Photocatalysts For H2 Production Research Articles

One-step synthesis of C quantum dots/C doped g-C3N4 photocatalysts for visible-light-driven H2 production from water splitting

Graphitic carbon nitride (g-C3N4) is gaining more and more attentions as a promising metal-free photocatalyst for H2 production. Nevertheless, from the perspective of practical applications, the photocatalytic performance over g-C3N4 in visible-light region needs a further improvement. In this work, C doping and C quantum dots (QDs) are co-integrated in g-C3N4 by a one-step thermal polymerization method to obtain an advanced C QDs/C doped g-C3N4 photocatalyst. The synergistic effects of C doping and C QDs modification promote the photocatalytic activity of g-C3N4 significantly. The optimal C QDs/C doped g-C3N4 exhibits a significant improvement on visible-light-driven photocatalytic hydrogen production (205 μmol g−1 h−1) with an apparent quantum yield (AQE) at 420 nm reaching 1.24%, which is approximately nine-fold enhancement than that of pristine g-C3N4. The increased photocatalytic activity mainly benefits from the enhanced visible light absorption and carrier separation efficiency. This study may open a new perspective for the design and fabrication of C-modified g-C3N4 for photocatalytic hydrogen production.

A novel 3D floral spherical composites with double p-n heterojunctions for enhanced photocatalytic hydrogen production under visible light

Rational design of nanostructures of heterogeneous photocatalysts is important to improve their performance and stability. In this study, 3D flower spherical ZnCdS/CuS/Cu9S5 with a double p-n heterojunction tandem heterojunction mechanism was designed and constructed for the first time by solvothermal method and physical mixing process. The construction of the double p-n heterojunction system promotes the electron-hole separation of charges. The 3D flower spherical structure is formed, which not only possesses superior dispersion and slows down the agglomeration, but also can provide channels for charge transport and promote the reaction. Benefiting from the special flower sphere-like surface structure and the synergistic effect between CuS/Cu9S5 and ZnCdS, the optimized 3D ZnCdS/CuS/Cu9S5 nanocomposites show a high H2 evolution rate of 694.1 μmol after 5 h of light exposure, which is 6 times higher than that of the pristine ZnCdS material. Meanwhile, the optimal sample exhibited an apparent quantum efficiency of 8.87% at 475 nm and good stability under 20 h of irradiation. This work provides a new idea for the design of efficient spatially separated and synergistic double p-n heterojunctions photocatalysts for H2 production.

Laser Ablation Nanoarchitectonics of Au-Cu Alloys Deposited on TiO2 Photocatalyst Films for Switchable Hydrogen Evolution from Formic Acid Dehydrogenation.

The regulation of H2 evolution from formic acid dehydrogenation using recyclable photocatalyst films is an essential approach for on-demand H2 production. We have successfully generated Au–Cu nanoalloys using a laser ablation method and deposited them on TiO2 photocatalyst films (AuxCu100–x/TiO2). The Au–Cu/TiO2 films were employed as photocatalysts for H2 production from formic acid dehydrogenation under light-emitting diode (LED) irradiation (365 nm). The highest H2 evolution rate for Au20Cu80/TiO2 is archived to 62,500 μmol h–1 g–1 per photocatalyst weight. The remarkable performance of Au20Cu80/TiO2 may account for the formation of Au-rich surfaces and the effect of Au alloying that enables Cu to sustain the metallic form on its surface. The metallic Au–Cu surface on TiO2 is vital to supply the photoexcited electrons of TiO2 to its surface for H2 evolution. The rate-determining step (RDS) is identified as the reaction of a surface-active species with protons. The results establish a practical preparation of metal alloy deposited on photocatalyst films using laser ablation to develop efficient photocatalysts.

Construction and performance of CdS/MoO2@Mo2C-MXene photocatalyst for H2 production

Nowadays, photocatalytic technologies are regarded as promising strategies to solve energy problems, and various photocatalysts have been synthesized and explored. In this paper, a novel CdS/MoO2@Mo2C-MXene photocatalyst for H2 production was constructed by a two-step hydrothermal method, where MoO2@Mo2C-MXene acted as a binary co-catalyst. In the first hydrothermal step, MoO2 crystals with an egged shape grew on the surface of two-dimensional (2D) Mo2C MXene via an oxidation process in HCl aqueous solution. In the second hydrothermal step, CdS nanorods were uniformly assembled on the surface of MoO2@Mo2C-MXene in ethylenediamine with an inorganic cadmium source and organic sulfur source. The CdS/MoO2@Mo2C-MXene composite with MoO2@Mo2C-MXene of 5 wt% exhibits an ultrahigh visible-light photocatalytic H2 production activity of 22,672 µmol/(g·h), which is ∼21% higher than that of CdS/Mo2C-MXene. In the CdS/MoO2@Mo2C-MXene composite, the MoO2 with metallic nature separates CdS and Mo2C MXene, which acts as an electron-transport bridge between CdS and Mo2C MXene to accelerate the photoinduced electron transferring. Moreover, the energy band structure of CdS was changed by MoO2@Mo2C-MXene to suppress the recombination of photogenerated carriers. This novel compound delivers upgraded photocatalytic H2 evolution performance and a new pathway of preparing the low-cost photocatalyst to solve energy problems in the future.

Precisely decorating CdS on Zr-MOFs through pore functionalization strategy: A highly efficient photocatalyst for H2 production

Different materials, such as metal sulphides, are often combined with metal-organic frameworks (MOFs) to develop multi-functional composites and improve their photocatalytic properties. However, the high interfacial energy barrier limits the formation and nano-assembly of the heterogeneous junctions between MOFs and metal sulphides. Herein, the heterostructured Zr-MOF-S@CdS are successfully constructed through a sequential synthesis method, in which the mesoporous Zr-MOF are firstly decorated with thioglycolic acid through pore functionalization, and followed by the S2- anion exchange process resulting in the surface close attached growth of CdS onto Zr-MOF-S materials. Due to the presence of molecules linkers, the CdS can be precisely decorated onto Zr-MOF-S without aggregation, which can provide more active sites. Moreover, the intimate connections and the suitable band structures between two materials can also facilitate the photogenerated electron-hole pairs separation. Therefore, the resulting Zr-MOF-S@CdS with appropriate ratio exhibits high photocatalytic activity for water reduction, in which the H2 evolution rate can reach up to 1861.7 μmol·g−1·h−1, 4.5 times higher than pure CdS and 2.3 times higher than of Zr-MOF/CdS, respectively. Considering the promising future of MOF-based photocatalysts, this work may provide an avenue for the further design and synthesis MOF-based composite photocatalysts for efficient H2 evolution.

Enhanced photocatalytic activity in water splitting for hydrogen generation by using TiO2 coated carbon fiber with high reusability

In this study, TiO2 coated carbon fiber (TiO2@CF) was synthesized and used for the improvement of hydrogen (H2) evolution. Obtained results from scanning electron microscopy (SEM), X-ray diffraction (XRD), gas adsorption analysis (BET), UV–vis diffuse (UV–vis), and X-ray photoelectron spectroscopy (XPS) confirmed that the surface area and light absorption of the material was significantly improved. The synthesized TiO2@CF photocatalyst exhibited improved photocatalytic performance toward hydrogen generation. The enhancement of photocatalytic H2 evolution capacity by TiO2@CF was ascribed to its narrowed bandgap energy (2.76eV) and minimized recombination of photogenerated electron-hole pairs The hydrogen production rate by the TiO2@CF reached 3.238 mmolg−1h−1, which was 4.8 times higher than unmodified TiO2 (0.674 mmolg−1h−1). The synthesized TiO2@CF was relatively stable with no distinct reduction in photocatalytic activity after five recycling runs. The photoluminescence and photocurrent were employed to support the photocatalytic H2 production mechanism proposed mechanism.Based on these results, TiO2@CF with unique properties, easy handle, and high reusability could be suggested as an efficient strategy to develop a high-performance photocatalyst for H2 production.

Surface modulation of MoS2/O-ZnIn2S4 to boost photocatalytic H2 evolution

To realize the continuous production of hydrogen energy, the efficient photocatalysts are required in the heterogeneous reaction for water splitting. Herein, we reported a surface modulation strategy, via doping oxygen atoms to tune the surface state of ZnIn2S4 nanosheets with cocatalyst MoS2 modification, to enhance water adsorption and surface catalytic reaction for boosting the photocatalytic activity. Consequently, MoS2/O-ZnIn2S4 photocatalysts showed a remarkably superior photocatalytic H2 production performance of 4.002 mmol g−1 h−1 and an apparent quantum yield (AQY) of ∼2.53%, 5.4 folds higher than ZnIn2S4. Using operando infrared spectroscopy and DFT calculation, we revealed the dynamic structural evolution, as well as the active sites for water adsorption and the catalytic reaction at the MoS2/O-ZnIn2S4 interface. This work reveals the effect of surface modulation on the photocatalytic activity for MoS2/O-ZnIn2S4 and offers a feasible method to devise excellent nanomaterial photocatalysts for H2 production.

Modulation of Z-Scheme Heterojunction Interface between Ultrathin C3N5 Nanosheets and Metal-Organic Framework for Boosting Photocatalysis.

Fabricating heterojunction photocatalysts for H2 production is promising for the development of clean energy. For boosting the photocatalytic activity, modulating the heterojunction interface can facilitate the electron-hole separation and solar energy utilization, but it is highly challenging in synthesis. In this work, by facilely exfoliating the bulk C3N5, ultrathin C3N5 nanosheets (N-CN) with large surface area, improved light absorption, and efficient charge transport were synthesized and further applied to the construction of NH2-UiO-66/N-CN heterojunctions. The optimized NH2-UiO-66/N-CN-2 exhibits high hydrogen evolution rate and cycling stability with Pt as the cocatalyst. Combined with the experimental results, the density functional theory calculation reveals that the high photocatalytic performance is attributed to the promoted photogenerated carrier transfer by the formation of well-contacted and stable Z-scheme heterojunction interface. This contribution renders an insight into the modulation of the heterojunction interface for enhancing the activity of MOF-based photocatalysts.

Electrospun Semiconductor‐Based Nano‐Heterostructures for Photocatalytic Energy Conversion and Environmental Remediation: Opportunities and Challenges

Harvesting solar energy to drive the semiconductor photocatalysis offers a promising tactic to address ever‐growing challenges of both energy shortage and environmental pollution. Design and synthesis of nano‐heterostructure photocatalysts with controllable components and morphologies are the key factors for achieving highly efficient photocatalytic processes. One‐dimensional (1D) semiconductor nanofibers produced by electrospinning possess a large ratio of length to diameter, high ratio of surface to volume, small grain sizes, and high porosity, which are ideally suited for photocatalytic reactions from the viewpoint of structure advantage. After the secondary treatment of these nanofibers through the solvothermal, gas reduction, in situ doping, or assembly methods, the multi‐component nanofibers with hierarchical nano‐heterostructures can be obtained to further enhance their light absorption and charge carrier separation during the photocatalytic processes. In recent years, the electrospun semiconductor‐based nano‐heterostructures have become a “hot topic” in the fields of photocatalytic energy conversion and environmental remediation. This review article summarizes the recent progress in electrospinning synthesis of various kinds of high‐performance semiconductor‐based nano‐heterostructure photocatalysts for H2 production, CO2 reduction, and decomposition of pollutants. The future perspectives of these materials are also discussed.

Fabrication of solar-driven hierarchical ZnIn2S4/rGO/SnS2 heterojunction photocatalyst for hydrogen generation and environmental pollutant elimination

As a solution to the energy crisis and environmental pollution, photocatalytic production of hydrogen (H2) in conjunction with organic pollutant degradation has received broad attention. As a proof of concept, ternary ZnIn2S4/rGO/SnS2 heterojunction photocatalyst with high performance and stability were prepared by a one-step hydrothermal method. Experimentally, the composite has been examined for its microstructures and morphologies, as well as its photocatalytic generation of hydrogen (H2) and tetracycline (TC) degradation performance. The results indicate that ZnIn2S4/rGO/SnS2 heterojunctions possessed the higher photocatalytic activities towards hydrogen production and TC degradation ability (7847 μmol g-1h−1, 96.5%) than that of SnS2 (756 μmol g-1h−1, 60.9%), SnS2/rGO (1680 µmol g-1h−1, 69%), ZnIn2S4 (540 μmol g-1h−1, 64.1%), ZnIn2S4/rGO (1242 μmol g-1h−1, 75%), and ZnIn2S4/SnS2 (4654 μmol g-1h−1, 84%), respectively. Moreover, it demonstrated excellent reusability and stability after five consecutive cycles for both H2 generation and TC photodegradation. The intermediates of the photodegradation process were identified by GC–MS methods. Due to the hexagonal and layer structured material and the synergetic effect, the photocatalytic efficiency is greatly improved in the ZnIn2S4/rGO/SnS2 heterojunction photocatalyst, which also enhanced the separation of charge carriers. In this study, we developed a non-toxic, low-cost, highly efficient and recyclable photocatalyst for H2 production and TC degradation.

Evaluation of in-situ formed La2O3–TiO2–La2O2CO3 nanocomposite photocatalyst for H2 production

The photocatalytic evolution of H2 over La2O3 decorated TiO2 catalyst was examined under solar light. It was observed that during the course of the reaction, the transformation of La2O3/TiO2 into La2O3–TiO2–La2O2CO3 occurred and these species effectively suppressed electron-hole pair recombination by forming electron trapping centres on the surface, resulting in an increased visible light absorption and improved H2 yield. The 2 wt%La2O3/TiO2 nanocomposite demonstrated better H2 yield (∼8.76 mmol (gcat)−1) than the bare TiO2 (∼1.1 mmol (gcat)−1). The catalyst was stable even after several consecutive recycles with no substantial loss of hydrogen production rate. The H2 rates were correlated with the physicochemical characteristics of the catalysts examined by BET–SA, H2-TPR, XRD, UV-DRS, Raman spectroscopy, FTIR, HRTEM, EPR and PL spectroscopy.

Water-assisted formation of amine-bridged carbon nitride: A structural insight into the photocatalytic performance for H2 evolution under visible light

Carbon nitride (C3N4) exhibits significant potential as a metal-free photocatalyst for H2 production using visible light. While the C3N4 network consists of tri-s-triazine building units linked by H bonds, it is still controversial how the H bonds affect the photocatalytic performance. In this study, we present a water-assisted method for production of polymeric carbon nitride to control intraplanar structures associated with H bonds and amine bridges. The C3N4 samples produced with a thermal treatment using water and humidified air gas (CN-H) exhibit excellent photocatalytic activities for the hydrogen evolution reaction. From structural and photophysical characterizations, it is found that CN-H samples contain fewer H bonds and more amine bridging groups as well as possess larger domains than C3N4 samples produced without using water (CN-A). These structural changes induced by the water treatment lead to efficient intraplanar migration of photoexcited charge carriers and thus are responsible for the enhanced photocatalytic performances.

High surface area TiO2 photocatalyst for H2 production through silicon micromachining

The development of an efficient photocatalyst capable of producing enough hydrogen for applications in everyday life under direct sunlight exposure is still challenging. In this work, a new concept for a three-dimensional microstructured photocatalyst is proposed, in which a standard deep-reactive ion etching process allows for the optimization, fabrication and subsequent deposition of TiO2 thin films by physical vapor deposition for H2 production by direct water splitting. After the development of enlarged surface microstructures, the composition and morphology of the 3D TiO2 photocatalyst were characterized by XRD, XPS, UV/Vis spectroscopy and SEM. Furthermore, the influence of the area enlargement factor on the 3D photocatalyst surface morphology and its photocatalytic performance under UV–visible irradiation was thoroughly analyzed and corroborated by electrochemical experiments. The photocatalyst exhibited an increase in H2 production by almost a factor of 12 compared to conventional planar TiO2 films. The H2 production was further improved by a factor of 4 through the introduction of Au nanoparticles grown on top of the TiO2 layer. The advantages and development of robust and hierarchical photocatalysts using microelectromechanical fabrication techniques are highlighted as potential solutions for a broad range of applications from photocatalysis, electronics, and sensing elements to 3D metamaterials.

Modulation of Surface Oxygen Defects on ZnO/ZnS Catalysts to Promote Photocatalytic H2 Production

AbstractZinc oxide/zinc sulfide (ZnO/ZnS) microparticles with enriched surface oxygen defects (Dso) were prepared via a hydrothermal sulfurization modulated by doping sliver/copper ions (Ag+/Cu2+). Microsized ZnO precursors with different structures were firstly prepared in the presence of Ag+/Cu2+. A subsequent surface sulfurization of the precursor led to the formation of ZnS nanostructure, forming ZnO/ZnS with modulated Dso simultaneously. In addition, this in‐situ sulfurization ensured the homogeneous distribution of Ag/Cu species with ZnO/ZnS (ACZS), which significantly improved the electric conductivity of these hybrid materials. Because of the structural, compositional, and defect features, the ACZS6 sample delivered a maximum photocatalytic hydrogen (H2) production rate of 769 μmol g−1 h−1 with almost 100 % of rate retention even after 9 h under UV‐vis light. Thus, this study may provide an efficient strategy to engineering oxygen defects within microsized photocatalysts for H2 production.

Indium-Based Metal-Organic Framework for Efficient Photocatalytic Hydrogen Evolution.

In this work, an indium-based metal-organic framework was successfully constructed, namely, as In-MOF, by elaborately selecting an InIII center with unique properties and a functional tetracarboxylic acid with unsaturated and open-coordinated nodes. Interestingly, the InIII center was connected to a single-metal-node-based porous three-dimensional pts net. Its structure was dentified by single-crystal and powder X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, etc. Considering the special luminescent characteristic of an indium-based framework, as-prepared In-MOF was explored as a photocatalyst for H2 production from water splitting. The testing results demonstrate that In-MOF as a promising photocatalyst with a suitable band gap realizes a H2 evolution efficiency of 777.65 μmol g-1 h-1.

Step-scheme ZnO@ZnS hollow microspheres for improved photocatalytic H2 production performance

Constructing a step-scheme heterojunction at the interface between two semiconductors is an efficient way to optimize the redox ability and accelerate the charge carrier separation of a photocatalytic system for achieving high photocatalytic performance. In this study, we prepared a hierarchical ZnO@ZnS step-scheme photocatalyst by incorporating ZnS into the outer shell of hollow ZnO microspheres via a simple in situ sulfidation strategy. The ZnO@ZnS step-scheme photocatalysts had a large surface area, high light utilization capacity, and superior separation efficiency for photogenerated charge carriers. In addition, the material simulation revealed that the formation of the step-scheme heterojunction between ZnO and ZnS was due to the presence of the built-in electric field. Our study paves the way for design of high-performance photocatalysts for H2 production.

One-step construction of Y, C, and O tridoped g-C3N4 as a bifunctional photocatalyst for H2 evolution and organic pollutant degradation under visible light irradiation

We successfully synthesized a series of Y, C, O tridoped g-C3N4 photocatalysts using a simple one-step thermal polymerization method as a bifunctional photocatalyst for H2 production and pollutant degradation under visible-light irradiation.

Synergistic effect of biomass-derived carbon decoration and nitrogen defects on seaweed-like tubular g-C3N4 for enhanced photocatalytic H2 evolution

This work presents biomass-derived carbon modified N-deficient seaweed-like tubular g-C3N4 by facile thermal polymerization of freeze-dried sodium alginate, KOH and urea mixture, generating efficient and low-cost photocatalyst for H2 production.

Construction and Performance of Cds/Moo2@Mo2c-Mxene Photocatalyst for H2 Production

Construction and Performance of Cds/Moo2@Mo2c-Mxene Photocatalyst for H2 Production

Multifunctional Ni nanoparticles decorated SiC nanofibers/g-C3N4 nanosheets heterojunctions for drastically increased LED-light-driven hydrogen generation

The development of hydrogen (H2) production photocatalyst with low cost, non-precious metal and high-activity for commercial application is a long-term target and challenge. In this work, novel silicon carbide (SiC) nanofibers/graphitic carbon nitride (g-C3N4) nanosheets (SiC/CNNS) decorated via multipurpose nickel (Ni) nanoparticles were prepared by an easy heat treatment followed byhydrothermalmethod. The tight Ni interface layers as cocatalyst and electron transfer mediator can significantly enhance the H2 production property over SiC/CNNS nanoheterojunctions under light-emitting diode (LED) illumination. The optimal Ni/SiC/CNNS with a massfraction of 10% Ni loading shows the mostsuperior H2-generation rate of 6183 μmol g−1h−1, which is approximately 53, 3 and 227 times compared to CNNS, 10 %Ni/CNNS and SiC/CNNS, respectively. The metallic Ni nanoparticles play the leading and multifunctional roles in improving photocatalyticactivity, includingcollecting the photo-generated electrons efficiently, transferring and separating the charge carriers rapidly, facilitating the H2-production kinetics and decreasing the overpotentials of surface reactions for H2-production. It is highly expected that the multipurpose and non-preciousmetal cocatalyst to form tight interface layers can supply a simple and universal strategy to design high-efficiency cocatalyst-semiconductor–semiconductor photocatalysts for H2 production.