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.     

V2O5 nanoribbons/N-deficient g-C3N4 heterostructure for enhanced visible-light photocatalytic performance

Visible-light-induced heterostructure photocatalysts have been regarded as promising candidates in clean energy production and environmental treatment of organic pollutants. In this study, we have prepared nanocomposites of V₂O₅/N-deficient g-C₃N₄ (VO/Ndef-CN), which have been characterized by a variety of techniques. The as-synthesized nanocomposites show efficient bifunctional photocatalytic properties toward hydrogen generation and pollutants degradation (dye and antibiotic). The optimized 5VO/Ndef-CN photocatalyst exhibits improved photoactivity for H₂ production (5892 μmol g^?1 h^?1), with a high quantum yield of 6.5%, and fast degradation of organic pollutants, as well as high photocatalytic stability under visible light irradiation. The high photocatalytic efficiency is due to the presence of N defects and S-scheme heterojunction formation, which leads to rapid charge separation, enhanced visible-light absorption, and increased active sites. Furthermore, the possible activity-enhanced mechanism and the photodegradation pathway are proposed based on the experimental and density functional theory (DFT) investigations.     

Heterostructured boron doped nanodiamonds@g-C3N4 nanocomposites with enhanced photocatalytic capability under visible light irradiation

Boron doped nanodiamonds (BDND) were coupled with graphitic carbon nitride (g-C₃N₄) nanosheets to form a heterojunction via a facile pyrolysis approach. The BDND@g-C₃N₄ heterojunction exhibits enhanced visible-light absorbance, improved charge generation/separation efficiency and prolonged lifetime of carriers, which lead to the enhanced photocatalytic activities for the hydrogen evolution and organic pollution under visible-light irradiation. The optimal H₂ evolution rate and apparent quantum efficiency at 420 nm of the BDND@g-C₃N₄ heterojunction is 96.3 μmol h⁻¹ and 6.91%, which is about 5 and 2 times higher than those of pristine g-C₃N₄ nanosheets (18.2 μmol h⁻¹ and 3.92%). No obvious decrease in hydrogen generation rate is observed in the recycling experiment due to the high photo-stabilization of the BDND@g-C₃N₄ composite. The degradation kinetic rate constant of organic pollution of the BDND@g-C₃N₄ structure is 0.1075 min⁻¹, which is 3 times higher compared to pristine g-C₃N₄. This work may provide a promising route to construct highly efficient non-metal photocatalysts for hydrogen evolution and organic pollution degradation under visible light irradiation.     

Construction of Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture for visible-light-driven hydrogen production

In this paper, a novel Au/g-C₃N₄/ZnIn₂S₄ plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture has been successfully constructed by integrating Au/g-C₃N₄ plasmonic photocatalyst composite with 3D ZnIn₂S₄ nanosheet through a simple hydrothermal process. The Au nanoparticles were firstly anchored on the surface of pristine g-C₃N₄ material to get Au/g-C₃N₄ plasmonic photocatalyst. Ascribing to the surface plasmon resonance of Au nanoparticles, the obtained Au/g-C₃N₄ plasmonic photocatalyst shows a significant improved photocatalytic activity toward hydrogen production from water with visible light response comparing with pristine g-C₃N₄. Further combining Au/g-C₃N₄ plasmonic photocatalyst with 3D ZnIn₂S₄ nanosheet to construct a heterojunction composite. Owing to the synergistic effect of the surface plasmon resonance of Au nanoparticles in Au/g-C₃N₄ and the heterojunction structure in the interface of Au/g-C₃N₄ and ZnIn₂S₄, the prepared Au/g-C₃N₄/ZnIn₂S₄ plasma photocatalyst heterojunction composite shows an excellent photocatalytic activity toward hydrogen production from water with visible light response, which is around 7.0 and 6.3 times higher than that of the pristine C₃N₄ and Znln₂S₄ nanosheet, respectively. The present work might provide some insights for exploring other efficient heterojunction photocatalysts with excellent properties.     

Fabrication of hollow g-C3N4@α-Fe2O3/Co-Pi heterojunction spheres with enhanced visible-light photocatalytic water splitting activity

For the first time, g-C₃N₄@α-Fe₂O₃/Co-Pi heterojunctional hollow spheres were successfully fabricated via thermal condensation method followed by solvothermal and photo-deposition treatment, which showed excellent photocatalytical property. Except for the Z-scheme charge transfer between α-Fe₂O₃ and g-C₃N₄, the Co-Pi could further reduce the combination of photogenerated electrons and holes as a hole storage agent, resulting in remarkably enhanced visible-light photocatalytic water splitting activity with the H₂ production rate of 450 μmol h⁻¹g⁻¹, which is 15.7 times higher than that of g-C₃N₄. Moreover, the photocatalytic activity of the prepared ternary hollow photocatalysts showed almost no significant weakness after five cycles, which indicated their good performance stability. The as-prepared g-C₃N₄@α-Fe₂O₃/Co-Pi also possessed good activity for overall water splitting with the hydrogen production rate reaching 9.8 μmol h⁻¹g⁻¹. This synthesized g-C₃N₄@α-Fe₂O₃/Co-Pi composite is expected to be a promising candidate for water splitting.     

Redox couple mediated charge carrier separation in g-C3N4/CuO photocatalyst for enhanced photocatalytic H2 production

Graphitic carbon nitride (g-C₃N₄) is one of the promising two-dimensional metal-free photocatalysts for solar water splitting. Regrettably, the fast electron-hole pair recombination of g-C₃N₄ reduces their photocatalytic water splitting efficiency. In this work, we have synthesized the CuO/g-C₃N₄ heterojunction via wet impregnation followed by a calcination method for photocatalytic H₂ production. The formation of CuO/g-C₃N₄ heterojunction was confirmed by XRD, UV–vis and PL studies. Notably, the formation of heterojunction not only improved the optical absorption towards visible region and also enhanced the carrier generation and separation as confirmed by PL and photocurrent studies. The photocatalytic H₂ production results revealed that CuO/g-C₃N₄ photocatalyst demonstrated the increased photocatalytic H₂ production rate than bare g-C₃N₄. The maximum H₂ production rate was obtained with 4 wt % CuO loaded g-C₃N₄ photocatalyst. Importantly, the rate of H₂ production was further improved by introducing simple redox couple Co²⁺/Co³⁺. Addition of Co²⁺ during photocatalytic H₂ production shuttled the photogenerated holes by a reversible conversion of Co²⁺ to Co³⁺ with accomplishing water oxidation. The effective shuttling of photogenerated holes decreased the election-hole pair recombination and thereby enhancing the photocatalytic H₂ production rate. It is worth to mention that the addition of Co²⁺ with 4 wt % CuO/g-C₃N₄ photocatalyst showed ∼7.5 and ∼2.0 folds enhanced photocatalytic H₂ production rate than bare g-C₃N₄/Co²⁺ and CuO/g-C₃N₄ photocatalysts. Thus, we strongly believe that the present simple redox couple mediated charge carrier separation without using noble metals may provide a new idea to reduce the recombination rate.     

Morphology and defects design in g-C3N4 for efficient and simultaneous visible-light photocatalytic hydrogen production and selective oxidation of benzyl alcohol

Small surface area, deficient reaction sites, and poor visible-light harvest ability of the original graphitic carbon nitride (g-C₃N₄) severely restrict its photocatalytic H₂ production activity. Here, an ultrathin porous and N vacancies rich g-C₃N₄ (V_N-UP-CN) was fabricated by thermal oxidation exfoliation and high-temperature calcination under the Ar atmosphere. The ultrathin porous morphology increases the surface area and reaction sites of original g-C₃N₄, moreover, the produced N vacancies greatly broaden the light harvest ability of ultrathin porous g-C₃N₄ (UP–CN). Therefore, V_N-UP-CN displays the maximal H₂ production rate of 2856.7 μmol g^?1 h^?1 in triethanolamine solution under visible-light, and adding 0.5 M of K₂HPO₄ can further improve its H₂ production rate to 4043.9 μmol g^?1 h^?1. Importantly, V_N-UP-CN also shows good performance in simultaneous photocatalytic H₂ production and benzyl alcohol oxidation to benzaldehyde with the activities of 196.08 and 198.28 μmol g^?1 h^?1, respectively, which avoids the waste of sacrificial agent and photogenerated holes. This work affords an achievable way to design the efficient g-C₃N₄ photocatalyst by morphology and defect regulation, which can effectively utilize both photogenerated electrons and holes for H₂ and value-added chemical production.     

A direct one-step synthesis of ultrathin g-C3N4 nanosheets from thiourea for boosting solar photocatalytic H2 evolution

Two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanosheets, as the promising photocatalyst with fascinating properties, have become a “rising star” in the field of photocatalysis. Although g-C₃N₄ nanosheets exfoliated from the bulk g-C₃N₄ powders are extensively emerged, developing a simple synthetic approach is still full of challenge. To this end, here we report a direct polymerization strategy to fabricate the ultrathin g-C₃N₄ nanosheets, that is only heating treatment of thiourea in air without addition of any template. The photocatalytic activities of as-prepared samples were evaluated by photoreduction of water to hydrogen (H₂) using triethanolamine as sacrificial agent and Pt as co-catalyst under visible-light irradiation (λ > 420 nm). As a result, our few-layered g-C₃N₄ nanosheets with an average thickness of 3.5 nm exhibit a superior visible-light photocatalytic H₂ evolution rate (HER) of 1391 μmol g⁻¹ h⁻¹ and a remarkable apparent quantum efficiency of 6.6% at 420 nm. Eventually, the HER of as-fabricated ultrathin g-C₃N₄ nanosheets is not only much higher than the dicyandiamide-derived g-C₃N₄ or melamine-derived g-C₃N₄, but also greater than the thermal-oxidation etched g-C₃N₄ nanosheets under the same condition.     

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.     

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.     

Construction of Cu7.2S4/g-C3N4 photocatalyst for efficient NIR photocatalysis of H2 production

Graphite-like carbon nitride (g-C₃N₄) has been regarded as a promising photocatalyst for solar-to-chemical conversion. Nevertheless, the narrow absorption of light extremely limited its photocatalytic performance under near-infrared (NIR) irradiation. Herein, the Cu₇.₂S₄ with outstanding NIR absorption was successfully introduced to g-C₃N₄ nanosheets through a simple in-situ growth procedure. As expected, the constructed Cu_7.2S₄/g-C₃N₄ (CSCN) photocatalysts exhibit superior H₂ production activity of 82 μmol g⁻¹ h⁻¹ under NIR light irradiation (λ > 800 nm), which outperforms currently reported g–C₃N₄–based NIR-driven H₂ production systems. Especially, the optimal sample CSCN-5 displays a robust activity of 66 μmol g⁻¹ h⁻¹ at λ = 850 nm monochromatic light irradiation. The excellent photocatalytic performance is linked to the extended optical absorption as well as the efficient separation efficiency of photoinduced carriers, which are evidenced by the UV-visible absorption spectroscopy and photoelectrochemical test. This work provides an effective approach for constructing a Cu_7.2S₄/g-C₃N₄ photocatalytic system for the transformation of NIR solar energy into hydrogen.     

Highly efficient Bi2O3/MoS2 p-n heterojunction photocatalyst for H2 evolution from water splitting

The design of p-n heterojunction photocatalysts to overcome the drawbacks of low photocatalytic activity that results from the recombination of charge carriers and narrow photo-response range is promising technique for future energy. Here, we demonstrate the facile hydrothermal synthesis for the preparation of Bi₂O₃/MoS₂ p-n heterojunction photocatalysts with tunable loading amount of Bi₂O₃ (0–15 wt%). The structure, surface morphology, composition and optical properties of heterostructures were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL), electrochemical impedance spectroscopy (EIS). Compare to pure Bi₂O₃ and MoS_2, the Bi₂O₃/MoS₂ heterostructures displayed significantly superior performance for photocatalytic hydrogen (H₂) production using visible photo-irradiation. The maximum performance for hydrogen evolution was achieved over Bi₂O₃/MoS₂ photocatalyst (10 μmol h⁻¹g⁻¹) with Bi₂O₃ content of 11 wt%, which was approximately ten times higher than pure Bi₂O₃ (1.1 μmol h⁻¹g⁻¹) and MoS₂ (1.2 μmol h⁻¹g⁻¹) photocatalyst. The superior performance was attributed to the robust light harvesting ability, enhanced charge carrier separation via gradual charge transferred pathway. Moreover, the increased efficiency of Bi₂O₃/MoS₂ heterostructure photocatalyst is discussed through proposed mechanism based on observed performance, band gap and band position calculations, PL and EIS data.     

Preparation,structure and application of g-C3N4/BiOX composite photocatalyst

Graphite-like carbon nitride (g-C₃N₄) has attracted great attention for pollutant degradation and clean energy production. The heterojunctions of bismuth halide (BiOX, X = Cl, Br, I) and g-C₃N₄ are proposed to overcome the shortcomings of the g-C₃N₄ photocatalyst, such as low charge separation rate and high charge recombination rate. This review paper systematically discusses the progress in synthesis, structure, and applications of heterojunction photocatalytic composites made of g-C₃N₄ and BiOX based on the understanding of their photocatalytic reaction mechanism. We clarify and summarize structural mechanisms of a single and compound semiconductor to reveal the factors that affect photocatalytic performances. We discuss and compare advantages and disadvantages of versatile preparation processes. Particularly, we focus on the understanding of the structure and characteristics of type II, Z-type, n-n, and p-n heterojunctions and their applications, specifically in pollutant degradation, H₂ production by water splitting, CO₂ reduction, and medical sterilization. The future prospects of g-C₃N₄/BiOX composites are also discussed from aspects of their preparation, application, and research methods. This work may offer a good avenue and data reference to develop novel g-C₃N₄ photocatalytic materials to meet the ever-increasing environmental pollution and energy shortage.     

A facile one-step strategy to construct 0D/2D SnO2/g-C3N4 heterojunction photocatalyst for high-efficiency hydrogen production performance from water splitting

Fabricating 0D/2D heterojunctions is considered to be an efficient mean to improve the photocatalytic activity of g-C₃N₄, whereas their applications are usually restricted by complex preparation process. Here, the 0D/2D SnO₂/g-C₃N₄ heterojunction photocatalyst is prepared by a simple one-step polymerization strategy, in which SnO₂ nanodots in-situ grow on the surface of g-C₃N₄ nanosheets. It shows the outstanding photocatalytic H₂ production activity relative to g-C₃N₄ under the visible light, which is due to the formation of 0D/2D heterojunction significantly contributing to the separation of photogenerated charge carriers. In particular, the H₂ production rate over the optimal SnO₂/g–C₃N₄–1 sample is 1389.2 μmol h⁻¹ g⁻¹, which is 6.06 times higher than that of g-C₃N₄ (230.8 μmol h⁻¹ g⁻¹). Meanwhile, the AQE value of H₂ production over the SnO₂/g–C₃N₄–1 sample reaches up to a maximum of 4.5% at 420 nm. This work develops a simple approach to design and fabricate g–C₃N₄–based 0D/2D heterojunctions for the high-efficiency H₂ production from water splitting.     

In- situ solid-phase fabrication of Ag/AgX (X=Cl,Br, I)/g-C3N4 composites for enhanced visible-light hydrogen evolution

In this work, a series of Ag/AgX (X = Cl, Br, I)/g-C₃N₄ (Ag/AgX/CN) composites were successfully fabricated by an in-situ solid phase method. The morphology and structure, photoluminescence and photoelectrochemical properties of composites were investigated in detail. The as-prepared Ag/AgX/CN composites were used as H₂ evolution photocatalysts under visible-light irradiation with a sacrificial agent. The experimental results revealed that Ag/AgI/CN-4 composite possesses highest-H₂ evolution rate (up to 59.22 μmol g⁻¹ h⁻¹) which are approximately 31 times higher than that of pure g-C₃N₄ (1.94 μmol g⁻¹ h⁻¹). In addition, Ag/AgCl/CN-4 and Ag/AgBr/CN-4 composites also present high photocatalytic activities yielding, 26.39 and 18.05 μmol_H2 g⁻¹ h⁻¹_, respectively. The enhanced photocatalytic activities of Ag/AgI/CN-4 composite might be attributed to the synergistic effect between Ag/AgI nanoparticles and g-C₃N₄ and the localized surface plasmon resonance effect of metallic Ag. Moreover, Ag/AgI/CN-4 composite showed excellent recyclability and stability after five cycling photocatalytic tests (about 25 h). Furthermore, the possible photocatalytic mechanism of Ag/AgI/CN composites is proposed.     

Boosting photocatalytic hydrogen evolution of g-C3N4 via enhancing its interfacial redox activity and charge separation with Mo-doped CoSx

To achieve low-cost photocatalytic hydrogen (H₂) production, it is necessary to develop low-priced transition metal co-catalysts to replace the roles of noble metals for photocatalytic H₂ evolution. Herein, a co-catalyst of Mo-doped CoS_x (Mo-CoS_x) was synthesized by using the hydrothermal procedure, then attached to g-C₃N₄ to construct a composite photocatalyst. As a co-catalyst, Mo-CoS_x can work as an electron acceptor, it is utilized to receive electrons generated by g-C₃N₄ photocatalyst on the surface of the catalyst, and inhibit the recombination of those electrons, thus showing enhanced charge transfer ability as well as reduction ability. The optimized Mo-CoS_x/g-C₃N₄ delivered a prominent photocatalytic H₂ evolution rate of 2062.4 μmol h^?1 g^?1, which was ～193 times higher than g-C₃N₄. Its AQE at 400 nm and 420 nm were 11.05% and 6.83%, respectively. This work provides a novel non-precious metal co-catalyst/g-C₃N₄ photocatalyst that is expected to be an acceptable cost route to solar energy conversion.     

The charge transfer pathway of g-C3N4 decorated Au/Bi(VO4) composites for highly efficient photocatalytic hydrogen evolution

In this report, a novel g-C₃N₄/Au/BiVO₄ photocatalyst has been prepared successfully by assembling gold nanoparticles on the interface of super-thin porous g-C₃N₄ and BiVO₄, which exhibits outstanding photocatalytic performance toward hydrogen evolution and durable stability in the absence of cocatalyst. FESEM micrograph analysis suggested that the intimate contact between Au, BiVO₄, and g-C₃N₄ in the as-developed photocatalyst allows a smooth migration and separation of photogenerated charge carriers. In addition, the XRD, EDX and XPS analysis further confirmed the successful formation of the as-prepared g-C₃N₄/Au/BiVO₄ photocatalyst. The photocatalytic hydrogen production activity of the developed photocatalyst was evaluated under visible-light irradiation (λ > 420 nm) using methanol as a sacrificial reagent. By optimizing the 5-CN/Au/BiVO₄ composite shows the highest H₂ evolution rate (2986 μmolg⁻¹h⁻¹), which is 15 times higher than that of g-C₃N₄ (199 μmolg⁻¹h⁻¹) and 10 time better than bare BiVO₄ (297 μmolg⁻¹h⁻¹). The enhancement in photocatalytic activity is attributed to efficient separation of the photoexcited charges due to the anisotropic junction in the g-C₃N₄/Au/BiVO₄ system. The enhancement in photocatalytic activity is attributed to efficient separation of the photoexcited charges due to the anisotropic junction in the g-C₃N₄/Au/BiVO₄ system.     

Surface plasmon assisted photocatalytic hydrogen generation with Ag decorated g-C3N4 coupled SnO2 nanophotocatalyst under visible-light driven photocatalysis

Photocatalytic hydrogen evolution from water is a feasible technique to solve energy crises and reduce dependance on carbon fuels. As for this, silver nanoparticles were grown on the surface of SnO₂ coupled g-C₃N₄ nanocomposite for the generation of hydrogen gas from water under visible light photocatalysis. The prepared samples were properly characterized to investigate their light absorption characteristics followed by charge generation and separation for water splitting. The optimized nanocomposite produced 270 μmol h⁻¹ g⁻¹ hydrogen which was much superior to pure g-C₃N₄ and SnO₂. These upgraded photocatalytic activities were attached to the extended visible-light absorption due to the presence of Ag nanoparticles characterized by surface plasmon resonance (SPR) and suitable conduction bands position of g-C₃N₄ and SnO₂ for the separation of excited charges. The photoluminescence study, amount of produced hydroxyl free radicals and electrochemical investigation confirmed the long-rooted charge separation capability of the nanocomposites. We believe that this work will have more positive impacts on the synthesis of low cost SPR assisted photocatalysts for energy production and environmental purification.     

Synthesis of mesoporous g-C3N4/S-PAN π-conjugation heterojunction via sulfur-induced cyclization reaction for enhanced photocatalytic H2 production

Simultaneously extended π-conjugated system and provide abundant pore structure of semiconductor photocatalysts for hydrogen (H₂) production is highly desirable. Hence, a novel mesoporous sulfurized polyacrylonitrile modified g-C₃N₄ (g-C₃N₄/S-PAN) π-conjugation heterojunction is firstly fabricated by one-step strategy under the sulfur-induced cyclization reaction and pore-creating effect. Excitedly, the g-C₃N₄/S-PAN π-conjugation heterojunction extends the π-conjugated system in favor of speeding up the photogenerated electron transfer, which is due to strengthen the π-π interactions between the S-PAN and g-C₃N₄ and S-PAN is more apt to accept electrons. And the obtained g-C₃N₄/S-PAN π-conjugation heterojunction with mesoporous structure also provide abundant active sites for proton reduction. Accordingly, the g-C₃N₄/S-PAN-2 π-conjugation heterojunction shows the optimal photocatalytic H₂ evolution (PHE) activity (736.24 μmol h⁻¹g⁻¹), which is approximately 2.15 times higher than pristine g-C₃N₄. In addition, the relationships of the optical and photoelectrochemical properties with photocatalytic activity are revealed in depth based on the first-principles calculations of band structure and density of states (DOS). This work provides a new one-step strategy to obtain g-C₃N₄-based π-conjugation heterojunction with the unique microstructure for improving PHE activity.     

Exfoliated and plicated g-C3N4 nanosheets for efficient photocatalytic organic degradation and hydrogen evolution

Exfoliated and plicated g-C₃N₄ nanosheets (CNsF) were prepared through a thermal-chemical exfoliation in which the bulk g-C₃N₄ was obtained first under thermal exfoliation, and then was exposed to an acidic etching using hydrofluoric acid under hydrothermal condition. The acidic etching not only exfoliated g-C₃N₄ nanosheets by disrupting weak van der Waals forces between layers, which led to formation of a monolayer or a few layers of g-C₃N₄ nanosheets, but also made disordered defects on its surface and created plicated g-C₃N₄ nanosheets. Under visible-light illumination, the optimized sample (CNsF-6%) showed a hydrogen evolution rate of 54.13 μmol h^?1g^?1 (without co-catalyst) and a specific surface area of 121.4 m² g^?1, which were about 4.7 and 2.5 times, respectively, higher than pristine g-C₃N₄. It also showed remarkably enhanced photocatalytic performance in removing various organic pollutants. This remarkable improvement probably arises from the porous nanosheets and an increased number of active sites resulting from the CNsF, which subsequently enhanced the charge separation efficiency. This work provided an alternative way to obtain highly active g-C₃N₄ photocatalysts.