MoS2 grown in situ on CdS nanosheets for boosted photocatalytic hydrogen evolution under visible light

A novel nano-heterojunction photocatalysts of CdS/MoS₂ with appropriate interfacial contact was successfully obtained by the facile two-step hydrothermal synthesis. The MoS₂ ultrathin layer was well combined with CdS nanosheets and formed the interaction, which facilitated the transfer and separation of charges. The CdS/MoS₂ 15 wt% possessed much higher H₂ evolution photocatalytic performance (35.24 mmol h^?1 g^?1), exhibiting an 85.95 times enhancement as compared to that of pure CdS (0.41 mmol h^?1 g^?1). Moreover, the photochemical stability of CdS/MoS₂ heterojunctions was excellent, which showed no significant decrease in activity after four cycles of experiments. The finding provides a novel method to integrate the structure of MoS₂ with CdS, which exhibits great potential in solar energy conversion.     

MoS2/CdS rod-like nanocomposites as high-performance visible light photocatalyst for water splitting photocatalytic hydrogen production

This study demonstrates a high-performance visible-light-driven photocatalyst for water splitting H₂ production. CdS nanorods (30 nm in diameters) with shorter radial transfer paths and fewer defects were prepared by a solvothermal method. To mitigate the recombination of electrons and holes, MoS₂ nanosheets with rich active sites were modified on the surface of CdS nanorods by a room-temperature sonication treatment. The photocatalytic water splitting tests show that the MoS₂/CdS nanocomposites exhibit excellent H₂ evolution rates. The highest H₂ evolution rates (63.71 and 71.24 mmol g^?1h^?1 in visible light and simulated solar light irradiation) was found at the 6% MoS₂/CdS nanocomposites, which was 14.61 times and 13.39 times higher than those of the corresponding pristine CdS nanorods in visible light and simulate solar light irradiation, respectively. The apparent quantum efficiency (AQE) of the 6% MoS₂/CdS nanocomposites at 420 nm was calculated to be 33.62%. The electrochemistry tests reveal that the enhanced photocatalytic activity is a result of extra photogenerated charge carries, greatly enhanced charge separation and transfer ability of the MoS₂/CdS composites. This study may give new insights for the rational design and facile synthesis of high-performance and cost-effective bimetallic sulfide photocatalysts for solar-hydrogen energy conversion.     

Promoted charge separation on 3D interconnected Ti3C2/MoS2/CdS composite for enhanced photocatalytic H2 production

The construction of heterojunction has been regarded as an effective way to promote photocatalytic H₂ evolution activity, in which an intimately interfacial contact between the materials forming heterojunction is a positive effect on enhancing activity. Herein, a ternary 3D interconnected nanocomposite Ti₃C₂/MoS₂/CdS was synthesized by a hydrothermal method. MoS₂ nanosheet with a vertically aligned structure grew on the surface of multi-layered Ti₃C₂ to form 3D Ti₃C₂/MoS₂ with tightly interfacial contact, which works as a cocatalyst for enhancing photocatalytic H₂ evolution. CdS as a photocatalyst covered the surface of Ti₃C₂/MoS₂ to absorb light energy. Benefitting to the synergistic effect between Ti₃C₂ and MoS₂, the Ti₃C₂/MoS₂ further accelerates electron transfer and inhibits the recombination of carriers. The H₂ evolution rate of Ti₃C₂/MoS₂/CdS reaches 15.2 mmol h^?1 g^?1 and the apparent quantum yield is 42.1% at λ = 420 nm. The result provides a useful insight for developing cocatalysts with new nanostructures via controlled interfacial engineering.     

CuS-modified ZnO rod/reduced graphene oxide/CdS heterostructure for efficient visible-light photocatalytic hydrogen generation

Solar energy utilization is a promising strategy for the photocatalytic generation of H₂ from water. Herein, a CuS-modified ZnO rod/reduced graphene oxide (rGO)/CdS heterostructure was fabricated via Cu-induced electrochemical growth with Zn powder at room temperature. The resulting powder revealed good interfacial bonding and promoted photoexcited carrier transport. The CuS nanoparticles played a pivotal role in enhancing visible-light responses and demonstrated excellent catalytic performance. A high visible-light photocatalytic H₂ generation rate of 1073 μmol h⁻¹ g⁻¹ was obtained from the CuS–ZnO/rGO/CdS heterostructure containing 0.23% CuS and 1.62% CdS. Increased photoexcited electron lifetimes, improved carrier transport rates, and decreased fluorescence intensities confirmed the synergistic effects of each of the components of the heterostructure. This study provides an innovative strategy for constructing multi-component heterostructures to achieve efficient visible-light H₂ evolution.     

One-pot synthesis of CdS-MoS2/RGO-E nano-heterostructure with well-defined interfaces for efficient photocatalytic H2 evolution

Quality of interfaces is a key factor determining photoexcited charge transfer efficiency, and in turn photocatalytic performance of heterostructure photocatalysts. In this paper, we demonstrated CdS-MoS₂/RGO-E (RGO-E: reduced graphene oxide modified by ethylenediamine) nanohybrid synthesized by using a facile one-pot solvethermal method in ethylenediamine, with CdS nanoparticles and MoS₂ nanosheets intimately growing on the surface of RGO. This unique high quality heterostructure facilitates charge separation and transportation, and thus effectively suppressing charge recombination. As a result, the CdS-MoS₂/RGO-E exhibits a state-of-the-art H₂ evolution rate of 36.7 mmol g^?1 h^?1 and an apparent quantum yield of 30.5% at 420 nm, which is the advanced performance among all the same-type photocatalysts (see Table S1), and far exceeding that of bare CdS by higher than 104 times. This synthesis strategy gives an inspiration for the synthesis of other compound catalysts, and higher performance photocatalyst may be obtained.     

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.     

Strategy modulation of energy transfer for the plasmon-promoted hydrogen evolution in ternary CdS–Au–MoS2

Nano noble metals with surface plasmon resonance effect have been widely applicated in photocatalytic hydrogen production, however, the poor oxidation/reduction efficiency is the major obstruction for the extensive application of the water splitting. In this study, the ternary nanocomposite, CdS–Au–MoS₂, is structured for the strategic modulation of the energy transfer of the incident light. Comparing with pristine CdS nanowires, an obvious improvement with the maximum H₂ evolution rate of 11.43 mmol·g^?1·h^?1 was obtained after the conjunction of Au nanorods, and the photocatalytic activity was further promoted about ～2.04 times through the surface modification of the MoS₂ quantum dots. A positive synergistic effect of the plasmon and co-catalyst was proposed, where the Au nanorods acted as the source of hot electrons while the MoS₂ quantum dots served as the active sites for hydrogen evolution reaction. Compared with similar nanostructures reported previously, the present superior photoactivity response is ascribed to the plasmon-promoted effect combined with the co-catalyst, which corresponds to the electric field distribution of the finite-difference-time-domain simulation. These intriguing results expanded the comprehensive understanding of plasmon-assisted photochemistry and provided a promising strategy for the rational design of novel plasmonic photocatalysts.     

Efficient interfacial charge transfer of 2D/2D CoP/CdS heterojunction for extremely boosted photocatalytic H2 evolution performance

Constructing 2D/2D heterojunction photocatalysts has attracted great attentions due to their inherent advantages such as larger interfacial contact areas, short transfer distance of charges and abundant reaction active sites. Herein, 2D/2D CoP/CdS heterojunctions were successfully fabricated and employed in photocatalytic H₂ evolution using lactic acid as sacrificial reagents. The multiple characteristic techniques were adopted to investigate the crystalline phases, morphologies, optical properties and textual structures of heterojunctions. It was found that integrating 2D CoP nanosheets as cocatalysts with 2D CdS nanosheets by Co–S chemical bonds would significantly boost the photocatalytic H₂ evolution performances, and the 7 wt% 2D/2D CoP/CdS heterojunction possessed the maximal H₂ evolution rate of 92.54 mmol g^?1 h^?1, approximately 31 times higher than that of bare 2D CdS nanosheets. Photoelectrochemical, steady photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements indicated that there existed an effective charge separation and migration over 2D/2D CoP/CdS heterojunction, which then markedly lengthened the photoinduced electrons average lifetimes, retarded the recombination of charge carriers, and caused the dramatically boosted photocatalytic H₂ evolution activity. Moreover, the density functional theory (DFT) calculation further corroborated that the efficient charge transfer occurred at the interfaces of CoP/CdS heterojunction. This present research puts forward a promising strategy to engineer the 2D/2D heterojunction photocatalysts endowed with an appealing photocatalytic H₂ evolution performance.     

Noble-metal-free CdS@MoS2 core-shell nanoheterostructures for efficient and stabilized visible-light-driven H2 generation

Photocatalytic water splitting is considered to be a green H₂ generation approach and has potential to be applied in the future. As a photocatalytic active material for H₂ evolution, CdS is a good candidate. However, the pristine CdS still suffers from low efficiency and poor stability. To address those issues, we developed noble-metal-free CdS@MoS₂ core-shell nanoheterostructures which exhibit outstanding photocatalytic H₂ evolution performance thus far with rate of 62.55 mmol g⁻¹ h⁻¹, which exceeds that of pristine CdS by a factor of 148. Meanwhile, the photocatalytic stability can be well retained with no deterioration of activity in 24 h reaction. The excellent performance can be reasonably attributed to the low crystallinity of MoS₂ with numerous active sites provided, and the band alignment of CdS and MoS₂ as determined by valence band-XPS and Mott-Schottky plots analysis, which significantly promotes charge transportation and separation. The enhanced photocatalytic stability here should be ascribed to the intimate growth of MoS₂ shells which significantly passivate the surface trap states of CdS cores and thus the photocorrosion is remarkably retarded. This novel strategy will inspire the fabrication of other photocatalytic systems, and may high-efficient photocatalysts be obtained.     

Facile in-situ synthesis of α-NiS/CdS p-n junction with enhanced photocatalytic H2 production activity

Constructing active sites on photocatalysts is one of the most effective approaches for promoting photocatalytic H₂ production activity. In this paper, a p-type semiconductor α-NiS is in-situ grown on an n-type semiconductor CdS by a simple solid state method, which results in a strong interfacial contact between α-NiS and CdS. Benefitting from the built-in electric field caused by a p-n junction, the photoinduced electrons of CdS and holes of α-NiS migrate to their interface and recombine rapidly, which results in the formation of a Z system. The more negative CB potential of α-NiS/CdS possesses stronger ability to reduce H⁺ to H₂, thereby exhibiting higher photocatalytic H₂ evolution activity. Furthermore, the strong interface contact is beneficial to the charge migration and promotes the charge separation efficiency. The H₂ evolution rate of 1.0% α-NiS/CdS reaches 9.8 mmol h^?1 g^?1, corresponding to an AQY of 65.7% at λ = 420 nm.     

Z-scheme heterojunction ZnSnO3/rGO/MoS2 nanocomposite for excellent photocatalytic activity towards mixed dye degradation

In this work, a novel (ZnSnO₃/rGO/MoS₂) nanocomposite was prepared and its photocatalytic performances were investigated. The synthesised ZnSnO₃ spheres were well dispersed over the surface of rGO sheet and MoS₂ layers (ZSGM). The structural, morphological and elemental properties of the composites were examined by XRD, SEM, HRTEM and EDS. The surface chemical composition and functional groups of the elements interlinked in the composites were identified from XPS and FTIR analysis. BET and Raman analysis indicate the effective formation between MoS₂/rGO/ZnSnO₃ ternary heterostructure nanocomposite. The suppressed photogenic charge carrier's recombination rate was investigated by PL analysis. From UV analysis, the bandgap of ZSGM nanocomposite was successfully tuned from 3.13 eV to 2.70 eV, leading to high photocatalytic performance by mixed dye pollutant under UV-visible light illumination. The ZSGM photocatalyst achieved highest removal rate of 0.0131 min^?1 for Rh B degradation, and 0.0153 min^?1 for MB dye degradation and efficiency was 78% (Rh B) and 86% (MB), respectively in 100 min, which shows dramatically enhanced activity than other samples. In the presence of rGO/MoS₂ in ZS, ZSGM photocatalysts exhibit higher catalytic activity due to a lower bandgap, more absorption in the visible region, and suppressed recombination rate of photogenerated e^?/h⁺ pairs.     

Solvothermal fabrication of MoS2 anchored on ZnIn2S4 microspheres with boosted photocatalytic hydrogen evolution activity

The MoS₂/ZnIn₂S₄ composites with MoS₂ anchored on the surface of ZnIn₂S₄ microspheres were fabricated by a facile solvothermal method. To clarify the crystal phases, morphologies, chemical compositions, optical properties, and special surface areas of the obtained photocatalysts, the corresponding characterization measurements were performed. The photocatalytic H₂ evolution activities of MoS₂/ZnIn₂S₄ composites were evaluated and compared with using lactic acid as sacrificial reagents. The results showed that integrating MoS₂ with ZnIn₂S₄ could remarkably boost the photocatalytic H₂ evolution performance and the maximum H₂ evolution rate of 201 μmol h^?1 was achieved over 1 wt% MoS₂ loading on the ZnIn₂S₄, corresponding to the apparent quantum efficiency (AQE) about 3.08% at 420 nm monochromatic light. The photoelectrochemical tests and photoluminescence spectra (PL) versified that the efficient charge transfer and separation were achieved over MoS₂/ZnIn₂S₄ composite in contrast with single ZnIn₂S₄, which would significantly benefit the enhancement of photocatalytic H₂ activity. This work provides a desired strategy to design and synthesize the visible-light-response photocatalysts with MoS₂ as cocatalysts to enhance the photocatalytic activity.     

Hydrogen generation by photocatalytic reforming of glucose with heterostructured CdS/MoS2 composites under visible light irradiation

A binary heterostructured CdS/MoS₂ flowerlike composite photocatalysts was synthesized via a simple one-pot hydrothermal method. This photocatalyst demonstrated higher photocatalytic hydrogen production activity than pure MoS₂. The heterojunction formed between MoS₂ and CdS seems to promote interfacial charge transfer (IFCT), suppress the recombination of photogenerated electron–hole pairs, and enhance the hydrogen generation. Based on the good match between the conduction band (CB) edge of CdS and that of MoS₂, electrons in the CB of CdS can be transferred to MoS₂ easily through the heterojunction between them, which prevents the accumulation of electrons in the CB of CdS, inhibiting photocorrosion itself and greatly enhancing stability of catalyst. Hydrogen evolution reaction (HER) using Na₂S/Na₂SO₃ or glucose as sacrificial agents in aqueous solution was investigated. The ratio between CdS and MoS₂ plays an important role in the photocatalytic hydrogen generation. When the ratio between CdS and MoS₂ reaches 40 wt%, the photocatalyst showed a superior H₂ evolution rate of 55.0 mmol g⁻¹ h⁻¹ with glucose as sacrificial agent under visible light, which is 1.2 times higher than using Na₂S/Na₂SO₃ as sacrificial agent. Our experimental results demonstrate that MoS₂-based binary heterostructured composites are promising for photocorrosion inhibition and highly efficient H₂ generation.     

Crafty design of chemical bonding to construct MoO2/CdS nanorod photocatalysts for boosting hydrogen evolution

An efficient MoO₂/CdS photocatalyst has been successfully constructed by a relatively facile way to construct a specific combination mode through chemical bond, which results in strong interaction between MoO₂ nanoparticles and CdS nanorods. X-ray photoelectron spectroscopy further confirms the formation of Mo–S bonding, which acts as a connection bridge and develops an intimate contact between CdS-NRs and MoO₂ nanoparticles. Benefitting from the synergic effect of the enhancement on the light absorption, carriers’ efficient separation and lower the overpotential of hydrogen evolution, the obtained MoO₂/CdS composite has shown an excellent enhancement in photocatalytic H₂ generation and the optimal H₂ evolution rate reaches as high as 30 times than that of pure CdS nanorods. We have experimentally shed light on the mechanism of this excellent enhancement performance in detail. Moreover, our work can broaden the construction and the application of developing other efficient photocatalytic material containing transition metal oxide.     

Phase controlled synthesis and the phase dependent photo-and electrocatalysis of CdS@CoMo2S4/MoS2 catalyst for HER

Herein we report a heterostructure with ultrathin nanosheets of Co-doped molybdenum sulfide on CdS nanorod array (donated as CdS@CoMo₂S₄/MoS₂) by hydrothermal synthesis. Firstly, elemental Co doping MoS₂ (CoMo₂S₄) delivers the double benefits of increased active sites and enhanced conductivity. Secondly, the structural characteristics maximally exposes the MoS₂ edges and enlarges interfacial contact area between the composite catalyst and electrolyte, as well as the efficient interfacial charge transfer. The ratio of CoMo₂S₄/MoS₂ in CdS@CoMo₂S₄/MoS₂ plays a crucial role for the enhanced photo-assistant electrocatalytic hydrogen evolution reaction (HER). We can tune the ratio of CoMo₂S₄/MoS₂ by controlling the preparation time or the ratio of precursor of Co/Mo. The catalyst with predominant MoS₂ phase shows superior photocatalytic HER performance with a high H₂ production rate of 46.60 μmol mg⁻¹ h⁻¹. Meanwhile, the catalyst with predominant CoMo₂S₄ phase exhibits not only relatively low overpotential of 172 mV at 10 mA cm⁻², which outperforms most values that have been reported on catalyst supported on ITO substrate, but also possesses H₂ production rate of 23.47 μmol mg⁻¹ h⁻¹. The superior photo-assistant electrocatalytic HER activity results from the synergistically structural and electronic modulations, as well as the proper energy band alignment between MoS₂ and CdS. This investigation could provide an approach to integrate the electro- and photocatalytic activities for HER, especially the photo responding behaviour at a bias potential which is meaningful to produce H₂ for actual application.     

Boosting charge transfers in cadmium sulfide nanorods with a few layered Ni-doped MoS2 nanosheets for enhanced photocatalytic hydrogen evolution

The molybdenum sulfide (MoS₂) is a promising low-cost photocatalyst aimed at the hydrogen production reactions, however, obtaining a detailed understanding of its catalytic site has proved to be a challenging task. Several studies indicated that the active sites for catalytic reaction are mainly associated with the edge sites of 2D-layered MoS₂, and their basal plane (in-plane) displays poor activity toward catalytic reactions. Herein, we established the simple approaches to enhance the activity of MoS₂ by conversion of in-plane active sites into active surface edge sites by transition metal (Ni) doping followed by exfoliation. These activated MoS₂ was utilized for enormous upgrading of CdS photocatalytic activity for hydrogen production and is roughly 249 mmol h^?1 g^?1, which is 70 times higher than pure CdS, showed ～140 h stable H₂ production. The amended conductivity, improved surface area and huge active sites are extremely advantageous properties expanded by metal doping to MoS₂ and exfoliation. Additionally, another reason for the enhanced activity of Ni–MoS₂/CdS system was due to promotion of catalytic kinetics by Ni and Mo sits, they are admirable activity of water dissociation and higher ability of hydrogen adsorption correspondingly. These modifications made of superior photogenerated charge carriers’ separation and migration for effective utilization. As far as we know, this system demonstrates the utmost effective performance among inclusive reported MoS₂ based CdS composites. Remarkably, these outcomes will have abundant potential for the progress of immensely actual photocatalytic systems.     

Influence of the reduction of graphene oxide (rGO) on the structure and photoactivity of CdS-rGO hybrid systems

Solvothermal and chemical reduction of graphene oxide with N₂H₄ or HI affect the surface composition, rupture and delamination degree of reduced graphene oxide (rGO). Higher reduction and stacking of rGO was achieved by chemical reduction with HI, while solvothermal reduction and, especially, the chemical reduction with N₂H₄ lead to higher delamination of rGO. The incorporation of the different rGO to CdS implies changes in the characteristics and photoactivity of the CdS-rGO hybrids. A promoter effect was observed in all CdS-rGO hybrids respect to the photoactivity of bare CdS, observing the better photoactivity on the hybrid in which the graphene oxide was reduced with HI (CdS-rGO/HI). The variations in the photoactivity of CdS-rGO hybrids are analyzed in terms of changes in the structure, surface and light absorption ability of CdS and also analyzing the contact of CdS with rGO. The greater concentration of small CdS nanostructures with strong quantum confinement is in the origin of the enhancement in photoactivity observed in the CdS-rGO/HI hybrid.     

Vertically-heterostructured TiO2-Ag-rGO ternary nanocomposite constructed with {001} facetted TiO2 nanosheets for enhanced Pt-free hydrogen production

TiO₂ nanosheets with high ratio of {001} facets were coupled with reduced graphene oxide (rGO) nanosheets through the link of silver (Ag) nanoparticles, forming a novel ternary nanocomposite photocatalyst with a vertical heterostructure, TiO₂-Ag-rGO. The vertical anchoring of TiO₂-Ag nanosheets between rGO sheets was confirmed by transmission electron microscopy (TEM), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Due to excellent separation of electron-hole pairs in the TiO₂ nanosheets, enhanced electron transfer to rGO via Ag nanoparticles, the TiO₂-Ag-rGO nanocomposite exhibited an outstanding performance in photocatalytic hydrogen production, with a hydrogen production rate of 593.56 μmol g^?1 h^?1. This study provides new insights to the development of Pt-free photocatalysts for hydrogen production.     

Noble-metal-free CuS/CdS composites for photocatalytic H2 evolution and its photogenerated charge transfer properties

CuS/CdS composites have been successfully prepared by a simple hydrothermal and cation exchange method. Even without noble-metal cocatalyst, the prepared CuS/CdS composites exhibited enhanced photocatalytic H₂ evolution activity. CuS content had a great influence on photocatalytic activity and an optimum amount of CuS was determined to be ca. 3 mol%, at which the CuS/CdS displayed the highest photocatalytic activity, giving an H₂ evolution rate of 332 μmol g⁻¹ h⁻¹, exceeding that of pure CdS by 3.5 times. The results of SPV (surface photovoltage) and SPC (surface photocurrent) revealed that photogenerated electrons were captured by CuS loaded. TPV (transient photovoltage techniques) indicated that photogenerated charges lifetime in CdS, was prolonged with CuS loaded. Those are the main reasons for the improvement of photocatalytic H₂ evolution.