ZnIn2S4 Research Articles

Artificial Photosynthetic System with Spatial Dual Reduction Site Enabling Enhanced Solar Hydrogen Production.

Although S-scheme artificial photosynthesis shows promise for photocatalytic hydrogen production, traditional methods often overly concentrate on a single reduction site. This limitation results in inadequate redox capability and inefficient charge separation, which hampers the efficiency of the photocatalytic hydrogen evolution reaction. To overcome this limitation, a double S-scheme system is proposed that leverages dual reduction sites, thereby preserving energetic photo-electrons and holes to enhance apparent quantum efficiency. The design features a double S-scheme junction consisting of CdS nanospheres decorated with anatase TiO2 nanoparticles coupled with graphitic C3 N4 . The as-prepared catalyst exhibits a hydrogen evolution rate of 26.84mmolg-1 h-1 and an apparent quantum efficiency of 40.2% at 365 nm. This enhanced photocatalytic hydrogen evolution is ascribed to the efficient charge separation and transport induced by the double S-scheme. Both theoretical calculations and comprehensive spectroscopy tests (both insitu and exsitu) affirm the efficient charge transport across the catalyst interface. Moreover, substituting the reduction-type catalyst CdS with other similar sulfides like ZnIn2 S4 , ZnS, MoS2 and In2 S3 further confirms the feasibility of the proposed double S-scheme configuration. The findings provide a pathway to designing more effective double S-scheme artificial photosynthetic systems, opening up fresh perspectives in enhancing photocatalytic hydrogen evolution performance.

Fast Interfacial Carrier Dynamics Modulated by Bidirectional Charge Transport Channels in ZnIn2 S4 -based Composite Photoanodes Probed by Scanning Photoelectrochemical Microscopy.

Limited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single-side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2 C3 Tx MXene quantum dots (MQDs) and α-Fe2 O3 nanodots (FO) are anchored on the surface of ZnIn2 S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as "electron extractor" and S-O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high-performance composite electrodes.

Fast Interfacial Carrier Dynamics Modulated by Bidirectional Charge Transport Channels in ZnIn2S4‐based Composite Photoanodes Probed by Scanning Photoelectrochemical Microscopy

AbstractLimited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single‐side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2C3Tx MXene quantum dots (MQDs) and α‐Fe2O3 nanodots (FO) are anchored on the surface of ZnIn2S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as “electron extractor” and S−O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high‐performance composite electrodes.

Interface charge separation in Cu2CoSnS4/ZnIn2S4 heterojunction for boosting photocatalytic hydrogen production

The practical application of hexagonal ZnIn2S4 (ZIS) as a visible-light photocatalyst for hydrogen (H2) production is hindered by rapid internal charge recombination. In this study, we successfully synthesized Cu2CoSnS4 (CCTS) nanocrystals and loaded them onto the surface of ZIS nanosheets to create a p-n heterojunction photocatalyst. The optimized Cu2CoSnS4/ZnIn2S4 (CCTS/ZIS) heterojunction exhibited a significantly higher visible-light photocatalytic H2 evolution rate of 4.90 mmol·g−1·h−1 compared to ZIS and CCTS alone. The enhanced photocatalytic efficiency was attributed to improved electron transfer and charge separation at the heterojunction interface. The formation of p-n heterojunction facilitated the accumulation of valence band electrons in ZIS and conduction band holes in CCTS, effectively suppressing the recombination of photogenerated electrons and holes. Theoretical calculations, spectroscopic, and photoelectrochemical characterizations supported the findings. This work presents a promising approach for designing efficient p-n heterojunction semiconductor photocatalysts for practical applications in visible-light-driven hydrogen evolution.

Reinforcing flower-like Znln2S4 via interfacial charge separation to boost CO2 photoreduction

CO2 Photoreduction through C–O bond cleavage and C–H bond formation has aroused as an alternative to fabricate high-value chemical fuels that are independent of fossil reserves. However, sluggish charge transfer and neglected light-induced heat utilization are thermodynamically and kinetically challenging. Herein, we subtly design a three-dimensional ultrathin composite consisting of flower-like ZnIn2S4 (ZIS) and low-cost biochar (BC). The as-prepared ZIS/BC photocatalyst displays an optimized performance and stability toward CO2 conversion, with a high CO yield of 20.7 μmol g−1 h−1 and a small yield of CH4, C2H4, and C2H6 in comparison with ZIS and BC counterparts. This exciting activity originates from high electron conduction efficiency, light-harvesting ability, and the photothermal effect, which is produced from the intense interfacial contact of BC and ZIS. This work suggests that traditional photocatalysts can be elevated by inhibiting photocorrosion by introducing highly economical and electron conductivity biomass carbon in solar-induced green-chemical feedstock production.

Substitutional Cd Dopant as Photohole Transfer Mediator Boosting Photoelectrochemical Solar Energy Conversion of 2D Cd-ZnIn2 S4 Photoanode.

Fast recombination dynamics of photocarriers competing with sluggish surface photohole oxidation kinetics severely restricts the photoelectrochemical (PEC) conversion efficiency of photoanode. Here, a defect engineering strategy is developed to regulate photohole transfer and interfacial injection dynamics of 2DZnIn2 S4 (ZIS). Via selectively introducing substitutional Cd dopant at Zn sites of the ZIS basal plane, energy band structure and surface electrochemical activity are successfully modulated in the Cd-doped ZIS (Cd-ZIS) nanosheet array photoanode. Comprehensive characterizations manifest that a shallow acceptor level induced by Cd doping and superior electrochemical activity make surface Cd dopants simultaneously act as capture centers and active sites to mediate photohole dynamics at the reaction interface. In depth photocarrier dynamics analysis demonstrates that highly efficient photohole capture of Cd dopants brings about effective space separation of photocarriers and acceleration of surface reaction kinetics. Therefore, the optimum 2D Cd-ZIS achieves excellent PEC solar energy conversion efficiency with a photocurrent density of 5.1mA cm-2 at 1.23 VRHE and a record of applied bias photon-to-current efficiency (ABPE) of 3.0%. This work sheds light on a microstructure design strategy to effectively regulate photohole dynamics for the next-generation semiconducting PEC photoanodes.

Construction of oxygen-deficient In2O3/ZnIn2S4 with hollow tubular heterostructure for photocatalytic CO2 reduction to syngas and benzyl alcohol oxidation

To reduce the recombination of the photogenerated charge carriers (PCCs), increase the utilization of the PCCs may be an effective method. In this work, the heterojunction catalysts of MIL-68 derived In2O3 (IO) microtube and ZnIn2S4 (ZIS) nanosheets were prepared by self-template and in-situ growth strategy. By growing ZnIn2S4 nanosheets on the surface of oxygen-deficient IO microtube, these two distinct semiconductors are integrated into hierarchical tubular hybrids with heterogeneous interfacial contacts. To improve the utilization rate of PCCs, the photocatalytic CO2 reduction is proceeded on IO/ZIS composite coupling with benzyl alcohol (PhCH2OH) oxidation. With the mass ratio of IO and ZIS adjusted, 30% IO/ZIS performs the best photocatalytic activity of CO2 reduction, which is 64.19 times higher than that of pure ZIS. The largely enhanced photocatalytic activity of IO/ZIS is attributed to the intimate interfacial contacts between IO and ZIS, which accelerates the separation and migration of PCCs via the Z-scheme model. The separated electrons and holes are respectively participated in the CO2 reduction and the PhCH2OH oxidation, as the reduction and oxidation products are close to 1: 1. This work not only provides the guideline for the design and construction of complex semiconductor-based photocatalysts, but an effective way to increase the utilization of PCCs.

Super-strong Zn and S atomic terminals in an organic/inorganic hybrid S-scheme polyimide based heterojunction for efficient photocatalytic treatment of mixed pollutant wastewater

Integrated oxidation and reduction reactions in the field of wastewater treatment with mixed high concentrations of sewage achieved by photocatalysis are highly desirable but still challenging. The construction of the S-scheme heterojunction system is expected to be a promising strategy to provide carriers with strong redox ability for oxidation of oxytetracycline hydrochloride (OTC) with simultaneous reduction of hexavalent chromium (Cr(VI)). Reduced graphene oxide (rGO) and ZnIn2S4 (ZIS) were successively assembled on perylene diimide polymer (PDIP) nanorods to form the S-scheme ZIS/rGO/PDIP heterojunction. The construction of organic–inorganic systems achieves wide light absorption, enhanced exciton dissociation and accelerated charge separation. A non-radiation-quenched electron transport path is formed in the ZIS/rGO/PDIP system from the conduction band of PDIP through rGO to the valence band of ZIS. The electronic energy state of the S-scheme ZIS/rGO/PDIP heterojunction was changed, and the Zn and S atomic terminals can realize strong adsorption of OTC and Cr(VI).

Realizing Unassisted Photo-Charging of Zinc-Air Batteries by Anisotropic Charge Separation in Photoelectrodes.

Solar rechargeable zinc-air battery is a promising approach for capturing and storing intermittent solar energy through photoelectrochemical reactions. However, unassisted photo-charging of zinc-air batteries is challenging due to suboptimal carrier accumulation on photoelectrodes, resulting in sluggish reaction kinetics. Here, unassisted photo-charging of zinc-air battery is achieved by investigating anisotropic photogenerated charge separation on a series of representative semiconductors (ZnIn2 S4 , TiO2 , and In2 O3 ), among which the exceptional anisotropic charge separation on a ZnIn2 S4 photoelectrode is revealed based on anisotropic charge diffusion capabilities. The charge separation is facet-dependent, which is observed using Kelvin probe force microscopy, verifying a cause-and-effect relationship between the photo-charge accumulation on photoelectrodes and their photo-charging performance in zinc-air batteries. This work achieves an unassisted photo-charging current density of 1.9mAcm-2 with a light-to-chemical energy conversion efficiency of 1.45%, highlighting the importance of anisotropic semiconductors for unassisted photo-charging of zinc-air batteries via efficient photogenerated charge separation.

MOFs-derived TiO2 composite ZnIn2S4 to construct Z-scheme heterojunction for efficient photocatalytic hydrogen evolution under visible light

The ultra-high specific surface area of metal-organic frameworks (MOFs) with a large number of mesopores makes them good platforms for photocatalytic reactions. The materials derived from MOFs can usually retain the original framework structure and have more reaction sites. TiO2 is a practical and stable photocatalyst, but its wide bandgap (3.2 eV) results in low utilization of solar energy. ZnIn2S4 (ZIS) has a suitable bandgap (2.4 eV) and well visible light absorption, which could be a good photocatalytic material, but its chemical stability is poor. In this paper, a simple route was used to composite porous MOF-derived TiO2 with ZIS to prepare a core-shell-like Z-scheme heterojunction composite photocatalyst to produce hydrogen via photocatalysis. Porous TiO2 provided a larger specific surface area and fuller close contact with ZIS. The direct Z-scheme heterojunction greatly improved the separation and migration of carriers, and ZIS/TiO2 presented the superior hydrogen evolution rate under visible light (λ＞400 nm) which was 2.1515 mmol/g/h, which is twice that of ZIS and 119.5 times that of MOF-derived TiO2. Various methods such as in-situ XPS and theoretical calculation were used to deeply explore the heterojunction types of the photocatalyst and its photocatalytic mechanism. This study presents the enormous research potential of MOF-derived materials for photocatalysis and the superiority of Z-scheme heterojunction composite materials.

Assembling Ti3C2MXene on a S‐Scheme Heterojunction with Oxidative Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution

Photocatalytic evolution of hydrogen is a very promising and sustainable technology. However, studying multiple composite systems that include oxidized covalent organic frameworks (COFs) for the purpose of photocatalytic hydrogen production poses a significant challenge. This challenge arises from the rapid charge recombination introduced by individual photocatalysts, as well as the limited availability of oxidative COFs. Herein, ZnIn2S4(ZIS)–COF (TPN‐COF) S‐scheme heterojunction loaded with Ti3C2MXene (MX) is rationally designed for efficient photocatalytic H2evolution. The best‐performing sample, MX/TPN‐COF@ZIS (with a ZIS:TPN‐COF mass ratio of 3:2, with 2% MX), reaches an H2production rate of 4.01 mmol g−1 h−1under visible light irradiation. Experimental and theoretical investigation reveals that the formation of S‐scheme heterojunctions between ZIS and COF can achieve the transfer of the electrons from COF to ZIS driven via the in‐built electric field while allowing the migration of electrons from ZIS to MX. Furthermore, multiple in‐built electric fields not only stimulate effective separation and migration of charges, but also inhibit recombination of carriers in a single semiconductor. This triple‐coupled photocatalytic system serves as a practical guideline for promoting the development of hydrogen.

Efficient visible-light-driven CO2 reduction into tunable syngas by cobalt phthalocyanine modified flower-like ZnIn2S4 nanosheets

Photocatalytic carbon dioxide (CO2) reduction into syngas (the mixture of CO and H2) has been considered as an attractive method to solve the greenhouse effect and energy shortage. Polychalcogenides semiconductors such as ZnIn2S4 (ZIS) have been widely utilized in photocatalysis but are still hampered by limited photo-induced charge separation and poor product selectivity. Molecular catalysts for CO2 reduction possess superior selectivity for specific reduction products but suffer from low stability and recycling difficulty. Herein, we modified a molecular phthalocyanine (Pc) on flower-like ZIS nanosheets. This hybrid exhibited enhanced photocatalytic CO2 reduction and exhibited a tunable ratio of CO/H2 in syngas (0.01–4.65) under visible light irradiation. The enhanced photocatalytic activity of ZIS-Pc hybrids can be attributed to dimension-matched ultrathin heterojunction, which facilitated charge separation, broad light utilization, and recycling stability. The unique design holds great potential for other highly efficient photocatalytic reactions.

Hollow Plasmonic P-Metal-N S-Scheme Heterojunction Photoreactor with Spatially Separated Dual Cocatalysts toward Artificial Photosynthesis.

Semiconductor-based step-scheme (S-scheme) heterojunctions possess many merits toward mimicking natural photosynthesis. However, their applications for solar-to-chemical energy conversion are hindered by inefficient charge utilization and unsatisfactory surface reactivity. Herein, two synergistic protocols are demonstrated to overcome these limitations based on the construction of a hollow plasmonic p-metal-n S-scheme heterojunction photoreactor with spatially separated dual noble-metal-free cocatalysts. On one side, plasmonic Au, inserted into the heterointerfaces of CuS@ZnIn2 S4 core-shell nanoboxes, not only accelerates the transfer and recombination of useless charges, enabling a more thorough separation of useful ones for CO2 reduction and H2 O oxidation but also generates hot electrons and holes, respectively injects them into ZnIn2 S4 and CuS, further increasing the number of active carriers participating in redox reactions. On the other side, Fe(OH)x and Ti3 C2 cocatalysts, separately located on the CuS and ZnIn2 S4 surface, enrich the redox sites, adjust the reduction potential and pathway for selective CO2 -to-CH4 transformation, and balance the transfer and consumption of photocarriers. As expected, significantly enhanced activity and selectivity in CH4 production are achieved by the smart design along with nearly stoichiometric ratios of reduction and oxidation products. This study paves the way for optimizing artificial photosynthetic systems via rational interfacial channel introduction and surface cocatalyst modification.

Modulating charge centers and vacancies in P-CoNi loaded phosphorus-doped ZnIn2S4 nanosheets for H2 and H2O2 photosynthesis from pure water

Photocatalytic water splitting has recently attracted increasing interests for solar to chemical energy conversion. Nevertheless, the high-efficiency process for photocatalytic water splitting is driven by recombination of photogenerated electron-hole pairs and the resultant low H2 productivity. Herein, we demonstrate that P-doping induced positive charge centers (Pδ+) and indium vacancies (VIn) in ZnIn2S4 (ZIS) nanosheets can significantly promote photosplitting pure water to simultaneously produce H2 and H2O2. Microstructural and spectroscopic analysis suggest that Pδ+ and VIn can trap photogenerated electrons and holes, respectively, as a result of enhanced separation of electron-hole pairs. The optimal catalyst of P-CoNi/ZIS displays a stoichiometric H2 and H2O2 productivity of 1228.7 and 1105.5 μmol h−1 g−1, respectively, with an apparent quantum efficiency of 6.2% at 365 nm. Impressively, H2 productivity of P-CoNi/ZIS has surpassed most reported catalysts for photocatalytic pure water splitting. This work provides a unique strategy to create efficient photocatalyst for pure water splitting.

Tailoring the bandgap of zinc indium sulfide/boroncarbonitride heterostructure for efficient photocatalytic CO2 reduction

Many efforts have been devoted to the reduction of atmospheric CO2 and the development of a route map for sustainability in the energy and environmental sectors. The present work describes the bandgap tailoring of the ternary metal sulfide ZnIn2S4 (ZIS) with two-dimensional (2D) boroncarbonitride (BCN) and a constructed heterostructure. The ratio of BCN to ZIS has been varied in different ratios and examined for morphological, structural, and optical characterization. The crystalline structure of the synthesized materials was subjected to Materials Studio software, which examined the geometry, stacking, and interaction between ZIS and layered BCN. ZIS/BCN-1 is found to be efficient compared to all other counter catalysts under study. Diffuse reflectance infrared Fourier transform (DRIFT) and Gas Chromatography Mass spectrophotometry (GC-MS) analysis confirm the formation of carbon monoxide and methane gas. In the presence of ZIS/BCN-1, it was found to produce 158 and 57 μmol g−1h−1 of CO and CH4, respectively, during CO2 reduction under visible light. The effect of sacrificial agents has been investigated, and found that triethanolamine (TEOA) showed enhanced activity compared to others. The mechanism of photocatalysis has been discussed in detail and found to form type-II heterostructure through the interface between ZIS and BCN. The stability of ZIS/BCN-1 is good even after 5 cycles of the CO2 reduction experiment, and no structural changes were found.

Facile synthesis of ZnIn2S4/Cu2O hierarchical heterostructures for enhanced selectivity and sensitivity of NH3 gas at room temperature

The development of an effective and reliable sensor with the capability to detect ammonia (NH3) gas at room temperature exerts a significant influence on the sensor industry. The gas sensing performance is notably improved by the formation of a heterostructure between metal oxide with metal sulfides. In this study, pure ZnIn2S4 (ZIS), Cu2O and heterostructures of ZIS with 5, 10 and 20 wt% of Cu2O were successfully prepared using hydrothermal, co-precipitation and heat treatment methods, respectively. A thorough investigation has been carried out to examine the sensing capabilities of all the materials upon exposure to NH3 with different concentrations (1, 5, 10, 15, 20, 25 and 50 ppm) at room temperature (RT). Impressively, the composite material 0.9ZnIn2S4/0.1Cu2O (ZIS-10) has exhibited remarkable gas sensitivity compared to pristine ZIS and Cu2O towards 25 ppm NH3, low limit of detection (1 ppm) with fast response/recovery times (37/25 sec). The improved performance of the ZIS-10 composite sensor may be ascribed to the synergistic effect between ZIS and Cu2O, which facilitates the electron transfer from ZIS to the Cu2O at the interface. The plausible gas-sensing mechanism and the pathways responsible for enhanced sensing are also discussed in detail.

Carbonized polymer dots modified ZnIn2S4 microspheres for visible-light-driven hydrogen evolution promotion performance

To effectively separate electron-hole pairs produced by light, a heterojunction arrangement can be employed, thereby improving photocatalytic efficiency. In this study, a simple hydrothermal process is used to manufacture carbonized polymer dots/ZnIn2S4 (CPDs/ZIS) heterostructure, which enhances the light absorption and charge carrier lifetime in comparison to bare ZnIn2S4 (ZIS). Upon irradiation with visible light, the 3-CPDs/ZIS composite generates hydrogen at a rate of 133 μmol g−1 h−1, which is 8.9 times faster than that of pure ZIS. The addition of CPDs can increase the range of light that can be absorbed, extend the service life of the optical charge, increase the specific surface area, and promote charge separation and transmission, which could effectively accelerate the photocatalytic reduction reaction. The presence of CPDs results in the introduction of multiple transition energy states and a decrease in the H* adsorption free energy, which enhances the hydrogen evolution activity according to the theoretical calculation findings of density functional theory (DFT) and Gibbs free energy of the hydrogen evolution process. Combining theoretical calculations and experimental results, a direct Z-type heterojunction mechanism is proposed for the hydrogen evolution promotion effectiveness of CPDs/ZIS under visible light.

Highly stable and durable ZnIn2S4 nanosheets wrapped oxygen deficient blue TiO2(B) catalyst for selective CO2 photoreduction into CO and CH4

Developing new and highly stable efficient photocatalysts is crucial for achieving high performance and selective photocatalytic CO2 conversion. In this paper, we designed a one-dimensional oxygen-deficient blue TiO2(B) (BT) catalyst for improved electron mobility and visible light accessibility. In addition, hexagonal ZnIn2S4 (ZIS) nanosheets with a low bandgap and great visible light accessibility are employed to produce effective heterostructures with BT. The synthesized materials are tested for photocatalytic conversion of CO2 into solar fuels (H2, CO and CH4). The optimized composite yields 71.6 and 10.3 μmol g−1h−1 of CO and CH4, three and ten times greater than ZIS, respectively. When ZIS nanosheets are combined with a one-dimensional oxygen-deficient BT catalyst, improved electron mobility and visible light accessibility are achieved, charge carriers are effectively segregated, and the transfer process is accelerated, resulting in efficient CO2 reduction. The photocatalytic CO2 conversion activity of the constructed BT/ZIS heterostructures is very stable over a 10-day (240-hour) period, and CO and CH4 production rates increase linearly with time; however, as time goes on, the rates of H2 production decrease. Further, a five-time recycling test confirmed this, revealing essentially equal activity and selectivity throughout the experiment. As a result, CO2 to CO and CH4 conversion has high selectivity and longer durability. The band structure of the BT/ZIS composite is determined using Mott-Schottky measurement, diffuse reflectance spectroscopy, and valence band X-ray photoelectron spectroscopy. This research demonstrates a novel approach to investigating effective, stable, and selective photocatalytic CO2 reduction systems for solar-to-chemical energy conversion.

Boosting photocatalytic hydrogen evolution: Electronic redistribution of ZnIn2S4 nanosheets via halogen ion doping

Designing a visible light responsive photocatalyst is the path to enhancing the efficiency of solar power for hydrogen generation. Herein, we provide a method that makes use of doping I atoms to regulate the surface state of ZnIn2S4 (ZIS) nanosheets and enhance surface reaction processes in order to increase photocatalytic performance. The optimized I-ZIS photocatalyst achieves a high hydrogen yield of 4.73 mmol g−1 h−1, which is 29.56 folds more than pure ZIS. Experiment measurements and first-principles simulations demonstrate that the shallow energy level formed by I doping optimizes the local electronic distribution of ZIS, strengthens the electrons’ delocalization capacity of S atoms for high electrical conductivity, and inhibits the regrouping of photo-generated electron and hole pairs, leading to an increase in the photocatalytic activity of the I-ZIS photocatalyst for hydrogen evolution. The research presents a novel viewpoint that a shallow energy level enhances the ability to separate photo-excited electron and hole pairs and accelerates the rate of hydrogen production.

Construction of novel photocatalysts for efficient hydrogen evolution: The key role of natural halloysite nanotubes

Hydrogen (H2) evolution by photocatalytic water splitting is a potential strategy to solve worldwide energy shortage. Sulfide nanocatalysts showed great potential for H2 evolution, but suffered from low charge separation efficiency and easy agglomeration. In this work, ZnIn2S4 (ZIS) nanoflowers were anchored onto the surface of halloysite nanotubes (HNTs) modified by ethylenediaminetetraacetic acid (EDTA). Photocatalyst 3ZnIn2S4-HNTs/EDTA3 (3ZIS-HNTs/E3) displayed the optimum H2 evolution rate of 10.4 mmol·g−1·h−1, being 3.4 times as that of the original ZIS. Moreover, 3ZIS-HNTs/E3 presented satisfied property in the photocatalytic hydrogenation reaction of 4-nitrophenol to produce 4-aminophenol. HNTs as substrates not only hindered the growth and agglomeration of ZIS, but also induced more S vacancies in ZIS. The production of Schottky junctions between ZIS and Pt, the high utilization of light energy in tubular HNTs, and the trapping effect of EDTA for photogenerated h+ were all favorable for enhancing the catalytic property. The density functional theory (DFT) calculations showed that 3ZIS-HNTs/E3 with more S vacancies had the lowest adsorption energy and the most appropriate ΔGH* for H* to enhance the H2 evolution efficiency, which was consistent with the experimental catalytic results. This study contributes a novel thought for synthesizing composites on the basis of natural minerals for taking part in and enhancing the catalytic performance.