Photocatalytic Hydrogen Production Activity Research Articles

Defect Engineering Simultaneously Regulating Exciton Dissociation in Carbon Nitride and Local Electron Density in Pt Single Atoms Toward Highly Efficient Photocatalytic Hydrogen Production.

The high exciton binding energy (Eb) and sluggish surface reaction kinetics have severely limited the photocatalytic hydrogen production activity of carbon nitride (CN). Herein, a hybrid system consisting of nitrogen defects and Pt single atoms is constructed through a facile self-assembly and photodeposition strategy. Due to the acceleration of exciton dissociation and regulation of local electron density of Pt single atoms along with the introduction of nitrogen defects, the optimized Pt-MCT-3 exhibits a hydrogen production rate of 172.0µmolh-1 (λ ≥ 420nm), ≈41 times higher than pristine CN. The apparent quantum yield for the hydrogen production is determined to be 27.1% at 420nm. The experimental characterizations and theoretical calculations demonstrate that the nitrogen defects act as the electron traps for the exciton dissociation, resulting in a decrease of Eb from 86.92 to 43.20meV. Simultaneously, the stronger interaction between neighboring nitrogen defects and Pt single atoms directionally drives free electrons to aggregate around Pt single atoms, and tailors the d-band electrons of Pt, forming a moderate binding strength between Pt atoms and H* intermediates.

Multishelled hollow CaTiO3 cubes decorated with Co0.2Cd0.8S nanoparticles for efficient photocatalytic H2 evolution via S-scheme charge transfer

Rationally designing S-scheme heterostructures with boosted charge separation efficiency and superior redox ability is regarded as an appealing strategy to conquer the shortcomings of mono-component and conventional heterojunction photocatalysts. Herein, a novel hierarchical S-scheme heterostructured photocatalyst was constructed by integrating Co0.2Cd0.8S nanoparticles on multishelled hollow CaTiO3 cubes to substantially improve the photocatalytic hydrogen production activity. An internal electric field (IEF) is formed at the heterojunction interfaces owing to the significant disparity in Fermi level (EF) between Co0.2Cd0.8S and CaTiO3, accompanied by the energy band bending, which enables the S-scheme charge transport route in the Co0.2Cd0.8S/CaTiO3 heterostructure, as verified by electron paramagnetic resonance and theoretical calculations. Benefiting from the boosted separation efficiency and superior redox capability of photocarriers within the constructed S-scheme heterostructure, the optimized Co0.2Cd0.8S/CaTiO3 sample exhibited a significantly improved photocatalytic hydrogen evolution rate of 8.13 mmol h−1 g−1, far exceeding that of mono-component counterparts and previously reported Co0.2Cd0.8S- or CaTiO3-based photocatalysts. This study is anticipated to inspire the strategic development of other economical and efficient S-scheme photocatalytic systems with enhanced H2 evolution activity.

Coupling Reliable Interfacial Carrier Migration Channels with Visible-Light Response Antennas in ZnO-Based Heterostructure for Ameliorated Photocatalytic Hydrogen Generation.

Engineering targeted and reliable charge transfer pathways in multiphase photocatalysts remains a challenge. Herein, we conceptualize the Cd@CdS-ZnO/reduced graphene oxide (rGO)/ZnS heterostructures coupled with reliable carrier migration channels and visible-light response antennas by building rGO-integrated electrochemical nanoreactors and an ion-exchange process. In this ternary catalyst, the Cd clusters and rGO perform as charge relays to boost carrier transport via the Z-scheme route and accelerate photogenerated carriers to react with surface-adsorbed substances. Meanwhile, thanks to CdS, the heterostructures have photocatalytic properties under visible light illumination and can also inhibit self-corrosion by shielding Cd clusters to avoid disrupting charge transfer channels. Therefore, the special heterostructure demonstrates fascinating photocatalytic hydrogen production activity without the intervention of cocatalysts. This work provides a feasible protocol for improving the interfaces between metals and semiconductors to achieve efficient photocatalytic hydrogen generation.

Heteroatom‐Doped Ag25 Nanoclusters Encapsulated in Metal–Organic Frameworks for Photocatalytic Hydrogen Production

AbstractAtomically precise metal nanoclusters (NCs) with unique optical properties and abundant catalytic sites are promising in photocatalysis. However, their light‐induced instability and the difficulty of utilizing the photogenerated carriers for photocatalysis pose significant challenges. Here, MAg24 (M=Ag, Pd, Pt, and Au) NCs doped with diverse single heteroatoms have been encapsulated in a metal–organic framework (MOF), UiO‐66‐NH2, affording MAg24@UiO‐66‐NH2. Strikingly, compared with Ag25@UiO‐66‐NH2, the MAg24@UiO‐66‐NH2 doped with heteroatom exhibits much enhanced activity in photocatalytic hydrogen production, among which AuAg24@UiO‐66‐NH2 presents the best activity up to 3.6 mmol g−1 h−1, far superior to all other counterparts. Moreover, they display excellent photocatalytic recyclability and stability. X‐ray photoelectron spectroscopy and ultrafast transient absorption spectroscopy demonstrate that MAg24 NCs encapsulated into the MOF create a favorable charge transfer pathway, similar to a Z‐scheme heterojunction, when exposed to visible light. This promotes charge separation, along with optimized Ag electronic state, which are responsible for the superior activity in photocatalytic hydrogen production.

Donor-acceptor type conjugated porous polymers based on benzotrithiophen and triazine derivatives: Effect of linkage unit on photocatalytic water splitting

Donor-acceptor conjugated polymers have received significant attention as the most promising photocatalysts for efficient photocatalytic hydrogen production (PHP). Nonetheless, achieving high photocatalytic PHP performance relies on molecular framework design and the judicious selection of different structural units. Herein, benzotrithiophene (BTT) and triazine derivatives were used as the basic units of organic polymers, and two conjugated porous polymers (CPPs) named as CP1 and CP2 were successfully synthesized by Stille coupling reaction. Compared with benzene as the linkage unit of triazine, it is evident that the incorporation of the thiophene unit in CP2 broadens its light response range, and promotes the generation of electrons/holes induced by light. Density functional theory (DFT) calculations and femtosecond transient absorption(fs-TA) spectroscopy reveal that CP2 effectively inhibits the photogenerated electron-hole pair recombination and promotes carrier transport. Remarkably, CP2 with Pt co-catalyst exhibited a notably superior PHP performance compared with that of CP1 polymer, which achieved an impressive hydrogen evolution rate (HER) of 21702.4 μmol/g/h, surpassing CP1 by approximately 3.7 times. This work provides a new tactic for enhancing the intrinsic PHP activity and reveals the underlying mechanism for the enhanced photocatalytic activity by regulating the different structural units of the donor-acceptor conjugated polymers.

Enhanced visible light photocatalytic performance of carbon and oxygen co-doped carbon nitride with a three-dimensional structure: Performance and mechanism study

As a cost-effective photocatalyst, carbon nitride (g-C3N4) holds tremendous promise for addressing energy shortages and environmental pollution. However, its application is limited by disadvantages such as low specific surface area and easy recombination of photogenerated electron-hole pairs. This study introduces C and O co-doped g-C3N4 with a three-dimensional (3D) structure achieved through a straightforward one-step calcination process, demonstrating excellent photocatalytic activity of hydrogen production and oxytetracycline degradation, with superoxide radicals as the primary active species. We propose a plausible enhanced mechanism based on systematic characterizations and density functional theory calculations. The 3D structure confers a substantial specific surface area, enhancing both the adsorption area and active sites of catalysts while bolstering structural stability. Co-doping optimizes the band structure and electric conductivity of the catalyst, facilitating rapid migration of photogenerated charges. The synergistic effects of these enhancements significantly elevate the photocatalytic performance. This study presents a convenient and feasible method for the preparation of dual-regulated photocatalysts with outstanding performance.

Heteroatom-Doped Ag25 Nanoclusters Encapsulated in Metal-Organic Frameworks for Photocatalytic Hydrogen Production.

Atomically precise metal nanoclusters (NCs) with unique optical properties and abundant catalytic sites are promising in photocatalysis. However, their light-induced instability and the difficulty of utilizing the photogenerated carriers for photocatalysis pose significant challenges. Here, MAg24 (M=Ag, Pd, Pt, and Au) NCs doped with diverse single heteroatoms have been encapsulated in a metal-organic framework (MOF), UiO-66-NH2, affording MAg24@UiO-66-NH2. Strikingly, compared with Ag25@UiO-66-NH2, the MAg24@UiO-66-NH2 doped with heteroatom exhibits much enhanced activity in photocatalytic hydrogen production, among which AuAg24@UiO-66-NH2 presents the best activity up to 3.6 mmol g-1 h-1, far superior to all other counterparts. Moreover, they display excellent photocatalytic recyclability and stability. X-ray photoelectron spectroscopy and ultrafast transient absorption spectroscopy demonstrate that MAg24 NCs encapsulated into the MOF create a favorable charge transfer pathway, similar to a Z-scheme heterojunction, when exposed to visible light. This promotes charge separation, along with optimized Ag electronic state, which are responsible for the superior activity in photocatalytic hydrogen production.

Salt-assisted construction of hydrophilic carbon nitride photocatalysts with abundant water molecular adsorption sites for efficient hydrogen production

Polymer carbon nitride (PCN), as an affordable and easily prepared photocatalyst, has acquired extensive attention for hydrogen production. However, bulk carbon nitride material exhibits poor dispersibility in water due to the relatively inert surface which limits its quantum efficiency in photocatalytic hydrogen production. In this study, a hydrophilic carbon nitride (HCN) is successfully synthesized by a novel salt-assisted heating process. The heightened water adsorption capacity may contribute additional active sites conducive to the photocatalytic hydrogen production reaction. Meanwhile, potassium ion doping and material size reduction greatly enhance the charge transfer and separation ability of HCN. Consequently, HCN exhibits highly efficient photocatalytic activity for hydrogen production, achieving a rate of 392 μmol·h−1, which is 16 times greater than that of pristine PCN. The simply developed synthetic strategy adopted here provides a novel concept for functionalizing carbon nitride and opening a distinct pathway for the construction of exceptionally efficient photocatalytic systems.

Functionalized Linear Conjugated Polymer/TiO2 Heterojunctions for Significantly Enhancing Photocatalytic H2 Evolution.

Conjugated polymers (CPs) have attracted much attention in recent years due to their structural abundance and tunable energy bands. Compared with CP-based materials, the inorganic semiconductor TiO2 has the advantages of low cost, non-toxicity and high photocatalytic hydrogen production (PHP) performance. However, studies on polymeric-inorganic heterojunctions, composed of D-A type CPs and TiO2, for boosting the PHP efficiency are still rare. Herein, an elucidation that the photocatalytic hydrogen evolution activity can actually be improved by forming polymeric-inorganic heterojunctions TFl@TiO2, TS@TiO2 and TSO2@TiO2, facilely synthesized through efficient in situ direct C-H arylation polymerization, is given. The compatible energy levels between virgin TiO2 and polymeric semiconductors enable the resulting functionalized CP@TiO2 heterojunctions to exhibit a considerable photocatalytic hydrogen evolution rate (HER). Especially, the HER of TSO2@TiO2 heterojunction reaches up to 11,220 μmol g-1 h-1, approximately 5.47 and 1260 times higher than that of pristine TSO2 and TiO2 photocatalysts. The intrinsic merits of a donor-acceptor conjugated polymer and the interfacial interaction between CP and TiO2 account for the excellent PHP activity, facilitating the separation of photo-generated excitons. Considering the outstanding PHP behavior, our work discloses that the coupling of inorganic semiconductors and suitable D-A conjugated CPs would play significant roles in the photocatalysis community.

One-step synthesis of seamlessly contacted non-precious metal cocatalyst modified CdS hollow nanoflowers spheres for photocatalytic hydrogen production

This study ingeniously synthesized a novel CdS/NiS hollow nanoflower sphere (HNS) using a one-step method to enhance photocatalytic hydrogen production activity. Compared to conventional preparation methods, this approach features seamlessly interfaced contact that facilitates efficient electron transfer across the interface. The internal hollow structure allows for multiple light reflections, maximizing light absorption, while the exterior shell and inner surfaces simultaneously offer active sites for reactions. The modification with non-noble metal NiS enables the extraction of electrons from CdS to the NiS surface, achieving rapid charge separation. Furthermore, adsorption-free energy calculations reveal that the NiS surface is more conducive to photocatalytic hydrogen generation, providing additional reaction active sites. The results demonstrate a hydrogen production rate of 2.18 mmol g–1 h–1 for CdS/NiS HNS, which is 9.48 times greater than that of pristine CdS. This work presents a novel approach for synthesizing seamlessly interfaced contacts between photocatalysts and cocatalysts, offering new insight into efficient one-step synthesis for enhanced photocatalytic performance.

Spontaneous Deposition of Single Platinum Atoms on Anatase TiO2 for Photocatalytic H2 Evolution.

Single-atom (SA) decoration has emerged as a frontier in catalysis due to its unique characteristics. Recently, decorated Pt single atoms on titania have shown promise in photocatalytic hydrogen evolution. In this work, we demonstrate that Pt SAs can spontaneously deposit on the surface, driven by electrostatic forces; the key is to determine the golden pH and surface potential. We conducted a comprehensive investigation into the influence of the pH of the deposition precursor on the spontaneous adsorption of Pt SAs onto TiO2 nanosheets (TiNSs). We introduced a straightforward pH-dependent and charge-dependent strategy for the solid electrostatic anchoring of Pt SAs on TiO2. Furthermore, we established that the level of Pt loading can be controlled by adjusting the precursor pH. X-ray photoelectron spectroscopy (XPS) and high-angle annular dark-field imaging scanning transmission electron microscopy (HAADF-STEM) were used to evaluate the Pt SA-decorated samples. Photocatalytic hydrogen production activity was assessed under ultraviolet (UV) (365 nm) irradiation. Notably, we found that at a pH of 8, slightly below the measured point of zero charge (PZC), a unique mixture of Pt clusters and single atoms was deposited on the surface of TiNSs. This unique composition significantly improved hydrogen production, resulting in ∼3.7 mL of hydrogen generated after 8 h of UV exposure by only 10 mg of the Pt-decorated TiNS (with Pt loadings of 0.12 at. %), which is ∼300 times higher than the undecorated TiNS.

Detailed studies on characterization and photocatalytic hydrogen production of ammonium tetrathiomolybdate and tetrathiotungstate pyrolysis products

MoS2 and WS2 are two promising candidates for photocatalytic hydrogen production, and pyrolysis is one of the conventional and useful methods for their preparations. However, systematic investigations about the influences of pyrolysis conditions on their photocatalytic hydrogen production performances are still unreported. Then in this paper, a series of pyrolysis products of ammonium tetrathiomolybdate (ATM) and ammonium tetrathiotungstate (ATT) were prepared by changing the pyrolysis temperature and time. Besides, detailed characterizations were conducted to find out the changes in composition, crystallinity, and morphology. Especially, to get optimal pyrolysis conditions for the preparation of high-performance MoS2 and WS2, their photocatalytic hydrogen production activities were investigated. The results showed that although along with the changes in pyrolysis conditions, the overall changes in composition, crystallinity and morphology are similar for ATM and ATT products, there are significant differences in their performances. For the pyrolysis of ATM, the products obtained under lower temperatures exhibit relatively higher activity than those obtained under higher temperatures. The performance of sample ATM-400-1 (the pyrolysis product obtained under 400 °C 1 h) is the highest and those of two ATM-600 samples (obtained under 600 °C 1 h and 600 °C 2 h) are the lowest. On the contrary, for the pyrolysis of ATT, the higher-temperature products possess much higher performance than the lower-temperature ones. The activity of ATT-400-2 is the highest and those of two ATT-250 samples are the lowest. On the other hand, unconventional crystallized WS3 was unexpectedly obtained through the pyrolysis of ATT at 300 °C for the first time. This work can offer useful information for the preparation of WS2 and MoS2-based photocatalysts.

Construction of isotype heterojunctions in polymeric carbon nitride with thermal modulation and improved photocatalytic hydrogen production activity

Subtle structural changes in polymeric carbon nitrides (PCN) influence their photocatalytic activities. Herein, we present a strategy to construct isotype heterojunctions by thermal condensation of dicyandiamide as a single precursor. This avoids the complications that differences in the electronegativity of the coupled materials incur. Heterojunctions were created by depositing a carbon nitride layer processed at 500 °C over the carbon nitride processed at 600 °C utilizing structural defects and uncondensed moieties to form an interconnected structure. This enables the directional stacking of the PCN layers leading to changes in physicochemical properties and electronic band structure. The detailed characterization and testing revealed a type-II heterojunction configuration, whereby photoluminescence quenching measurements confirm longer exciton lifetimes and differences in Mott-Schottky flat band potential energies and low interfacial resistance facilitate mobility of charge carriers. Heterojunction materials exhibit high photocurrent generation and H2 production with visible light, and AQY surpasses 5%. Overall, efficient charge separation owing to the intrinsic electric field of closely related band offsets at the interface of the heterojunction materials enhances the photocatalytic response. The work highlights the importance of fine structural changes in improving the activity of polymeric photocatalytic systems.

Effective Utilization of Sulfur Wastewater by Photocatalytic System Using B/CuO/ZnO

B-doped zinc oxide/copper oxide composites prepared using a simple method showed high photocatalytic hydrogen production activity in the presence of aqueous sulfide solutions. Co-modification of the CuO composite with B-doping caused an increase in the charge separation efficiency and light absorption capacity. The sacrificial effect was thermodynamically enhanced by manipulating the composition of the sulfide solution. A maximum hydrogen production activity of 224 μmol g−1 h−1 was achieved under 450 nm light irradiation in a photocatalytic system with optimized B doping, a CuO composite, and a sulfide sacrificial agent concentration.

Ultrathin Cu2MoS4/g-C3N4 nanosheets for promoting charge separation with strong redox ability and enhanced photocatalytic hydrogen production activity

Hydrogen energy stands out as one of the most auspicious clean energy prospects, with photocatalytic water splitting emerging as the preeminent method for the efficient production of hydrogen. Combining carbon nitride (g-C3N4) with an oxidized cocatalyst Cu2MoS4 significantly enhances the process for separation of photoinduced holes and photoinduced electrons. In this study, 2D–2D Cu2MoS4/g-C3N4 heterostructure materials using the oil bath method was successfully achieved. The hydrogen production rate of ultrathin 2D–2D Cu2MoS4/g-C3N4 nanosheets is increased by 66 times, reaching 2385 μmol·h−1·g−1. Additionally, insights have been provided through density functional theory (DFT) calculations, showing that the S-type heterojunction formation is a critical factor, which made it possible for photogenerated electrons in g-C3N4 and photogenerated holes in Cu2MoS4 with excellent redox ability to be efficiently separated spatially. This article underscores the significance of interface engineering strategies to control the disjunction of photoinduced holes and electrons.

Boosting the photocatalytic hydrogen production activity of marigold-like Zn2In2S5 by using noble-metal-free Ni2P as cocatalyst

To enhance the activity of photocatalysts, it is crucial to use non-noble metal as a cocatalyst instead of noble metal in the arena of photocatalysis. In this study, to boost the photocatalytic hydrogen activity of pristine Zn2In2S5, XNi2P/ZIS5 composite photocatalysts were prepared using noble-metal-free Ni2P as cocatalyst. Before photocatalytic hydrogen production experiments, the physicochemical properties of the synthesized materials were systematically characterized by advanced characterization methods. The experiment results demonstrate that the load of Ni2P cocatalyst can noticeably enhances the photocatalytic performance of Zn2In2S5 and the photocatalytic hydrogen generation activities are observably influenced by the mass ratio of Ni2P to Zn2In2S5. Among XNi2P/ZIS5, the 10Ni2P/ZIS5 sample presents the optimal hydrogen production rate of 17.74 mmol g−1 h−1, which is 7.58 times as high as that of pristine Zn2In2S5. The increased photocatalytic hydrogen evolution activity could be attributed to the introduction of noble-metal-free cocatalyst Ni2P, which serves as an electronic collector and reduction sites remarkably facilitates the separation and migration of photoexcited electrons of Zn2In2S5. Meanwhile, the rate of reactions is significantly accelerated.

Preparation of NiMoO4/CdS and its Application as a Photocatalyst in H2 Evolution Reaction

AbstractThe construction of heterojunction is considered to be an effective strategy for achieving efficient photocatalyst. The pure CdS shows low hydrogen production activity, for the low charges separation efficiency and the short electron and hole lifetime, which greatly limit its practical application. Therefore, we constructed heterojunction photocatalysts of NiMoO4/CdS by a simple solvothermal method. The photocatalytic hydrogen production activity of CdS was obviously improved by NiMoO4 loaded. The NiMoO4/CdS‐2 sample shows the highest H2 generation rate, which could reach 5830.49 μmolg−1 h−1, which is 122.3 times higher than that of pure CdS. The construction of heterojunction between CdS and NiMoO4 inhibits the recombination of photogenerated charges, prolongs the lifetime of photogenerated charges and improves photocatalytic hydrogen production performance. This work is important for the construction of an efficient catalytic system for the photocatalytic H2 evolution from water splitting.

Noble metal-free 0D-1D CoOx/Mn0.3Cd0.7S nanocomposites for efficient visible-light hydrogen production

Here, a series of MnxCd1-xS sosoloid composite photocatalysts with visible-light activity were first prepared by a solvothermal process. The element ratio of Cd2+ to Mn2+ was optimized to be Mn0.3Cd0.7S in MnxCd1-xS sosoloid on account of its photocatalytic activity for H2 evolution from H2O in response to visible light excitation. And on this basis, the CoOx nanopariticles were loaded on the surface of Mn0.3Cd0.7S sosoloid composite to obtain a binary p-n heterojunction of CoOx/Mn0.3Cd0.7S composite through a facile impregnation process and a high temperature sintering procedure. Benefitting from the synergistic effect of the built-in electric field, binary p-n heterojunction structure, and rearrange of the Fermi level equilibrium, the as-synthesized CoOx/Mn0.3Cd0.7S composite presents a highly enhanced photocatalytic activity for hydrogen production from H2O in response to visible light excitation, which is demonstrated to be 53.4 and 4.0 times higher than that of the primitive CdS and Mn0.3Cd0.7S, respectively. Furthermore, after 4 times circles of photocatalytic H2 production tests, the CoOx/Mn0.3Cd0.7S composite still keeps 92.0 % of the original photocatalytic activity. Considering its reasonable photochemistry stability and excellent photocatalytic activity for hydrogen evolution from H2O under with visible light excitation, the as-synthesized CoOx/Mn0.3Cd0.7S composite has potential applications in solar hydrogen production areas.

CdS Deposited In Situ on g-C3N4 via a Modified Chemical Bath Deposition Method to Improve Photocatalytic Hydrogen Production

Ultra-thin two-dimensional materials are attracting widespread interest due to their excellent properties, and they are becoming ideal candidates for a variety of energy and environmental photocatalytic applications. Herein, CdS nanorods are successfully grown in situ between a monolayer of g-C3N4 using a chemical water bath method. Continuous ultrasound is introduced during the preparation process, which effectively prevents the accumulation of a g-C3N4 layer. The g-C3N4@CdS nanocomposite exhibits significantly enhanced photocatalytic activity for hydrogen production under visible-light irradiation, which is attributed to a well-matched band structure and an intimate van der Waals heterojunction interface. The mechanism of photocatalytic hydrogen production is discussed in detail. Moreover, our work can serve as a basis for the construction of other highly catalytically active two-dimensional heterostructures.

Red Phosphorus Grafted High‐Index (116) Faceted Anatase TiO2 for Z‐Scheme Photocatalytic Pure Water Splitting

AbstractRed phosphorus (RP) is an emerging visible‐light‐responsive photocatalyst, yet the rapid charge recombination has limited photocatalytic hydrogen production activity. In this work, a Z‐scheme heterostructure with RP nanolayer coated on high‐index (116) faceted anatase TiO2 nanoparticles (TiO2@RP) is designed and fabricated via chemical vapor deposition. Compared with pristine TiO2 and RP, the optimized TiO2@RP Z‐scheme heterostructure exhibits a significantly boosted photocatalytic activity for pure water splitting, with hydrogen evolution rate reaching 12.9 µmol·h−1, under simulated solar light irradiation. The strong interfacial interaction and staggered band alignment between (116) faceted TiO2 and RP result in the formation of built‐in electric field, which can drive the directional charge migration from the conduction band (CB) of TiO2 to the valance band (VB) of RP under light irradiation, with photoelectrons and holes of high redox ability maintained at the CB of RP and the VB of TiO2, respectively. This well‐designed heterostructure greatly promotes photogenerated charge separation and migration via a direct Z‐scheme charge transfer pathway.