Visible light-driven hydrogen evolution by using mesoporous carbon nitride-metal ferrite (MFe2O4/mpg-CN; M: Mn,Fe, Co and Ni) nanocomposites as catalysts

Four different earth-abundant ferrite nanoparticles (MFe₂O₄, M: Mn, Fe, Co, Ni) with spinel structure were synthesized by using the surfactant-assisted high temperature thermal decomposition methods and then assembled on mesoporous graphitic carbon nitride (mpg-CN) to study their comparative catalysis for the photocatalytic hydrogen evolution reaction (HER) in the presence of Eosin-Y (EY) as a visible-light sensitizer. The yielded monodisperse ferrite nanoparticles and the MFe₂O₄/mpg-CN nanocomposites were characterized by using advanced analytical techniques including TEM, XPS, XRD, ICP-MS, and UV–Vis DRS. All the tested MFe₂O₄/mpg-CN nanocomposites provided the better catalytic performance than that of pristine mpg-CN in the photocatalytic HER and their photocatalytic HER rates are in the order of NiFe₂O₄/mpg-CN > CoFe₂O₄/mpg-CN > MnFe₂O₄/mpg-CN > Fe₃O₄/mpg-CN > mpg-CN. Among the tested MFe₂O₄/mpg-CN nanocomposites, NiFe₂O₄/mpg-CN nanocomposite provided the highest hydrogen generation of 14.56 mmol g⁻¹, which is 6.75 times greater than that of pristine mpg-CN and, using EY as a visible light sensitizer and triethanolamine (TEOA) as a sacrificial reagent. According to the optical properties and energy band positions of the nanocomposites, a plausible mechanism for the NiFe₂O₄/mpg-CN catalyzed HER is proposed to give insights on the highest activity of NiFe₂O₄/mpg-CN nanocomposites among others.     

A facile synthesis of metal ferrites (MFe2O4, M = Co,Ni, Zn,Cu) as effective electrocatalysts toward electrochemical hydrogen evolution reaction

Developing low-cost, stable, and robust electrocatalysts for hydrogen evolution reaction (HER) is highly desirable for large-scale application. In this study, a highly efficient electrocatalysts of metal ferrites (MFe₂O₄, M = Co, Ni, Zn, Cu) with superior activity and durability are successfully fabricated on copper substrate through a facile co-precipitation method followed by doctor-blading deposition. The electrocatalytic performance of CoFe₂O₄, NiFe₂O₄, ZnFe₂O₄ and CuFe₂O₄ electrodes for hydrogen evolution reaction is studied in alkaline media using polarization curves and electrochemical impedance spectroscopy (EIS). Among them, CoFe₂O₄ presented the best electrocatalytic activities for HER with extremely low overpotentials of 270 mV (vs. RHE) at a current density of 10 mA cm^?2 in 1 M KOH. The electrocatalytic activity of MFe₂O₄ (M = Co, Ni, Zn, Cu) for HER to generate current density of 10 mA cm^?2 with low overpotential followed the order of CoFe₂O₄ > CuFe₂O₄ > NiFe₂O₄ > ZnFe₂O₄. The highly improved HER performance of CoFe₂O₄ is mainly due to a large number of exposed active sites, high electrical conductivity and low apparent activation energy, which are confirmed by a remarkable electrochemically active surface area (ECSA = 53.17 cm²), Nyquist plots analysis and Arrhenius plots measurement, respectively. Moreover, the CoFe₂O₄ electrode showed outstanding electrocatalytic stability even after 1000 cyclic voltametry tests. These results provide a promising avenue for developing cost-effective and high-efficiency electrocatalysts based on earth-abundant transition metal ferrite as advanced electrodes for large-scale energy conversion processes.     

Catalyst support effect on ammonia decomposition over Ni/MgAl2O4 towards hydrogen production

Ammonia is a prospective fuel for hydrogen storage and production, but its application is limited by the high cost of the catalysts (Ru, etc.) to decompose NH₃. Decomposing ammonia using non-precious Ni as catalysts can therefore improve its prospects to produce hydrogen. This work proposes several Ni/MgAl₂O₄ with the support properties tuned and investigates the support effect on the catalytic performance. Ni/MgAl₂O₄-LDH shows high NH₃ conversion (～88.7%) and H₂ production rate (～1782.6 mmol g^?1 h^?1) at 30,000 L. kg^?1 h^?1 and 600 °C, which is 1.68 times as large as that of Ni/MgAl₂O₄-MM. The performance remains stable over 30 h. The characterizations manifest that the high specific surface area of Ni/MgAl₂O₄-LDH can introduce highly dispersed Ni on the surface. Kinetics analysis implies promoted NH₃ decomposition reaction and alleviated H₂ poisoning for Ni/MgAl₂O₄-LDH. A roughly linear relationship is obtained by fitting the curves of dispersed Ni on the surface vs the reaction orders regarding H₂ and NH₃. This indicates that enhanced NH₃ decomposition performance can be ascribed to the strengthened NH₃ decomposition reaction and weakened H₂ poisoning by the highly dispersed Ni on the MgAl₂O₄-LDH surface. This work provides an opportunity to develop highly active and cost-effective catalysts to produce hydrogen via NH₃ decomposition.     

CoFe2O4@methyl cellulose core-shell nanostructure and their hybrids with functionalized graphene aerogel for high performance asymmetric supercapacitor

Recently, the use of asymmetric supercapacitors (ASC) has attracted much attention due to their optimum storage of energy and a high range of voltage. Here, we have indicated the design and fabrication of a unique ASC based on metal-spinel core-shell nanocomposite (CoFe₂O₄@MC) as a positive electrode and a p-phenylenediamine (PPDA)-graphene aerogel composite (AP) as a negative electrode in aqueous KOH electrolyte solution. The CoFe₂O₄@MC nanocomposite was prepared by the chemical deposition method. The AP was also effortlessly organized using the hydrothermal method. Considering the incorporation of methylcellulose carbohydrate polymer (MC) into the CoFe₂O₄ nanomaterial and consequently having a porous structure, a specific capacitance of 433.3 F g^?1 was obtained at the current density of 1 A g^?1 with the configuration of three electrodes. The CoFe₂O₄@MC//AP-ASC operates in the voltage range up to 2.3 V and provides a specific capacitance of 99 in 1 A g^?1. It presents an impressive energy density and power density of ~73 W h Kg^?1 and 1056 W kg^?1, respectively which prove its quality. The most important feature seems to be good cycling stability and capacity retention of 89% after 2000 cycles. These splendid outcomes show that CoFe₂O₄@MC nanocomposite possibly seems to be a satisfying choice for the next generation of devices with the capability of energy storage.     

Usage of natural leaf as a bio-template to inorganic leaf: Leaf structure black TiO2/CdS heterostructure for efficient photocatalytic hydrogen evolution

Herein, first time we report that highly efficient sheet like leaf structure black TiO₂ (LBT)/CdS hetero-structure (LBT/CdS). Photocatalytic hydrogen generation was tested for different material in the presence of visible light (λ ≥ 420 nm) irradiation. 10 wt% of LBT loaded CdS (10LBT/CdS) exhibit maximum photocatalytic H₂ generation rate about ~10 mmol h^?1 g^?1, which is higher than the H₂ production results of pristine CdS (6 mmol h^?1 g^?1) and leaf black-TiO₂ 5.1 mmol h^?1 g^?1) respectively. Detailed characterization revealed that higher photocatalytic activity was mainly attributed to enormous spatial transfer efficiency of photo-excited charge carriers at the hetero-junction between LBT and CdS in LBT/CdS. Additionally, introduction of 2D black leaf-TiO₂ to CdS act as a mat and enhances the mobility of charge carriers. In addition, presence of anatase-rutile surface-phase junction in leaf TiO₂ (synthesized at 750 °C) and more edges, steps and corners on the CdS synergistically increased the photocatalytic H₂ generation and photocurrent response of LBT/CdS.     

Interfacially bonded Co-N boosts photocatalytic H2 evolution in a closely coupled CoFe2O4/g-C3N4 composite structure

To create hybrid composites for highly effective photocatalytic hydrogen evolution reactions, the photogenerated charge separation efficiency at the hybrid interface and the surface reaction kinetics at the reactive sites are key factors. In this work, CoFe hydroxide nanosheets prepared by dealloying were first mixed with graphitic carbon nitride (g-C₃N₄) to synthesize a CoFe₂O₄/g-C₃N₄ composite with strong Co-N bonds at the interface by a simple hydrothermal method. It was found that the presence of Co-N bonds between the components in the composites enhances the separation and transfer by photogenerated carriers at the composite interface. Furthermore, the presence of Co-N bonds enhanced the synergistic effect of the hybrid, which significantly boosts their photocatalytic performance in comparison to their counterparts. Under full-spectrum light, the composite photocatalyst has a greater efficiency of photocatalytic water H₂ evolution (6.793 mmol/g⁻¹·h⁻¹) and exceptional stability when compared to pure g-C₃N₄ (0.236 mmol/g⁻¹·h⁻¹) and CoFe₂O₄ (0.088 mmol/g⁻¹·h⁻¹). Under visible irradiation, the photocatalytic activity of the composite (0.556 mmol/g⁻¹·h⁻¹) for H₂ evolution increased by factors of 28.37 and 75.8 when compared to pure g-C₃N₄ and CoFe₂O₄, respectively.     

Rational design of plasmonic Ag@CoFe2O4/g-C3N4 p-n heterojunction photocatalysts for efficient overall water splitting

Highly efficient and direct photocatalytic H₂ evolution from water via water splitting without using sacrificial reagents is a challenging approach to convert solar energy into renewable and storable chemical energy. Herein, by amalgamating the architecture recommendations and energy band engineering principles into the design formulation, a novel Ag@CoFe₂O₄/g-C₃N₄ plasmonic p-n heterojunction photocatalytic system is designed and constructed for the first time. The Ag@CoFe₂O₄/g-C₃N₄ photocatalyst so designed, under the illumination of the visible-light (λ > 420 nm), produced H₂ and O₂ in 2:1 stoichiometric amount at the rates of 335 μmol h^?1 and 186 μmol h^?1, respectively, with an apparent quantum yield reaching 3.35% at 420 nm, demonstrating that Ag@CoFe₂O₄ dimer colloids are responsible for oxidation and g-C₃N₄ for reduction. Moreover, in the presence of triethanolamine, the apparent quantum yield achieved by Ag@CoFe₂O₄/g-C₃N₄ is 16.47% with hydrogen produced at the rate 3.5 times higher than the CoFe₂O₄/g-C₃N₄ heterojunction photocatalyst with AQY of 5.49%. The combination of Ag plasmonic effect and internal electric field established at the interface of p-type CoFe₂O₄ and n-type g-C₃N₄ boosts the separation efficiency of photoexcitons from CoFe₂O₄ to g-C₃N₄, extending the visible-light absorption capacity of the systems. The generation of optimum amount of defects like oxygen vacancies at the p-n heterojunction interface due to the structural distortion of CoFe₂O₄ also plays a prominent photocatalytic enhancement by providing active sites for the adsorption of water molecules for the light driven catalytic reactions. Our work introduces a potential avenue to design efficient photocatalysts by constructing several other suitable p-n heterojunction semiconductor photocatalysts toward practical application in solar energy conversion.     

Novel 0D/1D ZnBi2O4/ZnO S-scheme photocatalyst for hydrogen production and BPA removal

Developing interfacial connections is one of the breakthrough strategies to improve the photocatalytic activity. Herein, ZnBi₂O₄ nanoparticles-ZnO nanorods heterojunction was successfully synthesized and used, as a dual-function photocatalyst, for photocatalytic degradation of Bisphenol A and hydrogen production with improved photocatalytic activity under simulated sunlight irradiation. The highest H₂ production (3.44 mmol g^?1 h^?1) was obtained for ZnO-20 wt% ZnBi₂O₄ sample, which is around 12.7 times higher than pure ZnO. According to the HRTEM result, the intimate interfacial connections are formed between ZnO and ZnBi₂O₄ which could act as trapping centers for charge carriers and results in the boosted photocatalytic activity. Further, a high aspect ratio of 1D ZnO nanorods and small size of 0D ZnBi₂O₄ nanoparticles (~10 nm) increases the number of interfacial contacts and thus the charge carriers’ recombination was suppressed more efficiently. Based on the trapping experiments, ESR and Mott-Schottky analysis, ZnBi₂O₄–ZnO hybrid photocatalyst followed the S-scheme charge transfer mechanism.     

Non-precious metal MoO2 co-catalysts efficiently enhance hydrogen production of ZnIn2S4 under visible light

Photogenerated electron-hole separation and transfer and band gap modulation are the main reasons for the performance of semiconductor catalysts. These problems can be effectively solved by the proper use of co-catalysts. However, the current co-catalysts are generally noble metal co-catalysts, which cannot be used industrially because of their high cost. Therefore, it is important to use non-noble metal co-catalyst to solve these problems. In this study, MoO₂ with localized surface plasmon resonance (LSPR) effect loaded onto ZnIn₂S₄ (ZIS) by primary hydrothermal method and structured to form type II heterojunctions. The formation of the heterojunctions not only tunes the band gap to improve the light absorption intensity, but also reduces the charge transfer resistance and promotes electron-hole directed movement to improve the electron-hole separation efficiency. The tuning of the band gap and the increase in the electron-hole separation rate lead to improved performance of all ZIS/MoO₂ heterojunctions under visible light (λ ≥ 420 nm). Among them, ZIS/MoO₂-4% has the best photocatalytic performance of 2.757 mmol g^?1 h^?1, which is 3.75 times higher than that of pure ZIS (0.736 mmol g^?1 h^?1). This study provides a new strategy for the preparation of high performance catalysts without precious metals.     

Enhanced photocatalytic performance of NiFe2O4 nanoparticle spinel for hydrogen production

The spinel NiFe₂O₄, prepared from nitrates precursors, was characterized by thermal analyses, X-Ray Diffraction, UV-Vis diffuse reflectance, Scanning electron microscopy, X-Ray Fluorescence spectrometry, X-ray photoelectron spectroscopy and photo-electrochemistry measurements. The X-ray diffrcation analysis of the powder indicates a cubic phase with a lattice constant of 8.327(8) Å and crystallite size of 19 nm. The X-Ray Fluorescence spectrometry indicates a stoichiometry, very close to NiFe₂O₄ catalyst calcined at 900 °C The X-ray photoelectron spectroscopy analysis confirmed the valences and crystallographic sites of the transition elements. The direct optical gap of NiFe₂O₄ (1.78 eV), due to the crystal field splitting of the 3d orbital in the octahedral site, is well suited for the solar spectrum and attractive for photo-electrochemical H₂ production. The flat band potential (E_fb = 0.47 V_SCE) was obtained from the capacitance-potential (C^?2 - E) characteristic in NaOH (0.1 M) electrolyte. A conduction band of ?1.11 V_SCE, more cathodic than the H₂ level (?0.8 V_SCE), enabled the use of NiFe₂O₄ for the water reduction into hydrogen. The H₂ evolution rate of 46.5 μmol g^?1 min^?1 was obtained under optimal conditions (1 mg of catalyst/mL, NaOH and 50 °C) in the presence of SO₃^2? (10^?3 M) as hole scavenger under visible light flux of 23 mW cm^?2. A deactivation effect of only 1% was obtained.     

High-temperature sulfurized synthesis of MnxCd1-xS composites for enhancing solar-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this paper, Mn_xCd_1-xS composites were in-situ fabricated via the high-temperature sulfurization to enhance the solar-light photocatalytic capacity of H₂ evolution. Benefiting from the S defects and junction interface between MnS and CdS, Mn_xCd_1-xS composites exhibited the better H₂ evolution rate than pure MnS. The H₂ evolution rate of optimal Mn_0.5Cd_0.5S with a Mn(II) content of 22.52% and a Mn/Cd mole ratio of 0.95:1 was 9.27 mmol g^?1 h^?1, which was 35.65 and 2.38 times higher than pure MnS (0.26 mmol g^?1 h^?1) and CdS (3.89 mmol g^?1 h^?1), respectively. In addition, H₂ evolution capacity of Mn_0.5Cd_0.5S decreased from 44.83 to 41.66 mmol g^?1 after three cycles. Mn_0.5Cd_0.5S prepared via the high-temperature sulfurization was thus a potential material for solar-light induced H₂ generation.     

An efficient ternary Mn0.2Cd0.8S/MoS2/Co3O4 heterojunction for visible-light-driven photocatalytic H2 evolution

An efficient ternary Mn_0.2Cd_0.8S/MoS₂/Co₃O₄ heterojunction was prepared and displayed excellent photocatalytic performance. The ternary Mn_0.2Cd_0.8S/MoS₂/Co₃O₄ heterojunction with 0.62 wt% of MoS₂ and 1.51 wt% of Co₃O₄ achieved the highest H₂ evolution activity (16.45 mmol g⁻¹ h⁻¹), which was well above Mn_0.2Cd_0.8S (2.72 mmol g⁻¹ h⁻¹). The improved H₂ evolution activity was ascribed to the synergistic effect of the Mn_0.2Cd_0.8S/Co₃O₄ p–n heterojunction and the modification of MoS₂ as a co-catalyst. This work can offer a new perspective for the application of Mn_xCd_1−xS-based ternary heterojunction towards solar energy conversion.     

MoS2/CdS nanosheet-on-nanorod: An efficient photocatalyst for H2 generation from lactic acid decomposition

The CdS shows high selectivity on H₂ for photocatalytic lactic acid decomposition. However, the low efficiency caused by ultrafast charge recombination was not well addressed. Herein, MoS₂/CdS nanoheterostructure with intimate contact interface was synthesized in-situ and used as an efficient photocatalyst for H₂ generation. The optimum H₂ generation rate of MoS₂/CdS is 45.20 mmol g^?1 h^?1 which significantly boosts the activity of CdS (0.27 mmol g^?1 h^?1) by more than 167 folds. Band alignment of MoS₂ and CdS promoting charge transfer and separation contributes to the enhanced catalytic activity, which was well verified by multiple characterization approaches.     

An excellent H2 production photoelectrode based on mixed valence Sn3O4 nanoflake arrays treated by H2O2 hydrothermal reaction

To design nanostructured photoelectrodes with unique morphology and suitable band structure is a crucial step for potential photoelectrochemical application. For above purpose, the compact Sn₃O₄ nanoflakes with the smooth surface have been directly grown on carbon paper substrate by a simple hydrothermal method. It is found that the molar ratio of Sn²⁺ and Sn⁴⁺ ions in Sn₃O₄ nanoflakes can be modulated by the subsequent H₂O₂-assisted hydrothermal treatment. The effect of different molar ratio on the energy band has been investigated systematically, together with the evolution of the surface morphology of nanoflakes. Finally, a highly efficient photoelectrode based on Sn₃O₄ nanoflake has been prepared by the H₂O₂-assisted hydrothermal process, which is of larger active surface area and suitable band structure, and therefore exhibits the excellent photocurrent response and photocatalytic performance for H₂ production. The photoelectrode based on Sn₃O₄ nanoflake displays enhanced photocurrent with 40 μA cm^?1 at a basis of 0 V and higher H₂ generation rate with 1.43 × 10⁴ μmol h^?1 g^?1, much better than those of the original sample. Such superior performance can be probably attributed to the combined effect of unique porous nanoflake-structured, higher active surface area and suitable band structure.     

Fe2O3/spinel NiFe2O4 heterojunctions in-situ wrapped by one-dimensional porous carbon nanofibers for boosting oxygen evolution/reduction reactions

One-dimensional (1D) nanofiber structure of electrocatalyst has attracted increasing attention in oxygen evolution/reduction reactions (OER/ORR) owing to its unique structural properties. Here, MIL-53(Fe) and Ni(NO₃)₂·6H₂O are incorporated into the electrospun carbon nanofibers (CNFs) to prepare the nickel-iron spinel-based catalysts (Fe₂O₃/NiFe₂O₄@CNFs) with 1D and porous structure. The marked Fe₂O₃/NiFe₂O₄@CNFs-2 catalyst has a tube diameter of approximately 300 nm, a high surface area of 282.4 m² g^?1 and a hydrophilic surface (contact angle of 16.5°), which obtains a promising bifunctional activity with ΔE = 0.74 V (E_1/2 = 0.84 V (ORR) and E_j10 = 1.58 V (OER)) in alkaline media. Fe₂O₃/NiFe₂O₄@CNFs-2 has a higher catalytic stability (93.35%) than Pt/C (89.36%) for 30,000 s tests via an efficient 4e^? ORR pathway. For OER, Fe₂O₃/NiFe₂O₄@CNFs-2 obtains a low overpotential of 350 mV and a high Faraday efficiency of 92.7%. NiFe₂O₄ (Ni²⁺ in tetrahedral position) relies on its variable valence states (NiOOH and/or FeOOH) to obtain good catalytic activity and stability for OER, while CNFs wrap/protect the active components (Fe–N and graphic N) in the carbon skeleton to effectively improve the charge transfer (conductivity), activity and stability for ORR. Porous 1D nanofiber structure provides abundant smooth pathways for mass transfer. It indicates that the bimetallic active substances can promote bifunctional activity by synergistically changing the oxide/spinel interface structure.     

Facile one pot sonochemical synthesis of CoFe2O4/MWCNTs hybrids with well-dispersed MWCNTs for asymmetric hybrid supercapacitor applications

In this study, a facile sonochemical strategy is used for the fabrication of CoFe₂O₄/MWCNTs hybrids as an electrode material for supercapacitor applications. FE-SEM image demonstrates the uniformly well-distributed MWCNTs as well as porous structures in the prepared CoFe₂O₄/MWCNTs hybrids, suggesting 3D network formation of conductive pathway, which can enhance the charge and mass transport properties between the electrodes and electrolytes during the faradic redox reactions. The as-fabricated CoFe₂O₄/MWCNTs hybrids with the MWCNTs concentration of 15 mg (CFC15) delivers maximum specific capacitance of 390 F g⁻¹ at a current density of 1 mA cm⁻², excellent rate capability (275 F g⁻¹ at 10 mA cm⁻²), and outstanding cycling stability (86.9% capacitance retention after 2000 cycles at 3 mA cm⁻²). Furthermore, the electrochemical performance of the CFC15 is superior to those of pure CoFe₂O₄ and other CoFe₂O₄/MWCNTs hybrids (CFC5, CFC10 and CFC20), indicating well-dispersion MWCNTs and uniform porous structures. Also, as-fabricated asymmetric supercapacitor device using the CoFe₂O₄/MWCNTs hybrids as the positive electrode and activated carbon as the negative electrode materials shows the outstanding supercapacitive performance (high specific capacitance, superior cycling stability and good rate capability) for energy storage devices. It delivers a capacitance value of 81 F g⁻¹ at 3 mA cm⁻², ca. 92% retention of its initial capacitance value after 2000 charge-discharge cycles and excellent energy density (26.67 W h kg⁻¹) at high power density (~319 W kg⁻¹).     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).     

Efficient photocatalytic hydrogen evolution on amorphous MoSx-modified CdS/KTaO3 heterojunctions under visible light irradiation

Constructing heterostructures with efficient charge separation is a promising route to improve photocatalytic hydrogen production. In this paper, MoS_x/CdS/KTaO₃ ternary heterojunction photocatalysts were successfully prepared by a two-step method (hydrothermal method and photo deposition method), which improved the photocatalytic hydrogen evolution activity. The results show that the rate of hydrogen evolution for the optimized photocatalyst is 2.697 mmol g^?1·h^?1under visible light, which is 17 times and 2.6 times of the original CdS (0.159 mmol g^?1 h^?1) and the optimal CdS/KTaO₃(1.033 mmol g^?1 h^?1), respectively, and the ternary photocatalyst also shows good stability. The improvement on photocatalytic hydrogen evolution performance can be attributed to the formation of heterojunction between the prepared composite materials, which effectively promotes the separation and migration of photo-generated carriers. Amorphous MoS_x acts as an electron trap to capture photogenerated electrons, providing active sites for proton reduction. This provides beneficial enlightenment for hydrogen production by efficiently utilizing sunlight to decompose water.     

Insight into NiCo-based nanosheets modified MnS/Mn0·2Cd0·8S hybrids for enhanced visible-light photocatalytic H2 evolution

Bimetallic compounds nanocrystals exhibited great potential in catalysis due to the synergistic effects and encouraging performance. Herein, a series of NiCo-based nanosheets, including NiCo LDH/NiCo(OH)₂, NiCo, and NiCo₂O₄, have been developed to modify MnS/Mn_0·2Cd_0·8S (MMCS) nanoparticles for photocatalytic H₂ production under visible light (λ > 420 nm). The two-dimensional (2D) NiCo₂O₄ and NiCo were derived from the oxidation and reduction process of the as-prepared NiCo LDH/NiCo(OH)₂ nanosheets, respectively. MMCS nanoparticles were prepared using a one-pot solvothermal method and then integrated into three different NiCo-based nanosheets through a simple hybridization approach. Compared to pure MMCS, the resultant NiCo-based nanosheets/MMCS hybrids show dramatically improved visible-light photocatalytic activities. Moreover, among the three types of composites, NiCo₂O₄-MMCS (7%NiCo₂O₄-MMCS) displays the highest H₂ production rate of 3.31 mmol g^?1 h^?1 with the apparent quantum efficiency of 6.42% at 420 nm, approximately 22 and 5 times that of pure MMCS (0.15 mmol g^?1 h^?1) and Pt/MMCS (0.67 mmol g^?1 h^?1), respectively. The remarkably enhanced photocatalytic activities of the NiCo LDH/NiCo(OH)₂-MMCS, NiCo-MMCS, and NiCo₂O₄-MMCS are mainly ascribed to the formed type-II, Schottky, and p-n heterojunctions, respectively, which efficiently boost photogenerated charge carrier separation and migration. In this paper, we intensively investigate the roles of three different NiCo-based nanosheets in the Mn_xCd_1-xS-based system. This work provides an effective strategy to design and construct the innovative 2D bimetallic compounds-based catalysts for high-efficiency photocatalytic H₂ production.     

Well-designed NiS/CdS nanoparticles heterojunction for efficient visible-light photocatalytic H2 evolution

Heterojunction photocatalysts based on semiconducting nanoparticles show excellent performance in many photocatalytic reactions. In this study, 0D/0D heterojunction photocatalysts containing CdS and NiS nanoparticles (NPs) were successfully synthesized by a chemical precipitation method. The NiS NPs were grown in situ on CdS NPs, ensuring intimate contact between the semiconductors and improving the separation efficiency of hole-electron pairs. The obtained NiS/CdS composite delivered a photocatalytic H₂ evolution rate (7.49 mmol h^?1 g^?1), which was 39.42 times as high as that of pure CdS (0.19 mmol h^?1 g^?1). This study demonstrates the advantages of 0D/0D heterojunction photocatalysts for visible light-driven photocatalytic hydrogen production.