Bimetallic PtNi alloy modified 2D g-C3N4 nanosheets as an efficient cocatalyst for enhancing photocatalytic hydrogen evolution

Platinum-based alloy materials as effective cocatalysts in improving the performance of photocatalytic H₂ production have raised great interest. Herein, a facile strategy of chemical reduction is established to synthesize bimetallic PtNi nanoparticles on 2D g-C₃N₄ nanosheets with excellent photocatalytic activity. The addition of PtNi nanoparticles can provide new H⁺ reduction sites and increase more active sites of the material. The synergistic effect between PtNi alloy nanoparticles and 2D g-C₃N₄ nanosheets can regulate electronic structure, narrow the band, accelerate charge transfer efficiency and inhabit the recombination of photo-induced electron (e⁻) and hole pairs (h⁺), contributing to the improvement of hydrogen evolution activity. The optimal hydrogen evolution rate of Pt_0.6Ni_0.4/CN shows higher hydrogen evolution rate (9528 μmol·g⁻¹·h⁻¹), which is 13.1 times than that of pure g-C₃N₄ nanosheets. Besides, a possible mechanism of photocatalytic hydrogen generation has been brought up according to a series of physical and chemical characterization. This work also provides a potential idea of developing cocatalysts integrating metal alloys with 2D g-C₃N₄ nanosheets for promoting photocatalytic hydrogen evolution.     

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.     

Facile synthesis of CeO2/g-C3N4 nanocomposites with significantly improved visible-light photocatalytic activity for hydrogen evolution

Ceria dioxide supported on graphitic carbon nitride (CeO₂/g-C₃N₄) composites were facilely synthesized to be application for photocatalytic hydrogen (H₂) generation in this present work. The physical and chemical properties of CeO₂/g-C₃N₄ nanocomposites were determined via a series of characterizations. The CeO₂/g-C₃N₄ composites prepared by facile thermal annealing and rotation-evaporation method exhibit excellent photocatalytic H₂ evolution with visible-light illumination. The best hydrogen generation rate of CeO₂/g-C₃N₄ composite with 1.5 wt% Pt is 0.83 mmol h⁻¹ g⁻¹, which is almost same as that of composite with 3 wt% Pt prepared by simple physical mixing method. The significantly developed photocatalytic activity of CeO₂/g-C₃N₄ composite is majorly ascribed to the stronger interfacial effects with the more visible-light absorbance and faster electron transfer. This work reveals that construction of the CeO₂/g-C₃N₄ composite with high disperse and close knit by the facile thermal annealing and rotation-evaporation method could be an effective method to achieve excellent photocatalytic hydrogen evolution performance.     

A visible-light-driven heterojunction for enhanced photocatalytic water splitting over Ta2O5 modified g-C3N4 photocatalyst

The photocatalytic water splitting for generation of clean hydrogen energy has received increasingly attention in the field of photocatalysis. In this study, the Ta₂O₅/g-C₃N₄ heterojunctions were successfully fabricated via a simple one-step heating strategy. The photocatalytic activity of as-prepared photocatalysts were evaluated by water splitting for hydrogen evolution under visible-light irradiation (λ > 420 nm). Compared to the pristine g-C₃N₄, the obtained heterojunctions exhibited remarkably improved hydrogen production performance. It was found that the 7.5%TO/CN heterojunction presented the best photocatalytic hydrogen evolution efficiency, which was about 4.2 times higher than that of pure g-C₃N₄. Moreover, the 7.5%TO/CN sample also displayed excellent photochemical stability even after 20 h photocatalytic test. By further experimental study, the enhanced photocatalytic activity is mainly attributed to the significantly improve the interfacial charge separation in the heterojunction between g-C₃N₄ and Ta₂O₅. This work provides a facile approach to design g-C₃N₄-based photocatalyst and develops an efficient visible-light-driven heterojunction for application in solar energy conversion.     

Investigation of Photo(electro)catalytic water splitting to evolve H2 on Pt-g-C3N4 nanosheets

g-C₃N₄ has shown great potentials in photocatalytic water splitting to produce hydrogen. Herein, we successfully synthesized g-C₃N₄ nanosheets via exfoliating bulk g-C₃N₄. And different metal nanoparticles were photo-deposited onto the surface of g-C₃N₄ nanosheets. The photocatalytic H₂ production activity of g-C₃N₄ nanosheets increased from 0 to 11.2 μmol/h/g_cat. The Pt loaded g-C₃N₄ nanosheets manifested the highest H₂ production activity with a rate of 589.4 μmol/h/g_cat. In addition, the hydrogen evolution rate was further enhanced with addition of external bias to fabricate a photoelectrocatalytic (PEC) system. And the maximum hydrogen production rate (23.1 mmol/h/m²) was obtained at a voltage of 0.6 V (vs. Ag/AgCl). The enhancement in H₂ production may be due to the following reasons: (1) Two-dimensional atomic flakes is beneficial to increase the specific surface area of g-C₃N₄, enhance the mobility of carriers, and improve the energy band structure, (2) Pt nanoparticles play an important role in g-C₃N₄ electron transport, (3) the g-C₃N₄ nanosheets loaded with Pt nanoparticles exhibited significant enhancement in photoelectrocatalytic performance, which may be attributed to its enhanced electronic conductivity and photoelectrochemical surface area, (4) Pt inhibited the recombination of photogenerated carriers and significantly improved the photocatalytic performance. The enhancement mechanism was deeply discussed and explained in this work.     

Two-dimensional carbon nitride-based composites for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution plays a critical role in the exploration of the clean and sustainable energy. Owing to its special structure and features, two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) has attracted tremendous attention. However, some deficiencies of pristine g-C₃N₄ inhibit its photocatalytic application, particularly the low quantum efficiency of hydrogen evolution. Therefore, it is valuable to develop 2D new composites based on g-C₃N₄ so that the synergistic effects of the two original materials can be achieved. This article attempts to summarize the modification strategies of 2D g-C₃N₄-based composites, including the construction of heterojunctions, morphology control, doping method, surface modification and co-catalyst loading. The application and progress in photocatalytic hydrogen evolution are also highlighted. The limitations are taken into account to provide further information for the improvement in the quantum efficiency of hydrogen by 2D g-C₃N₄-based composites.     

The synergistic effect of potassium ions and nitrogen defects on carbon nitride for enhanced photocatalytic hydrogen evolution

Ion doping is an effective method to improve the photocatalytic activity of graphitic carbon nitride (g-C₃N₄) by providing a photocarriers transfer channel. But limited by the bonds in heptazine rings, photoelectrons are still trapped in the structure. Therefore, both potassium ions and nitrogen defects were successfully introduced into g-C₃N₄ by high temperature calcination to accelerate the charges transfer between both interlayers and intralayer of g-C₃N₄. The results showed that the hydrogen production rate of g-C₃N₄ modified simultaneously by nitrogen defects and potassium ions reaches 1722.4 μmol·g⁻¹·h⁻¹, which is 8 times that of pristine g-C₃N₄. Based on various characterization techniques and DFT calculations, we attributed the enhanced photocatalytic hydrogen evolution to the improved light adsorption, more delocalized HOMO-LUMO, and stronger interlayer interactions. This work will provide a promising way to enhance photocatalytic hydrogen evolution of g-C₃N₄ and a possible mechanism was proposed.     

Phosphorylation of NiAl-layered double hydroxide nanosheets as a novel cocatalyst for photocatalytic hydrogen evolution

In previous studies, it has been shown that phosphorus and phosphate can improve the conductivity, change the electronic structure, and accept electrons from catalysts. In this study, we obtained phosphorylated NiAl-layered double hydroxide (P-LDH) nanosheets and used them as a novel cocatalyst in photocatalytic hydrogen evolution. After assembly with g-C₃N₄ via an in situ process, these noble-metal-free composite photocatalysts showed superior photocatalytic hydrogen evolution activity. It was also found that the efficiency of H₂ production on the optimal composite was 1.5 times that of Pt-modified g-C₃N₄. Characterization of the photocatalysts revealed that the effects of P-LDH were different from those of other bimetallic LDHs, showing a lower overpotential and faster reaction kinetics of H₂ evolution. Moreover, it was found that P-LDH has a higher surface work function than that of g-C₃N₄, leading to the formation of an interfacial electric field from CN toward P-LDH. Therefore, modifying P-LDH can efficiently improve the interfacial charge transfer rate, suppress photogenerated charge recombination, and lower the surface overpotential of g-C₃N₄. This study serves as guidance on the design of more effective cocatalysts for photocatalytic hydrogen evolution reactions.     

Magnetic Fe3C@C nanoparticles as a novel cocatalyst for boosting visible-light-driven photocatalytic performance of g-C3N4

In photocatalytic field, it is a significant challenge to synthesize cocatalyst with high performance, noble-metal free and facile methods to recycle. Herein, carbon layer coated Fe₃C (Fe₃C@C) nanoparticles were prepared by one-step method and for the first time utilized as highly efficient cocatalysts for improving visible-light-driven hydrogen evolution activity of g-C₃N₄. The photocatalytic hydrogen evolution rate of optimal Fe₃C@C/g-C₃N₄ was about 27.2 times of bare g-C₃N₄ samples. Furthermore, the Fe₃C@C/g-C₃N₄ composite catalyst showed excellent stability and reusability. The apparent quantum yield (AQY) of the optimized FeC@C/g- C₃N₄ reaches 0.501% and 0.124% at 400 nm and 420 nm, respectively. The AQY of the FeC@C/g- C₃N₄ is 26.2 times higher than that of g-C₃N₄ at 400 nm Fe₃C@C has an extraordinary cocatalytic effect for g-C₃N₄ photocatalytic hydrogen evolution mainly due to three aspects: Firstly, the Fe₃C acts as a trap to lure electrons because of its lower Fermi energy level and higher conductivity, which can increase the hydrogen production activity by trapping the photogenerated electrons produced by g-C₃N₄; Secondly, the coated carbon layer can provide chemical protection for Fe₃C nanoparticles and promote the transfer of photogenic electrons, thus further improving the efficiency and stability of photocatalytic hydrogen production; Thirdly, the strong magnetic property of Fe₃C@C nanoparticles gives Fe₃C@C/g-C₃N₄ photocatalysts the advantages of low cost and high recovery efficiency. It is believed that this work provides a new strategy and possibility for the application of photocatalytic hydrogen production.     

An orderly assembled g-C3N4, rGO and Ni2P photocatalyst for efficient hydrogen evolution

On account of on the dominant performance of Ni₂P, rGO and g-C₃N₄ itself, with a view to conquer the disadvantages of Ni₂P, rGO and g-C₃N₄ its own, the g-C₃N₄/rGO/Ni₂P is successfully designed and prepared by a simple hydrothermal reaction, which is used in dye-sensitized system for high-efficient photocatalytic H₂ evolution. The rGO is adhered to the outside appearance of the g-C₃N₄ nanosheets and fish-scale shape Ni₂P is anchored on the surface of rGO and g-C₃N₄. The above three forms a synergistic effect. The maximum amount of H₂ evolution reaches about 266 μmol for 5 h over the g-C₃N₄/rGO/Ni₂P photocatalyst when the content of rGO is 8%, which is 10.6 times higher than g-C₃N₄. Synergy between the above three materials is certified by some characterizations and the results of which are consistent with each other. In addition, the possible mechanism of photocatalytic hydrogen production is proposed.     

Construction of MOFs/g-C3N4 composite for accelerating visible-light-driven hydrogen evolution

In this work, we researched the effect of PCN-222 (M = Ni, Fe, Co) (PM) with different metal ligands on their photocatalytic performance. Compared with PFe and PCo, PNi has the highest photocatalytic hydrogen evolution efficiency due to the narrowest bandgap and the highest conduction band (CB) position. Furthermore, PCN-222(M)/g-C₃N₄ (PM/CN) heterojunctions was synthesized by one-pot solvothermal method in which PNi/CN displayed the most outstanding photocatalytic activity for H₂ evolution. PNi/CN-1 displayed the highest photocatalytic activity. Its hydrogen evolution rate is 19.3 and 3.7 times higher than that of PNi and CN, respectively. A mechanism is proposed to expound the roles of PNi and the enhancement of visible-light photocatalytic performance of the PNi/CN. This work presents a new perspective for the development of high performance photocatalysts for hydrogen production under visible-light driven.     

Synthesis and characterization of composite visible light active photocatalysts MoS2–g-C3N4 with enhanced hydrogen evolution activity

Molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) composite photocatalysts were prepared via a facile impregnation method. The physical and photophysical properties of the MoS₂–g-C₃N₄ composite photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microcopy (HRTEM), ultraviolet–visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The photoelectrochemical (PEC) measurements were tested via several on–off cycles under visible light irradiation. The photocatalytic hydrogen evolution experiments indicate that the MoS₂ co-catalysts can efficiently promote the separation of photogenerated charge carriers in g-C₃N₄, and consequently enhance the H₂ evolution activity. The 0.5wt% MoS₂–g-C₃N₄ sample shows the highest catalytic activity, and the corresponding H₂ evolution rate is 23.10 μmol h⁻¹, which is enhanced by 11.3 times compared to the unmodified g-C₃N₄. A possible photocatalytic mechanism of MoS₂ co-catalysts on the improvement of visible light photocatalytic performance of g-C₃N₄ is proposed and supported by PL and PEC results.     

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.     

In situ fabrication of CDs/g-C3N4 hybrids with enhanced interface connection via calcination of the precursors for photocatalytic H2 evolution

Novel carbon dots (CDs)/graphitic carbon nitride (g-C₃N₄) hybrids were fabricated via an in situ thermal polymerization of the precursors, urea and glucose. This heterojunction catalyst exhibited enhanced photocatalytic H₂ evolution activity under visible-light (λ > 420). A sample of CDs/g-C₃N₄ hybrids, CN/G0.5, which was prepared from 0.5 mg of glucose in 6.0 g of urea (8.3 × 10^?3 wt% glucose), exhibited the best photocatalytic performance for hydrogen production from water under visible light irradiation, which is about 4.55 times of that of the bulk g-C₃N₄ (BCN). The improvement of photocatalytic activity was mainly attributed to the construction of built-in electric field at the interface of CDs and g-C₃N₄, which could improve the separation of photogenerated electron-hole pair. Moreover, the tight connection of CDs with g-C₃N₄ would serve as a well electron transport channel, which could promote the photocatalytic H₂ evolution ability.     

g-C3N4/B doped g-C3N4 quantum dots heterojunction photocatalysts for hydrogen evolution under visible light

Developing high activity and eco-friendly photocatalysts for water splitting is still a challenge in solar energy conversion. In this paper, B doped g-C₃N₄ quantum dots (BCNQDs) were prepared via a facile molten salt method using melamine and boron oxide as precursors. By introducing BCNQDs onto the surface of g-C₃N₄, g-C₃N₄/BCNQDs heterojunction was constructed via hydrothermal treatment. The resulting g-C₃N₄/BCNQDs heterojunction exhibits enhanced hydrogen evolution performance for water splitting under visible light irradiation. The mechanism underlying the improved photocatalytic activity was explored and discussed based on the formation of heterojunction between g-C₃N₄ and BCNQDs with well-matched band structure.     

Rationally designed ternary CdSe/WS2/g-C3N4 hybrid photocatalysts with significantly enhanced hydrogen evolution activity and mechanism insight

Excellent light harvest, efficient charge separation and sufficiently exposed surface active sites are crucial for a given photocatalyst to obtain excellent photocatalytic performances. The construction of two-dimensional/two-dimensional (2D/2D) or zero-dimensional/2D (0D/2D) binary heterojunctions is one of the effective ways to address these crucial issues. Herein, a ternary CdSe/WS₂/g-C₃N₄ composite photocatalyst through decorating WS₂/g-C₃N₄ 2D/2D nanosheets (NSs) with CdSe quantum dots (QDs) was developed to further increase the light harvest and accelerate the separation and migration of photogenerated electron-hole pairs and thus enhance the solar to hydrogen conversion efficiency. As expected, a remarkably enhanced photocatalytic hydrogen evolution rate of 1.29 mmol g⁻¹ h⁻¹ was obtained for such a specially designed CdSe/WS₂/g-C₃N₄ composite photocatalyst, which was about 3.0, 1.7 and 1.3 times greater than those of the pristine g-C₃N₄ NSs (0.43 mmol g⁻¹ h⁻¹), WS₂/g-C₃N₄ 2D/2D NSs (0.74 mmol g⁻¹ h⁻¹) and CdSe/g-C₃N₄ 0D/2D composites (0.96 mmol g⁻¹ h⁻¹), respectively. The superior photocatalytic performance of the prepared ternary CdSe/WS₂/g-C₃N₄ composite could be mainly attributed to the effective charge separation and migration as well as the suppressed photogenerated charge recombination induced by the constructed type-II/type-II heterojunction at the interfaces between g-C₃N₄ NSs, CdSe QDs and WS₂ NSs. Thus, the developed 0D/2D/2D ternary type-II/type-II heterojunction in this work opens up a new insight in designing novel heterogeneous photocatalysts for highly efficient photocatalytic hydrogen evolution.     

Hierarchical TiO2 spheroids decorated g-C3N4 nanocomposite for solar driven hydrogen production and water depollution

A novel hierarchical TiO₂ spheroids embellished with g-C₃N₄ nanosheets has been successfully developed via thermal condensation process for efficient solar-driven hydrogen evolution and water depollution photocatalyst. The photocatalytic behaviour of the as-prepared nanocomposite is experimented in water splitting and organic pollutant degradation under solar light irradiation. The optimal ratio of TiO₂ spheroids with g-C₃N₄ in the nanocomposite was found to be 1:10 and the resulting composite exhibits excellent photocatalytic hydrogen production of about 286 μmol h^?1g^?1, which is a factor of 3.4 and 2.3 times higher than that of pure TiO₂ and g-C₃N₄, respectively. The outstanding photocatalytic performance in this composite could be ascribed as an efficient electron-hole pair's separation and interfacial contact between TiO₂ spheroids with g-C₃N₄ nanosheets in the formed TiO₂/g-C₃N₄ nanocomposite. This work provide new insight for constructing an efficient Z-scheme TiO₂/g-C₃N₄ nanocomposites for solar light photocatlyst towards solar energy conversion, solar fuels and other environmental applications.     

Greatly enhanced photocatalytic hydrogen production on CdS/(Pt/g-C3N4) via dual functions of Pt on semiconductors interface

CdS and g-C₃N₄ are famous semiconductors in photocatalytic hydrogen evolution, however, their low efficiencies limit their further application. Here, a highly efficient ternary catalyst CdS/(Pt/g-C₃N₄) was reported and its photocatalytic hydrogen production activity reached up to 1465.9 μmol/h/g, which is 5.3 times of Pt/CdS and 4.0 times of Pt/g-C₃N₄, respectively. TEM and HRTEM images demonstrate the Pt nanoparticles exists on the interface of between CdS and g-C₃N₄ acting as a cocatalyst for hydrogen evolution. SPV spectra and electrochemical tests demonstrate that Pt as bridge between CdS and g-C₃N₄ also accelerates the electrons transforming which benefits for the inhibition of the recombination of photoexcited electrons and holes. This study demonstrated the dual roles of interface Pt and provides a new method to design a highly efficient photocatalyst.     

0D/2D heterojunction constructed by high-dispersity Mo-doped Ni2P nanodots supported on g-C3N4 nanosheets towards enhanced photocatalytic H2 evolution activity

Development of low cost and efficient non-noble-metal cocatalyst is still a hot topic to improve the activity of g-C₃N₄ in photocatalytic water splitting to produce H₂. As a potential cocatalyst in photocatalytic application, transition metal phosphides (TMPs) have been proved to greatly enhance the photocatalytic H₂ evolution performance comparable to noble metal Pt. Modifying TMPs by incorporation of hetero-metal has also been reported as an effective strategy for their electronic structure regulation and optimizing the intermediates absorption energy, however, which is rarely reported in the field of photocatalysis. Herein, the 0D/2D heterojunction is constructed by high-dispersity Mo-doped Ni₂P nanodots supported on g-C₃N₄ nanosheets, which exhibits the significantly improved photocatalytic H₂ evolution performance compared with that of Ni₂P/g-C₃N₄ and Pt/g-C₃N₄. Specifically, the optimal H₂ evolution rate reaches 67.6 μmol h⁻¹ over Mo–Ni₂P/g-C₃N₄ sample, which is 6.0 and 2.4 times higher than those of Pt/g-C₃N₄ and Ni₂P/g-C₃N₄, respectively. The fascinating result mainly stems from the improved separation efficiency of charge carriers and more effective electron donating reaction sites resulted from the electronic structure adjustment through doping Mo element into Ni₂P as cocatalyst. This work provides a valid evidence for the modification of cocatalyst to realize high H₂ evolution performance, opening up new opportunities and possibilities for the application of TMPs in the photocatalytic field.     

A review on graphitic carbon nitride (g-C3N4) – metal organic framework (MOF) heterostructured photocatalyst materials for photo(electro)chemical hydrogen evolution

Graphitic carbon nitride (g-C₃N₄)-based heterostructured photocatalysts have recently attracted significant attention for solar water splitting and photocatalytic hydrogen (H₂) evolution, because of their alterable physicochemical, optical and electrical properties, such as tunable band structure, ultrahigh specific surface area and controllable pore size, defect formation and active sites. On the other hand, metal-organic frameworks (MOFs) possess a favorable surface area, permanent porosity and adjustable structures that allow them to be suitable candidates for diverse applications. In this review, we therefore comprehensively discuss the structural properties of heterogeneous g-C₃N₄/MOF-based photocatalysts with a special emphasis on their photocatalytic performance regarding the mechanism of heterogeneous photocatalysis, including advantages, challenges and design considerations.