Efficient Photocatalytic Hydrogen Evolution Research Articles

2D Porphyrin-Based Covalent Organic Framework/PEG Composites: A Rational Strategy for Photocatalytic Hydrogen Evolution.

Two-dimensional porphyrin-based covalent organic frameworks (2D-por-COFs) have gained significant attention as attractive platforms for efficient solar light conversion into hydrogen production. Herein, we found that introducing transition metal zinc and polyethylene glycol (PEG) into 2D-por-COFs can effectively improve the photocatalytic hydrogen evolution performance. The photocatalytic hydrogen evolution rate of ZnPor-COF is 2.82 times higher than that of H2Por-COF. Moreover, ZnPor-COF@PEG has the highest photocatalytic hydrogen evolution efficiency, which is 1.31 times and 3.7 times that of pristine ZnPor-COF and H2Por-COF, respectively. The filling of PEG makes the layered structure of COFs more stable. PEG reduced the distortion and deformation of the carbon skeleton after the experiment of photocatalytic hydrogen evolution. The layered stacking and crystallization of 2D-por-COFs are also enhanced. Meanwhile, the presence of PEG also accelerates the transfer of excited electrons and enhances the photocatalytic hydrogen evolution activity. This strategy would provide valuable insights into the design of 2D-por-COFs as efficient solid photocatalysts for solar-driven hydrogen production. This article is protected by copyright. All rights reserved.

Rod-like Mn0.2Cd0.8S wrapped in foliated CeO2 promote efficient photocatalytic hydrogen evolution

The Mn0.2Cd0.8S/CeO2 heterojunction is synthesized by means of hydrothermal coupling. Short rod-like Mn0.2Cd0.8S is wrapped in leaf like CeO2 to construct a tight heterointerface, which stimulated the photocatalytic activity to the great extent. Due to the remarkable catalytic and electrochemical properties of Mn0.2Cd0.8S, the CeO2 surface active site is driven. CeO2 has excellent specific surface area, suitable pore volume aperture and Mn0.2Cd0.8S match to optimize the internal interface charge transfer path. At the same time, the heterointerface can coordinate the interface electron flow and promote the H2 reduction ability. The results show that the optimal hydrogen production of Mn0.2Cd0.8S/CeO2 with S-type heterostructure is 291.8 μmol, and the internal lattice and surface morphology of Mn0.2Cd0.8S/CeO2 are not easily damaged due to good catalytic stability. The photocatalytic mechanism of Mn0.2Cd0.8S/CeO2 is studied by finding the short distance interfacial charge transfer path and enriching the photogenerated electrons required for hydrogen evolution.

Enhanced visible light-driven hydrogen evolution in non-precious metal Ni2P/CdIn2S4 S-type heterojunction via rapid interfacial charge transfer

Strong light absorption capacity and effective separation of photogenerated charge are the keys to photocatalytic water decomposition, which is usually solved by constructing heterojunction methods. In this work, a novel n-n interwoven Ni2P/CdIn2S4 S-type heterojunction photocatalyst was prepared by hydrothermal method for efficient photocatalytic hydrogen evolution. After a series of characterization and performance tests, under simulated sunlight irradiation at 6 °C (λ > 420 nm), the hydrogen production of Ni2P/CdIn2S4 composite with the best performance can reach 6 mmol/g/h, which is not only 48 times that of pure CdIn2S4, but also 17.2 times that of the expensive metal Pt (CIS–1Pt). By changing the temperature, the hydrogen production of Ni2P/CdIn2S4 reached 8.7 mmol/g/h at 27.5 °C, while its AQY reached 7.7 % and 6.6 % at 420 nm and 475 nm, respectively. In addition, the possible photocatalytic mechanism was analyzed by band structure and XPS diagram, and it was confirmed that the internal electric field of the S-type heterojunction accelerated the photogenerated charge transition and enhanced the hydrogen evolution ability. This effectively compensated for the limitations of severe carrier recombination and low active sites in CdIn2S4 photocatalysts. Therefore, this work provides some help for the construction of non-precious metal S-type heterojunctions for photocatalytic hydrogen production.

Facile synthesis of CuOx-decorated TiO2 nanoparticles via oxygen-limited pyrolysis of Cu(II) complex for efficient photocatalytic hydrogen evolution

CuOx-decorated TiO2 (CuOx/TiO2) nanoparticles have been prepared by the pyrolysis of Cu(II) complex on TiO2 in an oxygen-limited atmosphere. A solution phase deposition method combined with freeze drying was employed for depositing the 2-methylimidazole-Cu(II) complex onto TiO2 nanoparticles. The effect of decoration of CuOx on TiO2 nanoparticles in terms of the crystal phase, morphology, chemical compositions, surface area, surface elemental states, optical absorption and emission properties, was investigated using a series of characterization tools. The oxygen-limited pyrolysis of 2-methylimidazole resulted in the reduction of partial Ti4+ and Cu2+ ions into Ti3+, Cu+ and Cu0 species, respectively. The surface decoration of CuOx was found to improve the separation and migration of photogenerated electron-hole pairs and increase the life time of excitons. Furthermore, the photocatalytic performance of CuOx/TiO2 nanoparticles was evaluated for hydrogen evolution in aqueous methanol solution under UV–visible light irradiation. The CuOx/TiO2 photocatalyst with the optimal cocatalyst loading achieved hydrogen evolution rate of 4.34 mmol h−1 g−1, with 71- and 5.5-fold enhancement in activity over neat TiO2 and CuOx/P25, respectively. It is expected that the combination of deposition and pyrolysis of 2-methylimidazole-Cu(II) complex could be an effective approach for the decoration of Cu and its oxides on other supports.

C3N5 nanosheets decorated with Cu–Pt alloy nanoparticles toward efficient photocatalytic hydrogen evolution

The construction of highly efficient photocatalysts for generating high-purity hydrogen (H2) through a sustainable water decomposition system is a feasible option to replace conventional non-renewable energy resources. Here, we report a simple chemical reduction approach to embed Cu–Pt alloy nanocrystals on the C3N5 (CN) matrix, creating a Schottky heterojunction. The structural morphology, crystal phase, light-harvesting capacity, and photo-electrochemical properties of as-prepared heterostructures were investigated. The uniformly anchored Cu–Pt alloy nanocrystals improve the photocatalytic H2 evolution (PHE) activity by promoting the separation and transfer of photogenerated carriers and inhibiting recombination. Meanwhile, the alloyed nanocrystals strengthen the absorption of incident light energy, inducing photothermal energy. This improves the charge carrier separation and promotes the surface reaction kinetics. The PHE performance of as-developed catalysts could be adjusted by optimizing the molar ratio of Cu/Pt ions. Among them, the optimal Cu1Pt3/CN photocatalyst yields a higher PHE performance (672.85 μmol g−1 h−1). Notably, the Cu1Pt3/CN catalyst also reveals an enhanced photocatalytic activity for H2 evolution in natural seawater. The possible PHE mechanism in CuPt/CN heterostructures is discussed toward the role of CuPt alloy deposition in boosting photocatalytic efficiency.

Coal-based carbon quantum dots modified Ni-MOF and Co/Zr-MOF heterojunctions for efficient photocatalytic hydrogen evolution

NS-CQDs were synthesized by a hydrothermal method using high-sulfur lignite as the carbon source. Modification of Ni-MOF and Co/Zr-MOF using NS-CQDs to explore the performance of composite photocatalysts for hydrogen production. It was found that NS-CQDs significantly enhanced the hydrogen precipitation performance of the composite photocatalysts compared with the MOFs catalysts alone, and the highest hydrogen precipitation rate of the novel composite photocatalyst 5%NS-CQDs/NCZ2 reached 3662.68 μmol g−1 h−1. It can be inferred from the conduction band and valence band positions of Ni-MOF, Co/Zr-MOF and NS-CQDs that a double S-type heterojunction is formed. The presence of thiophene and pyrrole nitrogen in NS-CQDs can promote electron transport, reduce the rate of electron-hole pair complexation, and improve the hydrogen evolution activity of the 5%NS-CQDs/NCZ2.

Linkage-Mediated Electronic Structure Modulation in Multicomponent Covalent Organic Frameworks for Dramatically Promoted Photocatalytic Hydrogen Evolution.

Linkage chemistry is an essential aspect to covalent organic framework (COF) applications; it is highly desirable to precisely modulate electronic structure mediated directly by linkage for efficient COF-based photocatalytic hydrogen evolution, which however, remains substantially challenging. Herein, as a proof of concept, a collection of robust multicomponent pyrene-based COFs with abundant donor-acceptor (D-A) interactions has been judiciously designed and synthesized through molecularly engineering linkage for photogeneration of hydrogen. Controlled locking and conversion of linkage critically contribute to continuously regulating COFs' electronic structures further to optimize photocatalytic activities. Remarkably, the well-modulated optoelectronic properties turn on the average hydrogen evolution rate from zero to 15.67 mmol g-1 h-1 by the protonated quinoline-linked COF decorated with the trifluoromethyl group (TT-PQCOF-CF3). Using diversified spectroscopy and theoretical calculations, we show that multiple modifications toward linkage synergistically lead to the redistribution of charge on COFs with extended π-conjugation and reinforced D-A effect, making TT-PQCOF-CF3 a promising material with significantly boosted carrier separation and migration. This study provides important guidance for the design of high-performance COF photocatalysts based on the strategy of linkage-mediated electronic structure modulation in COFs.

Microwave-Assisted Synthesis of SnO2@ZnIn2S4 Composites for Highly Efficient Photocatalytic Hydrogen Evolution.

This research successfully synthesized SnO2@ZnIn2S4 composites for photocatalytic tap water splitting using a rapid two-step microwave-assisted synthesis method. This study investigated the impact of incorporating a fixed quantity of SnO2 nanoparticles and combining them with various materials to form composites, aiming to enhance photocatalytic hydrogen production. Additionally, different weights of SnO2 nanoparticles were added to the ZnIn2S4 reaction precursor to prepare SnO2@ZnIn2S4 composites for photocatalytic hydrogen production. Notably, the photocatalytic efficiency of SnO2@ZnIn2S4 composites is substantially higher than that of pure SnO2 nanoparticles and ZnIn2S4 nanosheets: 17.9-fold and 6.3-fold, respectively. The enhancement is credited to the successful use of visible light and the facilitation of electron transfer across the heterojunction, leading to the efficient dissociation of electron-hole pairs. Additionally, evaluations of recyclability demonstrated the remarkable longevity of SnO2@ZnIn2S4 composites, maintaining high levels of photocatalytic hydrogen production over eight cycles without significant efficiency loss, indicating their impressive durability. This investigation presents a promising strategy for crafting and producing environmentally sustainable SnO2@ZnIn2S4 composites with prospective implementations in photocatalytic hydrogen generation.

Ohmic junction ZnIn2S4/MoP for efficient photocatalytic hydrogen evolution

In this paper, coupling MoP onto ZIS surface using solvothermal method to form ohmic heterojunction. The photocatalytic performance of ZIS/MoP is significantly better than that of ZIS and MoP monomers, and the hydrogen evolution efficiency of the composite material reaches 2.031 mmol g−1 h−1, 50 and 18 times the hydrogen production efficiency of MoP and ZIS. The quantum apparent efficiency (AQE) reaches 10.5 %. The improvement of the photocatalytic performance of ZIS/MoP is attributed to the generation of Ohmic heterojunctions. An Ohmic heterojunction is formed when MoP attaches to the surface of ZIS as an electron acceptor, In one aspect, the electron transfer path of Ohmic heterojunctions improves the separation efficiency of electrons and holes, enhances the charge transfer efficiency. ln the other aspect, ZIS greatly improves the visible light absorption of ZIS/MoP. To confirm the photocatalytic mechanism and Ohmic heterojunction structure, characterization methods such as X-ray photoelectron spectroscopy (XPS), ultraviolet electron spectroscopy (UPS), and band structure were used. This study aims to improve photocatalytic performance by designing and constructing ohmic heterojunctions, and provides a new design approach for improving photocatalytic performance.

Amorphous nitrogen-doped carbon layers forming the interfacial channel for rapid charge transfer in ZnIn2S4/BiVO4 Z-scheme photocatalyst for enhancing organic pollutants degradation with simultaneous hydrogen evolution

Efficient photocatalytic hydrogen evolution from the organic wastewater represents an ideal solution for simultaneously addressing energy shortages and environmental pollution. However, the sluggish transport of photogenerated carriers at contact interface poses a key obstacle to enhancing photocatalytic activity. Here, ZnIn2S4/BiVO4@N-C (ZIS/BVO@N-C) Z-scheme photocatalysts were successfully constructed by a simple hydrothermal-impregnation method. ZIS/BVO@N-C-10% demonstrated outstanding photocatalytic performance, achieving a hydrogen evolution rate of 2695.68 μmol·g−1·h−1 and a degradation rate of 492.96 mmol·g−1·h−1 under visible light, surpassing those of ZIS (851.52 μmol·g−1·h−1 and 174.83 mmol·g−1·h−1) and ZIS/BVO-10% (1228.98 μmol·g−1·h−1 and 277.78 mmol·g−1·h−1). Characterization results and density functional theory (DFT) calculations revealed that the introduction of the N-C layer reduced interfacial impedance and enhanced the strength of interfacial electric field, overcoming the interfacial barrier and improving the photogenerated separation and migration efficiency at the interface, and ultimately enhancing the photocatalytic activity of ZIS/BVO@N-C. Based on experimental and characterization results, the photocatalytic mechanism of ZIS/BVO@N-C Z-scheme has been proposed. Furthermore, ZIS/BVO@N-C exhibited excellent stability, highlighting its potential for practical applications. This work also presents a new strategy for designing highly active Z-scheme photocatalysts for organic wastewater treatment and simultaneous hydrogen energy recovery.

Surface vacancy engineering powered reverse cation exchange in preparing CuZnS hollow nanoboxs for efficient photocatalytic hydrogen evolution

The cation exchange technology plays a significant role in designing high-performance photocatalysts at atomic scale. However, the chemical kinetic energy barrier greatly limits the application of cation exchange strategies. Herein, an effective surface vacancy engineering powered reverse cation exchange strategy was exploited to realize energy-unfavored cation exchange reactions. Cu vacancies are created on the surface of Cu2-xS nanoboxs (Cu2-xS NBs), which are subsequently occupied by Zn2+ ions. A hollow CuZnS nanoboxs (CuZnS NBs) were successfully prepared for photocatalytic hydrogen evolution. The prepared CuZnS NBs has abundant interfacial Zn-S bonds, which promote interfacial charge transfer (IFCT) as a rapidly electron bridge. In particular, the photocatalytic hydrogen evolution rate of CuZnS NBs under visible light is 2.06 mmol·g−1·h−1, which is 5.9 times higher than that of Cu2-xS. The synthetic mechanism and photocatalytic mechanism of the CuZnS was investigated from experiment and theoretical calculations. The surface vacancy powered reverse cation exchange strategy offers a new opportunity for the rational tailoring new-generation photocatalysts at the atomic scale.

Acid etching-induced nanocutting of LaNiO3 transplanting self-assembled photodiode array-like LaNiO3/N,P-RGO nanoreactor for efficient photocatalytic hydrogen evolution

Nanoscale graphene-semiconductor composite photocatalysts with fascinating properties in the photocatalytic hydrogen evolution have inspired numerous interests in broad research fields. The architectures with efficient light response and promoting charge separation at the interface between reduced graphene oxide (RGO) and semiconductor are critical, yet synthesizing them remains a formidable challenge. Herein, the photodiode array-like LaNiO3/N,P-RGO (LNO/N,P-RGO) nanoreactor was constructed using an innovative strategy of acid etching-induced nanocutting self-assembly. Ammonium dihydrogen phosphate working as both a nitrogen phosphorus co-dopant and an acid etching reagent, cuts perovskite LaNiO3 (LNO) nanoparticles into nanorods, which are bonded evenly on the nitrogen phosphorus co-doped reduced graphene oxide (N,P-RGO) to form an n-n semiconductor heterojunction LNO/N,P-RGO as a photodiode array-like nanoreactor via hydrothermal treatment. The photodiode array-like nanostructure exposes more active sites that are conducive to light absorption. The robust Ni-C and P-O bonds promote the narrowing of space-charge region at the interface by UV irradiation, thereby improving the transport of photogenerated carriers by visible light irradiation. The LNO/N,P-RGO nanoreactor exhibits excellent photocatalytic hydrogen evolution performance with a yield of up to 354 μmol g−1 h−1 under UV–visible light, which is 50 times higher than that of pure perovskite LNO, and it also displays favorable recycling stability.

Active Sites Formed on InVO4/Co3O4 S‐Scheme Heterostructure for Photocatalytic Hydrogen Production

AbstractThe reasonable design of S‐scheme heterojunction to avoid unwanted charge transfer paths in hybrid semiconductors is considered to be an attractive method to obtain efficient photocatalytic hydrogen evolution activity. The photocatalytic hydrogen evolution performance of the system was improved by loading ultra‐thin InVO4 nanosheets on the surface of hollow cube Co3O4 to form an S‐scheme heterojunction. Benefiting from the unique nano‐cage structure derived from the zeolitic imidazolate frameworks (ZIF) series, it not only provides a good carrier for activating and stabilizing InVO4 nanosheets but also effectively avoids the masking of active sites caused by self‐agglomeration, which is more conducive to the exposure of more active sites. In the presence of sensitizer and sacrificial reagent, the optimized InVO4/Co3O4 has a more competitive H2 production, which is undoubtedly due to the construction of S‐scheme heterojunctions and unique spatial structure that facilitates the spatial separation of photoexcited charges. It is further confirmed that the photogenerated carrier transfer follows the S‐scheme mechanism by in‐situ irradiation XPS test.

Acceleration of the electron transfer for efficient photocatalytic hydrogen evolution via regulating the surfactant around the active center in 2D MOFs

Although surfactants have been proved to be effective in controlling the size and morphology to prepare high-quality two-dimensional (2D) MOF nanosheets, the impact of surfactants remaining on the 2D MOF nanosheets on their microenvironment is rarely reported. In this paper, polyvinylpyrrolidone (PVP) was used as surfactant to synthesize Co-TCPP(Pd) (abbreviated as Co-Pd) nanosheets, and the content of PVP attached to Co-Pd nanosheets was controlled by ethanol treatment, to regulate the microenvironment around Co-Pd nanosheets. The XRD, FT-IR, XPS, TEM, and TG were used to confirm that after ethanol ultrasonic treatment, the PVP content on Co-Pd nanosheets was gradually reduced without damaging the original structure and morphology of Co-Pd nanosheets. PVP attached to Co-Pd nanosheets will slow down the electron migration rate, affecting the microenvironment around co-catalyst Pd, which has been confirmed by EIS, PL and DFT etc. The results exhibited that the Co-Pd-6 obtained by ethanol ultrasonic treatment 6 times showed the more excellent photocatalytic hydrogen evolution activity (8284.25 umol·g−1·h−1), which was 4.02 times as that of Co-Pd-0 (2059.59 umol·g−1·h−1) without ethanol ultrasonic treatment), indicating that PVP will have a negative impact on the microenvironment around the co-catalyst, thereby affecting the photocatalytic hydrogen evolution performance. This study indicates that efficient photocatalytic hydrogen evolution can be achieved via adjusting the microenvironment around the co-catalyst to promote electron transfer.

An All-In-One Integrating Strategy for Designing Platinum(II)-Based Supramolecular Polymers for Photocatalytic Hydrogen Evolution.

Organic polymer photocatalysts have achieved significant progress in photocatalytic hydrogen evolution, while developing the integrated organic polymers possessing the functions of photosensitizer, electron transfer mediator, and catalyst simultaneously is urgently needed and presents a great challenge. Considering that chalcogenoviologens are able to act as photosensitizers and electron-transfer mediators, a series of chalcogenoviologen-containing platinum(II)-based supramolecular polymers is designed, which exhibited strong visible light-absorbing ability and suitable bandgap for highly efficient photocatalytic hydrogen evolution without the use of a cocatalyst. The hydrogen evolution rate (HER) increases steadily with the decrease in an optical gap of the polymer. Among these "all-in-one" polymers, Se-containing 2D porous polymer exhibited the best photocatalytic performance with a HER of 3.09mmolg-1h-1 under visible light (>420nm) irradiation. Experimental and theoretical calculations reveal that the distinct intramolecular charge transfer characteristics and heteroatom N in terpyridine unit promote charge separation and transfer within the molecules. This work could provide new insights into the design of metallo-supramolecular polymers with finely tuned components for photocatalytic hydrogen evolution from water.

Organizing Photosensitive and Photothermal Single-Sites Uniformly in a Trimetallic Metal-Organic Framework for Efficient Photocatalytic Hydrogen Evolution.

Effective combination of the photosensitivity and photothermal propertyin photocatalyst is vital to achievethe maximum light utilization for superior photocatalytic efficiency. Herein, this work successfully organizes photosensitive Cd-NS single-sites and photothermal Ni-NS single-sites uniformly at a molecular level within a tailored trimetallic metal-organic framework. The optimized Ho6-Cd0.76Ni0.24-NS exhibits a superior photocatalytic hydrogen evolution rate of 40.06 mmol g-1 h-1 under visible-light irradiation and an apparent quantum efficiency of 29.37% at 420nm without using cocatalysts or photosensitizers. A systematical mechanism study reveals that the uniformly organized photosensitive and photothermal single-sites have synergistic effect, which form ultrashort pathways for efficient transport of photoinduced electrons, suppress the recombination of photogenerated charge carriers, hence promote the hydrogen evolution activity. This work provides a promising approach for organizing dual-functional single-sites uniformly in photocatalyst for high-performance photocatalytic activity.

Tailoring the morphology and charge transfer pathways of ultrathin Cd0.8Zn0.2S nanosheets via ionic liquid-modified Ti3C2 MXenes towards remarkable photocatalytic hydrogen evolution

Small-sized CdxZn1–xS solid solution nanomaterial is an important candidate for efficient photocatalytic hydrogen evolution (PHE), but it still suffers from easy agglomeration, severe photo corrosion, and fast photogenerated electron-hole recombination. To tackle these issues, herein, we propose a new strategy to modify CdxZn1–xS nanoreactors by the simultaneous utilization of ionic-liquid)-assisted morphology engineering and MXene-incorporating method. That is, we designed and synthesized a novel hierarchical Cd0.8Zn0.2S/Ti3C2 Schottky junction composite through the in-situ deposition of ultrathin Cd0.8Zn0.2S nanosheets on unique IL-modified Ti3C2 MXenes by a one-pot solvothermal method for efficiently PHE. The unique construction strategy tailors the thickness of ultrathin Cd0.8Zn0.2S nanosheets and prevents them from stacking and agglomeration, and especially, optimizes their charge transfer pathways during the photocatalytic process. Compared with pristine Cd0.8Zn0.2S nanosheets, Cd0.8Zn0.2S/Ti3C2 has abundant photogenerated electrons available on the Ti3C2 surface for proton reduction reaction, owing to the absence of deep-trapped electrons, suppression of electron-hole recombination in Cd0.8Zn0.2S and high-efficiency charge separation at the Cd0.8Zn0.2S/Ti3C2 Schottky junction interface. Moreover, the hydrophilicity, electrical conductivity, visible-light absorption capacity, and surficial hydrogen desorption of Cd0.8Zn0.2S/Ti3C2 heterostructure are significantly improved. As a result, the heterostructure exhibits outstanding photocatalytic stability and super high apparent quantum efficiency, being rendered as one of the best noble-metal-free Cd-Zn-S-based photocatalysts. This work illustrates the mechanisms of morphology control and heterojunction construction in controlling the catalytic behavior of photocatalysts and highlights the great potential of the IL-assisted route in the synthesis of high-performance MXene-based heterostructures for photocatalytic hydrogen evolution.

Coupling amorphous WO3 with WP as a cocatalyst for efficient dye-sensitizated photocatalytic hydrogen evolution

Tungsten phosphide (WP) as an excellent hydrogen evolution reactions (HER) catalyst has attracted widespread attention, but its HER activity is low in alkaline media due to high water dissociation barrier. Herein, noble-metal-free cocatalyst WP/WO3 composite was synthesized by adjusting the P/W molar ratio in the raw material using a simple solid phosphidation reaction. The structure, morphology, composition, and optoelectronic properties of the as-synthesized samples were characterized by XRD, SEM, TEM, XPS, UV–vis DRS, PL techniques, and electrochemical methods. Under visible light irradiation (λ ≥ 420 nm), the photocatalytic HER activities of the as-prepared samples using Eosin-Y (EY) dye as a sensitizer and trimethylamine (TMA) as an electron donor were investigated. The result shows that WP/WO3 composite as a cocatalyst exhibits excellent photocatalytic HER activity and good stability. The highest apparent quantum yield (AQY) reaches 32.8 %. The presence of amorphous WO3 in crystalline WP can improve the separation efficiency of photogenerated electrons and holes, reduce HER overpotential, and promote the dissociation of H2O in alkaline media. Therefore, the photocatalytic HER activity of WP/WO3 composite is higher than that of single crystalline WP.

Molecular engineering in tunable crystallinity of 2D covalent organic frameworks for efficient photocatalytic hydrogen evolution

The strategy of molecular engineering has been employed to build the structure–property–activity relationship for covalent organic frameworks (COFs) with efficient photocatalytic water splitting for hydrogen production. However, previous reports focus on the impact of molecular design on COFs’ physicochemical properties, the crystallinity differences are usually ignored and related studies remain rare. Herein, we describe the preparation of a series of structurally related COFs with similar chemical compositions but have different numbers of nitrogen (N) atoms in the central aromatic ring via an efficient crystallization strategy using of 2,4,6-triformyl resorcinol (TFR). On one hand, the introduction of N atoms reduces π-π stacking interaction during the formation of framework, leading to a decrease in crystallinity. On the other hand, it contributes to enhancing the photocatalytic performance of the materials by varying the electronic structures. Consequently, our results revealed that the photocatalytic hydrogen evolution (PHE) rate is 61.22 mmol g−1 h−1 for COF-905-1N, significantly higher than COF-905-3N (40.60 mmol g−1 h−1) and COF-905 (26.23 mmol g−1 h−1). This study not only provide fundamental insights into formation mechanism of COFs, but also provide a practical approach to enhance COF-based photocatalytic performance.

Metal-free thiophene-based covalent organic frameworks achieve efficient photocatalytic hydrogen evolution by accelerating interfacial charge transfer

Photocatalysis is widely recognized as an efficient and environmentally friendly pathway for the conversion of solar energy into chemical energy. In recent years, designing efficient hydrogen evolution to obtain green clean energy has been one of the major challenges faced by researchers. Covalent organic frameworks (COFs) are considered as new and effective photocatalyst due to the inherent porosity, high crystallinity and structural adjustability. In this study, two metal-free thiophene-based covalent organic frameworks (JLNU-308 and JLNU-309) were constructed by solvothermal method through effective modulation sites. Because JLNU-COFs has a narrow band gap and good absorption capacity in the spectral range, the interfacial charge transfer speed is accelerated to solve the problem of low charge separation efficiency. Remarkably, JLNU-309 displays an impressive hydrogen evolution rate of 2868.57 μmol g−1 h−1 under visible light irradiation (λ > 420 nm). The superior hydrogen evolution reaction (HER) activity is due to the triazine units, which have high visible light absorption capacity, one-dimensional nanochannels of two-dimensional COFs and synergy with charge mobility. The photoelectrochemical measurements and calculation of density functional theory (DFT) supports the accuracy of the experiment. This work opens an avenue for constructing functional covalent organic frameworks for environmentally relevant critical applications. In addition, the simple synthesis process, excellent activity and high chemical stability indicate that JLNU-COFs are promising photocatalytic hydrogen production materials.