Highly efficient photocatalytic H2 evolution over NiCo2S4/Mn0.5Cd0.5S: Bulk twinned homojunctions and interfacial heterojunctions

Rationally designed CaTiO3/Mn0.5Cd0.5S/Ni3C S-scheme/Schottky integrated heterojunction for efficient photocatalytic H2 evolution

Developing effective photocatalysts to achieve stable and efficient solar-induced hydrogen production remains a significant challenge due to rapid photocarrier recombination and sluggish hydrogen evolution kinetics. Here, a multi-interfacial engineering strategy involving the decoration of metallic Ni3C onto CaTiO3/Mn0.5Cd0.5S was proposed to create an S-scheme/Schottky hybrid heterostructure with multiple carrier transport paths for effective photocatalytic H2 production. Exploiting the synergy between S-scheme heterojunction and Schottky barrier, the engineered ternary CaTiO3/Mn0.5Cd0.5S/Ni3C hybrid heterojunction exhibits outstanding photostability and significantly enhanced hydrogen evolution activity of 79.1 mmol g-1 h-1, which was about 4.55, 3.22 and 2.59 times greater than Mn0.5Cd0.5S, Mn0.5Cd0.5S/Ni3C, and CaTiO3/Mn0.5Cd0.5S, respectively. By creating an S-scheme heterojunction between CaTiO3 and Mn0.5Cd0.5S, accompanied by a robust internal electric field (IEF), spatial charge separation can be effectively accelerated while ensuring the simultaneous preservation of highly active electrons and holes. Meanwhile, Ni3C nanoparticles, acting as a Schottky-junction H2 generation cocatalyst, can efficiently trap the photoinduced electrons to establish multiple charge transfer channels and supply ample active sites for photoreduction reaction, thereby further optimizing the hydrogen generation kinetics. The integration of a Schottky barrier and S-scheme heterojunction in this research is expected to offer new perspectives for designing other highly effective hybrid catalysts for solar-to-hydrogen fuel conversion.

Double S-scheme Cu2-xSe/twinned-Cd0.5Zn0.5S homo-heterojunctions with surface plasmon effects for efficient photocatalytic H2 evolution

The enhancement of charge separation and utilization efficiency in both the bulk phase and interface of semiconductor photocatalysts, as well as the expansion of light absorption range, are crucial research topics in the field of photocatalysis. To address this issue, twinned Cd0.5Zn0.5S (T-CZS) homojunctions consisting of wurtzite Cd0.5Zn0.5S (WZ-CZS) and zinc blende Cd0.5Zn0.5S (ZB-CZS) were synthesized via a hydrothermal method to facilitate the bulk-phase charge separation. Meanwhile, Cu2-xSe with localized surface plasmon resonance effect (LSPR) generated by Cu vacancies was also obtained through a hydrothermal process. Due to their opposite electronegativity, a solvent evaporation strategy was employed to combine Cu2-xSe and T-CZS by intermolecular electrostatic. After optimization, the photocatalytic hydrogen (H2) evolution rate of 5 wt% Cu2-xSe/T-CZS reached an impressive value of 60 mmol∙h-1∙g-1, which was 4.6 and 66.6 times higher than that of pure Cu2-xSe and T-CZS, respectively. Furthermore, this composites demonstrated a remarkable rate of 0.46 mmol∙h-1∙g-1 under near-infrared (NIR) wavelength (>800 nm). The enhanced performance observed in Cu2-xSe/T-CZS can be attributed to its unique and efficient double S-scheme charge transfer mechanism which effectively suppresses rapid recombination of electron-hole pairs both within the bulk phase and at the surface interfaces; this conclusion is supported by Density Functional Theory (DFT) calculations as well as electron paramagnetic resonance spectroscopy analysis. Moreover, incorporation of Cu2-xSe enables effective utilization ultraviolet visible-near infrared (UV-Vis-NIR) light by the composites while facilitating injection "hot electrons" into T-CZS for promoting photocatalytic reactions. This study provides a potential strategy for achieving efficient solar energy conversion through synergistic integration of non-stoichiometric plasmonic materials with photocatalysts with twinned-twinned structures.

P-doped Mn0.5Cd0.5S coupled with cobalt porphyrin as co-catalyst for the photocatalytic water splitting without using sacrificial agents

Photocatalytic water splitting over semiconductors is an important approach to solve the energy demand of human beings. Most photocatalytic H2 generation reactions are conducted in the presence of sacrificial agent. However, the use of sacrificial reagents increases the cost of hydrogen generation. Realizing photocatalytic water splitting for hydrogen production without the addition of sacrificial agents is a major challenge for photocatalysts. The porphyrin MTCPPOMe and P doped MnxCd1-xS make a significant contribution in facilitating the MnxCd1-xS photocatalytic pure water splitting to H2 reaction. Herein, a novel MTCPPOMe/P-MnxCd1-xS (M = 2H, Fe, Co, Ni) composite catalyst which can efficiently split pure water without using sacrificial agents is developed. As a result, the H2 generation rate of CoTCPPOMe/P-Mn0.5Cd0.5S is as high as 2.10 μmol h-1, which is 9.1 and 4.2 times higher than that of Mn0.5Cd0.5S (MCS) and P-Mn0.5Cd0.5S (P-MCS), respectively. P doped MnxCd1-xS inhibits the recombination of photogenerated carriers, and introduction of MTCPPOMe as co-catalyst enhances the reduction capacity. In summary, an efficient and economical photocatalystis prepared for pure water splitting to prepare hydrogen.

Synergistic optimization of triple phase junctions and oxygen vacancies over MnxCd1-xS/Ov-WO3 for boosting photocatalytic hydrogen evolution

Strengthening the separation of photogenerated charge carriers is crucial for improving the efficiency of photocatalytic hydrogen evolution. Herein, t-Mn0.5Cd0.5S/Ov-WO3 (t-MCSW) triple-phase junctions with rich oxygen vacancies were developed using the calcination-hydrothermal method. The corresponding morphology and structure of the samples were examined by XRD, TEM and XPS. The formation of the S-scheme heterostructure in t-MCSW has also been confirmed with in situ XPS, work function analysis and free radical capture tests. The experimental results demonstrate that t-MCSW-7 exhibited optimal activity (194.2 mmol g-1 h-1), which was about 4 times higher than that of the individual Mn0.5Cd0.5S (t-MCS, 48.8 mmol g-1 h-1). The apparent quantum yield of t-MCSW-7 is 29.14% at 420 nm, and the material exhibits excellent stability after seven cycles of photocatalytic reaction. The excellent photocatalytic activity of t-MCSW-7 is attributed to more efficient separation of charge carriers by triple-phase junctions connected by homojunctions and heterojunctions. Moreover, the existence of oxygen vacancies broadens absorption spectra and accelerates surface charge transfer. The synergistic effect of phase junctions and oxygen vacancies leads to an enhancement of hydrogen evolution activity. This work provides a new idea for preparing efficient photocatalysts.

A direct Z-scheme NiCo2O4/ZnIn2S4 heterojunction for highly efficient visible-light-driven H2 evolution

Exploiting efficient and stable photocatalysts is the primary goal of photocatalytic water splitting for H2 production. In this work, a sea urchin-like bimetallic NiCo2O4-decorated ZnIn2S4 heterojunction was fabricated via a solvent evaporation method. Investigation shows that the introduction NiCo2O4 can expand the UV-vis absorption range, enhance the absorption intensity, promote the charge separation, decrease the charge transfer resistance, induce more active sites, and decrease the H2 evolution overpotential of the composite. Besides, the charge transfer between NiCo2O4 and ZnIn2S4 follows a Z-scheme route based on the ˙OH radical capture experiments; this can preserve the strong oxidation-reduction reaction ability of photogenerated electrons and holes, leading to a faster H2 evolution rate, which reaches 17.28 mmol g-1 h-1 over the 4.8%-NiCo2O4/ZnIn2S4 composite under 300 W Xe lamp irradiation in 20 vol% triethanolamine (TEOA) solution and is 3.0 times higher than that of ZnIn2S4. In addition, NiCo2O4/ZnIn2S4 also has excellent stability during 5 consecutive cycles. This work provides an effective method for constructing a highly effective Z-scheme heterojunction system for photocatalytic H2 production.

Immobilization of photocatalytic materials for (waste)water treatment using 3D printing technology - advances and challenges

Photocatalysis has been considered a promising technology for the elimination of a wide range of pollutants in water. Various types of photocatalysts (i.e., homojunction, heterojunction, dual Z-scheme photocatalyst) have been developed in recent years to address the drawbacks of conventional photocatalysts, such as the large energy band gap and rapid recombination rate of photogenerated electrons and holes. However, there are still challenges in the design of photocatalytic reactors that limit their wider application for real (waste)water treatment, such as difficulties in their recovery and reuse from treated (waste)waters. 3D printing technologies have been introduced very recently for the immobilization of materials in novel photocatalytic reactor designs. The present review aims to summarize and discuss the advances and challenges in the application of various 3D printing technologies (i.e., stereolithography, inkjet printing, and direct ink writing) for the fabrication of stable photocatalytic materials for (waste)water treatment purposes. Furthermore, the limitations in the implementation of these technologies to design future generations of photocatalytic reactors have been critically discussed, and recommendations for future studies have been presented.

Manganese Cadmium Sulfide Nanoparticles Solid Solution on Cobalt Acid Nickel Nanoflakes: A Robust Photocatalyst for Hydrogen Evolution

Photocatalytic water splitting for hydrogen evolution is one of the most promising methods to mitigate environmental and energy-related issues. In this study, manganese cadmium sulfide (Mn_x Cd_1-x S) solid solution is used to construct a p-n heterostructure with NiCo₂ O₄ through a hydrothermal method. The Mn_0.25 Cd_0.75 S/NiCo₂ O₄ composites are used for photocatalytic hydrogen evolution reaction, and the optimal hydrogen rate with 40 mg of Mn_0.25 Cd_0.75 S/NiCo₂ O₄ 40 mg (MCS/NCO 40) is 61159 μmol g^-1  h^-1 , which is about 16.3 times than that of pure Mn_0.25 Cd_0.75 S. After combining with NiCo₂ O₄ , the light absorption scale, the separation efficiency of photogenerated carriers, and the reaction kinetics are enhanced. Moreover, the band offset of MCS/NCO composites is calculated by the core level alignment method, demonstrating the formation of a p-n heterostructure. The built-in electric field from the p-n heterostructure drives charge transfer and enhances separation efficiency, which results in improved photocatalytic performance.

Modification of the surface of Mn0.25Cd0.75S polyhedra with NiB: reducing the surface work function and promoting electron migration for enhanced photocatalytic hydrogen production

NiB is compounded on the surface of Mn0.25Cd0.75S to bring them into close contact. The photocatalytic hydrogen production rate of 10% NiB/Mn0.25Cd0.75S is 13.06 mmol g−1 h−1, which is 3.7 times higher than that of pure Mn0.25Cd0.75S.

S-Scheme heterojunction based on the in situ coated core–shell NiCo2S4@WS2 photocatalyst was constructed for efficient photocatalytic hydrogen evolution

A core–shell structure was formed on the surface of NCS in situ loaded with WS, and efficient photocatalytic hydrogen evolution was achieved by constructing a reasonable S-scheme heterojunction.

Amorphous CoSx decorated Cd0.5Zn0.5S with a bulk-twinned homojunction for efficient photocatalytic hydrogen evolution

Amorphous CoSx was combined with Twinned-Cd0.5Zn0.5S to construct homo-heterojunction for efficient photocatalytic H2 evolution. This work provides new ideas for constructing noble metal-free photocatalyst with homo-heterojunction.

Interface engineering of Co9S8/CdIn2S4 ohmic junction for efficient photocatalytic H2 evolution under visible light

The design and development of high-performance photocatalysts from three aspects of simultaneous enhancement of light harvest, carrier migration rate, and redox reaction rate is still a great challenge. Herein, a novel Co₉S₈/CdIn₂S₄ ohmic junction with a robust internal electric field (IEF) is successfully prepared via hydrothermal and in situ synthesis methods and is used for effective photocatalytic H₂ evolution (PHE). Under simulated visible light irradiation, the PHE rate of 5% Co₉S₈/CdIn₂S₄ can reach 1083.6 μmol h^-1 g^-1, which is 6.4 times higher than that of CdIn₂S₄ (170.5 μmol h^-1 g^-1). The enhanced PHE performance is mainly ascribed to the improved light harvest and carrier separation efficiency and fast surface H₂ evolution kinetics. Moreover, Co₉S₈ nanotubes serve as promising Co-based cocatalysts that can evidently enhance PHE activity. Additionally, Co₉S₈/CdIn₂S₄ shows superior stability because the photogenerated carrier transfer path restrains the photocorrosion behavior. The photocatalytic mechanism is proposed based on experimental results and DFT calculations. This work offers new insights for the design and development of highly active photocatalysts from interface engineering.

Cd0.5Zn0.5S/CoWO4 Nanohybrids with a Twinning Homojunction and an Interfacial S-Scheme Heterojunction for Efficient Visible-Light-Induced Photocatalytic CO2 Reduction

The construction of a phase junction photocatalyst can significantly enhance the photocatalytic performance with high selectivity for CO₂ reduction. In this study, an S-scheme junction Cd_0.5Zn_0.5S/CoWO₄ semiconductor with the coupling of a twin crystal Cd_0.5Zn_0.5S homojunction and CoWO₄ was designed through a hydrothermal method, which could convert CO₂ to CO with high efficiency under visible-light illumination. Cd_0.5Zn_0.5S-10%CoWO₄ exhibited the optimal performance and its CO yield and selectivity were up to 318.68 μmol·g^-1 and 95.90%, respectively, which were 4.54 and 1.62 times higher than that of twin crystal Cd_0.5Zn_0.5S. Moreover, the Cd_0.5Zn_0.5S homojunction with a zinc-blende and wurtzite phase and the S-scheme phase junction of Cd_0.5Zn_0.5S/CoWO₄ enhanced the property of CO₂ adsorption and accelerated the detachment of photogenerated carriers. The combination of photogenerated holes in Cd_0.5Zn_0.5S and the electrons of CoWO₄ can retain the reduction sites to improve photocatalytic performance. This study provides a neoteric concept and reference for the construction of the S-scheme phase junction.

Direct electrospinning preparation of Z-scheme mixed-crystal Bi2O3/g-C3N4 composite photocatalysts with enhanced visible-light photocatalytic activity

A novel Z-scheme mixed-crystal Bi₂O₃/g-C₃N₄ composite photocatalyst was successfully prepared by a simple electrospinning–calcination approach.