Extremely high photocatalytic H 2 evolution of novel Co 3 O 4 /Cd 0.9 Zn 0.1 S p–n heterojunction photocatalyst under visible light irradiation

Synthesize magnetic ZnFe2O4@C/Cd0.9Zn0.1S catalysts with S-scheme heterojunction to achieve extraordinary hydrogen production efficiency

Suppressing the electron-hole recombination rate of catalyst legitimately is one of the effective strategies to improve photocatalytic hydrogen evolution. Herein, carbon-coated metal oxide, ZnFe2O4@C (ZFO@C), nanoparticles were synthesized and employed to couple with quadrupedal Cd0.9Zn0.1S (CZS) via an ordinary ultrasonic self-assembly method combined with calcination to form a novel ZFO@C/CZS catalyst with step-scheme (S-scheme) heterojunction. The photocatalytic hydrogen evolution reaction (HER) was conducted to verify the enhanced photoactivity of ZFO@C/CZS. The optimal ZFO@C/CZS exhibits an extraordinary photocatalytic HER rate of 111.3 ± 0.9 mmol g-1 h-1 under visible-light irradiation, corresponding to an apparent quantum efficiency as high as (76.2 ± 0.9)% at 450 nm. Additionally, the as-synthesized ZFO@C/CZS composite exhibits high stability and recyclability. The excellent photocatalytic hydrogen evolution performance should arise from the formed S-scheme heterojunction and the unique ZFO@C core-shell structure, which inhibit electron hole recombination as well as provide more reactive sites. The pathway of S-scheme charge transfer was validated through density functional theory calculations and electrochemical measurements. This work provides a rational strategy for the synthesis of unique magnetic S-scheme heterojunction photocatalysts for water splitting under visible light irradiation.

One-pot hydrothermal synthesis of noble-metal-free NiS on Zn0.5Cd0.5S nanosheet photocatalysts for high H2 evolution from water under visible light

At present, the rational design and facile synthesis of highly active and low-cost photocatalysts are still facing great challenges. Herein, a series of Zn0.5Cd0.5S/NiS (x mol%) composite photocatalysts have been synthesized via a simple and mild one-pot hydrothermal method. Compared with pure Zn0.5Cd0.5S, the NiS-loaded samples exhibit enhanced photocatalytic hydrogen generation performance, in which the Zn0.5Cd0.5S/NiS-5% sample has the highest H2 production rate of 10 855 ± 461 μmol h-1 g-1 with a quantum yield of 11.82% at 365 nm, which is almost 6.3 times higher than that of pristine Zn0.5Cd0.5S. The high activity of the Zn0.5Cd0.5S/NiS nanosheets may be attributed to their distinct nanostructure, including a short transfer distance of photoinduced charge carriers, a large number of unsaturated surface atoms, and a large surface area. Moreover, the added NiS nanoparticles served as an effective cocatalyst to promote photoinduced electron transfer and enhance the surface kinetics of H2 evolution. Our work provides a simple and effective route for the preparation of sulphur-based photocatalysts, which can significantly improve the efficiency of hydrogen production from water.

Recent advances of modification effect in Co3O4-based catalyst towards highly efficient photocatalysis

Tricobalt tetroxide (Co3O4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co3O4 to achieve optimal photocatalytic performance. The pristine Co3O4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co3O4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co3O4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co3O4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers.

Construction of shell-core Co2P/Cd0.9Zn0.1S photocatalyst by electrostatic attraction for enhancing H2 evolution

Solar energy-driven photocatalytic decomposition of water to produce H₂ is of great significance for promoting the development of clean energy. To improve the efficiency of H₂ production, a novel spherical Co₂P/Cd_0.9Zn_0.1S (Co₂P/CZS) composite with shell-core structure was successfully synthesized by electrostatic attraction. Under visible light irradiation, the optimal Co₂P/CZS achieves an excellent H₂ rate of 16.05 mmol h^-1 g^-1 in benzyl alcohol (PhCH₂OH) solution, with a quantum efficiency of 34.3% at 450 nm. The Co₂P thin layer coated on the CZS surface not only facilitates the photogenerated charge transfer from Co₂P to CZS under visible light illumination, but reduces the energy barrier of PhCH₂OH oxidation and H₂ evolution. The present results show that shell-core Co₂P/CZS composite may be one of promising catalyst to enhance the activity of H₂ evolution, which provides an important reference basis for new catalyst design and wide prospects for further application of metal sulfides.

Recent advances in Co-based co-catalysts for efficient photocatalytic hydrogen generation

Recent progress in photocatalytic hydrogen generation reaction highlights the critical role of co-catalysts in enhancing the solar-to-fuel conversion efficiency of diverse band-matched semiconductors. Because of the compositional flexibility, adjustable microstructure, tunable crystal phase and facet, cobalt-based co-catalysts have stimulated tremendous attention as they have high potential to promote hydrogen evolution reaction. However, a comprehensive review that specifically focuses on these promising materials has not been reported so far. Therefore, this present review emphasizes the recent progress in the pursuing of highly efficient Co-based co-catalysts for water splitting, and the advances in such materials are summarized through the analysis of structure-activity relationships. The fundamental principles of photocatalytic hydrogen production are profoundly outlined, followed by an elaborate discussion on the crucial parameters influencingthe reaction kinetics. Then, the co-catalytic reactivities of various Co-based materials involving Co, Co oxides, Co hydroxides, Co sulfides, Co phosphides and Co molecular complexes, etc, are thoroughly discussed when they are coupled with host semiconductors, with an insight towards the ultimateobjective of achieving a rationally designed photocatalyst for enhancing water splitting reaction dynamics. Finally, the current challenge and future perspective of Co-based co-catalysts as the promising noble-metal alternative materials for solar hydrogen generation are proposed and discussed.

Efficient hydrogen production at a rationally designed MoSe2@Co3O4 p-n heterojunction

During the past several years, transition metal compounds have shown high activity in the field of photocatalysis. Therefore, the MoSe₂@Co₃O₄ with excellent photocatalytic properties through simple hydrothermal and physical mixing methods was prepared. This composite material was composed of n-type semiconductor MoSe₂ and p-type semiconductor Co₃O₄. After optimizing the loading of Co₃O₄, the optimal hydrogen production can reached 7029.2 μmol g^-1h^-1, which was 2.34 times that of single MoSe₂. In addition, some characterization methods were used to explore the hydrogen production performance of the composite catalyst under EY sensitized conditions. Among them, the UV-vis diffuse reflectance spectra suggests that MoSe₂@Co₃O₄ exhibits stronger visible light absorption performance than the single material. Fluorescence performance and photoelectrochemical characterization experiments further prove that, the special structure formed by MoSe₂ and Co₃O₄ and the existence of p-n heterojunction effectively accelerate the separation and transfer of carriers meanwhile inhibit the recombination probability of electron-hole pairs. Combined with other characterizations such as XRD, XPS, SEM and BET, the possible hydrogen production mechanism was proposed.

Simultaneous manipulation of ion doping and cocatalyst loading into Mn0.3Cd0.7S nanorods toward significantly improved H2 evolution

Ni₂P and Ni²⁺ jointly modified Mn_0.3Cd_0.7S photocatalysts were successfully fabricated via a facile solvothermal method. The loading of Ni₂P and the doping of Ni²⁺ proceeded simultaneously via a one-step process.

A sea-urchin-structured NiCo2O4 decorated Mn0.05Cd0.95S p–n heterojunction for enhanced photocatalytic hydrogen evolution

The development of low-cost and high-efficiency photocatalysts is an important way to realize photocatalytic hydrogen production.

Construction of direct Z-scheme system for enhanced visible light photocatalytic activity based on Zn0.1Cd0.9S/FeWO4 heterojunction

A novel direct Z-scheme Zn_0.1Cd_0.9S/FeWO₄ (ZCS/FW) photocatalyst was prepared by a facile calcination method. The photocatalytic performance was investigated by photodegradation rhodamine B (RhB) and photocatalytic production hydrogen (H₂) under visible light irradiation. Compared with the pure ZCS, the ZCS/FW composites show considerably improved photocatalytic activity for degradation RhB and production H₂. Noticeably, the ZCS/FW with 7 wt% of FW exhibits optimal photocatalytic activity with the H₂ evolution rate of 34.6 mmol g^-1 h^-1 and photodegradation of about 98% of RhB solution (10 mg l^-1) in 60 min. These outstanding photocatalytic performances were found to be ascribed to the formation of direct Z-scheme heterojunction, resulting in effective separation and transfer of photogenerated charge carriers. Moreover, active species trapping experiments further demonstrate the electrons transfer followed Z-scheme system, and the photocatalytic mechanism was proposed.

Synthesis of MnxCd1−xS nanorods and modification with CuS for extraordinarily superior photocatalytic H2 production

A series CuS/Mn_0.3Cd_0.7S photocatalysts with nanorod structures were successfully constructed and exhibited particularly high H₂ evolution performance from water splitting under visible light irradiation.

Effective electron-hole separation over a controllably constructed WP/UiO-66/CdS heterojunction to achieve efficiently improved visible-light-driven photocatalytic hydrogen evolution

The photocatalytic decomposition of water to produce hydrogen is an important strategy to effectively utilize solar energy and solve the energy crisis. In this study, a highly efficient WP-nanoparticle-modified composite catalyst was successfully prepared. WP nanoparticles have been used as an efficient and acid-stable co-catalyst for the HER owing to their specific electronic structure, metalloid characteristics and catalytic activity. On the one hand, the octahedral spatial structure of UiO-66 not only provides attachment space for CdS and WP nanoparticles, but also effectively reduces the particle size and increases the dispersion of CdS and WP nanoparticles. On the other hand, the potential difference and the matching energy band positions of UiO-66 and CdS provide a feasible thermodynamic path for the transmission of photogenerated electrons. The intimate contact between the abovementioned three compounds resulted in a strong synergistic effect, which improved the efficiency of the photocatalytic H2 production. Under visible-light irradiation, the maximum H2 production in 5 h over the [UiO-66@CdS/WP (10 wt%)] photocatalyst was 395 μmol, which was 26.33 times that of pure CdS. The physical and chemical information of the samples could be obtained through XRD, SEM, TEM, XPS, BET and UV-vis DRS characterizations. Furthermore, based on the photoluminescence spectra, photoelectrochemical experiments and Mott-Schottky curves, we could reasonably explain the separation and transfer mechanisms of the photogenerated electrons and holes. The lower recombination rate of charge, enhanced intensity of light absorption, a short fluorescence lifetime (2.11 ns), a faster electron injection rate (KET = 2.32 × 108 s-1), a larger efficiency of electron injection (ηinj = 49.1%), high photocurrent response, and smaller charge transfer resistance accelerate the efficient separation and transfer of spatial charges, finally enhancing the photocatalytic performance.

CdS p–n heterojunction co-boosting with Co3O4 and Ni-MOF-74 for photocatalytic hydrogen evolution

A high-efficiency Ni-MOF-74/CdS/Co₃O₄ composite catalyst, the CdS co-boosting with Ni-MOF-74 and Co₃O₄, is successfully prepared.