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1.
In this study, we describe the successful fabrication of CdS in ionic hydrogels by an in situ growth method and demonstrate that the as-prepared CdS in hydrogels (CdS/HGel) can be used as cost-effective and recyclable catalysts for photocatalytic hydrogen generation. The structure and morphology of CdS/HGels were characterized by various techniques including X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy. The resultant CdS in cationic hydrogel (CdS/HGelPDAM2) showed the best performance of photocatalytic hydrogen production and the hydrogen production rate was up to 10.35 or 7.70 mmol h−1 g−1 when triethanolamine or Na2S–Na2SO3 was used as sacrificial agent. However, CdS in anionic hydrogel (CdS/HGelPAAM) showed poor photocatalytic hydrogen production performance under the same conditions. The solution pH and sacrificial agent type are also indispensable factors that affect the photocatalytic hydrogen production. The enhancement of hydrogen production comes from interaction between polymer chains and Cd2+, high dispersibility of CaS nanoparticles in hydrogels, high hydrophilic and swelling ability of hydrogel, high diffusion rate of reactant in hydrogel, and inhibited binding possibility of photogenerated electron-hole pairs. Since CdS/HGelPDAM has excellent hydrogen production efficiency and ease recovery property, it will be a potential photocatalyst for photocatalytic reactions.  相似文献   

2.
Constructing heterostructures with efficient charge separation is a promising route to improve photocatalytic hydrogen production. In this paper, MoSx/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 MoSx 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.  相似文献   

3.
The photocatalytic production of H2 by low-cost semiconductors is a promising approach to store solar energy. Photocatalysts with heterojunctions convert visible light into H2 faster because of more efficient charge separation. The morphology, the structure, and the crystallinity are additional factors to consider when developing a photocatalyst. Here, highly-crystalline CdS nanorod (NR) were synthesized by a facile one-pot process. Under visible light, pure CdS NR produced H2 2.1 times faster than conventional CdS nanoparticles (NP). CdS NR were then combined with the semiconductor red phosphorus (RPh). A CdS NR-based heterojunction photocatalyst with RPh5% had an excellent photocatalytic H2 evolution rate of 11.72 mmol g−1 h−1, which was 3.6 times higher than pure CdS NR. The apparent quantum efficiency of RPh5%/CdS NR was 19.57%. Furthermore, RPh5%/CdS NR exhibited a superior photogenerated charge separation efficiency and was stable with little photocorrosion compared to CdS NP showing the high potential of this heterojunction photocatalyst.  相似文献   

4.
Photocatalytic efficient hydrogen evolution from pure water with non-noble metal system has more practical application value. In this study, the ZnCdS/Co@CoO composite photocatalyst was prepared by a simple hydrothermal reduction method. The hydrogen evolution rate from water can reach to 793 μmol·g?1·h?1 in sacrificial agent-free system, and 5445 μmol·g?1·h?1 with Na2S and Na2SO3 as sacrificial agent. The S-scheme heterojunction formed between ZnCdS and Co@CoO, as well as the abundant S vacancy were proved to be the key factors to effectively improve the photocatalytic performance. The study on the high hydrogen production efficiency and catalytic mechanism of ZnCdS/Co@CoO in sacrificial agent-free can provide ideas for the design and preparation of more efficient non-noble metal photocatalysts.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
Designing efficient photocatalytic systems for hydrogen evolution is extremely important from the viewpoint of the energy crisis. Highly crystalline heterostructure catalysts have been established, considering their interface electric field effect and structural features, which can help improve their photocatalytic hydrogen-production activity. In this study, we fabricated a highly crystalline heterojunction consisting of ZnFe2O4 nanobricks anchored onto 2D molybdenum disulfide (MoS2) nanosheets (i.e., ZnFe2O4/MoS2) via a hydrothermal approach. The optimized ZnFe2O4/MoS2 photocatalyst, with a ZnFe2O4 content of 7.5 wt%, exhibited a high hydrogen-production rate of 142.1 μmol h−1 g−1, which was 10.3 times greater than that for the pristine ZnFe2O4 under identical conditions. The photoelectrochemical results revealed that the ZnFe2O4/MoS2 heterojunction considerably diminished the recombination of electrons and holes and promoted efficient charge transfer. Subsequently, the plausible Z-scheme mechanism for photocatalytic hydrogen production under white-LED light irradiation was discussed. Additionally, the influence of cocatalysts on the photocatalytic hydrogen evolution for the ZnFe2O4/MoS2 heterostructure was investigated. This work has demonstrated a simplified coupling of one-dimensional or zero-dimensional structures with 2D nanosheets for improving the photocatalytic hydrogen production activity as well as confirmed that MoS2 is a viable substitute for precious metal-free photocatalysis.  相似文献   

8.
Tantalum oxynitride have narrow band gap and its band potentials are suitable for visible light induced hydrogen generation. However, due to fast electron-hole recombination, the efficiency of photocatalytic hydrogen evolution reaction is very low. Herein, we have synthesized semiconductor heterojunction photocatalyst, i.e., TaON/CdS with suitable band positions by a simple precipitation method. Ratio between two semiconductors is optimized to obtain maximum hydrogen evolution. XRD, XPS and TEM analysis demonstrate the formation of heterojunction between these semiconductors. Among the synthesized catalysts, 3% TaON/CdS heterostructure exhibits the highest hydrogen evolution activity with H2 production rate of 7.5 mmol h−1 under natural solar light, whereas the rate is 11 mmol h−1 under the visible light generated by xenon (Xe) lamp without the addition of any noble metal as the co-catalyst. The CdS and 3% TaON/CdS nanomaterials show an AQE of 5.1% and 12.2%, respectively. Combination of Mott-Schottky, UPS and DR UV–visible spectroscopy studies revealed the formation of S scheme semiconductor heterojunction between these nanomaterials with valence, conduction band positions, i.e., 1.46, −0.78 eV for CdS and 2.19, −0.66 eV for TaON, respectively. These band positions help in efficient e-h pair separation to produce hydrogen from water.  相似文献   

9.
An efficient Ni2P–CdS photocatalyst for photocatalytic hydrogen evolution was synthesized by phosphorizing β-Ni(OH)2 nanosheet with exposed (001) facets on CdS nanorods. The obtained Ni2P–CdS composite displays an outstanding and stable photocatalytic hydrogen generation rate of 68.47 mmol g−1 h−1 in 10 vol% lactic acid under visible light irradiation, more than 17 times higher than that for pure CdS nanorods. The transient photocurrent response, EIS measurement, Mott-Schottky plots, acidic LSV measurement, and PL spectra have proved that Ni2P loading can significantly improve the separation of photo-excited electron-hole pairs in CdS nanorods and enhance the hydrogen evolution capability for CdS. These improvements are achieved by features of Ni2P such as the high capability of trapping photo-generated electrons from CdS, lifting the total Fermi level and lowering the hydrogen evolution overpotential of the composite. The results show that β-Ni(OH)2 precursor with a high exposure degree of (001) facet is contributed to the epitaxial formation of (001)-facet-exposed Ni2P co-catalyst on CdS nanorods, resulting in that the Fermi level and the hydrogen evolution overpotential of the composite can be further lifted and lowered. This study has provided a novel precursor-derived route to fabricate high-performance co-catalysts with highly exposed active facets on CdS nanorods for effective photocatalytic hydrogen evolution.  相似文献   

10.
An oxygen-vacancy rich, bismuth oxide (Bi2O3) based MoS2/Bi2O3 Z-scheme heterojunction catalyst (2-BO-MS) was prepared in an autoclave hydrothermal method using ethanol and water. The performance of MoS2/Bi2O3 catalyst was examined for photocatalytic hydrogen evolution, photoelectrochemical activity, and crystal violet (CV) dye degradation by comparing with pristine Bi2O3 and MoS2. The hydrogen evolution performances of 2-BO-MS catalyst exhibited 3075.21 μmol g−1 h−1, which is 7.18 times higher than that of MoS2 (428.14 μmol g−1 h−1). The XPS, XRD and HRTEM analyses covered that the superior photocatalytic performance of 2-BO-MS catalyst might have stemmed out due to the existence of oxygen vacancies, enhanced strong interfacial interaction between MoS2 and Bi2O3 and specific surface area. The in-depth investigation has been performed for MoS2/Bi2O3 Z-scheme heterojunction using several characterization techniques. Moreover, the photocatalytic mechanism for hydrogen evolution and photodegradation were proposed based on trapping experiment results. This results acquired using MoS2/Bi2O3 Z-scheme heterojunction would be stepping stone for developing heterojunction catalyst towards attaining outstanding photocatalytic activity.  相似文献   

11.
The design of p-n heterojunction photocatalysts to overcome the drawbacks of low photocatalytic activity that results from the recombination of charge carriers and narrow photo-response range is promising technique for future energy. Here, we demonstrate the facile hydrothermal synthesis for the preparation of Bi2O3/MoS2 p-n heterojunction photocatalysts with tunable loading amount of Bi2O3 (0–15 wt%). The structure, surface morphology, composition and optical properties of heterostructures were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL), electrochemical impedance spectroscopy (EIS). Compare to pure Bi2O3 and MoS2, the Bi2O3/MoS2 heterostructures displayed significantly superior performance for photocatalytic hydrogen (H2) production using visible photo-irradiation. The maximum performance for hydrogen evolution was achieved over Bi2O3/MoS2 photocatalyst (10 μmol h−1g−1) with Bi2O3 content of 11 wt%, which was approximately ten times higher than pure Bi2O3 (1.1 μmol h−1g−1) and MoS2 (1.2 μmol h−1g−1) photocatalyst. The superior performance was attributed to the robust light harvesting ability, enhanced charge carrier separation via gradual charge transferred pathway. Moreover, the increased efficiency of Bi2O3/MoS2 heterostructure photocatalyst is discussed through proposed mechanism based on observed performance, band gap and band position calculations, PL and EIS data.  相似文献   

12.
One-dimensional CdS nanorods have garnered interest because of their highly visible light response, narrow bandgap, and negative potential at the conduction band edge, which are suitable for proton reduction. However, their poor charge separation and surface photocorrosion remain unresolved. In this study, CdS was synthesized with a 3D dendrite-like morphology to reduce its surface instability and junctioned with inexpensive FeS2 particles to extend the absorption region toward visible light and improve its photoactivity. The photocurrent density was increased 8.3 times, and the photoluminescence reduced by half in petal-shaped CdS/15% FeS2 compared with pure CdS. The petal-shaped CdS/15% FeS2 heterojunction catalyst exhibited significantly enhanced photostability and photocatalytic activity; when 10% lactic acid was used as a hole scavenger, the hydrogen generation rate was 22.91 mL g?1 for 10 h in pure CdS particles and 107.56 mL g?1 in the petal-shaped CdS/15% FeS2 particles. Moreover, the amount of hydrogen generated was maintained until 8th recycling experiments. The Cd and S ions eluted via photocorrosion were not detected after the reaction was complete. This was attributed to the petal-shaped CdS/FeS2 heterojunction system which protected the unstable CdS surface owing to its controlled morphology. The FeS2 junction improved visible light absorption facilitating the separation of photogenerated charges.  相似文献   

13.
Visible-light-driven CdS/HKLBT photocatalyst was prepared by ion exchange of Cd2+ in aqueous Cd(CH3COO)2 solutions, then by sulfurization in aqueous N2H8S solutions. The characterization by XRD, SEM, HRTEM and XRS revealed that CdS nanoparticles exist both on the surface and in the interlayer of HKLBT. The composite CdS/HKLBT showed higher photocatalytic activity for hydrogen evolution (504.2 μmol/h) than that of pure CdS (187.3 μmol/h), even than that of 0.5 wt%Pt/CdS (496.0 μmol/h) under visible light (λ > 400 nm) in the presence of lactic acid as sacrificial reagent. The enhancement of photocatalytic activity is attributed to the strong contact between CdS and HKLBT in CdS/HKLBT as well as the effective separation of photogenerated carrier in CdS through electron rapid injection into CB of HKLBT.  相似文献   

14.
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.  相似文献   

15.
The appropriate interfacial contact and charges transfer mode of heterojunction photocatalysts were critical for high-efficiency hydrogen production. Inter-step mode heterojunction composite had advantages of enhanced visible-light response, improved charge space separation rate, increased electron utilization, which could also protect catalyst anode from photocorrosion. Zinc-vacancy-rich ZnS decorated CdS heterojunction photocatalyst with inter-step mode was constructed in order to fundamentally enhance photocatalytic performance and overcome photocorrosion of CdS. The charge transfer mode was modulated from pervasive type-II to bran-new inter-step mode by defect engineering. Zinc vacancies functioned as acceptor level for charge separation and up-shifted conduction and valance band energy of ZnS. The defective engineered CdS/ZnS heterojunction displayed a reduced over-potential and enhanced photocatalytic activity. The optimal photocatalytic hydrogen production rate for CdS/ZnS reached 42.1 mmol?g?1 under visible light without any co-catalyst. An apparent quantum yield (AQY) of 38.75% at 450 nm was achieved, which was 269.3 and 71.9 times higher than pristine zinc-vacancy-rich ZnS and CdS, respectively. Meanwhile, holes aggregated on the surface of CdS were blocked and the oxidation corrosion process was suppressed. The charge transfer mechanism and kinetics of charge transfer and separation in inter-step mode heterojunction photocatalysts were investigated and discussed. This work will accelerate practical applications of photocatalysis with inter-step mode and give deep insights into understanding how inherent acceptor levels play a role in designing defect-engineered semiconductor with enhanced photocatalytic performance.  相似文献   

16.
CdS/Zn2GeO4 (CG) composites were synthesized through the simple hydrothermal process. The crystal structure, morphology and light absorption property of the products were studied in detail. The CG composites showed excellent photocatalytic hydrogen production performance upon visible light illumination. Especially, the CG-3 composite displayed the highest H2 evolution rate of 1719.8 μmol h−1 g−1, which was about 3.80 and 4.28 times higher than the pure CdS and Zn2GeO4. Besides, the cyclic stability of the CG-3 composite was also excellent. The PL, photocurrent response and EIS spectra results testified that the efficient separation and transfer of photoinduced charge carriers achieved between CdS and Zn2GeO4, which could result in the promotion of photocatalytic performance. Moreover, a possible mechanism of H2 generation over CdS/Zn2GeO4 heterojunction was discussed. The practicable way to construct heterojunction composites would be helpful for the design of other systems with excellent photocatalytic property.  相似文献   

17.
Increasing the separation efficiency and transfer rate of photogenerated charges is the dominant factor for improving photocatalytic activity. Herein, we successfully prepared semi-crystalline WP (SC-WP) with good optical properties and as a cocatalyst to modify CdS nanorods (CdS NRs) to construct SC-WP/CdS (PD) composite catalyst by simple electrostatic self-assembly method for photocatalytic hydrogen evolution. Two high-efficiency and stable photocatalytic hydrogen evolution systems were constructed with 1.0 M ammonium sulfite solution and 10 vol% lactic acid solution as sacrificial agents, respectively. Surprisingly, the maximum photocatalytic H2 production rate of 15446.21 μmol h−1 g−1 is obtained over 10PD composite, which is 10.58 times greater than that of pure CdS. The improved photocatalytic activity can be attributed to the fact that the SC-WP nanoparticles provides a large number of exposed active sites on the surface of CdS for hydrogen evolution reaction, which can efficiently capture photogenerated electrons from CdS nanorods and promotes the transport and separation of light-induced charges. And the introduction of SC-WP nanoparticles with excellent optical properties can efficiently improve the visible light absorption range and the utilization rate of the absorbed light of the PD composite. In addition, the SC-WP nanoparticles show semi-crystalline state, which is also conducive to enhancing the photocatalytic activity.  相似文献   

18.
In this work, we fabricate a 1D/2D heterojunction photocatalyst composed of n-type CdS nanorods and p-type CoSx nanoflake. This photocatalyst achieves a hydrogen evolution rate of 9.47 mmol g?1 h?1, which is 13.7 times higher than that of pure CdS nanorods. Scanning Kelvin Probe, Mott-Schottky plots, UV–Vis absorption spectra and surface photocarrier orienting reaction results indicate that the enhanced photocatalytic performance of CdS/CoSx is owing to the fabrication of direct Z-Scheme heterojunction system which greatly improves the utilization, migration and separation rate of photo-generated carriers. To the best of our knowledge, this work is the first time to describe a CdS/CoSx direct Z-scheme system with 1D/2D nanostructure, which can expedite the transfer process of photogenerated carriers with strong redox energy to participate in photocatalytic reactions.  相似文献   

19.
Due to superior light absorption abilities, porous materials are suitable to be served in photocatalytic reactions. In this study, porous Ni2P is target-constructed from porous Ni(OH)2 nanoflower. Promotion effect of the porous Ni2P as cocatalyst is confirmed on photocatalytic performance of Ni2P/CdS composite. The constructed porous Ni2P/CdS photocatalyst shows much higher photocatalytic H2 evolution rate (111.3 mmol h−1 g−1) from water and much higher CO (178.0 μmol h−1 g−1) and CH4 (61.2 μmol h−1 g−1) evolution rates from CO2 reduction than non-porous Ni2P/CdS photocatalyst. Characterizations including UV-Vis diffuse reflectance, photoluminescence, transient photocurrent response, electrochemical impedance and electron paramagnetic resonance are conducted to verify the role of porous Ni2P cocatalyst. The slow photon effect derived from porous structure Ni2P is found to improve light path and increase the absorption utilization of light. The enhanced photocurrent intensity and the lowered resistance of porous Ni2P/CdS due to the formed heterojunctions indicate much rapid isolation of photogenerated electron-hole pairs and rapid charge transfer of electrons. The higher signal of ⋅O2- radicals is detected in porous Ni2P/CdS than non-porous Ni2P/CdS, which result in the remarkable photocatalyst activities of porous Ni2P/CdS. Reaction mechanisms over Ni2P/CdS photocatalyst are illustrated with a Z-scheme charge transfer path.  相似文献   

20.
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.  相似文献   

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