A novel photothermal-assisted FeNi2S4@Mn0.3C0.7S S-scheme heterojunction for enhanced photo-catalytic hydrogen evolution

In addition to the intrinsic driving force of photocatalysis, the external thermal field from the photothermal effect can provide additional energy to the photo-catalytic system to improve the photo-catalytic hydrogen-evolution (PHE) efficiency. Herein, based on the results of density functional theory, we designed and constructed a hollow core-shell FeNi2S4@Mn0.3Cd0.7S (NFS@MCS) S-scheme heterojunction with a photothermal effect, thereby realising a significant enhancement of the PHE performance due to the thermal effect, S-scheme heterojunction and hollow core-shell morphology. As a light collector and heat source, the hollow NFS could absorb and convert photons into heat, resulting in the increased local temperature of photocatalyst particles. Moreover, the S-scheme charge path at the interface not only improved the carrier separation efficiency but also retained a higher redox potential. All these are favourable to increase the PHE activity. The PHE tests show that 0.5 %-NFS@MCS exhibits the highest PHE rate of 17.11 mmol·g-1·h-1, 7.7 times that of MCS. Moreover, through a combination of theoretical calculation and experimental evidence, the PHE mechanism of the NFS@MCS system is discussed and clarified in-depth.

Construction of 2D/1D Cu7S4 nanosheets/Mn0.3Cd0.7S nanorods heterojunction for highly efficient photocatalytic hydrogen evolution

Developing cost-effective cocatalyst-modified photocatalytic systems with boosted carrier separation and rapid surface catalytic reaction is an ideal strategy for effectively converting solar energy into desired fuels. Herein, a series of Cu7S4/Mn0.3Cd0.7S hierarchical heterostructures are designed and fabricated to achieve efficient and robust photocatalytic H2 evolution by coupling one-dimensional (1D) Mn0.3Cd0.7S nanorods with two-dimensional (2D) Cu7S4 nanosheets through a facile sonochemical strategy. Benefiting from dimensionality and cocatalyst effects, the constructed 2D/1D Cu7S4/Mn0.3Cd0.7S heterojunction photocatalyst containing 1.5 wt% Cu7S4 displays excellent photostability and superior photocatalytic H2 evolution rate up to 914.3 μmol h-1, which is 4.43 and 2.22-folds increment relative to bare Mn0.3Cd0.7S and the 3 wt% Pt/Mn0.3Cd0.7S, respectively. The various characterization results reveal that the utilization of semimetallic Cu7S4 nanosheets as the cocatalyst to form a Schottky heterojunction can promote the light-harvesting capability, suppress charge carrier recombination, and provide sufficient reaction sites for hydrogen generation, thereby resulting in the dramatically improved photocatalytic performance. This work clarifies the role of Cu7S4 nanosheets as the robust and cost-effective cocatalyst in the photocatalytic reaction and opens a new horizon for designing other Cu7S4-based cocatalyst/semiconductor Schottky heterostructures for efficient solar-to-fuel conversion.

Bandgap engineering control bifunctional MnxCd1-xS photocatalysts selectively reforming xylose to C3 organic acids and efficient hydrogen production

The simultaneous reforming of biomass into high value-added chemicals and H2 production by water splitting in a green and environmentally clean way is a very challenging task. Herein, we demonstrate the design of bifunctional MnxCd1-xS photocatalyst with a controllable band gap by bandgap engineering. Bandgap engineering effectively regulates the oxidation and reduction capacity of materials. The design of photocatalysts with suitable conduction bands and valence bands makes the targeted conversion of xylose possible. Innovative conversion of xylose to glyceric acid, lactic acid, and propanoic acid. The optimized Mn0.7Cd0.3S catalyst showed excellent performance in the production of H2 (14.06 mmol·gcat-1·h-1, 29.9 times more than CdS and 351.5 times more than MnS), xylose conversion (90%), and C3 organic acid yield (59.2%) without cocatalyst and any scavengers under visible light irradiation. This work shows that a rational photocatalyst design can achieve efficient simultaneous production of high value-added chemicals and clean energy.

Synthesis of Hierarchical CdS/NiS Photocatalysts Using Ni-MOF-74 as Template for Efficient Ethanol Conversion and Hydrogen Production under Visible Light

The conversion of ethanol into high-valuable chemicals and H2 by photocatalytic process provides a sustainable approach to produce carbon-chain-prolonged chemicals and hydrogen energy. In this article, Ni-MOF-74 was added to fabricate the hierarchical CdS/NiS-N composites with an elevated specific surface area during the hydrothermal synthesis of CdS microsphere, and the Ni-MOF-74 facilitate the self-assemble growth of CdS and provide a source of Ni for the formation of NiS. The as-prepared photocatalyst was subjected to photocatalytic ethanol conversion, and the hierarchical composite material CdS/NiS-N (100) formed by adding 100 mg of Ni-MOF-74 exhibits the highest photocatalytic activity and stability in an ethanol aqueous solution with a water content of 10 %. Under visible light irradiation, the conversion rate of ethanol reached 15.2 % at the photocatalytic reaction of 5 h. The selectivity of 2,3-butanediol(2,3-BDO) was 25 %, and the selectivity of acetaldehyde(AA) was 63 %. Through various characterizations, it has been proven that a large specific surface area and the coupling interface between CdS and NiS are key factors in improving photocatalytic performance. This work provides an effective strategy for constructing photocatalysts with coupled cocatalysts/semiconductors and large specific surface areas.

Synthesis of hierarchical Cd-Ni-MOF micro/nanostructures and derived Cd-Ni-MOF/CdS/NiS hybrid photocatalysts for efficient photocatalytic hydrogen evolution

Hierarchical micro/nanostructures assembled from nanorods and nanosheets have become promising candidates for photocatalysis. In this work, a series of hierarchical Cd-Ni-MOF micro/nanostructures, assembled from nanosheets and nanorods, were fabricated via a two-step solvothermal process involving the partial replacement of Ni²⁺ with Cd²⁺ in the Ni-MOF-74 structure. Different morphologies were obtained by considering different volume ratios of DMF and ethanol as the solvent during synthesis. Hierarchical Cd-Ni-MOF-T/CdS/NiS hybrid micro/nanostructures were synthesized by Ni²⁺ and Cd²⁺ exchange of Cd-Ni-MOFs with S^2-. The as-prepared samples, which were composed of thin nanosheets alone, exhibited the best photocatalytic H₂ evolution rate of about 40.08 mmol g^-1 h^-1. The p-n junction between CdS and NiS was found to be beneficial for the migration of photogenerated electrons from the conduction band (CB) of NiS to the CB of CdS. The heterojunction between CdS and Cd-Ni-MOF-T further promoted the transfer of an electron from the CB of CdS to the CB of Cd-Ni-MOF-T. Thus, this study demonstrated that hierarchical Cd-Ni-MOF-T/CdS/NiS architectures have a large specific surface area, leading to significantly improved photocatalytic activity.

Composition-dependent activity of Mn-doping NiS2 nanosheets for boosting photocatalytic H2 evolution

Two-dimensional transition metal disulfides are excellent photocatalytic materials, which can be significantly improved by optimizing the composition and structure. Herein, Mn-doping NiS2 of (Ni1-xMnx)-S with various Ni/Mn molar ratios is proposed via a facile and low-cost solvothermal method. The optimal (Ni4/6Mn2/6)-S exhibits pinecone-like morphology composed of tiny nanosheets with enlarged active sites, which facilitates the separation of photoinduced electrons and holes, improves the electron transfer ability and conductivity, and enlarges the active sites compared with pure NiS2 and MnS. Also, the negative shift of the conduction band derived from Mott-Schottky plots and the empirical formula provides a high thermodynamic driving force for hydrogen catalytic reaction. (Ni4/6Mn2/6)-S performs an ultrahigh hydrogen evolution rate of 24.86 mmol g-1 h-1 under UV-visible light irradiation, which is 1.5 times higher than pure NiS2 (16.92 mmol g-1 h-1) and 2.3 times higher than pure MnS (10.69 mmol g-1 h-1). The outstanding repeatability of 86.7% retention and apparent quantum yield of 46.9% are also achieved. Therefore, this work offers a novel bimetallic sulfide of (Ni1-xMnx)-S to improve the conversion efficiency of solar energy to chemical energy for photocatalytic hydrogen production.

PVP influence on Mn-CdS for efficient photocatalytic activity

Wastewater treatment is the most serious problem in this upcoming era. A harmful effluent like organic dyes, heavy metals, acids from industries mixed in wastewater is deteriorating the environment. To get rid of these poisonous materials and to recycle wastewater for domestic purposes, there are many steps which included photocatalytic dye degradation. PVP assisted Mn-CdS nanoparticles was prepared by novel hydrothermal technique. The characteristic behavior of pure and PVP (1% and 2%) assisted Mn-CdS samples were studied by further analysis. The structural, optical, vibrational, morphological, chemical composition behavior of synthesized pristine and surfactant induced Mn-CdS nanoparticles were analyzed. UV-Vis spectra revealed the optical behavior of the prepared pure and PVP (1% and 2%) assisted Mn-CdS samples. The bandgap obtained was 2.2, 2.06 and 1.99 eV for pure Mn-CdS, 1% PVP-Mn-CdS and 2% PVP- Mn-CdS. The narrow bandgap is one of the advantage of the material. Mn-CdS, 1% PVP-(Mn-CdS) and 2% PVP- (Mn-CdS) morphology were further investigated by Scanning Electron Microscopic studies (SEM). The surfactant (PVP) was added to enhance the morphology development and decrease agglomeration on the surface and the SEM images revealed a clear evidence for enhancement of morphology in all three samples. 2% PVP-(Mn-CdS) sample showed a good development in morphology when compared with other two samples and the best sample showed formation of nanorods below the surface of nanoparticles. Further, Mn-CdS, 1% PVP-(Mn-CdS) and 2% PVP- (Mn-CdS) was indulged to investigate the cationic degradation. The photocatalytic activities of three samples were carried out with loading different amount of the catalysts and 30 mg catalyst 2% PVP- (Mn-CdS) loaded dye solution showed a considerable degradation of methylene blue dye. The 30 mg catalyst (2% PVP-Mn-CdS) showed 98% efficiency under visible light irradiation for about 2 h. The best candidate, 30 mg catalyst (2% PVP-Mn-CdS) investigated for its reusability. The catalyst showed almost 98% of efficiency up to three cycles which confirmed the level of potential of the sample. 2% PVP-(Mn-CdS) sample would be promising candidate in wastewater treatment. It can be further utilized for removing dyes from wastewater in wastewater remediation process.

Visible-light-driven two dimensional metal-organic framework modified manganese cadmium sulfide for efficient photocatalytic hydrogen evolution

The morphology modification and the construction of heterojunction of the photocatalyst are considered as the main means to significantly improve the performance of photocatalytic hydrogen evolution. In this study, Mn_0.2Cd_0.8S nanorods are successfully assembled on the surface of Ni-MOF-74 with flake morphology. Specifically, the Ni-S bond is constructed between Ni-MOF-74 and Mn_0.2Cd_0.8S, which provides a unique transfer channel for photo-induced carriers. Meanwhile, the electrons in the conduction band of Mn_0.2Cd_0.8S can be injected into the conduction band of Ni-MOF-74 quickly due to the potential energy difference between the two. This shows that the recombination of photogenerated carriers in Mn_0.2Cd_0.8S can be greatly inhibited. Fluorescence spectroscopy and electrochemical characterization reveal that the composite catalyst has the longest carrier lifetime, the fastest charge transfer rate and the lowest overpotential compared with the Mn_0.2Cd_0.8S and Ni-MOF-74. The optimal hydrogen production rate of the composite can reach 7.104 mmol g^-1h^-1, which is 6.96 times that of Mn_0.2Cd_0.8S. This work provides a novel strategy for the modification of MnCdS-based photocatalysts by metal-organic framework materials.

Cauliflower-like Mn0.2Cd0.8S decorated with ReS2 nanosheets for boosting photocatalytic H2 evolution activity

A novel ReS2/Mn0.2Cd0.8S composite was fabricated and exhibited enhanced H2 evolution activity due to the modification of cauliflower-like Mn0.2Cd0.8S with ReS2 nanosheets.

p-n Heterojunction Photocatalyst Mn0.5Cd0.5S/CuCo2S4 for Highly Efficient Visible Light-Driven H2 Production

It is highly important to develop efficient and cheap photocatalysts for hydrogen production. Herein, a series of p-n heterojunction Mn_0.5Cd_0.5S/CuCo₂S₄ has been successfully synthesized for the first time by the hydrothermal impregnation method. Mn_0.5Cd_0.5S/CuCo₂S₄ loading with 12 wt % CuCo₂S₄ shows the highest H₂ evolution rate of 15.74 mmol h^-1 g^-1 under visible light (λ ≥ 420 nm) irradiation, which is about 3.15 and 15.28 times higher than that of bare Mn_0.5Cd_0.5S (4.99 mmol h^-1 g^-1) and CuCo₂S₄ (1.03 mmol h^-1 g^-1), respectively. In addition, it shows a relatively good stability during the five recycle tests, with about 20% loss of reaction rate compared to that of the first cycle. The superior photocatalytic performance is attributed to the effective separation and transfer of photogenerated charge carriers because of the formation of the p-n junction. The samples are systematically characterized by X-ray diffraction, ultraviolet-visible (UV-vis), diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray photoelectron spectroscopy, photoluminescence, EIS, and so on. UV-vis and EIS show that CuCo₂S₄ can effectively improve the visible light response of Mn_0.5Cd_0.5S/CuCo₂S₄ and promote the electron transfer from CuCo₂S₄ to the conduction band of Mn_0.5Cd_0.5S, so as to improve the photocatalytic efficiency. This study reveals that the p-n heterojunction Mn_0.5Cd_0.5S/CuCo₂S₄ is a promising photocatalyst to explore the photocatalysts without noble metals.

A novel p-n Mn0.2Cd0.8S/NiWO4 heterojunction for highly efficient photocatalytic H2 production

Constructing a p-n heterojunction has been regarded as an effective way to restrain charge recombination and boost photocatalytic H2 production activity. Herein, a novel Mn0.2Cd0.8S/NiWO4 composite was fabricated by a hydrothermal process and which exhibited enhanced H2 production activity and excellent photostability. Particularly, the composite with 30 wt% of NiWO4 achieved the optimal H2 production rate of 17.76 mmol g-1 h-1, which was 2.9 times higher than that of Mn0.2Cd0.8S. The increased H2 production property was mainly due to the p-n heterojunction between Mn0.2Cd0.8S and NiWO4, which provided an efficient path for charge transfer and inhibited the photocorrosion of Mn0.2Cd0.8S. This work can offer technical support for the design and development of p-n heterojunctions that can be applied for photocatalytic H2 production.

Noble metal-free 0D-1D NiCoP/Mn0.3Cd0.7S nanocomposites for highly efficient photocatalytic H2 evolution under visible-light irradiation

Efficient and noble metal-free co-catalyst loading is an effective solution for separating and transferring photo-generated carriers and lowering the overpotential in photocatalytic H₂ evolution activity. In this work, we designed and prepared a series of novel NiCoP/Mn_0.3Cd_0.7S (NCP/MCS) composites by modifying MCS nanorods with the co-catalyst NCP using a simple calcination method. Notably, the 10-NCP/MCS composite displays the optimum photocatalytic H₂ evolution rate of 118.5 mmol g^-1 h^-1 under visible-light irradiation. This is approximately 3.39 times higher than that of pure MCS. The corresponding apparent quantum efficiency is 10.2% at 420 nm. The superior photocatalytic activity of the NCP/MCS composites can be attributed to the efficient separation of photogenerated carriers caused by the intimate heterojunction interface between NCP and MCS, smaller transfer resistance, and lower overpotential of NCP. Moreover, the NCP/MCS composites exhibit remarkable photostability. A plausible mechanism is proposed.

MoS2-wrapped Mn0.2Cd0.8S nanospheres towards efficient photocatalytic H2 generation and CO2 reduction

MoS₂-wrapped Mn_0.2Cd_0.8S nanospheres with intimate interfacial contacts were fabricated, and exhibited excellent photocatalytic performances for H₂-generation and CO₂ reduction.

O-MoS2/Mn0.5Cd0.5S composites with enhanced activity for visible-light-driven photocatalytic hydrogen evolution

The reaction mechanism of O-MoS₂/Mn_0.5Cd_0.5S for photocatalytic hydrogen evolution is put forward and the satisfactory hydrogen production rate of the optimized composite is superior to most of the Mn–Cd–S based catalysts reported.

Efficient photocatalytic hydrogen production by Mn0.05Cd0.95S nanoparticles anchored on cubic NiSe2

In the field of catalysis, three critical factors for evaluating catalyst activity include charge separation efficiency, photoabsorption, and surface activity sites.

An amorphous CoSx modified Mn0.5Cd0.5S solid solution with enhanced visible-light photocatalytic H2-production activity

Amorphous noble metal-free CoS_x modified Mn_0.5Cd_0.5S with excellent photocatalytic hydrogen production activity has been successfully synthesized.