High-efficiency hydrogen evolution reaction photocatalyst for water splitting of Type-II β-AsP/g-C3N4 van der Waals heterostructure

Photocatalytic for water splitting to produce hydrogen is recognized as a low-cost, promising and attractive method to solve environmental problems and energy crises, but finding a high-performance photocatalyst is a big challenge. In this work, we designed a type-II β-AsP/g-C₃N₄ van der Waals heterostructure as an efficient photocatalyst and had the first principles calculations to analyze its stability, electronic properties, and photocatalytic performance. The results showed that the photocatalyst of β-AsP/g-C₃N₄ heterostructure met the proper band gap and band edge of the redox potential of water splitting, had effective charge separation of photogenerated electronic holes, and efficient visible light response. Importantly, our research showed that the β-AsP/g-C₃N₄ heterostructure could proceed spontaneously in thermodynamics and had an excellent photocatalytic performance in further study. It had quite good hydrogen evolution performance with the Gibbs free energy of ?0.02 eV, which is closer to zero than ?0.09 eV of Pt (111). The overpotential of its oxygen evolution reaction is as low as 0.57 V. This work showed excellent development prospects for β-AsP/g-C₃N₄ heterostructure in the field of photocatalysts, which will promote the development of g–C₃N₄–based photocatalytic for water splitting.     

A novel CoSeO3 photocatalyst assisting g-C3N4 in enhancing hydrogen evolution through Z scheme mode

A novel CoSeO₃/g-C₃N₄ composite photocatalyst with Z-scheme heterostructure is constructed through electrostatic self-assembly to be utilized in photocatalytic hydrogen evolution. The optimal photocatalytic H₂ evolution rate of CoSeO₃/g-C₃N₄ hybrids and apparent quantum yield (AQY) have raised about 65.4 times under full light irradiation with no noble metal cocatalyst loading than that of pure g-C₃N₄. The CoSeO₃ semiconductor is firstly prepared for assisting to elevate the photocatalytic hydrogen evolution activity. After combining with g-C₃N₄, CoSeO₃/g-C₃N₄ hybrids with a sheet-sheet structure enhance the contact area with water and broaden the light absorption region as well as reduce transfer resistance of carriers. Moreover, the photo generated carriers possess a typical direct Z scheme transmission, which decreases the recombination of electrons and holes. This work offers a new choice for constructing a Z scheme heterostructure to apply in photocatalytic water reduction, and offers a deep view to explain the elevated photocatalytic activity.     

Promoted interfacial charge transfer by coral-like nickel diselenide for enhanced photocatalytic hydrogen evolution over carbon nitride nanosheet

Seeking an efficient and non-precious co-catalyst for g-C₃N₄ (CN) remains a great demanding to achieve high photocatalytic hydrogen generation performance. Herein, a composite photocatalyst with high efficiency was prepared by modifying CN with coral-like NiSe₂. The optimal hydrogen evolution rate of 643.16 μmol g^?1 h^?1 is from NiSe₂/CN-5 under visible light. Superior light absorption and interfacial charge transfer properties including suppressed photogenerated carrier recombination and efficient separation of photogenerated electron-hole pairs have been observed, which account for the enhanced photocatalytic performance of CN.     

Chloroplast-granum-inspired porous nanorods composed of g-C3N4 ultrathin nanosheets as visible light photocatalysts for highly enhanced hydrogen production

Metal-free photocatalysts have attracted great attention in hydrogen production under visible light due to their low cost and abundance. Inspired by the structure of chloroplast-granum, here we prepare a new porous nanorod composed of F-doped g-C₃N₄ ultrathin nanosheet for photocatalytic hydrogen evolution. The obtained g-C₃N₄ (FCN-PNRs) show layer-by-layer stacked structure for highly efficient light hasting, exhibit F-doping for highly charge separation efficiency, and display porous structure for exposing a large amount of photocatalytic activity sites. These findings have been studied by various characterizations, such as Brunauer-Emmett-Teller, and Photoluminescence. As a result, the hydrogen production performance for the optimized FCN-PNRs photocatalyst reaches 2600 μmol h⁻¹ g⁻¹ under visible light, which is almost 16 times higher than bulk g-C₃N₄. This study not only reports a new chloroplast-granum-inspired g-C₃N₄ photocatalyst, but also provides new views to the fabrication and design of nature-inspired metal-free structures for catalysis applications.     

Accelerating photocatalytic hydrogen evolution of Ta2O5/g-C3N4 via nanostructure engineering and surface assembly

Despite that several strategies have been demonstrated to be effective for improving the catalytic hydrogen evolution activity of bulky g-C₃N₄, the large-scale hydrogen production over g–C₃N₄–based photocatalysts still confronts a big challenge. Here, a two-step calcination method is presented in constructing metal oxide/two-dimensional g-C₃N₄, i.e., Ta₂O₅/2D g-C₃N₄ photocatalyst. Thanks to the superiority of the synthetic method, nanostructure engineering forming 2D structure, and surface assembly with another semiconductor, can be realized simultaneously, in which ultrathin structure of 2D g-C₃N₄ and strong interfacial coupling between two components are two important characteristics. As a result, the structure engineered Ta₂O₅/2D g-C₃N₄ induces high photocatalytic hydrogen evolution half reaction rate of ~19,000 μmol g^?1 h^?1 under visible light irradiation (λ > 400 nm), and an external quantum efficiency (EQE) of 25.18% and 12.48% at 405 nm and 420 nm. The high photocatalytic performance strongly demonstrates the advance of the synchronous engineering of nanostructure and construction of heterostructure with tight interface, both of which are beneficial for the fast charge separation and transfer.     

Fabrication of alveolate g-C3N4 with nitrogen vacancies via cobalt introduction for efficient photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution is a promising method for converting solar energy into chemical energy. Herein, on the basis of graphitic carbon nitride (g-C₃N₄) material with alveolate structure prepared via the hard template method, transition-metal cobalt oxide nanoparticles were reasonably introduced, and a highly efficient cobalt oxide composite alveolate g-C₃N₄ (ACN) photocatalyst was successfully prepared. A series of test methods were used to characterize the structural properties of the prepared samples systematically, and the photocatalytic activity of the catalysts in photocatalytic hydrogen evolution was explored. The composite materials have excellent photocatalytic performance mainly because the synergistic effect of the alveolate structure of ACN provides multiple scattering effects; nitrogen vacancies serves as the centers of photogenerated carrier separation; and cobalt oxides accelerates electron transfer. This study provides a new idea for the design of g–C₃N₄–based photocatalysts with wide light responses and simple structures.     

Organic-inorganic composite of g-C3N4–SrTiO3:Rh photocatalyst for improved H2 evolution under visible light irradiation

The organic-inorganic composite g-C₃N₄–SrTiO₃:Rh was prepared for the first time as a photocatalyst for hydrogen production and the resulting hydrogen evolution rate under visible light irradiation from aqueous methanol solution was measured. A high hydrogen evolution rate of 223.3 μmol h⁻¹ was achieved by using 0.1 g of as-prepared photocatalyst powder comprised of 20 wt.% g-C₃N₄ 80 wt.% SrTiO₃:Rh (0.3 mol%). The hydrogen evolution rate was greater than that obtained by SrTiO₃:Rh (0.3 mol%) by a factor of 3.24. The quantum efficiency of as-prepared composite photocatalyst was 5.5% at 410 nm for hydrogen evolution. The high activity of the composite photocatalyst for hydrogen evolution stemmed from its electron–hole separation and transportation capabilities due to the hetero-junctions of the organic-inorganic composite materials. The proposed mechanism for the electron–hole separation and hydrogen evolution of the g-C₃N₄–SrTiO₃:Rh composite under visible light irradiation featured the reduced recombination of the photo-generated charge carriers. The doping of Rh ions into the SrTiO₃ has contributed to the high photocatalytic activity by forming a donor level from the valance band to the conduction band.     

Controlled photoinduced electron transfer from g-C3N4 to CuCdCe-LDH for efficient visible light hydrogen evolution reaction

Ample visible-light response and efficient charge transfers in semiconductor heterojunction are still enslaved to the limited photocatalytic water splitting. In most cases, the rational design of hybrid composites tune in atomic level interaction led to remarkable stability and superior activity. Here, this work is a systematic investigation of metal ion substitution in the LDH and LDH/g-C₃N₄ hybrid composites for hydrogen evolution reaction (HER) under visible light. The construction of heterostructure not only facilitates the charge separation and transfer owing to the formed heterojunction through band gap engineering and tunable optical properties which are inherited from morphology of as grown CuCdCe-LDH over the exfoliated g-C₃N₄ but also provides plenty of surface active sites due the increased surface area photostability. The CuCdCe-LDH/g-C₃N₄ exhibits superior HER rate of 3.5 mmolg^?1h^?1 with AQY of 5.78% over their binary counterparts. The density functional theory calculations also suggest that the HER activity of CuCdCe-LDH is substantially enhanced by coupling with g-C₃N₄ the electrochemical results leading to high photocurrent response. The high photocatalytic activity of the composite was due to efficient photoexcited charge transfer process and the synergistic effect between CuCdCe-LDH and g-C₃N₄. These finding will open scopes for designing inexpensive high performance materials for broad applications of photocatalytic energy conversion.     

Facile synthesis of AuPd/g-C3N4 nanocomposite: An effective strategy to enhance photocatalytic hydrogen evolution activity

AuPd bimetallic nanoparticle (NP) modified ultra-thin graphitic carbon nitride nanosheet photocatalysts were synthesized via photochemical deposition-precipitation followed by hydrogen reduction. The crystal structure, chemical properties, and charge carrier behavior of these photocatalysts were characterized by X-ray diffraction (XRD), surface photovoltage spectroscopy (SPS), transient photovoltage spectroscopy (TPV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and UV-Vis diffuse-reflectance spectroscopy (DRS). Photocatalytic H₂ evolution experiments indicate that the hydrogen treated AuPd nanoparticles can effectively promote the separation efficiency of electron-hole pairs photo-excited in the g-C₃N₄ photocatalyst, which consequently promotes photocatalytic H₂ evolution. The 1.0 wt% AuPd/g-C₃N₄ (H₂) composite photocatalyst showed the best performance with a corresponding photocatalytic H₂ evolution rate of 107 μmol h^?1. The photocatalyst can maintain most of its photocatalytic activity after four photocatalytic experiment cycles. These results demonstrate that the synergistic effect of light reduction and hydrogen reduction of AuPd and g-C₃N₄ help to greatly improve the photocatalytic activity of the composite photocatalyst.     

CNT/g‐C3N4 photocatalysts with enhanced hydrogen evolution ability for water splitting based on a noncovalent interaction

Graphite carbon nitride (g‐C₃N₄) as a novel photocatalyst has attracted growing attention, but its photocatalytic efficiency should be further improved. Based on the large work function and fast electron conductivity of carbon nanotubes (CNTs), here CNT/g‐C₃N₄ photocatalysts with improved H₂ evolution ability and stable water splitting ability were synthesized. The improvement was attributed to the synergistic effect between CNTs and g‐C₃N₄. As for the mechanisms, CNTs strongly attracted photoelectrons and, because of excellent conductibility, rapidly transferred photoelectrons from the catalyst interface. Thereby, the photoelectron migration rate and the photogenerated charge separation and the use efficiency of photoelectrons in g‐C₃N₄ were improved, which largely enhanced the hydrogen production ability. Moreover, the addition of CNTs improved the service life and stability of g‐C₃N₄‐based photocatalytic H₂ production. After 10 hours of visible light irradiation, the maximum H₂ yield from the 12‐mg/L CNT/g‐C₃N₄ (CG12) was 138.7 times larger than that of g‐C₃N₄ (6548.4 vs 47.2 μmol/g), and the H₂ evolution rate was 138.7 times that of g‐C₃N₄ (654.8 vs 4.72 μmol/g/h). After 50 hours, the apparent quantum efficiency of CG12 was up to 37.9%, indicating that the addition of CNTs improved the photocatalytic splitting and stability of g‐C₃N₄. The mechanism of photocatalytic hydrogen production and the roles of CNTs in improving water splitting were discussed through characterization and activity experiments. It was found that the addition of CNTs accelerated the migration, separation, and utilization of photoelectrons and thereby significantly enhanced the photocatalytic performance.     

High-efficiency charge separation of Z-scheme 2D/2D C3N4/C3N5 nonmetal VdW heterojunction photocatalyst with enhanced hydrogen evolution activity and stability

The interfacial charge transfer control is a key and arduous issue for propelling the migration/separation of photogenerated carriers for heterojunction photocatalysts. Here, a new 2D/2D C₃N₄/C₃N₅ nonmetal van der Waals (VdW) heterojunction is fabricated by the simple self-assembly technique in acidic medium, whose charge separation efficiency is promoted dramatically, thus being endowed with the high-efficiency photocatalytic hydrogen evolution (PHE) performance. The PHE rate reaches up to 3.33 mmol h^?1 g^?1 under the visible light and the apparent quantum efficiency (AQE) of 20.6% is achieved at 420 nm on the optimal 2D/2D C₃N₄/C₃N₅-5% sample. Furthermore, the 2D/2D C₃N₄/C₃N₅ nonmetal VdW heterojunction also exhibits the desired stability because there was no significant decrease after PHE reaction of 10 cycles with total 40 h. Such outstanding PHE activity and stability originate from the impelled separation of photoinduced charge carriers and the powerful interfacial interaction through forming Z-Scheme charge transfer path and π-π coupling effect between C₃N₄ and C₃N₅ nanosheets. This work takes a significant guiding and demonstration for designing and exploiting other novel nonmetallic polymer-based VdW heterojunctions in the photocatalytic application field.     

Composite of g-C3N4 and poly(3-hexylthiophene) prepared by polymerizing thiophene-3-acetic acid treated g-C3N4 and 3-hexylthiophene for enhanced photocatalytic hydrogen production

Composite of g-C₃N₄ and poly(3-hexylthiophene) (P3HT) with enhanced photocatalytic H₂ production activity was prepared by polymerizing 3-hexylthiophene and g-C₃N₄, which was treated with thiophene-3-acetic acid (T3A). The morphology, chemical structure, and light absorption properties of samples were characterized by SEM, TEM, BET, XRD, FT-IR, XPS, UV–visible diffuse reflectance spectra (UV–vis). The migration and separation efficiency of charge carriers were characterized by photoluminescence (PL) emission spectra, Time resolved photoluminescence spectra, transient photocurrent responses, and electrochemical impedance spectroscopy (EIS). The photocatalytic activity of the catalysts were tested as the H₂ evolution rate from water under visible light irradiation in the presence of triethanolamine as sacrifice agent. The results indicated that g-C₃N₄-P3HT composite shows significant enhanced migration and separation efficiency of charge carriers, and photocatalytic H₂ production activity from water. The intrinsic nature causing the significance enhanced photocatalytic performance was discussed. Our findings here may provide a new strategy to design composite photocatalyst with high photocatalytic activity.     

A mixed phase lanthanum vanadate in situ induced by graphene oxide/graphite carbon nitride for efficient photocatalytic hydrogen generation

A mixed phase LaVO₄ with high dispersion was in situ induced and implanted in graphene oxide-graphite carbon nitride composite. The obtained nanocomposite (GO–C₃N₄–LaVO₄) showed high and stable photocatalytic activity for hydrogen evolution, which significantly benefited from the improved charge separation and light absorption in the special composite photocatalyst as evidenced by UV–vis spectra, fluorescence spectrum, photocurrent response and electrochemical impedance. The fabrication strategy of mixed phase LaVO₄ in the GO-C₃N₄ provides a new idea for constructing cheap and active organic-inorganic semiconductor photocatalysts for hydrogen generation.     

Fabricating transfer channel and charge trap in carbon nitride ultrathin nanosheet for enhanced photocatalytic hydrogen evolution

Fabricating environmental and stable graphitic carbon nitride (g-C₃N₄) photocatalyst with highly efficient visible light response and charge separation is still a challenging work. Herein, g-C₃N₄ ultrathin nanosheets are synthesized via oxidation etching method. The as-synthesized samples show improved visible-light response and photogenerated charge separation, which is revealed to be brought from the synergy of hierarchical porous structure and nitrogen vacancies. On one hand, macropores can provide light transport channels for enhanced visible light absorption, meanwhile the photogenerated charge favors to be migrated on two-dimensional ultrathin planes and trapped in mesoporous structure to avoid the recombination. Also, macropore and mesopore promote the transport and adsorption of substrates. On the other hand, DFT calculations verify that nitrogen vacancies are conductive to the rearrangement of charge density distribution and the formation of defect levels in the band gap of g-C₃N₄, leading to the improvement of carrier mobility and separation. Thus, nitrogen vacancies promote more active sites generation. Consequently, the g-C₃N₄ ultrathin nanosheet presents a promising photocatalytic hydrogen evolution rate of 1.77 mmol .g^?1 .h^?1 in a long time run under visible light, which is far higher than that of comparison samples (0.18 and 0.29 mmol .g^?1.h^?1 respectively).     

In-situ growth of CdS quantum dots on g-C3N4 nanosheets for highly efficient photocatalytic hydrogen generation under visible light irradiation

Well dispersed CdS quantum dots were successfully grown in-situ on g-C₃N₄ nanosheets through a solvothermal method involving dimethyl sulfoxide. The resultant CdS–C₃N₄ nanocomposites exhibit remarkably higher efficiency for photocatalytic hydrogen evolution under visible light irradiation as compared to pure g-C₃N₄. The optimal composite with 12 wt% CdS showed a hydrogen evolution rate of 4.494 mmol h⁻¹ g⁻¹, which is more than 115 times higher than that of pure g-C₃N₄. The enhanced photocatalytic activity induced by the in-situ grown CdS quantum dots is attributed to the interfacial transfer of photogenerated electrons and holes between g-C₃N₄ and CdS, which leads to effective charge separation on both parts.     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).     

K and halogen binary-doped graphitic carbon nitride (g-C3N4) toward enhanced visible light hydrogen evolution

Water splitting driven by solar energy to produce hydrogen, which is highly dependent on the designing of semiconductor photocatalyst, is an efficient technology to address energy shortage problems and environment issues simultaneously. Here, the halogen and potassium binary-doped graphitic carbon nitride (named as X-K-C₃N₄, X = F, Cl, Br, I) photocatalysts were synthetized via simply one pot thermal polymerization method, which shown optimized band structure, enhanced optical absorption, higher separation rate of photogenerated carriers, and thus improved photocatalytic performance under visible light irradiation. As result, F–K–C₃N₄ is demonstrated to be highly efficient in the separation and transfer of carriers owing to the existence of C–F bond, CN triple bond and K junction. The F–K–C₃N₄ shows a highest H₂ evolution rate of 1039 μmol g⁻¹ h⁻¹ and a remarkable stability under visible light irradiation (λ ≥ 420 nm), which is about 8.5 times higher than that of pristine g-C₃N₄.     

Synthesis of NiS2/polyvinylpyrrolidone/(CuIn)0·2Zn1·6S2 type II heterojunction photocatalysts for high-efficiency photocatalytic hydrogen production under visible light

A robust NiS₂/polyvinylpyrrolidone/(CuIn)_0·2Zn_1·6S₂ (NiS₂/PVP/CIZS) photocatalyst was successfully synthesized through a sequential hydrothermal treatment. Firstly, the addition of PVP reduces the size of CIZS nanoparticles, resulting in appearing surface effect, and hence an improvement of chemical activity. Moreover, the small size of PVP/CIZS possesses a shorten transfer distance of photo-induced carriers. The photocatalytic H₂ evolution rate of 0.8 g PVP/CIZS elevates to 3112.7 μmol/g/h under visible light. After coupling with NiS₂, the light absorption range and separation efficiency of photo-induced carriers for NiS₂/PVP/CIZS composites have been elevated and the optimal photocatalytic hydrogen evolution rate of 15% NiS₂/PVP/CIZS reaches up to 5369.4 μmol/g/h. There forms a type Ⅱ heterostructure on NiS₂/PVP/CIZS, and the heterostructure facilitates to suppress the recombination and elevate the separation of photo generated electrons and holes. Therefore, the synergistic effect of size control and constructing a type Ⅱ heterostructure with NiS₂ on PVP/CIZS floriform photocatalyst helps to enhance photocatalytic performance of the composites. This work opens up a new way to prepare highly efficient photocatalysts under visible light.     

Cl-doped carbon nitride nanostrips for remarkably improving visible-light photocatalytic hydrogen production

Visible-light-driven photocatalysts for hydrogen production have been made great progress in recent years, there yet remain grand spaces to be improved further for implementing practical feasibility. We herein report a chlorine doped carbon nitride (Cl-p-C₃N₄) with ultrathin nanostrips morphology, which displays excellent photocatalytic hydrogen generation performance (5976 μmol h⁻¹ g⁻¹, 16.5 times higher than that of bulk C₃N₄) under visible light irradiation, with an apparent quantum yield of 8.91% at 420 nm. Experimental results and DFT calculations show that the ultrathin Cl-p-C₃N₄ nanostrips with heteroatom doping are greatly conducive to reduce the band gap, increase the surface area, and promote the separation efficiency of the photogenerated charge carrier, leading to the improvement of the charge carrier migration to the material surface or co-catalyst during the photocatalytic reaction. This work sheds light on the effective strategy to construct excellent photocatalyst by reasonably regulating the band structure and morphology.     

Facile synthesis of anatase/rutile TiO2/g-C3N4 multi-heterostructure for efficient photocatalytic overall water splitting

Rational design of high-efficiency heterostructure photocatalyst is an effective strategy to realize photocatalytic H₂ evolution from pure water, but remains still a considerable challenge. Herein, an anatase/rutile TiO₂/g-C₃N₄ (A/R/CN) multi-heterostructure photocatalyst was prepared by a facile thermoset hybrid method. The combination of two type-II semiconductor heterostructures (i.e., A/R and R/CN) significantly improve the separation and transfer efficiency of photogenerated carriers of anatase TiO₂, rutile TiO₂ and g-C₃N₄, and A/R/CN photocatalyst with high activity is obtained. The optimal A/R/CN photocatalyst exhibits significantly increased photocatalytic overall water splitting activity with a rate of H₂ evolution of 374.2 μmol g⁻¹h⁻¹, which is about 8 and 4 times that of pure g-C₃N₄ and P25. Moreover, it is demonstrated to be stable and retained a high activity (ca. 91.2%) after the fourth recycling experiment. This work comes up with an innovative perspective on the construction of multi-heterostructure interfaces to improve the overall photocatalytic water splitting performance.