Facile preparation of metallic 1T phase molybdenum selenide as cocatalyst coupled with graphitic carbon nitride for enhanced photocatalytic H2 production

MoSe2-NiSe dual co-catalysts modified g-C3N4 for enhanced photocatalytic H2 generation

Solar energy conversion into hydrogen (H₂) energy has attracted much attention. However, the low light utilization rate and fast carrier recombination of photocatalysts extremely limit the practical application of photocatalytic H₂ production. In this paper, MoSe₂-NiSe with abundant active sites and interfacial electronic structures as dual co-catalysts were assembled on g-C₃N₄ nanosheets (NSs) vis a solvothermal reaction process. MoSe₂-NiSe/g-C₃N₄ NSs composite exhibited improved light absorption and photoelectrochemical properties. The photocatalytic H₂ production rate of MoSe₂-NiSe/g-C₃N₄ composite achieved 2379.04 μmol·h^-1·g^-1, which is 99.25, 1.44, and 3.67 times those of pure g-C₃N₄ nanosheets (23.97 μmol·h^-1·g^-1), MoSe₂/C₃N₄ (1654.57 μmol·h^-1·g^-1), and NiSe/C₃N₄ (649.08 μmol·h^-1·g^-1), respectively. The apparent quantum efficiency (AQE) value of MoSe₂-NiSe/g-C₃N₄ achieved 4.07 % under light at λ = 370 nm. The corresponding characterization and experiments proved that 2D ultrathin g-C₃N₄ NSs with a large surface area and short charge-transfer distance could facilitate light scattering and the transport of photoexcited electrons. MoSe₂-NiSe, as a dual co-catalyst, showed strong electronic synergistic interaction between the interfaces, thus improving the conductivity and promoting the electron transfer process.

High-yield and crystalline graphitic carbon nitride photocatalyst: One-step sodium acetate-mediated synthesis and improved hydrogen-evolution performance

To avoid the drawbacks (such as multi-step operations and causing big quality loss) of currently reported molten salt-assisted strategy for the preparation of crystalline graphitic carbon nitride (g-C₃N₄) photocatalysts, in this study, an innovative and one-step sodium acetate (CH₃COONa)-mediated synthesis strategy has been designed to synthesize a high-yield and crystalline g-C₃N₄ photocatalyst. It is found that CH₃COONa can strongly combine with dicyandiamide (DCDA) to availably prevent the massive sublimation of DCDA and the following intermediates, causing the high-efficiency transformation of DCDA into g-C₃N₄ with a high yield (52.2 wt%). In addition to the promoted denitrification and quick polymerization of DCDA via CH₃COONa, the produced Na₂CO₃ from CH₃COONa decomposition at a higher temperature can further accelerate the polymerization reaction of 3-s-triazine units, leading to the final production of highly ordered and crystalline g-C₃N₄. Consequently, the resultant high-yield and crystalline g-C₃N₄ shows an obviously strengthened hydrogen (H₂)-evolution rate, about 2.4 times higher than that of bulk g-C₃N₄, which is due to the synergetic function of highly crystalline structure, reduced band gap and cyano-groups. The current one-step CH₃COONa-mediated synthesis strategy may open a novel horizon for the facile preparations and various applications of crystalline g-C₃N₄ materials.

Covalent Organic Framework/g-C3N4 van der Waals Heterojunction toward H2 Production

Photocatalytic water splitting into H₂ is the most economic and environmentally friendly strategy for H₂ production, and rationally constructing a heterojunction retains enormous influence on a photocatalytic system. Herein, 2D/2D covalent organic framework/graphitic carbon nitride (COF/CN) van der Waals heterojunctions were readily prepared via an ultrasonic method for high-efficiency visible-light photocatalytic H₂ production. The photocatalytic H₂ production performance of optimized COF/CN composites can reach up to 449.64 μmol·h^-1, which is approximately 5 times that of pure CN (89.08 μmol·h^-1). The characterization and experimental studies reveal that the synergistic effect between COF and CN contributes to promoting the interfacial migration and spatial separation of photoinduced e^--h⁺ pairs, further boosting the photocatalytic hydrogen production activity. This work may open a new window to design and fabricate effective heterojunction photocatalysts for photocatalytic energy conversion.

Dual cocatalysts and vacancy strategies for enhancing photocatalytic hydrogen production activity of Zn3In2S6 nanosheets with an apparent quantum efficiency of 66.20

Converting solar energy into hydrogen energy is a feasible means to solve the current energy crisis. However, developing an excellent photocatalyst with high light utilization and stability for hydrogen production remains a great challenge. In this work, CoS₂ nanoparticles as cocatalysts are growth on Zn₃In₂S₆ nanosheets with abundant sulfur vacancies for hydrogen evolution, and the optimal rate of hydrogen evolution is as high as 5.69 mmol h^-1 g^-1 in the absence of noble metal co-catalyst Pt, which is 2.87 and 2.29 times that of CoS₂/Zn₃In₂S₆ (with few sulfur vacancies) and Zn₃In₂S₆ (with rich sulfur vacancies). In addition, the hydrogen production rate of CoS₂/Zn₃In₂S₆ composite (with rich sulfur vacancies and 1 wt% Pt) is 24.17 mmol h^-1 g^-1, which is 4.25 and 1.90 times that of CoS₂/Zn₃In₂S₆ (with rich sulfur vacancies) and 1%-Pt/Zn₃In₂S₆ (with rich sulfur vacancies), respectively. The apparent quantum efficiency (AQE) of CoS₂/Zn₃In₂S₆ composite (with rich sulfur vacancies and 1 wt% Pt) reaches 66.20% under light irradiation at the wavelength of 370 nm. Above all indicate that dual cocatalysts (CoS₂ and Pt) and sulfur vacancies can promote the efficient hydrogen evolution activity of Zn₃In₂S₆ nanosheets. This work will provide new ideas and insights for the development of photocatalytic hydrogen production technology.

Formic acid assisted fabrication of Oxygen-doped Rod-like carbon nitride with improved photocatalytic hydrogen evolution

Rod-like carbon nitrides synthesized by calcinating supramolecular precursors prepared from acid (or alkali) and melamine have attracted great attention because they have large surface area and abundant accessible active sites. However, they are highly inefficient in separating charges, which limits their photocatalytic activity. Here, we prepared porous, rod-shaped carbon nitrides doped with oxygen by calcinating the precursors prepared from melamine and formic acid. The porous O-doped g-C₃N₄ nanorods have a large surface area of 81.4 m² g^-1. In particular, the oxygen doped into the catalyst enables it to have high efficiency in utilizing light in a range of 420-600 nm, and significantly improves its ability to separate photogenerated carriers. Under light irradiation (λ ≥ 420 nm), the prepared catalyst exhibits high photocatalytic activity with a hydrogen production rate of 12,766 μmol g^-1h^-1, which is 18.3 times that of pure carbon nitride. This research provides a novel way of preparing highly active non-metallic photocatalysts.

Review on 2D Molybdenum Diselenide (MoSe2) and Its Hybrids for Green Hydrogen (H2) Generation Applications

Hydrogen (H₂) is a green and economical substitute to traditional fossil fuels due to zero carbon emissions. Water splitting technology is developing at a rapid speed to sustainably generate H₂ through electro- and photolysis of water without the harmful emissions associated with steam methane reforming. Development of efficient catalysts for the hydrogen evolution reaction (HER) is pertinent for economical green H₂ generation. In this regard, 2D transition metal dichalcogenides (TMDCs) are considered to be excellent alternatives to noble metal catalysts. Among other TMDCs, 2D MoSe₂ is preferred due to the low Gibbs free energy for hydrogen adsorption, good electrical conductivity, and more metallic nature. Moreover, the physicochemical and electronic properties of MoSe₂ can be easily tailored to suit HER application by simple synthetic strategies. Herein, we comprehensively review the application of 2D MoSe₂ in the electrocatalytic HER, focusing on recent advancements in the modulation of the MoSe₂ properties through nanostructure design, phase transformation, defect engineering, doping, and formation of heterostructures. We also discuss the role of 2D MoSe₂ as a cocatalyst in the photocatalytic HER. The article concludes with a synopsis of current progress and prospective future trends.

A cation exchange strategy to construct Rod-shell CdS/Cu2S nanostructures for broad spectrum photocatalytic hydrogen production

Herein, Cu₂S as the outer shell is grown on CdS nanorods (NRs) to construct rod-shell nanostructures (CdS/Cu₂S) by a rapid, scalable and facile cation exchange reaction. The CdS NRs are firstly synthesized by a hydrothermal route, in which thiourea as the precursor of sulfur and ethylenediamine (EDA) as the solvent. And then, the outer shells of CdS NRs are successfully exchanged by Cu₂S via a cation exchange reaction. The obtained CdS/Cu₂S rod-shell NRs exhibit much enhanced activity of hydrogen production (640.95 μmol h^-1 g^-1) in comparison with pure CdS NRs (74.1 μmol h^-1 g^-1) and pure Cu₂S NRs (0 μmol h^-1 g^-1). The enhanced photocatalytic activity of CdS/Cu₂S rod-shell NRs owns to the following points: i) the photogenerated electrons generated by CdS quickly migrate to Cu₂S without any barrier due to rod-shell structure by the in-situ cation exchange reaction, a decreased carrier recombination is achieved; ii) Cu₂S as outer shells broaden the light absorption range of CdS/Cu₂S rod-shell NRs into visible or even NIR light, which can produce more electrons and holes. This work inspires people to further study the rod-shell structured photocatalyst through the cation exchange strategy to further solar energy conversion.

The fabrication of graphitic carbon nitride hollow nanocages with semi-metal 1T' phase molybdenum disulfide as co-catalysts for excellent photocatalytic nitrogen fixation

Improving the efficiency of photogenerated carrier separation is essential for photocatalytic N₂ fixation. Herein, the 2D semi-metal 1T'-MoS₂ was uniformly distributed in g-C₃N₄ nanocages (CNNCs) by a hydrothermal method, and the 1T'-MoS₂/CNNC composite was obtained. 1T'-MoS₂ as a co-catalyst can promote the transfer of electrons, improve the separation efficiency of photogenerated carriers, and also increase the number of effective active sites. In addition, the unique nanocage morphology of CNNCs is conducive to the scattering and reflection of incident light and improves the light absorption capacity. Therefore, the optimized 1T'-MoS₂/CNNC composite (5 wt%) shows a significantly improved photocatalytic N₂ fixation rate (9.8 mmol L^-1 h^-1 g^-1) and good stability, which is significantly higher than pure CNNCs (2.9 mmol L^-1 h^-1 g^-1), Pt/CNNC (8.2 mmol L^-1 h^-1 g^-1) and Pt/g-C₃N₄ nanosheet (CNNS, 6.3 mmol L^-1 h^-1 g^-1). This work guides guidance for the design of green and efficient N₂ fixation photocatalysts.

Octahedral Pt-MOF with Au deposition for plasmonic effect and Schottky junction enhanced hydrogenothermal therapy of rheumatoid arthritis

Hydrogen (H₂) therapy is a novel and rapidly developing strategy utilized to treat inflammatory diseases. However, the therapeutic efficacy of H₂ is largely limited with on-target off-synovium toxic effect, nonpolarity and low solubility. Herein, an intelligent H₂ nanogenerator based upon the metal-organic framework (MOF) loaded with polydopamine and Perovskite quantum dots is constructed for the actualization of hydrogenothermal therapy. The biodegradable polydopamine with excellent photothermal conversion efficiencies is used for photothermal therapy (PTT) of rheumatoid arthritis (RA) and perovskite quantum dots (QDs) with unique photophysical properties are used as fluorescent signals for positioning Pt-MOF@Au@QDs/PDA nanoparticles. In addition, the Pt-MOF@Au@QDs/PDA catalyzer combines Au's surface plasmon resonance excitation with Pt-MOF Schottky junction, and exhibits extremely efficient photocatalytic H₂ production under visible light irradiation. The Pt-MOF@Au@QDs/PDA achieves the aggregation of rheumatoid synovial cells by the extravasation through “ELVIS” effect (extravasation through leaky vasculature and subsequent inflammatory cell-mediated sequestration) and extremely efficient photocatalytic H₂ production. By combining PTT and H₂ therapy, the Pt-MOF@Au@QDs/PDA relieves the oxidative stress of RA, and shows significant improvement in joint damage and inhibition of the overall arthritis severity of collagen-induced RA mouse models. Therefore, the Pt-MOF@Au@QDs/PDA shows great potential in the treatment of RA and further clinical transformation.

Engineering a NiAl-LDH/CoSx S-Scheme heterojunction for enhanced photocatalytic hydrogen evolution

The use of semiconductors to construct heterojunctions to suppress the rapid recombination of photogenerated charges and holes is considered to be an effective way to improve the efficiency of photocatalytic hydrogen evolution. Herein, cobalt sulfide (CoS_x) nanoparticles are cultivated in situ in the folds of three-dimensional flower-like nickel-aluminium layered double hydroxides (NiAl-LDHs) using a facile solvothermal method. The hydrogen production rate of the binary CoS_x/NiAl-LDH heterojunction reaches 3678.59 μmol/g/h, which is 83.74 and 22 times the rates of CoS_x and NiAl-LDH, respectively. The unique three-dimensional structure of NiAl-LDH facilitates the growth of CoS_x and shortens the transfer pathway of photogenerated electrons. More importantly, the built-in electric field formed at the interface and the S-type charge transport mechanism caused by the bending of the energy band enhance not only charge separation but also maintain the strong oxidation ability of the holes. In this study, the newly designed S-scheme heterojunction offers a new strategy for enhancing photocatalytic water splitting.

Insights into the Operation of Noble-Metal-Free Cocatalyst 1T-WS2 -Decorated Zn0.5 Cd0.5 S for Enhanced Photocatalytic Hydrogen Evolution

Due to inefficient charge separation and low surface catalytic conversion efficiencies, cocatalysts are required for achieving photocatalytic hydrogen evolution. Being a noble-metal-free cocatalyst, metallic 1T-WS₂ with excellent conductivity can function for this reaction. Herein, 1T-WS₂ /Zn_0.5 Cd_0.5 S is constructed via a simple and feasible grinding approach. The composite containing 7.5 % 1T-WS₂ in 1T-WS₂ /Zn_0.5 Cd_0.5 S achieves a hydrogen evolution rate of 61.65 mmol g^-1  h^-1 and an external quantum efficiency of 8.04 % at 420 nm, which is 37 times that of bare Zn_0.5 Cd_0.5 S (1.67 mmol g^-1  h^-1 ). The electrical conductivity of metallic 1T-WS₂ reduces the transfer impedance at the interface and thus accelerates the non-radiative energy transfer and electron transport rate. The different Fermi levels of 1T-WS₂ and Zn_0.5 Cd_0.5 S form a Schottky junction, which promotes the transfer of photogenerated electrons from Zn_0.5 Cd_0.5 S to 1T-WS₂ . More importantly, the close interface contact between 1T-WS₂ and Zn_0.5 Cd_0.5 S results in strong electron interactions, which is conducive to the spatial separation of photogenerated electrons and holes. This work will further expand the application of 1T-WS₂ in the photocatalytic hydrogen evolution process.

Phosphorous-doped 1T-MoS2 decorated nitrogen-doped g-C3N4 nanosheets for enhanced photocatalytic nitrogen fixation

Herein, we report that the phosphorous-doped 1 T-MoS₂ as co-catalyst decorated nitrogen-doped g-C₃N₄ nanosheets (P-1 T-MoS₂@N-g-C₃N₄) are prepared by the hydrothermal and annealing process. The obtained P-1 T-MoS₂@N-g-C₃N₄ composite presents an enhanced photocatalytic N₂ reduction rate of 689.76 μmol L^-1 g^-1h^-1 in deionized water without sacrificial agent under simulated sunlight irradiation, which is higher than that of pure g-C₃N₄ (265.62 μmol L^-1 g^-1h^-1), 1 T-MoS₂@g-C₃N₄ (415.57 μmol L^-1 g^-1h^-1), 1 T-MoS₂@N doped g-C₃N₄ (469.84 μmol L^-1 g^-1h^-1), and P doped 1 T-MoS₂@g-C₃N₄ (531.24 μmol L^-1 g^-1h^-1). In addition, compared with pure g-C₃N₄ NSs (2.64 mmol L^-1 g^-1h^-1), 1 T-MoS₂@g-C₃N₄ (4.98 mmol L^-1 g^-1h^-1), 1 T-MoS₂@N doped g-C₃N₄ (6.21 mmol L^-1 g^-1h^-1), and P doped 1 T-MoS₂@g-C₃N₄ (9.78 mmol L^-1 g^-1h^-1), P-1 T-MoS₂@N-g-C₃N₄ (11.12 mmol L^-1 g^-1h^-1) composite also shows a significant improvement for photocatalytic N₂ fixation efficiency in the sacrificial agent (methanol). The improved photocatalytic activity of P-1 T-MoS₂@N-g-C₃N₄ composite is ascribed to the following advantages: 1) Compared to pure g-C₃N₄, P-1 T-MoS₂@N-g-C₃N₄ composite shows higher light absorption capacity, which can improve the utilization rate of the catalyst to light; 2) The P doping intercalation strategy can promote the conversion of 1 T phase MoS₂, which in turn in favor of photogenerated electron transfer and reduce the recombination rate of carriers; 3) A large number of active sites on the edge of 1 T-MoS₂ and the existence of N doping in g-C₃N₄ contribute to photocatalytic N₂ fixation.

Carbon nitride used as a reactive template to prepare mesoporous molybdenum sulfide and nitride

Carbon nitride C₃N₄ has been used as a sacrificial template to prepare inorganic materials with hierarchical pore structure. C₃N₄ impregnated with ammonium heptamolybdate was treated in reactive gas mixtures (H₂S/H₂ or NH₃/H₂). This approach allowed mesoporous molybdenum sulfide and molybdenum nitride materials to be obtained that replicate the morphology of the C₃N₄ template. Advantageous catalytic properties have been demonstrated in the thiophene hydrodesulfurization (HDS) and electrochemical hydrogen evolution reaction (HER). The highest rates in both reactions were observed for partially sulfidized Mo₂N solid.