effective degradation and rapid hydrogen production.     

Cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal synthesis of ZnIn2S4 as an efficient visible-light-driven photocatalyst for hydrogen production

A series of ZnIn₂S₄ photocatalysts was synthesized via a cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal method. These ZnIn₂S₄ products were characterized by X-ray diffraction (XRD), UV–visible absorption spectra (UV–vis) and scanning electron microscopy (FESEM). The effects of hydrothermal time and CTAB on the crystal structures, morphologies and optical properties of ZnIn₂S₄ products were discussed in detail. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic hydrogen production from water under visible-light irradiation. It was found that the photocatalytic activities of these ZnIn₂S₄ products decreased with the hydrothermal time prolonging while increased with the amount of CTAB increasing. The highest quantum yield at 420 nm of ZnIn₂S₄ photocatalyst, which was prepared through the CTAB (9.6 mmol)-assisted hydrothermal procedure for 1 h, was determined to be 18.4%. The optimum amount of Pt loaded for the ZnIn₂S₄ photocatalyst was about 1.0 wt%, under the present photocatalytic system.     

Highly efficient visible-light-driven photocatalytic hydrogen production on Cu7S4/Zn0.2Cd0·8S p-n binary heterojunctions

In this work, a series of Zn_xCd_1-xS solid solutions are firstly prepared by a solvothermal process. The optimized composition of Zn_xCd_1-xS solid solution is determined to be Zn_0·2Cd_0.8S. On this basis, the Cu₇S₄/Zn_0·2Cd_0·8S composite photocatalyst with a binary p-n heterojunction has been synthesized by a co-precipitation process followed by a solvothermal method. Owning to the synergistic effect of the heterojunction structure in the interface of Cu₇S₄ (p-type) and Zn_0·2Cd_0·8S (n-type) and the built-in electric field in binary p-n heterojunction, the as-prepared Cu₇S₄/Zn_0·2Cd_0·8S composite photocatalyst exhibits a significantly improved photocatalytic activity toward hydrogen production from water with visible light response, which is approximately 5.0 times and 16.5 times higher than of pristine Zn_0·2Cd_0·8S and CdS, respectively. The possible photocatalytic mechanism has been proposed basing on a series of experimental results. The current work might be valuable inspirations for designing highly efficient heterojunction composite photocatalyst for solar hydrogen evolution.     

Hierarchical ZnIn2S4: A promising cocatalyst to boost visible-light-driven photocatalytic hydrogen evolution of In(OH)3

Efficient separation of electrons and holes, associated with the reduction and oxidation, is of great importance in a photocatalytic reaction. 3D hierarchical core-shell-like ZnIn₂S₄@In(OH)₃ microspheres have been fabricated by a facile hydrothermal method via controlling the sulfur source. The marigold-like spherical ZnIn₂S₄ induced the in situ growth of cubic In(OH)₃ nanosheets as the outer shell, which efficiently transferred the photogenerated electrons and achieved efficient charge separation efficiency for highly photocatalytic H₂ production. Moreover, the intimate interfacial contact between ZnIn₂S₄ core and In(OH)₃ shell offered rectified charge transfer directions, which further boosted the charge separation. In consequence, the photocatalytic H₂ evolution under visible light irradiation was achieved on wide-gap In(OH)₃ owing to ZnIn₂S₄ as a cocatalyst, and a prominent photocatalytic H₂ production of 2088 μmol g⁻¹ was obtained on core-shell-like ZnIn₂S₄@In(OH)₃ structure with an apparent quantum efficiency of 1.45% (400 nm), which was nearly 2-folds higher of H₂ production rate than the pristine ZnIn₂S₄. This work provides a prototype material for high efficiency of hydrogen evolution, and gives a new insight for the development of efficient heterojunction photocatalysts.     

Eco-friendly synthesis of core/shell ZnIn2S4/Ta3N5 heterojunction for strengthened dual-functional photocatalytic performance

Reasonable design and fabrication of core/shell heterojunction has deemed as an efficient strategy to boost the transport and separation of photoinduced charge pairs in semiconductor-based photocatalytic system. Herein, a novel dual-functional ZnIn₂S₄/Ta₃N₅ (ZIS/TN) nanocomposite with intimate contacts was fabricated with a one-pot eco-friendly hydrothermal method. This core/shell heterojunction consisting of ZnIn₂S₄ nanosheet shell and Ta₃N₅ nanoparticle core is observed to possess the enhanced visible light harvesting capacity, increased specific surface areas, more high-speed charge nanochannels and accelerated charge transfer and separation. Thus, as prepared ZIS/TN nanocomposite displayed dramatically strengthened dual-functional photocatalytic performances of hydrogen production and tetracycline hydrochloride (TCH) photodegradation. As a result, the improved H₂-production activity of 834.86 μmol g⁻¹ h⁻¹ was obtained by sample ZIS/TN-2, which is 6.07 times higher than that of pure ZnIn₂S₄ nanosheet. Moreover, the highest TCH photodegradation efficiency of 89.95% is achieved by the sample ZIS/TN-3, which is 1.90 and 11.01 times more than those of bare ZnIn₂S₄ and Ta₃N₅. In addition, the core/shell heterojunction exhibits super photostability and reusability due to the protection of external ZnIn₂S₄ layer from the photocorrosion of Ta₃N₅ core. Furthermore, the possible reaction mechanisms and the degradation intermediate products of TCH were also put forwarded in depth based on transient photocurrent response, active species tapping experiment, electronspin response (ESR) technique and HPLC-MS method. This work could stimulate an innovative vision in constructing dual-functional Ta₃N₅-based core/shell heterostructure with wonderful photocatalytic H₂ evolution and antibiotic pollutant photodegradation activities.     

A novel direct Z-scheme heterojunction of CoTiO3/ZnIn2S4 for enhanced photocatalytic H2 evolution activity

The shortage of fossil energy has become a growing global concern. It is particularly important to make full use of the infinite solar energy resources, and transform them into sustainable and clean energy. The development of hydrogen energy has become a feasible solution to solve the energy shortage problem. The preparation of photocatalysts featuring efficient charge transfer channels and high hydrogen production activity provides a pathway for the development of hydrogen energy. In this paper, we report for the first time the direct assembly of 2D ZnIn₂S₄ (ZIS) nanosheets on the surface of CoTiO₃ (CTO). The synthesized CoTiO₃/ZnIn₂S₄ (CTO/ZIS) photocatalyst features a direct Z-scheme charge transfer channel, which enhances the separation rate of photogenerated carriers, and accelerates the photocatalytic H₂ evolution (PHE) rate. Without the assistance of any co-catalyst, the PHE rate of prepared CoTiO₃/ZnIn₂S₄ was as high as 5.21 mmol g^?1 h^?1. Moreover, the H₂ evolution rate of CoTiO₃/ZnIn₂S₄ almost did not decrease significantly after four consecutive 4 h cycles. This investigation provides a valuable approach for the exploitation of novel and efficient Z-scheme photocatalysts in the application of solar energy to hydrogen energy conversion.     

A thin clothe coated architecture of ZnIn2S4/H2Ta2O6 for enhanced photocatalytic hydrogen production

Focused on energy and environment issues, in present investigation, an economical and eco-friendly photocatalyst for hydrogen evolution in water splitting reaction has been designed and fabricated. The characteristics by XRD, TEM, XPS and AFM confirmed that an octahedral H₂Ta₂O₆ is uniformly capsuled by ZnIn₂S₄ thin clothes to form a package ZnIn₂S₄/H₂Ta₂O₆ heterojunction. The assembled ZnIn₂S₄/H₂Ta₂O₆ exhibits superior hydrogen generated performance with a value of 3217.31 μmol g⁻¹•h⁻¹ under simulated sunlight irradiation, without obvious deactivation in five consecutive cycles. The enhanced activity and reusability are mainly attributed to ultrathin clothe-like shell, the well-matched band structure and a large tight contact interface in the package type construction, which can promote redox ability, extend light harvesting range and boost charge separation efficiency. The present study proposes a new design idea to assemble a highly efficient and durable photocatalyst for solar hydrogen generation by splitting water.     

Design and fabrication of hollow structured Cu2MoS4/ZnIn2S4 nanocubes with significant enhanced photocatalytic hydrogen evolution performance

The unique architecture is very significant for photocatalysts to achieve high photocatalytic efficiency. Herein, hollow Cu₂MoS₄/ZnIn₂S₄ heterostructural nanocubes with intimate-contact interface have been prepared for the first time via a self-template way, which can promote the photocatalysis hydrogen evolution. First, novel hollow structured Cu₂MoS₄ nanocubes were successfully synthesized using Cu₂O as a precursor, then the ZnIn₂S₄ nanosheets were in-situ grew on the surface of hollow Cu₂MoS₄ nanocubes. The unique hollow heterostructures have markedly enhanced photocatalytic efficiency, and 15 wt% Cu₂MoS₄/ZnIn₂S₄ sample exhibits the highest hydrogen production rate of 8103 μmol·h⁻¹·g⁻¹, which is approximately four times higher than pure ZnIn₂S₄. The improved photocatalytic performance is mainly attributed to the following two points: (1) the hollow nanocube structure can provide rich active sites and increase light absorption; (2) forming a built-in electric field is conducive to transfer the holes generated by ZnIn₂S₄ to Cu₂MoS₄, which can effectively promote charge separation. This work may provide insights for the design of hollow architecture cage materials for high photocatalytic performance.     

Construction of ZnIn2S4/ZnO heterostructures with enhanced photocatalytic decomposition and hydrogen evolution under blue LED irradiation

The novel ZnIn₂S₄/ZnO heterostructures can prepare by combining a facile hydrothermal and wet chemical methods. Various microscale and nanoscale characterization techniques analyzed the surface topography, structural and optical properties of the ZnIn₂S₄/ZnO heterostructures. The addition amount of ZnIn₂S₄ nanosheets plays an essential role in controlling the optical properties of ZnIn₂S₄/ZnO heterostructures. ZnIn₂S₄/ZnO heterostructures can improve charge carriers separation and specific surface area for enhancing the photocatalytic decomposition of the 4-aminobenzoic acid solution and hydrogen evolution under blue LED irradiation. Furthermore, ZnIn₂S₄/ZnO heterostructures also revealed high photocatalytic stability and reusability for long-term reaction processes. Therefore, ZnIn₂S₄/ZnO heterostructures can be used as efficient visible-light-induced photocatalysts for the practical applications in water splitting and wastewater treatment.     

Visible-light-driven ZnIn2S4/CdIn2S4 composite photocatalyst with enhanced performance for photocatalytic H2 evolution

ZnIn₂S₄/CdIn₂S₄ composite photocatalysts (x = 0–1) were successfully synthesized via a hydrothermal route. Compositions of ZnIn₂S₄/CdIn₂S₄ composite photocatalysts were optimized according to the photocatalytic H₂ evolution rate. XRD patterns indicate the as-prepared samples are mixtures of hexagonal and cubic structures. FESEM and TEM images show that the as-prepared samples are composed of flower-like microspheres with wide distribution of diameter. There is obviously distinguishing distribution of Zn, Cd elements among the composite architectures. UV–vis absorption spectra of different compositions exhibit that absorption edges of ZnIn₂S₄/CdIn₂S₄ composites slightly move towards longer wavelengths with the increment of CdIn₂S₄ component. A typical time course of photocatalytic H₂ evolution from an aqueous Na₂SO₃ and Na₂S solution over unloaded and PdS-loaded ZnIn₂S₄/CdIn₂S₄ composite photocatalyst is carried out. The initial activity for H₂ evolution over 0.75 wt% PdS-loaded sample is up to 780 μmol h⁻¹. And the activity of unloaded sample also reaches 490 μmol h⁻¹ with consistent stability.     

Photocatalytic hydrogen generation in the presence of glucose over ZnS-coated ZnIn2S4 under visible light irradiation

ZnS coated ZnIn₂S₄ (ZnS–ZnIn₂S₄) photocatalysts were prepared in methanol by a facile solvothermal process. The photocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), UV–Vis diffusive reflectance spectroscopy (DRS), BET, and electrochemistry measurements. ZnS–ZnIn₂S₄ photocatalysts have hexagonal crystal phase and complex morphology such as micro-spheres, micro-tubes and micro-ribbons. Using glucose as an electron donor, photocatalytic hydrogen generation over Pt/ZnS–ZnIn₂S₄ was investigated. The results show that photoactivity of hydrogen generation over Pt/ZnS–ZnIn₂S₄ was improved notably with simultaneous degradation of glucose. The factors which affect photocatalytic hydrogen generation, such as composition of ZnS-ZnIn₂S₄, initial concentration of glucose and concentration of NaOH, were investigated. The prepared ZnS–ZnIn₂S₄ photocatalysts exhibit better activity for hydrogen generation than pure ZnIn₂S₄, which may be attributed to enhancement of the adsorption of glucose by ZnS on the ZnIn₂S₄ surface. The effect of glucose concentration on the hydrogen generation rate is consistent with a Langmuir model. The basic condition is favorable for the photocatalytic hydrogen generation. A large number of ·OH radicals generated in ZnS–ZnIn₂S₄ system, have been tested by a TA-FL (terephthalic acid-fluorescence) method. A possible mechanism was discussed.     

Microwave-assisted hydrothermal synthesis of transition-metal doped ZnIn2S4 and its photocatalytic activity for hydrogen evolution under visible light

Aiming at the enhancement of photocatalytic activity for hydrogen evolution over ZnIn₂S₄, different transition metals (Cr, Mn, Fe, Co) are doped into the lattices of ZnIn₂S₄ to narrow the band gap. The doped ZnIn₂S₄ is characterized by XRD, Raman, UV-vis spectra, photoluminescence spectra, SEM and XPS techniques. The photocatalytic evaluation shows that Mn-doped ZnIn₂S₄ performs photocatalytic activity 20% higher than undoped ZnIn₂S₄, while Cr-, Fe-, and Co-doped ZnIn₂S₄ perform poorer activities in an order of Cr > Fe > Co. Based on the combined characterization results, the band structures of doped ZnIn₂S₄ are schematically depicted, which illustrates the different effects of transition-metal doping on the photocatalytic activity for hydrogen evolution. For Mn-doped ZnIn₂S₄, the enhancement of photocatalytic activity could be due to narrowed band gap induced by Mn doping. However, for Cr-, Fe-, and Co-doped ZnIn₂S₄, the suppressed photocatalytic activities should be attributed to the dopant-related impurity energy levels localizing the charge carriers or acting as non-radiative recombination centers for photoexcited electrons and holes. Hence, this study indicates that it is of great importance to make the in-depth investigation on the effects of band structures on the photocatalytic activity, especially for the doped semiconducting photocatalysts.     

ZnIn2S4/In(OH)3 hollow microspheres fabricated by one-step l-cysteine-mediated hydrothermal growth for enhanced hydrogen production and MB degradation

An intervening barrier for photocatalytic water decomposition and pollutant degradation is the frustratingly quick recombination of e⁻ - h⁺ pairs. Delicate design of heterojunction photocatalysts by coupling the semiconductors at nanoscale with well-matched geometrical and electronic alignments is an effective strategy to ameliorate the charge separation. Here a facile and environment-friendly l-cysteine-assisted hydrothermal process under weakly alkaline conditions is demonstrated for the first time to fabricate ZnIn₂S₄/In(OH)₃ hollow microspheres with intimate contact, which are verified by XRD, SEM, (HR)TEM, XPS, N₂ adsorption-desorption, UV–Vis DRS and photoluminescence spectra. ZnIn₂S₄/In(OH)₃ heterostructure (L-cys/Zn²⁺ = 4, molar ratio) with a band-gap of 2.50 eV, demonstrates the best photocatalytic performance for water reduction and MB degradation under visible light, outperforming its counterparts (In(OH)₃ and ZnIn₂S₄). The excellent activity of ZnIn₂S₄/In(OH)₃ heterostructure arises from the intercrossed band-edge positions as well as the unique hollow structure with large surface area and wide pore-size distribution, which are beneficial for the efficient charge migration from bulk to surface as well as at the interface between ZnIn₂S₄ and In(OH)₃. This work provides an efficient and eco-friendly strategy for one-pot synthesis of heterostructured composites with intimate contact for photocatalytic application.