Construction of 3D/3D heterojunction between new noble metal free ZnIn2S4 and non-inert metal NiMoO4 for enhanced hydrogen evolution performance under visible light

Promoting the separation of electron and hole plays an important role in photocatalytic hydrogen production. However, single semiconductor materials cannot fully realize their potential due to the rapid recombination of photogenerated carriers. Therefore, in this experiment, a new photocatalyst ZnIn₂S₄/NiMoO₄ was prepared by using an electrostatic self-assembly method, which greatly improved the electron-hole recombination phenomenon. After 5 h reaction under visible light irradiation, ZIS/NMO-3 composite catalyst prepared in ethanol showed the best photocatalytic activity, and the hydrogen evolution capacity reached 173.09 μmol. The hydrogen evolution capacity of ZIS/NMO-3 was 2.47 and 25.83 times that of short rod-like NiMoO₄ and microflower-like spherical ZnIn₂S₄, respectively. Through some physical characterization and electrochemical experiments, it can be seen that NiMoO₄ and ZnIn₂S₄ have good composability. Meanwhile, the composite catalyst ZnIn₂S₄/NiMoO₄-3 has high current response characteristics. It can be seen from the fluorescence emission spectra that the composite catalyst presents the lowest peak value, which indicates that ZIS/NMO-3 can effectively inhibit the recombination of photogenerated electrons and holes. When ZnIn₂S₄ is loaded on NiMoO₄, the separation of photogenerated carrier will be accelerated due to the formation of heterojunction, thus improving the photocatalytic activity. At the same time, the large specific surface area will also provide more abundant active sites for the composite catalyst, which provides a good condition for photocatalytic hydrogen production. This work provides an efficient, uncomplicated and feasible method for the synthesis of ZIS/NMO-3 composite catalyst with excellent properties.     

Well-defined FeP/CdS heterostructure construction with the assistance of amine for the efficient H2 evolution under visible light irradiation

The photocatalyst is a crucial factor in determining solar-to-H₂ efficiency for solar-driven water splitting. Here, the FeP/CdS well-defined heterostructure was elaborately designed and successfully constructed in-situ to achieve efficient water splitting by using a simple and green solvothermal approach. In the synthetic process, the ethylenediamine plays an important role in the construction of intimate contact interface between FeP and CdS. This good quality FeP/CdS heterostructure can efficiently promote charge separation and transportation, and therefore the charge recombination of CdS was significantly suppressed. As a result, the as-synthesized FeP/CdS heterostructure showed excellent photocatalytic performance under visible-light irradiation with an optimal hydrogen evolution rate of 37.92 mmol g⁻¹ h⁻¹ and an apparent quantum yield of 31.50% at 420 nm far exceeding that of pristine CdS by more than 122 folds. This rate, to the best of our knowledge, outperforms other similar catalytic systems.     

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.     

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.     

Development of high quantum efficiency CdS/ZnS core/shell structured photocatalyst for the enhanced solar hydrogen evolution

Development of co-catalyst free, core/shell structured photocatalyst with ultra-thin shell is of great importance towards the stable and continuous hydrogen (H₂) production, where the shell prevents photo-corrosion of the core for longer stability with continuous H₂ generation. Accordingly, herein, we report a one-step, surfactant free hydrothermal process for synthesis of high-efficient CdS/ZnS core/shell structured catalyst for H₂ evolution under natural solar light. The structural and morphological characterizations using XRD and TEM techniques revealed the formation of phase pure CdS/ZnS system, with core and shell thickness of 395 and 15 nm, respectively. XPS studies revealed that the constituted elements in system exist in their native oxidation states, which indicated the stable structural integrity of the individual phase in the core/shell structure. The synergistic optical properties of CdS/ZnS showed the absorption edge around 500 nm and the decreased PL intensity indicated the improved charge recombination resistance in the system. The parametric studies such as synthesis time, core diameters and shell thickness optimization were conducted to study the formation kinetics of the core/shell structure and their photocatalytic efficiencies. Accordingly, the optimized core/shell catalyst showed around 763 and 2.4 folds superior activity when compared to the pristine CdS and ZnS, respectively. Further, the catalyst showed excellent stability for over 100 h with quantum efficiency of 8.78% under the irradiation of 20 W LED light at 420 nm. Based on the obtained results, the observed improved photocatalytic quantum efficiency could be ascribed to their synergistic effects of CdS and ZnS towards increased charge separation and spatial distributions of the carriers due to their core/shell configuration of the materials.     

Direct Z-scheme ZnIn2S4/LaNiO3 nanohybrid with enhanced photocatalytic performance for H2 evolution

The direct Z-scheme ZnIn₂S₄/LaNiO₃ nanohybrid based on ZnIn₂S₄ nanosheets and LaNiO₃ cubes was synthesized by a facile hydrothermal method. The ZnIn₂S₄/LaNiO₃ nanohybrid showed improved photocatalytic H₂ evolution and stability. The photocatalytic H₂ evolution activity of ZnIn₂S₄/LaNiO₃ nanohybrid is 3-fold enhanced than that of bare ZnIn₂S₄. The enhanced performance of ZnIn₂S₄/LaNiO₃ nanohybrid is mainly ascribed to the formation of heterojunction between LaNiO₃ and ZnIn₂S₄. The heterojunction can facilitate charge transport on the interface between LaNiO₃ and ZnIn₂S₄ and suppress the recombination of photo-generated charge carriers over ZnIn₂S₄/LaNiO₃ nanohybrid, which were well demonstrated by photoelectrochemical tests. Moreover, the direct Z-scheme photocatalytic reaction mechanism was proposed to elucidate the improved performance of ZnIn₂S₄/LaNiO₃ nanohybrid photocatalyst. This study may provide some guidance on the construction of direct Z-scheme photocatalytic system for photocatalytic H₂ evolution.     

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.     

Bandgap modulation of polyimide photocatalyst for optimum H2 production activity under visible light irradiation

A series of polyimide photocatalysts with different polymerization degrees were prepared by thermal condensation of melamine and pyromellitic dianhydride at different condensation temperatures between 250 °C and 350 °C. Fourier transform infrared (FT-IR) spectra, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) revealed that the polymerization degree increased with increasing condensation temperature. UV–Vis absorption spectra showed that the bandgap energy was lineally decreased with the increase of temperature. The theoretical calculations indicated that the level of conduction band downshifted and valence band upshifted upon the bandgap narrowing. Photocatalytic results displayed that the sample with moderate bandgap exhibited the highest H₂ evolution activity, which adapted the balance among many factors such as light absorption, band potentials, crystallinity, particle size and surface area.     

In2Se3/CdS nanocomposites as high efficiency photocatalysts for hydrogen production under visible light irradiation

Hydrogen energy is an important clean energy. Using visible light to produce hydrogen by semiconductor photocatalysts is one of the current research hotspots. In this work, In₂Se₃/CdS nanocomposite photocatalysts with different mass content of CdS are prepared. The In₂Se₃/CdS photocatalyst with 85.25% CdS mass content exhibits the optimal photocatalytic hydrogen evolution activity (1.632 mmol g^?1 h^?1), which is much higher than that of CdS (0.715 mmol g^?1 h^?1) and In₂Se₃ (trace). Moreover, the In₂Se₃/CdS photocatalyst still maintains a high hydrogen evolution rate after five cycles. The high photocatalytic activity and stability of the In₂Se₃/CdS nanocomposite is due to the formation of heterojunction between In₂Se₃ and CdS. The existence of heterojunction is confirmed by high resolution transmission electron microscopy image and X-ray photoelectron spectra. Theoretical calculations and experimental results indicate that the electron transfer route at the heterojunction is step-scheme. The step-scheme helps the separation of photogenerated electrons and holes, and maximize the hydrogen evolution activity. This work provides a high efficiency step-scheme photocatalyst for hydrogen production.     

NiS2 Co-catalyst decoration on CdLa2S4 nanocrystals for efficient photocatalytic hydrogen generation under visible light irradiation

NiS₂ nanoparticles as noble metal-free co-catalysts were deposited onto the CdLa₂S₄ nanocrystals through a hydrothermal process. The loading of NiS₂ co-catalyst resulted in remarkable enhancement for H₂ production over the CdLa₂S₄ photocatalyst under visible light irradiation. The optimal hybrid photocatalyst with 2 wt% NiS₂ loading exhibited a H₂ production rate of 2.5 mmol h⁻¹ g⁻¹, which was more than 3 times higher than that of the pristine CdLa₂S₄ photocatalyst. The promoted photocatalytic H₂ production by NiS₂-loading is attributed to the enhanced separation of photogenerated electrons and holes as well as the activation effect of NiS₂ for H₂ evolution.     

Photocatalytic H2 evolution on a novel CaIn2S4 photocatalyst under visible light irradiation

A novel visible-light-driven photocatalyst CaIn₂S₄ was synthesized using a facile hydrothermal method followed by a post-calcination process. The influence of the calcination temperature and time on the activities of the photocatalyst was investigated. CaIn₂S₄ exhibits optical absorption predominantly in visible region with an optical band gap of 1.76 eV. Considerable activity for hydrogen evolution from pure water was observed without any sacrificial agents or cocatalysts under visible light irradiation. The maximum hydrogen evolution rate achieved was 30.92 μmol g⁻¹ h⁻¹ without obvious deactivation of the photocatalytic activity for four consecutive runs of 32 h.     

Self-doped Ti3+ mediated TiO2/In2O3/SWCNTs heterojunction composite under acidic/basic heat medium for boosting visible light induced H2 evolution

Well-designed Ti³⁺/In³⁺ mediated TiO₂/SWCNTs heterojunction composite for photocatalytic H₂ evolution under visible light has been investigated. The samples, fabricated through one-step sol-gel approach with controlled acidic/basic heat treatment environment, were characterized by XRD, Raman, FE-SEM, TEM, XPS, UV–Vis and PL techniques. The maximum H₂ of 1244 ppm h⁻¹ was evolved over In/SWCNTs/TiO₂, a 4.69, 1.54 and 1.53 times higher than using TiO₂, In/TiO₂ and SWCNTs/TiO₂ samples, respectively. This enhancement was due to faster charges separation and higher visible light absorption by synergistic effect of In/SWCNTs. Using catalyst prepared under basic (H₂) treatment, Ti³⁺ was successfully embedded into In⁺³@TiO₂@SWCNTs, exhibited H₂ production of 1446 ppm h⁻¹ which was 12.49% and 15.02% higher compared to catalysts prepared under CO₂ and N₂ atmospheres, respectively. Thus, surface defects like Ti³⁺ inhibits charges recombination and enables visible light responsive. The quantum yield over Ti³⁺/In³⁺ mediated TiO₂/SWCNTs composite was 0.251%, a 1.13 and 1.2 folds higher compared to CO₂ and N₂ atmospheres, respectively. Besides, excellent stability for H₂ generation was observed in cyclic runs. A possible mechanism is proposed to understand synergistic effects between Ti⁺³/In⁺³ in TiO₂/SWCNTs composite catalyst and has great potential as a green photocatalyst in environmental and energy applications.     

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.     

The construction of 3D hierarchical CdS/NiAl-LDH photocatalyst for efficient hydrogen evolution

The development of excellent photocatalysts for hydrogen evolution is of great significance to solving the global energy crisis. In this work, a novel 3D hierarchical CdS/NiAl-LDH photocatalyst was fabricated by a facile electrostatic assembly strategy, which was composed of 1D CdS nanorods and 3D flower-like NiAl-LDH microspheres. Under the visible irradiation, the CNA-20 hierarchical photocatalyst presents the optimum hydrogen evolution rate achieved to 3.24 mmol g^?1 h^?1, which is improved 6.23-fold in comparison with the pure CdS. Through the analysis of energy band structures and first-principles calculation, the type-Ⅱ charge transfer mechanism was proposed. Driven by the built-in electric field, as well as the effect of intimate interface contact of CdS and NiAl-LDH, the photogenerated charge could be achieved rapidly separate and migrate, which effectively promotes the H₂ evolution. This well-designed synergistic 1D/3D interface interaction and provides an economic approach to rationally developing metal-free photocatalysts for hydrogen production.     

In-situ growth of mesoporous Nb2O5 microspheres on g-C3N4 nanosheets for enhanced photocatalytic H2 evolution under visible light irradiation

Large-surface-area mesoporous Nb₂O₅ microspheres were successfully grown in-situ on the surface of g-C₃N₄ nanosheets via a facile solvothermal process with the aid of Pluronic P123 as a structure-directing agent. The resultant g-C₃N₄/Nb₂O₅ nanocomposites exhibited enhanced photocatalytic activity for H₂ evolution from water splitting under visible light irradiation as compared to pure g-C₃N₄. The optimal composite with 38.1 wt% Nb₂O₅ showed a hydrogen evolution rate of 1710.04 μmol h^?1 g^?1, which is 4.7 times higher than that of pure g-C₃N₄. The enhanced photocatalytic activity could be attributed to the sufficient contact interface in the heterostructure and large specific surface area, which leads to effective charge separation between g-C₃N₄ and Nb₂O₅.     

A novel pathway toward efficient improvement of the photocatalytic activity and stability of CdS-based photocatalyst for light driven H2 evolution: The synergistic effect between CdS and SrWO4

It has been a research hot spot how to efficiently heighten the photocatalytic activity and stability of CdS-based photocatalysts for H₂ evolution. Here, SrWO₄/CdS nanoparticles which contained CdS/SrWO₄ heterojunctions were prepared. Meanwhile, their photocatalytic performance and stability were investigated in detail for H₂ evolution. At last, the photocatalytic mechanism of the SrWO₄/CdS nanoparticles was discussed roughly. The results show that the photocatalytic performance of CdS can be heightened significantly due to introduction of SrWO₄. The fastest evolution rate of H₂ over the SrWO₄/CdS nanoparticles is 392.5 μmol g⁻¹ h⁻¹, which is 5.8 times as high as that over the pure CdS nanomaterial. More interestingly, the SrWO₄/CdS nanoparticles possess excellent stability. The evolution rate of H₂ over the photocatalyst used 10 times can be up to 473 μmol g⁻¹ h⁻¹, which is the same as that over the once used sample, even is 37% higher than that over of the fresh one. In contrast, after used five times, the photocatalytic activity of the pure CdS nanomaterial is only 57% of that of the fresh sample. This study will supply a new idea for the design and development of highly stable and efficient CdS-based photocatalysts for H₂ evolution in the future.     

Highly efficient photocatalytic conversion of gas phase CO2 by TiO2 nanotube array sensitized with CdS/ZnS quantum dots under visible light

With the massive consumption of fossil fuels, energy crisis and effectively reducing CO₂ to curb global warming have become urgent and severe problems in the world. Photocatalytic conversion of CO₂ technology which can convert CO₂ into combustible compounds by using solar energy can solve both of the problems mentioned above. However, the photocatalytic conversion of CO₂ exhibits too low efficiency, especially under visible light. So, in order to improve the photocatalytic efficiency, the composite photocatalysts of TiO₂ nanotube array (TNTA) sensitized by CdS/ZnS quantum dots (QDs) were successfully prepared by anodization method and successive ionic layer adsorption and reaction (SILAR) method in this work. And the composite photocatalysts exhibited a high performance for photocatalytic conversion of gas-phase CO₂ to methanol under visible light. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), and X-ray photoelectric spectroscopy (XPS) were employed to characterize the ingredients and morphologies of the synthesized photocatalysts. And, UV–vis diffuse reflectance spectra (UV–Vis DRS) revealed that CdS/ZnS QDs enhanced the photo-absorption of composite photocatalyst in the visible light region. The main product methanol yield of CdS/ZnS-TNTA under visible light was 2.73 times that of bare TNTA when TNTA was treated by 10 SILAR cycles. Meanwhile, the product yield first increased before decreasing with the increase of the CO₂ flow rate. And the greatest product yield reached up to 255.49 nmol/(cm²-cat·h) with the increase of light intensity. The reaction mechanism was discussed in this paper. This high performance for photocatalytic reduction of CO₂ was primarily attributed to the CdS/ZnS QDs sensitization, which widens the response wavelength range of the catalyst to include visible light and partly inhibits the recombination of electron-hole pairs.     

SrS/CdS composite powder as a novel photocatalyst for hydrogen production under visible light irradiation

In this paper a novel SrS/CdS composite powders were prepared by coprecipitation method. The physicochemical properties of the photocatalysts were analyzed by XRD, UV–Vis, BET, PL and SEM. Photocatalytic hydrogen production results showed that these composite powders can work efficiently under visible light without loading noble metal, and it was found that the ratio of SrS/CdS equaling to 2/8 has the best performance among various SrS/CdS composite powders, and the hydrogen evolution rate amounted to 123 μmol/h under visible light irradiation. The apparent quantum yield for this photocalyst was calculated to be 2.85%, 4.59%, 9.63% at 420 nm, 440 nm and 480 nm respectively, and the apparent quantum yield under visible light was 5.83%. The reason for its high activity was analyzed.     

Synergistic effect of PANI and NiFe2O4 for photocatalytic hydrogen evolution under visible light

As an effective photocatalyst, PANI/NiFe₂O₄ nanocomposite was prepared by in situ polymerization of aniline. The physicochemical properties of the composite were characterized by TEM, XRD, FT-IR spectra, UV–vis spectroscopy, XPS and Photoelectrochemical Measurements. Compared with NiFe₂O₄ and PANI, PANI/NiFe₂O₄ nanocomposite has a better photocatalytic activity, which exhibited the remarkable property of hydrogen production under visible light. The photocatalytic mechanism was also discussed. The heterojunction of PANI and NiFe₂O₄ promoted the separation of photogenerated e^? and h⁺ on the surface of PANI/NiFe₂O₄. Besides, the structure of PANI/NiFe₂O₄ in the polymerization was detected by FT-IR. NiFe₂O₄ was proved that in favor of the formation of nucleate phenazine-like structure in the progress of in situ polymerization. Then the chain structure of conductive PANI was formed, which leading to the promotion of photocatalytic activity.