0D/2D heterojunction constructed by Ag2S quantum dots anchored on graphdiyne (g-CnH2n-2) nanosheets for wide spectrum photocatalytic H2 evolution.

Precisely crafting heterojunctions for efficient charge separation is a major obstacle in the realm of photocatalytic hydrogen evolution. A 0D/2D heterojunction was successfully fabricated by anchoring Ag2S quantum dots (Ag2S QDs) onto graphdiyne (GDY) nanosheets (Ag2S QDs/GDY) using a straightforward physical mixing technique. This unique structure allows for excellent contact between GDY and Ag2S QDs, thereby enhancing the rate of charge transfer. The light absorption capabilities of Ag2S QDs/GDY extend up to 1200 nm, enabling strong absorption of light, including infrared. Through DFT calculations and in-situ XPS analysis, it was demonstrated that incorporating Ag2S QDs onto GDY effectively modulates the electronic structure, promotes an internal electric field, and facilitates directional electron transfer. This directed electron transfer enhances the utilization of electrons by GDY and Ag2S QDs, with the added benefit of Ag2S QDs serving as electron reservoirs for efficient photocatalytic hydrogen evolution. A 7 %Ag2S QDs/GDY composite exhibited impressive efficiency and stable performance in photocatalytic hydrogen evolution (2418 µmol g-1 h-1), which is much higher than that of GDY and Ag2S QDs. This study conclusively demonstrates that the 0D/2D heterojunction formed by GDY and Ag2S QDs can establish high-quality contact and efficient charge transfer, ultimately enhancing photocatalytic performance.

P-Induced In Situ Construction of ZnCoMOF@CoP-5 S-Scheme Heterojunctions for Enhanced Photocatalytic H2 Evolution.

In view of the fact that the exposed catalytic active sites of single-metal MOFs cannot satisfy the efficient progress of the catalytic reaction, here we constructed a star-shaped bimetallic ZnCoMOF by introducing a Zn source by the partial ion exchange method and coprecipitation method. By controlling the quality of sodium hypophosphite, ZnCoMOF was subjected to different degrees of phosphating to optimize the experimental conditions. The introduction of the more electronegative P can attract more H+ to participate in the reduction reaction. The ZnCoMOF@CoP-5 S-scheme heterojunction was constructed in situ by generating CoP on the surface of ZnCoMOF under a PH3 reducing atmosphere, which exhibited excellent H2 evolution performance. This unique heterojunction effectively promotes the separation and transfer of e--h+ pairs, ensuring a strong redox capability. The best hydrogen-evolution performance of ZnCoMOF@CoP-5 under the EY sensitization system reaches 16 958 µmol h-1 g-1, which has significant advantages over the same type of materials and similar photocatalytic hydrogen-evolution work. Finally, the photocatalytic mechanism was demonstrated by an in situ XPS technique. Our work provides important ideas for the research of bimetallic MOFs in the field of photocatalytic hydrogen evolution.

Co2P/CoP quantum dots surface heterojunction derived from amorphous Co3O4 quantum dots for efficient photocatalytic H2 production.

Amorphous/crystalline heterostructures show excellent potential in the hydrogen evolution reaction (HER) as they can significantly facilitate surface adsorption and redox reactions. Herein, a unique amorphous Co2P/crystalline CoP quantum dots (Co2P/CoP QDs) Type-II surface heterojunction was derived from amorphous Co3O4 QDs via phosphorization. The intimate contact between Co2P QDs and CoP QDs was conducive to charge transfer, thereby promoting surface reaction kinetics. The unique structure and properties were beneficial to providing more active sites and controlling the electronic structures thus making amorphous/crystalline composites show superior photocatalytic hydrogen (H2) production performance. Additionally, the amorphous Co2P QDs had a plethora of unsaturated bonds and abundant defects; the disordered structure led to increased active sites that promoted surface reaction kinetics. Due to the synergistic effect of the quantum confinement of QDs and the surface heterojunction, the charge transfer efficiency of Co2P/CoP QDs was extremely high, and high H2 evolution activity and photostability were achieved. The maximum H2 generation rate over the Co2P/CoP QDs composite reached 11.88 mmol h-1 g-1 with an apparent quantum efficiency (AQE) of 3.88 % at 420 nm, which is roughly 20-times that of the pure Co3O4 QDs. In addition, high photostability was realized; even the photocatalyst that stood for a week reached initial photoactivity. This work offers a novel idea for reasonably establishing amorphous/crystalline photocatalysts to achieve efficient H2 evolution.

Amorphous Co3O4 quantum dots hybridizing with 3D hexagonal CdS single crystals to construct a 0D/3D p-n heterojunction for a highly efficient photocatalytic H2 evolution.

Herein, a novel amorphous monodisperse Co3O4 quantum dots/3D hexagonal CdS single crystals (0D/3D Co3O4 QDs/CdS) p-n heterojunction was constructed by a simple hydrothermal and electrostatic self-assembly method. The amorphous monodispersed Co3O4 QDs (≈4.5 nm) are uniformly and tightly attached to the surface of the hexagonal CdS single crystals. The sample, 0.5% CQDs/CdS exhibits outstanding hydrogen evolution activity of 17.5 mmol h-1 g-1 with a turnover number (TON) of 4214, up to 10.3 times higher than that of pure CdS. The enhanced photocatalytic activity can be attributed to the synergistic effect of the p-n heterostructure and the quantum confinement effect of Co3O4 QDs, which significantly promoted the separation efficiency of photo-generated electrons and holes. Additionally, the sulfur vacancy also can act as electron trappers to improve carrier separation and electron transfer. The photoelectrochemical and time-resolved fluorescence (TRPL) results further certify the effective spatial charge separation. This work gives an insight into the design of the 0D/3D Co3O4 QDs/CdS p-n heterostructure for a highly efficient photocatalysis.

A novel materials manganese cadmium sulfide/cobalt nitride for efficiently photocatalytic hydrogen evolution.

The CoN which with excellent performance was introduced into Mn0.2Cd0.8S through simple electrostatic self-assembly for the first time, then the composite photocatalyst with low cost and high catalytic activity was prepared. The introduction of CoN improves the absorption intensity of catalyst to visible light. CoN accepts photo-induced electrons from Mn0.2Cd0.8S as an excellent electron acceptor in the form of active sites due to its suitable conduction band position and good conductivity. The surface interaction of composite photocatalyst formed by electrostatic self-assembly is strong, which is conducive to the directional transfer of photogenic carriers from Mn0.2Cd0.8S to CoN, greatly inhibits the recombination of photogenic carriers and improves the separation and the transfer rate of photogenic carriers. The introduction of CoN greatly improved the hydrogen production rate of photocatalyst up to 14.612 mmol g-1 h-1, it was 17.3 times that of pure MCS. This work provides inspiration for transition metal nitrides as cocatalysts in the sphere of photocatalytic splitting of water for hydrogen production.

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.

ZnxCd1-xS nanoparticles dispersed on CoAl-layered double hydroxide in 2D heterostructure for enhanced photocatalytic hydrogen evolution.

CoAl-LDH and ZnxCd1-xS (ZCS) were successfully assembled. By studying the microstructure of the catalysts, it was found that the agglomerated ZCS nanoparticles were equably dispersed on the hexagonal plate-like CoAl-LDH surface. The increase of the specific surface area of the composite catalyst further proves that the agglomeration state of ZCS nanoparticles has been improved. When the mass of the introduced CoAl-LDH is 20% of the ZCS, the maximum hydrogen production after the optimization is 1516 µmol/5h, which is about 6.9 times that of pure ZCS. UV-vis DRS in the range of 250-800 nm proved that the visible light absorption intensity of the composite is enhanced compared to pure materials. Electrochemical and photoluminescence experiments proved that the heterostructure formed between ZCS and CoAl-LDH accelerates photoelectron transfer and inhibits the recombination of electrons and holes. In addition, possible mechanisms of the sample were explored by UV-vis DRS and Mott-Schottcky.

Rational design of a novel p-n heterojunction based on 3D layered nanoflower MoSx supported CoWO4 nanoparticles for superior photocatalytic hydrogen generation.

Enriching the active sites of catalysts and artificially regulating the directional migration of photogenerated carriers are effective means to improve the catalytic activity of photocatalysts. In this work, polyvinylpyrrolidone (PVP) is used as the morphological modifier to prepare MoSx with three-dimensional (3D) nanoflower structure. Compared with two-dimensional (2D) MoSx nanosheets, three-dimensional nanoflower structure weakens the van der Waals force between nanosheets and inhibits the stacking between layers, thus exposing the high-density active sites of MoSx nanoflower. The CoWO4 nanoparticles are successfully anchored to MoSx by in-situ growth, forming the MoSx/CoWO4 p-n heterojunction photocatalyst. The high photosensitivity of MoSx increases the utilization of MoSx/CoWO4 p-n heterojunction to visible light. The unique 3D nanoflower structure of MoSx results in that CoWO4 nanoparticles are dispersed well on the surface of MoSx, which prevents CoWO4 agglomeration. Based on the high efficiency of charge separation, abundant active sites and excellent property of visible light response, the hydrogen evolution rate of MoSx/CoWO4-40 reached 9414.4 µmol g-1 h-1.

Self-assembly of zinc cadmium sulfide nanorods into nanoflowers with enhanced photocatalytic hydrogen production activity.

ZnCdS solid solutions have been extensively studied due to their excellent photocatalytic hydrogen evolution performance. The change of the molar ratio of precursors affects the morphology and structure of ZnCdS, with the subsequent influence on the separation of photogenerated electron-hole pairs and the hydrogen production ability. The effect of the amount of nonmetallic elements on the photocatalytic activity has been scarcely explored. In this work, the morphology of ZnCdS is regulated by varying the amount of thioacetamide as S precursor. The structure of the samples is thoroughly analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller analysis. Their optical properties, photocatalytic hydrogen evolution ability, and photoelectrochemical performance are evaluated. Upon increasing the amount of thioacetamide, the crystallinity improves, the ZnCdS nanorods self-assemble into nanoflowers, and the number of defects decreases. The highest photocatalytic activity is achieved for a (Zn + Cd):S molar ratio of 1:3.5. Moreover, the photocatalyst exhibits excellent stability after six cycles. The one-dimensional nanorod structure contributes to the formation of a space charge region that drives the charge carriers along the nanorods. The self-assembled ZnCdS nanoflowers provide extra channels for the charge transfer, improving the separation of electron-hole pairs.

Amorphous tungsten phosphosulphide-modified CdS nanorods as a highly efficient electron-cocatalyst for enhanced photocatalytic hydrogen production.

Improving the utilization rate of photogenerated electrons generated by visible light excitation is an important factor to improve the activity of photocatalytic decomposition of water for hydrogen evolution. In this study, amorphous tungsten phosphosulphide nanoparticle (WPS NP)-modified CdS (WPS/CdS) catalysts were successfully prepared by a simple physical mixing method. The activity of the 15% WPS/CdS composite catalyst is the best, and the average hydrogen production rate reached 123 257 µmol g-1 in 5 h, and the highest AQE of 9.15% is derived at 420 nm for the 15% WPS/CdS composite catalyst. Simultaneously, five cycle stability tests were performed on the 15% WPS/CdS composite catalyst, and the results show that the 15% WPS/CdS composite catalyst exhibits a high stability. WPS NPs not only improve the visible light absorption rate, but also provide a large number of exposed active sites for the hydrogen evolution reaction. These active sites can capture photogenerated electrons on CdS NRs quickly, and can be used for the hydrogen evolution reaction quickly, promoting the transmission and separation of photogenerated charges and inhibiting the recombination of photogenerated electron and hole pairs. Thus, the utilization rate of photogenerated electrons generated by visible light is improved, and the activity of the photocatalyst is significantly increased.

CoSe2/CdS-diethylenetriamine coupled with P clusters for efficient photocatalytic hydrogen evolution.

The development of a highly active and stable non-noble-metal hydrogen-producing catalyst for renewable energy reserves and conversion remains a serious challenge. In this work, we described a novel binary solution (DETA/H2O) reaction for preparing a composite catalyst composed of CdS nanoparticles grown on CoSe2 nanobelts. The composite catalyst (CoSe2/CdSDETA) exhibits excellent catalytic activity for a hydrogen evolution reaction in an EY sensitized 15% (v/v) TEOA aqueous solution under visible light irradiation (λ ≥ 420 nm). Moreover, the catalytic activity of the P-doped sample (CoSe2/CdSDETA|P) was further improved. The excellent performance is ascribed to the synergy among DETA and atomic-level P-doping. Some essential characterization methods such as XRD, SEM, TEM, UV-vis diffuse spectroscopy, XPS, photoelectrochemistry, PL, etc. were carried out to support the related results and a possible reaction mechanism was put forward.