Hierarchical NiCo2S4/ZnIn2S4 heterostructured prisms: High-efficient photocatalysts for hydrogen production under visible-light

Boosted photocatalytic hydrogen evolution of S-scheme N-doped CeO2-δ@ZnIn2S4 heterostructure photocatalyst

The advancement of highly effective heterojunction photocatalysts with improved charge separation and transfer has become a crucial scientific perspective for utilizing solar energy. In this study, we developed the S-scheme heterostructure by depositing N-doped CeO2-δ (NC) nanoparticles onto two-dimensional ZnIn2S4 (ZIS) nanosheets via hydrolysis strategy for significantly enhanced photocatalytic hydrogen evolution reaction. The optimal H2 generation rate of ∼ 798 μmol g-1 h-1 was achieved for NC-3@ZIS under solar light irradiation, which is about 18 and 2 times higher than those of pristine CeO2 (∼44 μmol g-1 h-1) and ZIS (∼358 μmol g-1 h-1), respectively. The photogenerated electrons from NC interact with the photogenerated holes of ZIS driven by an internal electric field, confirmed by In-situ KPFM, DFT calculation, and XPS results. According to EPR and photoelectrochemical measurements, NC-3@ZIS composite shows dramatically high separation efficiency of photogenerated charge carriers. This study provides a new approach for developing non-noble metal S-scheme heterojunctions with enhanced photocatalytic hydrogen evolution.

Rational Photodeposition of Cobalt Phosphate on Flower-like ZnIn2S4 for Efficient Photocatalytic Hydrogen Evolution

The high electrons and holes recombination rate of ZnIn2S4 significantly limits its photocatalytic performance. Herein, a simple in situ photodeposition strategy is adopted to introduce the cocatalyst cobalt phosphate (Co-Pi) on ZnIn2S4, aiming at facilitating the separation of electron-hole by promoting the transfer of photogenerated holes of ZnIn2S4. The study reveals that the composite catalyst has superior photocatalytic performance than blank ZnIn2S4. In particular, ZnIn2S4 loaded with 5% Co-Pi (ZnIn2S4/5%Co-Pi) has the best photocatalytic activity, and the H2 production rate reaches 3593 μmol·g-1·h-1, approximately double that of ZnIn2S4 alone. Subsequent characterization data demonstrate that the introduction of the cocatalyst Co-Pi facilitates the transfer of ZnIn2S4 holes, thus improving the efficiency of photogenerated carrier separation. This investigation focuses on the rational utilization of high-content and rich cocatalysts on earth to design low-cost and efficient composite catalysts to achieve sustainable photocatalytic hydrogen evolution.

Carbon Dots as an Electron Acceptor in the ZnIn2S4@MIL-88A Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

In this study, visible-light-responsive carbon dots (CDs)/ZnIn2S4@MIL-88A (C/ZI@ML) photocatalysts were successfully prepared through in situ loading CDs and ZnIn2S4 nanosheets on MIL-88A(Fe) to form a ternary heterojunction. The detailed characterization indicated that the two-dimensional ZnIn2S4 nanosheets were uniformly coated on the surface of MIL-88A(Fe), and ZnIn2S4/MIL-88A(Fe) exhibited enhanced photocatalytic hydrogen production performance (1259.63 μmol h-1 g-1) compared to that of pristine MIL-88A(Fe) and ZnIn2S4 under visible light illumination. After introduction of CDs into ZnIn2S4/MIL-88A(Fe), the C/ZI@ML catalyst remarkably enhanced the photocatalytic activity and the hydrogen evolution rate of 1C/ZI@ML was up to 3609.23 μmol g-1 h-1. The photoinduced charge carriers of C/ZI@ML can be efficiently separated and migrated because of the close contacted interface, synergistic effect, and suitable band structure. In combination with photoelectrochemical experiments and electron paramagnetic resonance spectra, a possible photocatalytic mechanism over C/ZI@ML was proposed. This work demonstrated a facile preparation method for fabricating efficient visible-light-driven heterojunction photocatalysts.

Construction of ZnO/Zn3In2S6/Pt with integrated S-scheme/Schottky heterojunctions for boosting photocatalytic hydrogen evolution and bisphenol a degradation

Photocatalytic water splitting has been identified as a promising solution to tackle the current environmental and energy crisis in the world. However, the challenge of this green technology is the inefficient separation and utilization of photogenerated electron-hole pairs in photocatalysts. To overcome this challenge in one system, a ternary ZnO/Zn₃In₂S₆/Pt material was prepared as a photocatalyst using a stepwise hydrothermal process and in-situ photoreduction deposition. The integrated S-scheme/Schottky heterojunction in the constructed ZnO/Zn₃In₂S₆/Pt photocatalyst enabled it to exhibit efficient photoexcited charge separation/transfer. The evolved H₂ reached up to 3.5 mmol g^-1h^-1. Meanwhile, the ternary composite possessed a high cyclic stability against photo-corrosion under irradiation. Practically, the ZnO/Zn₃In₂S₆/Pt photocatalyst also showed great potential for H₂ evolution while simultaneously degrading organic contaminants like bisphenol A. It is hoped in this work that the incorporation of Schottky junctions and S-scheme heterostructures in the construction of photocatalysts would lead to accelerated electron transfer and high photoinduced electron-hole pair separation, respectively, to synergistically enhance the performance of photocatalysts.

Oxygen-Defect-Mediated ZnCr2O4/ZnIn2S4 Z-Scheme Heterojunction as Photocatalyst for Hydrogen Production and Wastewater Remediation

Photocatalysis has long been considered a promising technology in green energy and environmental remediation. Since the poor performance of single components greatly limits the practical applications, the construction of heterostructures has become one of the most important technical means to improve the photocatalytic activity. In this work, based on the synthesis of oxygen-vacancy-rich ZnCr₂O₄ nanocrystals, ZnCr₂O₄/ZnIn₂S₄ composites are prepared via a low-temperature in situ growth, and the oxygen-vacancy-induced Z-scheme heterojunction is successfully constructed. The unique core-shell structure offers a tight interfacial contact, increases the specific surface area, and promotes the rapid charge transfer. Meanwhile, the oxygen-vacancy defect level not only enables wide-bandgap ZnCr₂O₄ to be excited by visible light enhancing the light absorption, but also provides necessary conditions for the construction of Z-scheme heterojunctions promoting charge separation and migration and allowing more reactive charges. The reaction rates of visible-light-driven photocatalytic hydrogen production (3.421 mmol g^-1 h^-1), hexavalent chromium reduction (0.124 min^-1), and methyl orange degradation (0.067 min^-1) of the composite reach 3.6, 6.5, and 8.4 times those of pure ZnIn₂S₄, and 15.8, 41.3, and 67.0 times those of pure ZnCr₂O₄, respectively. This work presents a novel option for constructing high-performance photocatalysts.

Performance evaluation of Zr(CUR)/NiCo2S4/CuCo2S4 and Zr(CUR)/CuCo2S4/Ag2S composites for photocatalytic degradation of the methyl parathion pesticide using a spiral-shaped photocatalytic reactor

Zr(CUR)/NiCo₂S₄/CuCo₂S₄ and Zr(CUR)/CuCo₂S₄/Ag₂S ternary composites were synthesized as efficient photocatalysts, and well characterized through XRD, FTIR, DRS, FE-SEM, EDS, and EDS mapping techniques. The potential of a spiral-shaped photocatalytic reactor was evaluated for degradation of the methyl parathion (MP) pesticide using synthesized photocatalysts under visible light irradiation. Computational fluid dynamics (CFD) was applied for analysis of the hydrodynamics behaviour and mass transport occurring inside the reactor. The experiments were performed based on a developed CCD-RSM model, while the desirability function (DF) was used for optimization of the process. Findings showed that the highest MP degradation percentage was 98.70% at optimal operating values including 20 mg L^-1, 0.60 g L^-1, 8 and 40 min for MP concentration, catalyst dosage, pH, and reaction time, respectively. This study clearly demonstrated that high degradation efficiency can be achieved using a spiral-shaped photocatalytic reactor rather than a traditional annular reactor at same conditions. The increase in reaction rate is related to the higher average turbulence kinetic energy in the spiral-shaped reactor over the traditional reactor, which results in the increased diffusivity and improves the mass and momentum transfer.

Dispersible CdS1-xSex solid-solution nanocrystal photocatalysts: Photoinduced self-transformation synthesis and enhanced hydrogen-evolution activity

Modulating the electronic structure of Cadmium sulfide (CdS) by non-metallic elements to produce solid-solution photocatalysts serves as a potential route to improve its performance of photocatalytic hydrogen (H₂) evolution. However, exploring an effective synthetic route of CdS-based solid solution is still a great challenge. Herein, the CdS_1-xSe_x solid-solution nanocrystals were successfully synthesized by an accessible photoinduced self-transformation route, including the direct formation of dispersible CdS_1-x(SeS)_x and the in situ self-transformation of selenosulfide ((SeS)^2-) to Se^2- by photoexcited electrons. The prepared CdS_1-xSe_x solid-solution photocatalysts possess a small crystallite size of ca. 5 nm and their bandgaps can be easily tuned in a wide range of 1.84-2.28 eV by tailoring the mole ratio of Se/S. The resultant CdS_0.90Se_0.10 solid-solution photocatalyst realizes the highest H₂-production tempo of 94.6 μmol·h^-1, which is 1.6 folds higher than that of CdS. The experimental and theoretical studies supported that the incorporation of Se atoms could not only narrow the bandgap value to reinforce visible-light absorption, but also tune its electronic structure to optimize interfacial H₂-evolution dynamics, thus achieving an efficient photocatalytic H₂-production rate of the dispersible CdS_1-xSe_x solid solution. This study may deliver advanced inspirations for optimizing the electronic structure of photocatalysts towards sustainable H₂ production.

A MOF-derived hierarchical CoP@ZnIn2S4 photocatalyst for visible light-driven hydrogen evolution

A hierarchical CoP@ZnIn₂S₄ photocatalyst was prepared via a MOF-templated strategy. Owing to the unique composition and morphology that can facilitate the separation of photoexcited carriers, enhance light absorption and provide high surface area, CoP@ZnIn₂S₄ exhibited a H₂ evolution rate of 0.103 mmol h^-1 and remained stable over 24 hours.