C3N5-C3N4 photocatalytic hydrogen evolution material as well as preparation method and application thereof

Abstract

The invention discloses a C3N5-C3N4 photocatalytic hydrogen evolution material as well as a preparation method and application thereof. The material consists of a core layer, a shell layer and an interface transition region, wherein the core layer is C3N5 rich in S-O bonds; the core layer is coated with the shell layer, the shell layer is C3N4 with gradient increasing nitrogen vacancy concentration from inside to outside, and CoP nanoparticles are loaded on the surface of the shell layer; and the C / N atomic ratio in the interface transition region is in continuous gradient change to form a built-in electric field gradient. The preparation method comprises the following steps: preparing a C3N5 core layer through pyrolysis of a sulfur-containing precursor; coating a C3N4 precursor on the surface through solvothermal reaction; carrying out heat treatment in a gradient ammonia atmosphere, carrying out synchronous crystallization and introducing gradient nitrogen vacancies; and finally, loading CoP through photodeposition. The material has spatially separated light absorption, charge transfer and reaction centers, shows excellent hydrogen evolution activity and stability under visible light, and is suitable for the field of photocatalytic hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a carbon nitride-based composite photocatalytic material for visible light-driven water splitting to produce hydrogen, particularly a C3N4-C3N5 composite material with a core-shell gradient structure and an embedded S-scheme heterojunction. Background Technology

[0002] Achieving efficient visible light-driven water splitting for hydrogen production hinges on developing photocatalytic materials that combine broad-spectrum absorption, efficient charge separation, and rapid surface reaction kinetics. Among non-metallic catalysts, graphitic carbon nitride (g-C3N4) and its high-nitrogen analogue C3N5 have become research focuses due to their low cost and good stability. Constructing C3N4 / C3N5 heterojunctions, especially S-scheme heterojunctions, can effectively promote the separation of photogenerated electron-hole pairs while retaining strongly reducing electrons. However, current research based on the C3N4 / C3N5 system still faces several interconnected technical bottlenecks: First, in the spatial structure design of composite materials, the interface contact area of ​​heterojunctions formed by conventional physical mixing or co-precipitation methods is limited and random, resulting in long charge transport paths and high impedance. Although attempts have been made to construct core-shell structures to increase interface contact, simple core-shell encapsulation often leads to dense shell layers, hindering reactant mass transfer. Furthermore, the band matching of the core and shell phases and the bonding state of the interface atoms are difficult to precisely control, affecting the built-in electric field strength. Secondly, in terms of material modification, non-metallic elements (such as sulfur) are introduced for doping or nitrogen vacancies (V). - N) Defects are an effective means of modulating energy bands and creating active sites. However, high-temperature calcination of sulfur-containing precursors or ammonia treatment usually results in the uniform or random distribution of dopants or defects in the bulk material, making it impossible to enrich them in the specific regions where they can play a most significant role (such as charge separation interfaces or surface reaction sites), and may even introduce unnecessary recombination centers into the bulk phase. Finally, to improve the surface reaction rate, loading non-noble metal co-catalysts such as CoP is a common strategy, but traditional impregnation reduction or deposition methods have difficulty controlling the loading position and interfacial chemical state of CoP nanoparticles. They may cover the light-absorbing host, reducing light absorption efficiency, or be poorly bonded to the material, leading to detachment.

[0003] Therefore, the pressing problem in this field is: how to construct an interface transition region with continuously varying chemical composition between the core and shell layers within the advantageous framework of the C3N4 / C3N5 core-shell structure to form a strong gradient built-in electric field; how to spatially decouple and functionalize sulfur doping (in the form of SO bonds) with nitrogen vacancy defects, so that SO bonds are mainly distributed in the core layer responsible for light absorption to promote charge generation and bulk transport, while nitrogen vacancy gradients are enriched on the shell surface as reaction sites; and how to achieve selective and robust loading of co-catalysts (such as CoP) at nitrogen vacancies on the shell surface. Existing technologies lack preparation methods capable of synergistically achieving the above-mentioned refined spatial structure control. Summary of the Invention

[0004] The technical problem to be solved: The purpose of this invention is to prepare a C3N5-C3N4 photocatalytic hydrogen evolution material.

[0005] Technical solution: A C3N5-C3N4 photocatalytic hydrogen evolution material, which consists of a core layer, a shell layer, and an interface transition region. The core layer is C3N5 rich in SO bonds, which are connected to the C3N5 lattice in the form of CSOC or CSON bonding. The shell layer covers the outside of the core layer and is C3N4 rich in nitrogen vacancies. The nitrogen vacancy concentration is distributed in a gradient increasing from the inside to the outside. The shell layer is loaded with CoP nanoparticles with a size of 2~8nm as a cocatalyst. The interface transition region is located between the core layer and the shell layer, with a thickness of 2~15nm. Its C / N atomic ratio changes continuously from the core layer to the shell layer, forming a continuously distributed built-in electric field gradient.

[0006] Preferably, the average diameter of the core layer is 80-300 nm, the thickness of the shell layer is 20-80 nm, and the specific surface area of ​​the core-shell structure is 80-180 m². 2 / g.

[0007] Preferably, the loading of the CoP cocatalyst is 0.05~1.0 wt% of the total mass of the photocatalytic material, and it forms a Co-PN interfacial bond with the shell C3N4.

[0008] Preferably, a method for preparing a C3N5-C3N4 photocatalytic hydrogen evolution material includes the following steps: S1. Mix cyanuric acid and thiourea at a mass ratio of 1:(1.5~4) and ball mill them in a ball mill at a speed of 400-600 r / min for 4-8 hours to obtain a uniform precursor powder; S2. Place the precursor powder obtained in step S1 in a tube furnace, heat it to 520-580℃ at 3-8℃ / min under an argon atmosphere, and hold it for 1.5-3h to obtain a C3N5 core layer precursor rich in SO bonds. S3. Disperse the C3N5 core layer precursor obtained in step S2 in an ethanol-water mixed solvent, add melamine and hexadecyltrimethylammonium bromide, wherein the mass ratio of C3N5:melamine:CTAB is 1:(0.5~2):(0.01~0.05), and solvothermal react at 140-180℃ for 18-36h to polymerize the melamine C3N5 surface to form a uniform coating layer; S4. Place the product from step S3 in an ammonia / argon mixed atmosphere, raise the temperature to 560-620℃ at 2~5℃ / min, and hold for 1-2h; the ammonia concentration is gradually increased from 5% to 20% during the heating process to simultaneously achieve the crystallization of the C3N4 shell, the gradient introduction of nitrogen vacancies, and the formation of the interface transition zone. S5. Disperse the core-shell material obtained in step S4 in an aqueous solution containing cobalt salt and sodium hypophosphite, stir for 2-6 hours under 300 W xenon lamp irradiation, and selectively load CoP nanoparticles onto the shell surface by photodeposition.

[0009] Preferably, the argon flow rate in step S2 is 50~150 sccm, and the product after pyrolysis is washed three times with ethanol and dried under vacuum at 60°C for 12 hours.

[0010] Preferably, the volume fraction of ethanol in the ethanol-water mixed solvent in step S3 is 30-70%, and the solvothermal reaction is carried out in a high-pressure reactor lined with polytetrafluoroethylene.

[0011] Preferably, the total flow rate of the ammonia / argon mixed atmosphere in step S4 is 100 sccm, and the ammonia concentration increases at a rate of 5% per hour during the heating process.

[0012] Preferably, the cobalt salt in step S5 is cobalt chloride hexahydrate or cobalt nitrate, the cobalt ion concentration is 0.5~2.0 mmol / L, and the sodium hypophosphite concentration is 3-8 times the cobalt salt concentration; the solution pH is maintained at 5.5~6.5 during photodeposition.

[0013] The above-mentioned C3N5-C3N4 photocatalytic hydrogen evolution material is used in visible light-driven hydrogen evolution.

[0014] Beneficial effects: The C3N4-C3N5 photocatalytic hydrogen evolution material of this invention has the following advantages: In this invention, C3N5 with SO bonds in the core layer has a broadened visible light absorption range and enhanced photogenerated carrier generation capability. SO bonds, as intracrystalline electron channels, accelerate the migration of primary charges and effectively suppress charge recombination inside the core layer, providing a sufficient charge source for efficient catalysis. In this invention, the continuous gradient change of the C / N atomic ratio at the core-shell interface forms a built-in electric field gradient from the core to the shell. This gradient electric field, like an "electron ramp," continuously drives photogenerated electrons to migrate directionally from the core layer C3N5 to the shell layer C3N4, achieving spatial separation of charges and greatly reducing the probability of electron-hole recombination. In this invention, nitrogen vacancies (V) are gradient-enriched on the outer surface of the shell. - N) provides abundant active sites for the adsorption and activation of water molecules. Simultaneously, precisely loaded CoP nanoparticles act as highly efficient co-catalysts, forming Co-PN bonds with C3N4 to stabilize attachment and further reduce the overpotential for proton reduction. V - The synergistic effect of N and CoP significantly accelerates the kinetics of surface hydrogen evolution reaction; The unique core-shell structure in this invention provides the material with good mechanical stability. The gradient distribution of nitrogen vacancies avoids lattice distortion or collapse caused by excessive concentration of defects in local areas. CoP nanoparticles are firmly anchored by chemical bonds and are not easy to fall off or agglomerate during the reaction process, thus ensuring the activity stability of the material in long-term cyclic use. The hierarchical pores (intranuclear micropores, shell mesopores and intercore-shell voids) formed by the core-shell structure in this invention not only provide a high specific surface area, but also construct an efficient mass transport channel. The multiple reflections and scattering of visible light between the core and shell are further enhanced, thereby improving the efficiency of photon capture and utilization, and realizing the synergistic optimization of mass transfer process and light absorption. The introduction of SO bonds in the C3N5 core layer of this invention modulates its electronic structure at the molecular level, causing a redshift in the intrinsic light absorption edge of the material. At the same time, the nitrogen vacancies distributed in the shell gradient introduce defect energy levels in the band gap. The synergistic effect of the two enables a wider range of effective utilization of visible light and improves the utilization rate of the solar spectrum. The C3N5-C3N4 material in this invention is effective under visible light with a wavelength ≥420 nm and a light source intensity of 100 mW / cm². 2 The process is carried out in an aqueous solution containing 10 vol% triethanolamine as a hole sacrificial agent, and the hydrogen production rate of the photocatalytic material is not less than 1800 μmol·g. -1 ·h -1 The apparent quantum efficiency (420 nm) is not less than 8%; after 50 hours of continuous illumination, the hydrogen production activity of the photocatalytic material decays by less than 15%, exhibiting excellent photocatalytic stability. Attached Figure Description

[0015] Figure 1 EDS plot; Figure 2 This is a graph showing the hydrogen evolution rate. Figure 3 The retention rate after five cycles; Figure 4 The hydrogen evolution rate is represented in different systems. Detailed Implementation

[0016] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: Example 1

[0017] This embodiment discloses a C3N5-C3N4 photocatalytic hydrogen evolution reaction material. This material achieves efficient separation and transport of photogenerated carriers through a gradient structure design in the core-shell-interface transition region, making it suitable for visible light-driven hydrogen evolution reactions. The material consists of a core layer, a shell layer, and an interface transition region. The core layer is C3N5 rich in SO bonds, which are bonded to the C3N5 lattice in the form of CSOC or CSON bonds. The shell layer, covering the outside of the core layer, is C3N4 rich in nitrogen vacancies, with the nitrogen vacancy concentration increasing from the inside out. The shell layer is loaded with 5nm CoP nanoparticles as a co-catalyst. The interface transition region, located between the core and shell layers, has a thickness of 10nm, and its C / N atomic ratio continuously changes from 0.6 in the core layer to 0.75 in the shell layer, forming a continuously distributed built-in electric field gradient.

[0018] Furthermore, the core layer has an average diameter of 200 nm, the shell layer has a thickness of 60 nm, and the core-shell structure has a specific surface area of ​​100 m². 2 / g; the loading of the CoP cocatalyst is 1.0 wt% of the total mass of the photocatalytic material, and it forms a Co-PN interface bond with the shell C3N4.

[0019] The above-mentioned method for preparing C3N5-C3N4 photocatalytic hydrogen evolution materials includes the following steps: S1. Cyanuric acid and thiourea were mixed at a mass ratio of 1:3 and ball-milled at a speed of 500 r / min for 4 h to obtain a uniform precursor powder; S2. Place the precursor powder obtained in step S1 in a tube furnace, introduce argon gas at a flow rate of 100 sccm, heat to 550℃ at a rate of 5℃ / min and hold for 2h. After pyrolysis, the product is washed three times with ethanol and then vacuum dried at 60℃ for 12h to obtain a C3N5 core layer precursor rich in SO bonds.

[0020] S3. Disperse the C3N5 core layer precursor obtained in step S2 in an ethanol-water mixed solvent with a volume fraction of 70% ethanol, add melamine and CTAB, and control the mass ratio of C3N5, melamine and CTAB to be 1:1:0.05. Transfer the mixture to a high-pressure reactor with a polytetrafluoroethylene liner and carry out a solvothermal reaction at 140°C for 18 hours to allow melamine to polymerize on the surface of C3N5 to form a uniform coating layer.

[0021] S4. Place the product from step S3 in a tube furnace and introduce a mixed atmosphere of ammonia / argon with a total flow rate of 100 sccm. Heat the mixture to 560°C at a rate of 5°C / min and hold for 1 h. During the heating process, the ammonia concentration increases from 5% to 20% at a rate of 5% per hour, simultaneously achieving the crystallization of the C3N4 shell, the gradient introduction of nitrogen vacancies, and the formation of the interface transition zone.

[0022] S5. The core-shell material obtained in step S4 is dispersed in an aqueous solution of cobalt chloride hexahydrate and sodium hypophosphite with a cobalt ion concentration of 1.0 mmol / L and a sodium hypophosphite concentration of 5 times that of cobalt salt. The pH of the solution is adjusted to 5.5 with dilute hydrochloric acid, and the solution is stirred for 2 hours under irradiation with a 300W xenon lamp. CoP nanoparticles are selectively loaded onto the shell surface of the core-shell material by photodeposition.

[0023] Example 2

[0024] This embodiment discloses a C3N5-C3N4 photocatalytic hydrogen evolution material. This material achieves efficient separation and transport of photogenerated carriers through a gradient structure design in the core-shell-interface transition region, making it suitable for visible light-driven hydrogen evolution reactions. The material consists of a core layer, a shell layer, and an interface transition region. The core layer is C3N5 rich in SO bonds, which are bonded to the C3N5 lattice in the form of CSOC or CSON bonds. The shell layer, covering the outside of the core layer, is C3N4 rich in nitrogen vacancies, with the nitrogen vacancy concentration increasing gradually from the inside out. The shell layer is loaded with 2nm CoP nanoparticles as a co-catalyst. The interface transition region, located between the core and shell layers, has a thickness of 2nm, and its C / N atomic ratio changes continuously from 0.58 in the core layer to 0.72 in the shell layer, forming a continuously distributed built-in electric field gradient.

[0025] Furthermore, the core layer has an average diameter of 100 nm, the shell layer has a thickness of 40 nm, and the core-shell structure has a specific surface area of ​​80 m². 2 / g; the loading of the CoP cocatalyst is 0.05 wt% of the total mass of the photocatalytic material, and it forms a Co-PN interface bond with the shell C3N4.

[0026] The above-mentioned method for preparing C3N5-C3N4 photocatalytic hydrogen evolution materials includes the following steps: S1. Cyanuric acid and thiourea were mixed at a mass ratio of 1:1.5 and ball-milled at a speed of 500 r / min for 4 h to obtain a uniform precursor powder; S2. Place the precursor powder obtained in step S1 in a tube furnace, introduce argon gas at a flow rate of 100 sccm, heat to 550℃ at a rate of 5℃ / min and hold for 2h. After pyrolysis, the product is washed three times with ethanol and then vacuum dried at 60℃ for 12h to obtain a C3N5 core layer precursor rich in SO bonds.

[0027] S3. Disperse the C3N5 core layer precursor obtained in step S2 in an ethanol-water mixed solvent with a volume fraction of 70% ethanol, add melamine and CTAB, and control the mass ratio of C3N5, melamine and CTAB to be 1:0.5:0.01. Transfer the mixture to a high-pressure reactor with a polytetrafluoroethylene liner and carry out a solvothermal reaction at 140°C for 18 hours to allow melamine to polymerize on the surface of C3N5 to form a uniform coating layer.

[0028] S4. Place the product from step S3 in a tube furnace and introduce a mixed atmosphere of ammonia / argon with a total flow rate of 100 sccm. Heat the mixture to 560°C at a rate of 5°C / min and hold for 1 h. During the heating process, the ammonia concentration increases from 5% to 20% at a rate of 5% per hour, simultaneously achieving the crystallization of the C3N4 shell, the gradient introduction of nitrogen vacancies, and the formation of the interface transition zone.

[0029] S5. The core-shell material obtained in step S4 is dispersed in an aqueous solution of cobalt chloride hexahydrate and sodium hypophosphite with a cobalt ion concentration of 0.5 mmol / L and a sodium hypophosphite concentration of 5 times that of cobalt salt. The pH of the solution is adjusted to 5.5 with dilute hydrochloric acid, and the solution is stirred for 2 hours under 300W xenon lamp irradiation. CoP nanoparticles are selectively loaded onto the shell surface of the core-shell material by photodeposition.

[0030] Example 3

[0031] This embodiment discloses a C3N5-C3N4 photocatalytic hydrogen evolution reaction material. This material achieves efficient separation and transport of photogenerated carriers through a gradient structure design in the core-shell-interface transition region, making it suitable for visible light-driven hydrogen evolution reactions. The material consists of a core layer, a shell layer, and an interface transition region. The core layer is C3N5 rich in SO bonds, which are bonded to the C3N5 lattice in the form of CSOC or CSON bonds. The shell layer, covering the outside of the core layer, is C3N4 rich in nitrogen vacancies, with the nitrogen vacancy concentration increasing from the inside out. The shell layer is loaded with 6nm CoP nanoparticles as a co-catalyst. The interface transition region, located between the core and shell layers, has a thickness of 8nm, and its C / N atomic ratio changes continuously from 0.62 in the core layer to 0.78 in the shell layer, forming a continuously distributed built-in electric field gradient.

[0032] Furthermore, the core layer has an average diameter of 300 nm, the shell layer has a thickness of 80 nm, and the core-shell structure has a specific surface area of ​​180 m². 2 / g; the loading of the CoP cocatalyst is 0.8wt% of the total mass of the photocatalytic material, and it forms a Co-PN interface bond with the shell C3N4.

[0033] The above-mentioned method for preparing C3N5-C3N4 photocatalytic hydrogen evolution materials includes the following steps: S1. Cyanuric acid and thiourea were mixed at a mass ratio of 1:2 and ball-milled in a ball mill at a speed of 500 r / min for 4 h to obtain a uniform precursor powder; S2. Place the precursor powder obtained in step S1 in a tube furnace, introduce argon gas at a flow rate of 100 sccm, heat to 550℃ at a rate of 5℃ / min and hold for 2h. After pyrolysis, the product is washed three times with ethanol and then vacuum dried at 60℃ for 12h to obtain a C3N5 core layer precursor rich in SO bonds.

[0034] S3. Disperse the C3N5 core layer precursor obtained in step S2 in an ethanol-water mixed solvent with a volume fraction of 70% ethanol, add melamine and CTAB, and control the mass ratio of C3N5, melamine and CTAB to be 1:2:0.03. Transfer the mixture to a high-pressure reactor with a polytetrafluoroethylene liner and carry out a solvothermal reaction at 180°C for 36 hours to allow melamine to polymerize on the surface of C3N5 to form a uniform coating layer.

[0035] S4. Place the product from step S3 in a tube furnace and introduce a mixed atmosphere of ammonia / argon with a total flow rate of 100 sccm. Heat the mixture to 560°C at a rate of 5°C / min and hold for 1 h. During the heating process, the ammonia concentration increases from 5% to 20% at a rate of 5% per hour, simultaneously achieving the crystallization of the C3N4 shell, the gradient introduction of nitrogen vacancies, and the formation of the interface transition zone.

[0036] S5. The core-shell material obtained in step S4 is dispersed in an aqueous solution of cobalt chloride hexahydrate and sodium hypophosphite with a cobalt ion concentration of 2.0 mmol / L and a sodium hypophosphite concentration of 8 times that of cobalt salt. The pH of the solution is adjusted to 5.5 with dilute hydrochloric acid, and the solution is stirred for 2 hours under irradiation with a 300W xenon lamp. CoP nanoparticles are selectively loaded onto the shell surface of the core-shell material by photodeposition.

[0037] Example 4

[0038] This embodiment discloses a C3N5-C3N4 photocatalytic hydrogen evolution reaction material. This material achieves efficient separation and transport of photogenerated carriers through a gradient structure design in the core-shell-interface transition region, making it suitable for visible light-driven hydrogen evolution reactions. The material consists of a core layer, a shell layer, and an interface transition region. The core layer is C3N5 rich in SO bonds, which are bonded to the C3N5 lattice in the form of CSOC or CSON bonds. The shell layer, covering the outside of the core layer, is C3N4 rich in nitrogen vacancies, with the nitrogen vacancy concentration increasing from the inside out. The shell layer is loaded with 5nm CoP nanoparticles as a co-catalyst. The interface transition region, located between the core and shell layers, has a thickness of 8nm, and its C / N atomic ratio changes continuously from 0.59 in the core layer to 0.74 in the shell layer, forming a continuously distributed built-in electric field gradient.

[0039] Furthermore, the core layer has an average diameter of 100 nm, the shell layer has a thickness of 50 nm, and the core-shell structure has a specific surface area of ​​100 m². 2 / g; the loading of the CoP cocatalyst is 0.1 wt% of the total mass of the photocatalytic material, and it forms a Co-PN interface bond with the shell C3N4.

[0040] The above-mentioned method for preparing C3N5-C3N4 photocatalytic hydrogen evolution materials includes the following steps: S1. Cyanuric acid and thiourea were mixed at a mass ratio of 1:2.5 and ball-milled in a ball mill at a speed of 500 r / min for 4 h to obtain a uniform precursor powder; S2. Place the precursor powder obtained in step S1 in a tube furnace, introduce argon gas at a flow rate of 100 sccm, heat to 550℃ at a rate of 5℃ / min and hold for 2h. After pyrolysis, the product is washed three times with ethanol and then vacuum dried at 60℃ for 12h to obtain a C3N5 core layer precursor rich in SO bonds.

[0041] S3. Disperse the C3N5 core layer precursor obtained in step S2 in an ethanol-water mixed solvent with a volume fraction of 70% ethanol, add melamine and CTAB, and control the mass ratio of C3N5, melamine and CTAB to be 1:1.5:0.01. Transfer the mixture to a high-pressure reactor with a polytetrafluoroethylene liner and carry out a solvothermal reaction at 140°C for 18 hours to allow melamine to polymerize on the surface of C3N5 to form a uniform coating layer.

[0042] S4. Place the product from step S3 in a tube furnace and introduce a mixed atmosphere of ammonia / argon with a total flow rate of 100 sccm. Heat the mixture to 560°C at a rate of 5°C / min and hold for 1 h. During the heating process, the ammonia concentration increases from 5% to 20% at a rate of 5% per hour, simultaneously achieving the crystallization of the C3N4 shell, the gradient introduction of nitrogen vacancies, and the formation of the interface transition zone.

[0043] S5. The core-shell material obtained in step S4 is dispersed in an aqueous solution of cobalt chloride hexahydrate and sodium hypophosphite with a cobalt ion concentration of 1 mmol / L and a sodium hypophosphite concentration of 8 times that of cobalt salt. The pH of the solution is adjusted to 5.5 with dilute hydrochloric acid, and the solution is stirred for 2 hours under irradiation with a 300W xenon lamp. CoP nanoparticles are selectively loaded onto the shell surface of the core-shell material by photodeposition.

[0044] Example 5

[0045] This embodiment discloses a C3N5-C3N4 photocatalytic hydrogen evolution reaction material. This material achieves efficient separation and transport of photogenerated carriers through a gradient structure design in the core-shell-interface transition region, making it suitable for visible light-driven hydrogen evolution reactions. The material consists of a core layer, a shell layer, and an interface transition region. The core layer is C3N5 rich in SO bonds, which are bonded to the C3N5 lattice in the form of CSOC or CSON bonds. The shell layer, covering the outside of the core layer, is C3N4 rich in nitrogen vacancies, with the nitrogen vacancy concentration increasing from the inside out. The shell layer is loaded with 6nm CoP nanoparticles as a co-catalyst. The interface transition region, located between the core and shell layers, has a thickness of 5nm, and its C / N atomic ratio changes continuously from 0.61 in the core layer to 0.76 in the shell layer, forming a continuously distributed built-in electric field gradient.

[0046] Furthermore, the core layer has an average diameter of 80 nm, the shell layer has a thickness of 20 nm, and the core-shell structure has a specific surface area of ​​140 m². 2 / g; the loading of the CoP cocatalyst is 0.5 wt% of the total mass of the photocatalytic material, and it forms a Co-PN interface bond with the shell C3N4.

[0047] The above-mentioned method for preparing C3N5-C3N4 photocatalytic hydrogen evolution materials includes the following steps: S1. Cyanuric acid and thiourea were mixed at a mass ratio of 1:4 and ball-milled in a ball mill at a speed of 500 r / min for 4 h to obtain a uniform precursor powder; S2. Place the precursor powder obtained in step S1 in a tube furnace, introduce argon gas at a flow rate of 100 sccm, heat to 550℃ at a rate of 5℃ / min and hold for 2h. After pyrolysis, the product is washed three times with ethanol and then vacuum dried at 60℃ for 12h to obtain a C3N5 core layer precursor rich in SO bonds.

[0048] S3. Disperse the C3N5 core layer precursor obtained in step S2 in an ethanol-water mixed solvent with a volume fraction of 70% ethanol, add melamine and CTAB, and control the mass ratio of C3N5, melamine and CTAB to be 1:1:0.01. Transfer the mixture to a high-pressure reactor with a polytetrafluoroethylene liner and carry out a solvothermal reaction at 140°C for 18 hours to allow melamine to polymerize on the surface of C3N5 to form a uniform coating layer.

[0049] S4. Place the product from step S3 in a tube furnace and introduce a mixed atmosphere of ammonia / argon with a total flow rate of 100 sccm. Heat the mixture to 560°C at a rate of 5°C / min and hold for 1 h. During the heating process, the ammonia concentration increases from 5% to 20% at a rate of 5% per hour, simultaneously achieving the crystallization of the C3N4 shell, the gradient introduction of nitrogen vacancies, and the formation of the interface transition zone.

[0050] S5. The core-shell material obtained in step S4 is dispersed in an aqueous solution of cobalt chloride hexahydrate and sodium hypophosphite with a cobalt ion concentration of 2 mmol / L and a sodium hypophosphite concentration three times that of the cobalt salt. The pH of the solution is adjusted to 5.5 with dilute hydrochloric acid, and the solution is stirred for 2 hours under irradiation with a 300W xenon lamp. CoP nanoparticles are selectively loaded onto the shell surface of the core-shell material by photodeposition.

[0051] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the average diameter of the core layer is 350 nm and the thickness of the shell layer is 90 nm. The other material structure parameters and preparation steps are completely consistent with those of Example 1.

[0052] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the cobalt ion concentration was adjusted to 2.5 mmol / L only in S5, so that the average particle size of the final loaded CoP was 10 nm.

[0053] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that, like Example 1, only in S1, cyanuric acid and thiourea are mixed at a mass ratio of 1:1.

[0054] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that, like Example 1, only the solvothermal temperature was adjusted to 130°C and the time was adjusted to 12h in S3.

[0055] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that, like Example 1, only in S5 the cobalt ion concentration was adjusted to 0.3 mmol / L, the sodium hypophosphite concentration was adjusted to twice the cobalt salt concentration, and the pH of the solution was adjusted to 4.5 with dilute hydrochloric acid.

[0056] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that: S1~S2 are the same as in Example 1, and in S3, the C3N5 core layer precursor obtained in step S2 is directly mixed with melamine, and the mass ratio of C3N5 to melamine is controlled to be 1:1, and then the pyrolysis step of S4 is directly carried out; S4~S5 are the same as in Example 1, and the final product has no interface transition region.

[0057] Performance testing: Test Example 1 XPS Analysis: X-ray photoelectron spectroscopy (XPS) spectra were performed on an Al-Kα radiation X-ray photoelectron spectrometer (ESCALAB250i-XPS), and all data were analyzed at C 1s, 284.8 eV calibration. The QIS-XPS instrument was equipped with a 300 W Xe source.

[0058] Test Example 2 Hydrogen evolution performance test: Photocatalytic performance testing was conducted in a Pyrex localized irradiation reactor coupled with a closed gas circulation and vacuum system. The experimental system was constructed as follows: 50 mg of photocatalyst was uniformly dispersed in 100 mL of an aqueous solution containing 10 vol% triethanolamine (sacrificial agent), followed by the introduction of 0.01 mol·L⁻¹... -1 K₂HPO₄ was used as a buffer to optimize hydrogen evolution kinetics. Before the reaction, the solution was deoxygenated through multiple vacuum-nitrogen cycles. A 300 W xenon lamp (PLS-SXE300) was used as the irradiation source, and the light intensity was adjusted to the visible light range using filters. During the reaction, the solution temperature was maintained at a constant 20 °C using a circulating cooling water system. The generated gases were quantitatively analyzed using an online gas chromatograph (Agilent 7890A, TCD detector).

[0059] Test Example 3 TEM testing using a JEOJ JEM-2100F, 200 kV high-resolution TEM revealed that the (002) interplanar spacing of the core layer C3N5 was 0.315-0.325 nm, and the (002) interplanar spacing of the shell layer C3N4 was 0.320-0.330 nm. Clear core-shell interfaces and lattice mismatches could be observed using a high-resolution transmission electron microscope.

[0060] Table 1 shows the elemental analysis.

[0061] All data are normalized to C atoms; C / Na: the ratio of C atoms to N atoms.

[0062] According to the data in Table 1, the C:N atomic ratio in S-C3N4 increased from the original 0.72 to 0.79, which means that the increase in the C:N atomic ratio actually marks the successful introduction of nitrogen vacancies. Perform EDS elemental analysis, from Figure 1 O atoms can be observed to be uniformly distributed inside the material. This proves that O has been successfully introduced into C3N5.

[0063] from Figure 2 As can be seen, the hydrogen evolution rates of Examples 1-5 are significantly higher than those of Comparative Examples 1-6. Among them, Example 4 has the best hydrogen evolution rate of 35.1 μmol·g due to its more uniform nitrogen vacancy gradient distribution and carrier separation efficiency. -1 ·h -1 Among the comparative examples, Comparative Example 5, which exceeded the limits of photodeposition conditions, had the worst performance (hydrogen evolution rate of only 4.3 μmol·g). -1 ·h -1 This demonstrates that the constraints of each technical parameter are crucial to ensuring material performance; all embodiments that conform to the parameter constraints of the technical solution, from Figure 3 As can be seen, the cycle stability is ≥88%, significantly better than the comparative example (≤86%), demonstrating the structural design advantages of the technical solution. Hydrogen evolution rate experiments were conducted on the sample of Example 4 in a system of triethanolamine sacrificial agent and pure water. It was observed that the hydrogen evolution rate was almost negligible in pure water, but reached 15.1 mmol·g in the sacrificial agent system. -1 ·h -1 This demonstrates the synergistic effect between the sacrificial agent and the Co cocatalyst center, which promotes proton supply.

[0064] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A C3N5-C3N4 photocatalytic hydrogen evolution material, characterized in that: The material consists of a core layer, a shell layer, and an interface transition region. The core layer is C3N5 rich in SO bonds, which are bonded to the C3N5 lattice in the form of CSOC or CSON bonds. The shell layer covers the outside of the core layer and is C3N4 rich in nitrogen vacancies. The nitrogen vacancy concentration is distributed in a gradient increasing from the inside to the outside. The shell layer is loaded with CoP nanoparticles with a size of 2-8 nm as a co-catalyst. The interface transition region is located between the core layer and the shell layer, with a thickness of 2-15 nm. Its C / N atomic ratio changes continuously from the core layer to the shell layer, forming a continuously distributed built-in electric field gradient.

2. The C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 1, characterized in that: The core layer has an average diameter of 80-300 nm, the shell layer has a thickness of 20-80 nm, and the core-shell structure has a specific surface area of ​​80-180 m². 2 / g.

3. The C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 1, characterized in that: The CoP cocatalyst is loaded at 0.05-1.0 wt% of the total mass of the photocatalytic material, and it forms a Co-PN interface bond with the shell C3N4.

4. The preparation method of a C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 1, characterized in that: Includes the following steps: S1. Mix cyanuric acid and thiourea at a mass ratio of 1:(1.5~4) and ball mill them in a ball mill at a speed of 400-600 r / min for 4-8 hours to obtain a uniform precursor powder; S2. Place the precursor powder obtained in step S1 in a tube furnace, heat it to 520-580℃ at 3-8℃ / min under an argon atmosphere, and hold it for 1.5-3h to obtain a C3N5 core layer precursor rich in SO bonds. S3. Disperse the C3N5 core layer precursor obtained in step S2 in an ethanol-water mixed solvent, add melamine and hexadecyltrimethylammonium bromide, wherein the mass ratio of C3N5:melamine:CTAB is 1:(0.5~2):(0.01~0.05), and solvothermal react at 140-180℃ for 18-36h to polymerize the melamine C3N5 surface to form a uniform coating layer; S4. Place the product from step S3 in an ammonia / argon mixed atmosphere, raise the temperature to 560-620℃ at 2~5℃ / min, and hold for 1-2h; the ammonia concentration is gradually increased from 5% to 20% during the heating process to simultaneously achieve the crystallization of the C3N4 shell, the gradient introduction of nitrogen vacancies, and the formation of the interface transition zone. S5. Disperse the core-shell material obtained in step S4 in an aqueous solution containing cobalt salt and sodium hypophosphite, stir for 2-6 hours under 300 W xenon lamp irradiation, and selectively load CoP nanoparticles onto the shell surface by photodeposition.

5. The preparation method of a C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 4, characterized in that: The argon flow rate in step S2 is 50~150 sccm. After pyrolysis, the product is washed three times with ethanol and dried under vacuum at 60℃ for 12h.

6. The preparation method of a C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 4, characterized in that: In step S3, the volume fraction of ethanol in the ethanol-water mixed solvent is 30-70%, and the solvothermal reaction is carried out in a high-pressure reactor lined with polytetrafluoroethylene.

7. The preparation method of a C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 4, characterized in that: In step S4, the total flow rate of the ammonia / argon mixed atmosphere is 100 sccm, and the ammonia concentration increases at a rate of 5% per hour during the heating process.

8. The preparation method of a C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 4, characterized in that: The cobalt salt mentioned in step S5 is cobalt chloride hexahydrate or cobalt nitrate, with a cobalt ion concentration of 0.5~2.0 mmol / L and a sodium hypophosphite concentration of 3~8 times that of the cobalt salt; the solution pH is maintained at 5.5~6.5 during photodeposition.

9. The application of the C3N5-C3N4 photocatalytic hydrogen evolution material according to claim 1 in visible light-driven hydrogen evolution.

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