H2 Evolution Rate Research Articles

Fabrication of S-scheme FeCoS2/Red phosphorus heterojunction for efficient photocatalytic H2 evolution

Establishing efficient charge transfer channels remains a great challenge to improve the photocatalytic activity of red phosphorus (RP). Herein, the flower-like spherical FeCoS2 was employed to improve the activity of RP nanosheets, S-scheme FeCoS2/RP heterojunction was obtained through a facile solvent evaporation strategy. The optimized 5 wt% FeCoS2/RP exhibited an excellent H2 evolution rate of 2254.2 μmol g−1 h−1, which is 17.5 and 71.1-fold than that of pristine RP (129.1 μmol g−1 h−1) and FeCoS2 (31.7 μmol g−1 h−1), respectively. The analysis shows that bimetallic sulfides FeCoS2 can not only increase the electrochemically active surface area, decrease the H2 evolution overpotential and water contact angle of the composite, but also provide more photoinduced charges and reduce their transfer resistance, more importantly, the charge transfer between FeCoS2 and RP follows the S-scheme route, which can reserve the electrons and holes with higher the thermodynamic driving force. Further investigation shows that the activity of FeCoS2 is superior to monometallic sulfides FeS and CoS due to its synergistic effect between Fe and Co. This work provides new insights for constructing S-scheme RP-based heterojunction with high photocatalytic efficiency and stability.

Interfacial engineering of hematite photoanodes toward high water splitting performance

Efficient and scalable photoelectrochemical water splitting electrode designs are a challenge. This study focuses on hafnium-modified hematite (X%Hf-HEM) photoanodes, prepared via spin-coating polymeric precursor solutions with varying Hf4+/Fe3+ (mol) ratios (1.0%, 3.0%, 4.0%, and 5.0%) onto fluorine-doped tin oxide substrates. Structural, morphological, and compositional analyses confirm pure hematite phases in all X%Hf-HEM samples. Increasing Hf4+ content correlated with reduced grain size, thickness, and surface roughness due to Hf4+ segregation at grain boundaries during thermal treatment. Hafnium segregation at hematite grain boundaries and hematite|fluorine-doped tin oxide interfaces is confirmed using scanning transmission electron microscopy coupled with energy dispersive spectroscopy. Notably, the 4%Hf-HEM photoanode exhibits exceptional efficiency enhancement, outperforming HEM efficiency by 4.5 times. Gas chromatography results highlight O2 and H2 evolution rates of 14.49 ± 0.09 μmol/cm2/h and 8.1 ± 0.5 μmol/cm2/h, respectively, for 4%Hf-HEM, with a H2/O2 ratio close to 2:1. The charge dynamics investigated from intensity-modulated photocurrent spectroscopy evidence the main Hf4+ effect of improving charge separation, achieving greater efficiency for 4%Hf-HEM. Shifts in valence band maximum from ultraviolet photoelectron spectroscopy measurements indicate surface state presence, supported by ηtransfer trends calculated from intensity-modulated photocurrent spectroscopy. This research presents a scalable, cost-effective approach to multiinterface photoanode development, holding promise for innovative photoelectrochemical water splitting technologies.

Ultrafast electron transfer from CdS quantum dots to atomically-dispersed Pt for enhanced H2 evolution and value-added chemical synthesis

Photocatalytic hydrogen production is enchanting in solar energy utilization. And mechanism elucidation in interfacial electron transfer rate is a prerequisite for performance improvement. Herein, atomically dispersed Pt-modified CdS quantum dots (Pt-CdS QDs), prepared by a facile one-step in-situ deposited method, are used as a prototype. Benefiting from the maximized utilization of Pt cocatalyst as well as the strong electronic metal-support interaction, ultrafast electron transfer from CdS to Pt (∼1.7 ps) is achieved, as revealed by femtosecond transient absorption spectra. The optimal sample simultaneously realizes photocatalytic hydrogen evolution coupled with selective oxidation of 2-thiophene methanol (TM) into 2-thiophenecarboxaldehyde (TD). Specifically, it exhibits an enhanced H2-evolution rate, which is 70-fold higher than pristine CdS QDs. Moreover, a TM conversion rate of 95.3 % with a TD selectivity of 87.2 % is reached after 4 h. This work will provide some guidance for the design of photocatalytic systems with efficient interfacial electron transfer.

Enhancing H2 production rate in PGM-free photoelectrochemical cells by glycerol photo-oxidation

The photo-oxidation of glycerol was carried out by using TiO2 NTs photoanodes and Ni foam as the cathode for the Hydrogen Evolution Reaction. The photoanodes were prepared by anodizing Ti foils and titanium felt and then annealed under air exposure. They were tested in acidic aqueous solution without and with the addition of glycerol. When glycerol was present, the hydrogen production rate increased and allowed the simultaneous production of high value added partial oxidation compounds, i.e. 1,3-dihydroxyacetone (DHA), and glyceraldehyde (GA). The highest H2 evolution and partial oxidation compounds production rates were obtained by using home prepared TiO2 nanotubes (TiO2 NTs) synthesized on Ti fiber felt as the photoanode with an irradiated area of 90 cm2. These photoanodes were found to be highly stable both from a mechanical and a chemical point of view, so they can be reused after a simple cleaning step.

Fabrication of 2D+1D nanoarchitecture for transition metal oxide modified CdS nanorods: A comparative study on their photocatalytic hydrogen-generation efficiency

We report the formation of Mo1−xWxO3-CdS (0 ≤ x ≤1) nanophotocatalysts by a combination of solid-state and solution-impregnation processes. The formation of 2D+1D heterostructured composite was revealed by electron microscopy and the structure of ternary co-catalyst and photocatalysts were confirmed by spectroscopic analyses. The H2 evolution activity of the nanocomposites was assessed via photocatalytic splitting of water under the irradiation of visible light. All the nanocomposites studied here exhibit notable catalytic activity and good photostability using lactic acid as the sacrificial electron donor compared to a pristine compound. Among these nanocomposites, WO3-CdS shows superior activity with H2 evolution rates of 15.19 mmolg−1h−1, 28 times higher than the pure CdS. The WO3-CdS photoactivity is not only superior among all the composites studied here but also highest among the reported WO3 composite catalysts to date. The novel construction of the oxide-based nanocomposite photocatalyst shown here efficiently enhances the catalytic activity by effective separation of charge carriers and inhibits photocorrosion of CdS nanorods. The apparent quantum yield of the hydrogen evolution for WO3-CdS was found to be 8% in the visible spectral range. The disparity of the catalytic ability between MoO3 and WO3 and the variance among the compositions was unraveled through optical band-offset alignment with respect to CdS. Though the 2D+1D novel fabrication is common to all the composites, the difference in the type of band alignment MoO3 (type-I) and WO3 (type-II) with CdS plays a highly significant role in the co-catalytic activity.

Ingenious design and construction of Ti3+-TiO2/C nanofibers with significantly enhanced photocatalytic H2 evolution

Herein, the Ti3+-TiO2/C hybrid with fluffy mesh structure is successfully synthesized through carbothermal reduction method using the white sponge scarfskin of shaddock peel (denoted as SSP) as template and carbon source. During the preparation process, the SSP not only can contribute to building the fluffy mesh structure, but also can offer carbon source for reducing Ti4+ to Ti3+ in the Ti3+-TiO2/C composite. Furthermore, under argon atmosphere, the Ti3+ content in the composite can be adjusted via changing the calcining temperature of the tube furnace. In comparison with that of the individual TiO2, the resultant Ti3+-TiO2/C hybrids both exhibit superior photocatalytic H2 production property under visible light or simulated sunlight irradiation. In particular, the optimized hybrid of Ti3+-TC-350–600 exhibits excellent catalytic performance. The H2 production rates of it are 2341 and 6695 μmol g-1h−1 under visible light and simulated sunlight irradiation, respectively. The corresponding H2 evolution rate of the Ti3+-TC-350–600 is 5.5 or 2.2 times than that of the TiO2-350–600. According to the results of the hybrid composition and microstructure, optical and electrical property, H2 production performance and differential charge density, the Ti3+-TiO2/C hybrid exhibits favorable H2 production performance should be ascribed to the synergistic effect of the Ti3+, graphite-like carbon and fluffy mesh structure. Therefore, this study could offer a valuable thinking and reference for design and synthesis the Ti3+-TiO2/C photocatalyst for H2 evolution.

Ferroelectric Polarization in BaTiO3 Nanocrystals Controls Photoelectrochemical Water Oxidation and Photocatalytic Hydrogen Evolution.

Ferroelectric (FE) semiconductors such as BaTiO3 support a remnant polarization after the application of an electric field that can promote the separation of photogenerated charge carriers. Here, we demonstrate FE-enhanced photocatalytic hydrogen evolution and photoelectrochemical water oxidation with barium titanate nanocrystals for the first time. Nanocrystals of the ferroelectric tetragonal structure type were obtained by a hydrothermal synthesis from TiO2 and barium hydroxide in 63% yield. BaTiO3 nanocrystal films on tantalum substrates exhibit water oxidation photocurrents of 0.141 mA cm-2 at 1.23 V RHE under UV light (60 mW cm-2) illumination. Electric polarization at 52.8 kV cm-1 normal to the film plane increases the photocurrent by a factor of 2 or decreases it by a factor of 3.5, depending on the field polarity. It also shifts the onset potential by -0.15 or +0.09 V and it modifies the surface photovoltage signal. Lastly, exposure to an electric field increases the H2 evolution rate of Pt/BaTiO3 by a factor of ∼1.5, and it raises the selectivity of photodeposition of silver onto the (001) facets of the nanocrystal. All FE enhancements can be removed by heating samples above the Curie temperature of BaTiO3. These findings can be explained by FE dipole-induced changes to the potential drop across the space charge layer of the material. The ability to use the ferroelectric effect to enhance hydrogen evolution and water oxidation is of potential interest for the development of improved solar energy for fuel conversion systems.

Single-atom Pt anchored thiophene ring doped carbon nitride nanosheets for enhanced visible-light photocatalytic H2 evolution and ciprofloxacin degradation

A small amount of cocatalysts often play a crucial role in polymerization semiconductor photocatalytic reactions, and precious metals, like Pt, remain irreplaceable as cocatalysts in most applications due to their excellent properties. Meanwhile, maximizing the atomic utilization of cocatalysts and enhancing the host-guest interactions are important routes to enhance photocatalytic efficiency. Single Pt atoms anchored thiophene ring-doped carbon nitride nanosheets (Ptx-CNA) by a facile incipient wetness impregnation were successfully synthesized in this work. Single-atom Pt are uniformly embedded in CNA nanosheets through Pt–N coordination bonds. Coordinated electron-rich thiophene ring-doping and single-atom Pt modifications promote wider visible light response, enhanced charge response, and fast transport capability in Pt-CNA materials. Pt1.0-CNA sample displays the most outstanding photocatalytic H2 evolution rate (360.0 μmol h−1), which is nearly 5 times that of Pt1.0-CN (70.5 μmol h−1). Excellent photocatalytic degradation performance of ciprofloxacin is also achieved and the degradation rate constant of Pt1.0-CNA is 1.8 times that of CNA. Molecular modifications and single-atom cocatalytic together significantly improve the photocatalytic efficiency of polymer semiconductors.

Rational design and synthesis of bifunctional Dibenzo[g,p]chrysene-based conjugated microporous polymers for energy storage and visible light-driven photocatalytic hydrogen evolution

The importance of conjugated microporous polymers (CMPs) as active components in photocatalytic hydrogen evolution is growing due to its intense ultraviolet–visible (UV–vis) absorption, potent fluorescence, and high carrier transport capacity, dibenzo[g,p]chrysene shows notable photophysical and electrical features. This is because CMPs have stiff molecular structures with large π-conjugation. In this section, we describe our approach and syntheses of three types of polymers for the first time to determine the reactivity of dibenzo[g,p]chrysene (TBN)-based CMPs for photocatalytic H2 evolution and energy storage applications. Three TBN-based CMPs, TBN-TBN (D-D), TBN-TBN-TPA (A-D), and TBN-TBN-BT (D-A), were synthesized via Sonogashira–Hagihara coupling. TBN-CMP materials were used as working electrodes for energy storage applications. The TBN-TBN-BT CMP demonstrated excellent capacity retention (98.2%) over 2000 cycles and high capacitor (130 F g−1) at 0.5 A g−1, in accordance with electrochemical performance. Furthermore, the hydrogen evolution rate (HER) results are in the following order 8452, 9800, and 3060 μmol g−1h−1 for TBN-TBN, TBN-TBN-TPA, and TBN-TBN-BT CMPs, respectively. These findings suggest that using TBN as an acceptor increases the number of active sites for proton reduction, thereby boosting the rate of H2 evolution.

Highly selective photocatalytic CO2 reduction and hydrogen evolution facilitated by oxidation induced nitrogen vacancies on g-C3N4

The introduction of nitrogen vacancies into polymeric carbon nitride (PCN) has been attested to be a reliable strategy to enhance photocatalytic performance. Nitrogen vacancies were considered as active sites to promote the adsorption of target molecules and capture photoexcited electrons to inhibit the recombination of charge pairs, accelerate photoinduced electrons to participate in photocatalytic reaction. In this paper, a series of PCN with rich nitrogen vacancies were prepared by etching of chromic acid solution. Sample 20KCSCN had the highest photocatalytic performance whose evolution efficiency of CO2 to CO and CH4 can reach 3.9 and 0.5 μmol·g−1·h−1, respectively. These evolution efficiencies are 2.9 and 4 times higher than that of the PCN. Meanwhile, 20KCSCN demonstrates high CO conversion selectivity and stability. The successful introduction of nitrogen vacancies not only increases the active sites of PCN surface, but also optimizes the optical structure, which dramatically boosts the separation of photoexcited charge pairs and the reduction capacity of photogenerated electrons. The enhancement mechanism for photocatalytic CO2 reduction performance of PCN was proposed. Besides, photocatalytic H2 evolution experiments were performed on all samples to confirm the universality of PCN photocatalytic activity enhancement etched by chromic acid solution. H2 evolution rate on 20KCSCN can reach 652 μmol·g−1·h−1, which is 1.6-fold higher than that on PCN (254 μmol·g−1·h−1) after 4 h irradiation under a 300 W Xe lamp. This work offers new venue for introducing nitrogen vacancies in PCN to regulate photoexcited charge pairs transfer. The photocatalytic enhancement of CO2 reduction could be used to alleviate the serious issue of excessive CO2 emission and energy crisis.

Black Phosphorus as Promoter for Noble Metal‐Free Photocatalytic Hydrogen Production

AbstractPhotocatalysts which are stable to photocorrosion and noble metal‐free, are highly desirable to achieve a light‐driven hydrogen production which satisfies the criteria of low production cost and environmental sustainability. Herein, a new heterostructure TiO2/BP/CoP has been developed, in which the BP nanosheets interact strongly with TiO2 and CoP, speeding up the transfer of photogenerated electrons and thus increasing H2 production. Once BP is added to TiO2 (P25) as only 1 % wt., the H2 evolution rate increases up to 4 times reaching a value of 830 μmol/g ⋅ h under UV‐Vis light irradiation. By integrating CoP nanoparticles as a cocatalyst up to 2 % wt., H2 production is further promoted to 7400 μmol/g ⋅ h, 37 times higher than pristine TiO2. Photoluminescence and electrochemical impedance measurements show that this heterostructure achieves a much more efficient charge separation and reduction of the internal resistance in comparison to pristine TiO2. Combining these data with UV‐Vis diffuse reflectance and Mott‐Schottky, a plausible mechanism was proposed.

Modulating Photoinduced Electron Transfer between Photosensitive MOF and Co(II) Proton Reduction Sites forBoosting Photocatalytic Hydrogen Production.

Photocatalytic hydrogen production viawater splitting is the subject of intense research. Photoinduced electron transfer (PET) between a photosensitizer (PS) and a proton reduction catalyst is a prerequisite step and crucial to affecting hydrogen production efficiency. Herein, three photoactive metal-organic framework (MOF) systems having two different PET processes where PS and Co(II) centers are either covalently bonded or coexisting to drive photocatalytic H2 production arebuilt. Compared to these two intramolecular PET systems including CoII -Zn-PDTP prepared from the post-synthetic metalation toward uncoordinated pyridine N sites of Zn-PDTP and sole cobalt-based MOF Co-PDTP, the CoII (bpy)3 @Zn-PDTP system impregnated by molecular cocatalyst possessing intermolecular PET process achieves the highest H2 evolution rate of 116.8mmol g-1 h-1 over a period of 10h, about 7.5 and 9.3 times compared to CoII -Zn-PDTP and Co-PDTP in visible-light-driven H2 evolution, respectively. Further studies reveal that the enhanced photoactivity in CoII (bpy)3 @Zn-PDTP canbe ascribed to the high charge-separation efficiency of Zn-PDTP and the synergistic intermolecular interaction between Zn-PDTP and cobalt complexes. The present work demonstrates that the rational design of PET process between MOFs and catalytic metal sites can be a viable strategy for the development of highly efficient photocatalysts with enhanced photocatalytic activities.

Vacancy-Modified Porous g-C3N4 Nanosheets Controlled by Physical Activation for Highly Efficient Visible-Light-Driven Hydrogen Evolution and Organics Degradation.

As a promising photocatalyst material, g-C3N4 has great application potential in energy production and environmental improvement. In this work, surface-modified g-C3N4 nanosheets with excellent stability and high photocatalytic activity were successfully synthesized by physical steam activation. The charge transfer rate of carbon nitride was improved due to the synergistic effect of nitrogen defect and oxygen doping caused by steam activation. Meanwhile, the specific surface area and pore volume of the optimized sample reached 124.3 m2 g-1 and 0.42 cm3 g-1, respectively, which increased the exposed reaction sites of reactants, enhancing the photocatalytic activity of g-C3N4. In addition, this novel g-C3N4 displayed a great H2 evolution rate of 5889.39 μmol h-1 g-1 with a methylene blue degradation rate up to 6.52 × 10-3 min-1, which was 3.7 and 2.1 times of original g-C3N4, respectively. This study provided a simple and economical method to develop a highly efficient g-C3N4 photocatalyst for solar energy conversion.

Promoting CdS photocatalytic activity through a coating layer of solid electrolyte LiTi2(PO4)3

Two major challenges in photocatalysis are the separation and utilization of photogenerated charge carriers that have limited their wider applications. To address these issues, significant studies have been devoted to the surface modification of photocatalysts. Herein, CdS nanorods were surface-modified by an ion-conducting LiTi2(PO4)3 (LTP) shell. This modification could accelerate the rapid separation and efficient utilization of photoinduced charge carriers. Therefore, CdS@LTP composite photocatalyst displayed a photocatalytic H2 evolution rate of 26.01 mmol g−1h−1 without any addition of cocatalysts in a Na2S/Na2SO3 solution, which was over 6-fold compared to CdS, and showed improved stability. Furthermore, this shell can prevent the reverse reactions between H2 and O2 during photocatalytic water splitting. With the photo-deposition of Pt cocatalysts, CdS@LTP-Pt can achieve efficient overall water splitting with the highest H2 generation rate (351 μmol g−1h−1), which is 3.25 times higher than that of CdS-Pt. This study broadens the application of ionic conductor materials and provides a new way for the design of advanced photocatalysts for solar energy conversion.

4-Methyl-5-vinyl thiazole modified Ni-MOF/g-C3N4/CdS composites for efficient photocatalytic hydrogen evolution without precious metal cocatalysts

The construction of heterojunction systems is an effective way to efficiently generate hydrogen by water photolysis. In this work, Ni-MOF (trimesic acid, (BTC)) and g-C3N4 (denoted as CN) were combined, and then Ni-MOF/CN was modified by 4-Methyl-5-vinyl thiazole (denoted as MVTh). Finally, CdS was loaded on the surface of Ni-MOF/CN/MVTh to prepare the photocatalyst Ni-MOF/g-C3N4/MVTh/CdS (denoted as Ni/CN/M/Cd) with a triangular closed-loop path heterojunction for the first time. As a photocatalyst without precious metal cocatalysts, Ni/CN/M/Cd displayed high H2 evolution (17.844 mmol·g−1·h−1) under an optimum CdS loading of 40 wt%. The H2 evolution rate was approximately 79 times that of Ni-MOF/CN and exceeded those of almost all catalysts based on MOF/CN in the literature. The triangular closed-loop heterojunction formed between Ni-MOF, g-C3N4, and CdS could realize the directional migration of photocarriers and significantly diminished the transfer resistance of carriers. The Ni2+ in Ni-MOF provided many cocatalytic sites for H2 evolution via g-C3N4 and CdS. Furthermore, charge carrier separation in Ni-MOF/CN/CdS improved after the innovative addition of MVTh. This study provides a reference for the construction of a closed-loop heterojunction system without precious metal cocatalysts.

Boosting photocatalytic H2 generation by effective proton shuttle and hydrogen activation on AgBr-loaded g-C3N4

Two-dimensional (2D) materials have driven great interest due to a large specific surface area to volume ratio and adjustable surface behaviors, which show huge potentials for enhancing the activity of energy conversion and property optimization. In order to regulate the physicochemical properties of photocatalyst for water splitting reaction, defect engineering on 2D materials have drawn great attention. Meanwhile, a widely used strategy to improve the H2 evolution rate kinetics has been achieved. In this paper, we prepared AgBr/g-C3N4 catalyst by chemical precipitation. The obtained photocatalyst shows a unique charge transfer pathway. In addition, a deep understanding of the proton shuttle during H2 evolution reactions can offer profound opinion into heterostructure construction and property optimization. It is found that the enhanced performance is correlated to the superiority of the S-scheme heterojunction and defect engineering on graphitic carbon nitride 2D materials. This work offers a novel method for improving efficiency in terms of energy conversion and property optimization.

In Situ Topochemical Transformation of ZnIn2S4 for Efficient Photocatalytic Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Diformylfuran

AbstractPhotocatalytic selective oxidation of 5‐hydroxymethylfurfural (HMF) coupled H2 production offers a promising approach to producing valuable chemicals. Herein, an efficient in situ topological transformation tactic is developed for producing porous O‐doped ZnIn2S4 nanosheets for HMF oxidation cooperative with H2 evolution. Aberration‐corrected high‐angle annular dark‐field scanning TEM images show that the hierarchical porous O‐ZIS‐120 possesses abundant atomic scale edge steps and lattice defects, which is beneficial for electron accumulation and molecule adsorption. The optimal catalyst (O‐ZIS‐120) exhibits remarkable performance with 2,5‐diformylfuran (DFF) yields of 1624 µmol h−1 g−1 and the selectivity of >97%, simultaneously with the H2 evolution rate of 1522 µmol h−1 g−1. Mechanistic investigations through theoretical calculations show that O in the O‐ZIS‐120 lattice can reduce the oxidation energy barrier of hydroxyl groups of HMF. In situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) results reveal that DFF* (C4H2(CHO)2O*) intermediate has a weak interaction with O‐ZIS‐120 and desorb as the final product. This study elucidates the topotactic structural transitions of 2D materials simultaneously with electronic structure modulation for efficient photocatalytic DFF production.

The Keto‐Switched Photocatalysis of Reconstructed Covalent Organic Frameworks for Efficient Hydrogen Evolution

AbstractThe keto‐switched photocatalysis of covalent organic frameworks (COFs) for efficient H2 evolution was reported for the first time by engineering, at a molecular level, the local structure and component of the skeletal building blocks. A series of imine‐linked BT‐COFs were synthesized by the Schiff‐base reaction of 1, 3, 5‐benzenetrialdehyde with diamines to demonstrate the structural reconstruction of enol to keto configurations by alkaline catalysis. The keto groups of the skeletal building blocks served as active injectors, where hot π‐electrons were provided to Pt nanoparticles (NPs) across a polyvinylpyrrolidone (PVP) insulting layer. The characterization results, together with density functional theory calculations, indicated clearly that the formation of keto‐injectors not only made the conduction band level more negative, but also led to an inhomogeneous charge distribution in the donor‐acceptor molecular building blocks to form a strong intramolecular built‐in electric field. As a result, visible‐light photocatalysis of TP‐COFs‐1 with one keto group in the skeletal building blocks was successfully enabled and achieved an impressive H2 evolution rate as high as 0.96 mmol g−1 h−1. Also, the photocatalytic H2 evolution rates of the reconstructed BT‐COFs‐2 and ‐3 with two and three keto‐injectors were significantly enhanced by alkaline post‐treatment.

Facile construction of CuO/g-C3N4 heterojunctions with promoted photocatalytic hydrogen generation behaviors

The core issue of photocatalytic H2 generation from water decomposition is to explore high activity, ultra stability and environment-friendly photocatalytic materials. Graphitic carbon nitride (g-C3N4, GCN) is preferred by global scientists for the diversified superiorities, such as the characteristic of flake graphite-phase fabric, competitive cost, non-poisonous, ideal bandgap (∼2.7 eV) and decent stability. Nevertheless, by reason of the deficiencies in small specific surface area and rapid photo-excited charge pairs recombination, photocatalytic hydrogen evolution activity of g-C3N4 is undesirable and it cannot be put into large-scale industrial production for these reasons. Construction of heterojunctions to boost electrons/holes (e-/h+) segregation efficiency is identified as a resultful tactic to promote the activity of g-C3N4. In current work, CuO/g-C3N4 with disparate CuO/g-C3N4 mole ratio (0.5%, 1%, 1.5%, 2%) were prepared through an impregnating strategy and investigated via various methods. Photocatalytic properties of CuO/g-C3N4 (CuO/CN) photocatalysts exert superior H2 evolution rate and consistency under solar light illumination. The optimal H2 evolution activity with non-cocatalyst is 130.1 µmol·g−1·h−1 upon the 1.5% CuO/CN, realizing 46.1 folds as fast as that of GCN (2.8 µmol·g−1·h−1). Coupling with CuO is confirmed to narrow bandgap of the samples, thus enhancing the light absorptivity and utilization. Besides, photo-stimulated e-/h+ pairs have acquired more efficient separation after formation of CuO/g-C3N4 heterojunctions. The method for preparation of S-scheme CuO/g-C3N4 heterojunction catalysts furnishes a perception of boosting the photocatalytic H2 generation rate through coupling with transition metal oxides.

Construction of novel photocatalysts for efficient hydrogen evolution: The key role of natural halloysite nanotubes

Hydrogen (H2) evolution by photocatalytic water splitting is a potential strategy to solve worldwide energy shortage. Sulfide nanocatalysts showed great potential for H2 evolution, but suffered from low charge separation efficiency and easy agglomeration. In this work, ZnIn2S4 (ZIS) nanoflowers were anchored onto the surface of halloysite nanotubes (HNTs) modified by ethylenediaminetetraacetic acid (EDTA). Photocatalyst 3ZnIn2S4-HNTs/EDTA3 (3ZIS-HNTs/E3) displayed the optimum H2 evolution rate of 10.4 mmol·g−1·h−1, being 3.4 times as that of the original ZIS. Moreover, 3ZIS-HNTs/E3 presented satisfied property in the photocatalytic hydrogenation reaction of 4-nitrophenol to produce 4-aminophenol. HNTs as substrates not only hindered the growth and agglomeration of ZIS, but also induced more S vacancies in ZIS. The production of Schottky junctions between ZIS and Pt, the high utilization of light energy in tubular HNTs, and the trapping effect of EDTA for photogenerated h+ were all favorable for enhancing the catalytic property. The density functional theory (DFT) calculations showed that 3ZIS-HNTs/E3 with more S vacancies had the lowest adsorption energy and the most appropriate ΔGH* for H* to enhance the H2 evolution efficiency, which was consistent with the experimental catalytic results. This study contributes a novel thought for synthesizing composites on the basis of natural minerals for taking part in and enhancing the catalytic performance.