A CN / CoNC nanocomposite photocatalyst and its preparation method and application

Abstract

The present invention belongs to the technical field of photocatalytic materials and specifically relates to a CN / CoNC nanocomposite photocatalyst, its preparation method, and application. The present invention prepares a CN / CoNC nanocomposite photocatalyst, which enhances photocatalytic performance by embedding MOF-derived Co single atoms (CoSA) into carbonized nitrogen (NC) and integrating it with CN. The CN / CoNC nanocomposite material enables efficient charge transport, enhances visible light absorption, and accelerates the formation of hydrogen production active centers, thereby significantly improving photocatalytic activity under visible light (λ ≥ 420 nm). Furthermore, by optimizing the distribution of CoSA within the NC and its integration with the CN framework, the photocatalyst maintains high stability, providing a potential solution for promoting the field of photocatalytic hydrogen production.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and in particular relates to a CN / CoNC nanocomposite photocatalyst and a preparation method and application thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Energy is fundamental to the sustainable development of human society. However, the rapid global consumption of fossil fuels and the increase in waste generation have triggered serious energy crises and environmental problems, necessitating the development of clean, efficient alternative energy sources. Hydrogen energy, due to its clean, pollution-free nature and its combustion without byproducts, offers a promising solution. Photocatalytic water splitting, a cutting-edge field in solar energy conversion and utilization, can directly convert solar energy into chemical energy, achieving highly efficient energy conversion and providing a green and sustainable path to alleviate energy shortages and environmental degradation. The core of this technology lies in the development of photocatalysts with high catalytic performance. Its research is of great strategic significance for promoting the development of clean energy and addressing global energy and environmental challenges.

[0004] Polymeric graphitic carbon nitride (g-C3N4, abbreviated as CN) is a new type of non-metallic photocatalyst. Graphitic carbon nitride has a graphite-like layered material structure with triazine rings as structural units. It has a stable chemical structure, high corrosion resistance, and a unique electronic and energy band structure. It is a very promising photocatalyst. Polymeric graphitic carbon nitride shows potential for photocatalytic hydrogen production due to its visible light absorption and photostability. However, polymeric graphitic carbon nitride has many defects in hydrogen production due to its low charge separation and migration ability, limited active centers, and poor light absorption ability. Although researchers have modified it through strategies such as element doping, heterostructure construction, and morphology control, there are still huge challenges in maintaining material stability while improving catalytic activity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a CN / CoNC nanocomposite photocatalyst, its preparation method, and application. This material is prepared by embedding cobalt single atoms (CoSA) derived from a metal-organic framework (MOF) into carbonized nitrogen (NC) (referred to as CoNC), which is then introduced into CN. This enhances photocatalytic activity while maintaining high material stability.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a CN / CoNC nanocomposite photocatalyst, comprising the following steps:

[0008] S1, respectively preparing methanol solutions of cobalt salt and 2-methylimidazole;

[0009] The methanol solution of the cobalt salt is evenly added to the methanol solution of 2-methylimidazole, ultrasonicated, and evenly mixed. The mixed solution is subjected to a solvent thermal reaction and then dried to obtain ZIF-67.

[0010] S2. Mix ZIF-67 and urea, grind them, and calcine them under inert atmosphere to obtain CN / CoNC nanocomposite photocatalyst.

[0011] In some embodiments, in step S1, the cobalt salt is selected from any one of cobalt chloride, cobalt nitrate, and cobalt sulfate, preferably cobalt nitrate; and the mass ratio of the cobalt salt to 2-methylimidazole is 1:1-1.3.

[0012] In some embodiments, in step S1, ultrasonic treatment is performed for 20-40 minutes. Ultrasonication can ensure uniform mixing of the solution and avoid local concentration unevenness. Ultrasonication can also promote dispersion of reactants, accelerate initial nucleation, and form more uniform crystal nuclei.

[0013] In some embodiments, in step S1, the solvothermal treatment is maintained at 110-120°C for 3-5 hours. For example, the temperature may be 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, or 119°C. Too low a temperature results in a slow reaction, while too high a temperature may lead to framework decomposition or by-product formation. Insufficient time may result in incomplete crystallization, while too long a time may lead to excessive crystal growth or agglomeration.

[0014] In some embodiments, in step S1, the drying operation is performed in a vacuum oven at 70-90° C. for 20-24 h.

[0015] In some embodiments, in step S2, the mass ratio of ZIF-67 to urea is (1-9):10000, wherein the mass ratio of ZIF-67 to urea is (1-9):10000, wherein the mass ratio can be any value between 1-9 and 10000, such as: 2, 3, 4, 5, 6, 7, 8. Preferably, the mass ratio of ZIF-67 to urea is 5:10000. A low content of ZIF-67 may result in insufficient Co loading, thereby reducing photocatalytic activity. On the other hand, exceeding this mass ratio may lead to aggregation or shielding effects, reducing the dispersibility of CoSA, thereby reducing activity.

[0016] In some embodiments, in step S2, the inert atmosphere is argon or nitrogen, and the calcination operation is to increase the temperature to 550-600°C at a heating rate of 4-6°C / min and hold the temperature for 3-5 hours, preferably 3-4 hours. The heating rate can be 4°C / min, 5°C / min, or 6°C / min, with a heating rate of 5°C / min being preferred. After the above calcination, the mixture is cooled naturally to obtain the CN / CoNC nanocomposite photocatalyst.

[0017] The calcination temperature in the present invention is preferably 550-600°C. Excessively high calcination temperatures may completely carbonize the organic ligand 2-methylimidazole, forming nitrogen-doped cobalt nanoparticles. The cobalt nanoparticles may even aggregate further, forming a sintered body of metallic cobalt, further graphitizing the carbon layer and reducing nitrogen doping. Furthermore, this temperature range ensures that urea forms graphite-phase carbon nitride. A slow heating rate of 4-6°C / min helps form a uniform CoNC structure in ZIF-67. Rapid heating can cause local collapse of the carbon matrix or the formation of macropores, potentially destroying the polyhedral structure and forming irregular porous carbon or a fragmented morphology.

[0018] In a second aspect, the present invention provides a CN / CoNC nanocomposite photocatalyst prepared by the preparation method described in the first aspect of the present invention.

[0019] The CN / CoNC nanocomposite photocatalyst achieves efficient charge transfer, enhances visible light absorption, and accelerates the formation of hydrogen production active centers, significantly improving photocatalytic activity. The bond between CoNC and CN maintains the catalyst's high stability.

[0020] In a third aspect, the present invention provides a use of the CN / CoNC nanocomposite photocatalyst described in the second aspect of the present invention in photocatalytic water decomposition to produce hydrogen.

[0021] In a fourth aspect, the present invention provides a method for producing hydrogen by photocatalytic water decomposition, comprising the following steps:

[0022] (1) CN / CoNC nanocomposite photocatalyst, sacrificial agent and water are mixed to obtain a suspension;

[0023] (2) depositing Pt on the CN / CoNC nanocomposite photocatalyst to obtain a mixed solution;

[0024] (3) Applying a light source to the mixed solution to perform photocatalytic hydrolysis under visible light to generate hydrogen.

[0025] In some embodiments, in step (1), the sacrificial agent is triethanolamine (TEOA), and the mass volume ratio of the CN / CoNC nanocomposite photocatalyst to the sacrificial agent is (4-6):1 mg / mL.

[0026] In some embodiments, the amount of Pt loaded in step (2) is 1-3% of the weight of the photocatalyst. Pt, as an auxiliary agent, is beneficial for reducing the overpotential in the hydrogen production process and concentrating photoelectrons in the photocatalytic reaction process. There is no limitation on the Pt loading method, and conventional operations known to those skilled in the art can be performed. For example, the following method can be used: a certain amount of H2PtCl6 solution is added to the above mixed solution, and after magnetic stirring for 5 minutes, the rotation speed is 500-700 r / min; the suspension is then irradiated with visible light from a 300 W xenon lamp for 10-30 minutes, and then vigorously stirred for 20 minutes.

[0027] In some embodiments, the visible light in step (3) is provided by a 300W xenon lamp with a pass filter (λ ≥ 420nm).

[0028] Under visible light irradiation, photoexcited electrons migrate from the conduction band (CB) of CN to the CoSA sites in CoNC, which are the main active sites for electron accumulation. CoSA promotes initial electron transport and plays a vital role in improving carrier separation and migration. After electrons migrate to the CoSA sites, they further migrate to the Pt co-catalyst, where protons (H + ) is reduced to generate H2. The NC component in CoNC stabilizes CoSA and helps direct electrons from CN to CoSA, enabling efficient charge transfer and preventing electron recombination. Simultaneously, holes generated in the CN valence band (VB) are consumed by triethanolamine (TEOA), which acts as a sacrificial agent, donating electrons to CN and maintaining efficient electron transfer. This strategy promotes effective charge separation and transport, thereby enhancing photocatalytic hydrogen production activity.

[0029] The beneficial effects of the present invention are:

[0030] (1) The CN / CoNC nanocomposite photocatalyst prepared by the present invention realizes the precise construction and distribution of CoSA single atoms in NC and combines them with the CN network to improve the photocatalytic hydrogen production performance while maintaining the photocatalytic stability. The best CN / CoNC-5 has a hydrogen production performance of 1794.1 μmol h -1 g -1 ) is much higher than that of pure CN (292.4 μmol h -1 g -1 ).

[0031] (2) The present invention optimizes the calcination temperature and time of the precursor mixture in a tube furnace to achieve the highest density of MOF-derived CoSA embedded in NC while maintaining the structural integrity and high stability of the NC framework. The calcination process is precisely controlled in a tube furnace with argon flow to avoid structural deformation, thereby achieving efficient embedding of CoSA into NC and successful bonding with CN. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0033] Figure 1 X-ray diffraction spectra of CoNC, CN and CN / CoNC-5.

[0034] Figure 2 Fourier transform infrared spectra of CN, CoNC and CN / CoNC-5 photocatalysts.

[0035] Figure 3 UV-visible diffuse reflectance spectra of CN and CN / CoNC-5.

[0036] Figure 4 Photoluminescence spectra of CN and CN / CoNC-5 photocatalysts.

[0037] Figure 5 Comparison of the photocatalytic hydrogen production rates of CN and CN / CoNC photocatalysts prepared in Example.

[0038] Figure 6 This is the cyclic stability test diagram of CN / CoNC-5 nanocomposite photocatalyst. DETAILED DESCRIPTION

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0040] The technical solution of the present invention is further described below with reference to specific embodiments.

[0041] Example 1:

[0042] Synthesis of ZIF-67:

[0043] (1) Add 1.539 g of Co(NO3)2·6H2O to 45 mL of methanol and disperse evenly to obtain a methanol solution of Co(NO3)2·6H2O.

[0044] (2) Disperse 1.731 g of 2-methylimidazole in 45 mL of methanol to obtain a methanol solution of 2-methylimidazole.

[0045] (3) Then, the methanol solution of Co(NO3)2·6H2O was evenly added to the methanol solution of 2-methylimidazole and ultrasonicated for 30 minutes.

[0046] (4) The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave and reacted at 120°C for 4 hours.

[0047] (5) The resulting precipitate was collected by centrifugation and washed several times with ethanol.

[0048] (6) ZIF-67 was obtained after drying in a vacuum oven at 80 °C for 24 h.

[0049] Example 2:

[0050] Synthesis of CN / CoNC-1 photocatalyst:

[0051] (1) 1 mg of ZIF-67 and 10 g of urea were placed in an agate mortar and ground for 1 h to ensure that ZIF-67 and urea were thoroughly mixed.

[0052] (2) The mixed solid powder was placed in a ceramic dish, and heated to 600°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, kept at this temperature for 4 h, and naturally cooled to room temperature to obtain the CN / CoNC-1 photocatalyst.

[0053] Example 3:

[0054] Synthesis of CN / CoNC-3 photocatalyst:

[0055] (1) 3 mg of ZIF-67 and 10 g of urea were placed in an agate mortar and ground for 1 h to ensure that ZIF-67 and urea were thoroughly mixed.

[0056] (2) The mixed solid powder was placed in a ceramic dish, and heated to 600°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, kept at this temperature for 4 h, and naturally cooled to room temperature to obtain the CN / CoNC-3 photocatalyst.

[0057] Example 4:

[0058] Synthesis of CN / CoNC-5 photocatalyst:

[0059] (1) 5 mg of ZIF-67 and 10 g of urea were placed in an agate mortar and ground for 1 h to ensure that ZIF-67 and urea were thoroughly mixed.

[0060] (2) The mixed solid powder was placed in a ceramic dish, and heated to 600°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, kept at this temperature for 4 h, and naturally cooled to room temperature to obtain the CN / CoNC-5 photocatalyst.

[0061] Example 5:

[0062] Synthesis of CN / CoNC-7 photocatalyst:

[0063] (1) 7 mg of ZIF-67 and 10 g of urea were placed in an agate mortar and ground for 1 h to ensure that ZIF-67 and urea were thoroughly mixed.

[0064] (2) The mixed solid powder was placed in a ceramic dish, and heated to 600°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, kept at this temperature for 4 h, and naturally cooled to room temperature to obtain the CN / CoNC-7 photocatalyst.

[0065] Example 6:

[0066] Synthesis of CN / CoNC-9 photocatalyst:

[0067] (1) 9 mg of ZIF-67 and 10 g of urea were ground in an agate mortar for 1 h to ensure that ZIF-67 and urea were thoroughly mixed.

[0068] (2) The mixed solid powder was placed in a ceramic dish, and heated to 600°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, kept at this temperature for 4 h, and naturally cooled to room temperature to obtain the CN / CoNC-5 photocatalyst.

[0069] Comparative Example 1:

[0070] Synthesis of CN photocatalyst:

[0071] (1) 10 g of urea was placed in an agate mortar and ground for 1 hour.

[0072] (2) The white solid powder was then placed in a ceramic dish, heated to 600°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, kept at this temperature for 4 h, and naturally cooled to room temperature to obtain the CN photocatalyst.

[0073] Experimental Example 1

[0074] The photocatalytic H2 production rates of CN and CN / CoNC-5 photocatalysts were measured and studied.

[0075] Photocatalytic H2 evolution measurement device:

[0076] The photocatalytic water splitting experiments were performed in a 500 mL Pyrex top irradiation reactor equipped with a closed gas circulation and vacuum device (Labsolar-6A, Perfectlight, Beijing, China).

[0077] Following conventional methods, 50 mg of the photocatalyst was loaded into 100 mL of an aqueous solution containing 10% by volume TEAO. 1 wt% of Pt was then loaded onto the photocatalyst by photodeposition of H2PtCl6·6H2O. The reaction mixture was evacuated several times to remove air before irradiation with a 300 W xenon lamp (λ ≥ 420 nm). During the reaction, the solution was continuously stirred and maintained at 6°C with circulating cooling water. The generated H2 was determined by gas chromatography (GC 1120, SHP Shanghai) using a thermal conductivity detector and a 5A molecular sieve column with N2 as the carrier gas.

[0078] Performance Analysis

[0079] Figure 1 The X-ray diffraction (XRD) spectra of CoNC, CN and CN / CoNC-5 are shown in Figure 2. Figure 1 As shown in the figure, CoNC shows broad peaks at 44.3°, 51.5° and 76.0°, corresponding to the (111), (200) and (220) planes of metallic Co, respectively, proving the presence of cobalt nanoparticles in NC. Pure CN shows two characteristic diffraction peaks at 13.1° and 27.7°, which are attributed to the (100) and (002) crystal planes of graphitic carbon nitride, respectively. Among them, the diffraction peak at 13.1° originates from the tri-triazine group within the plane, while the strong peak at 27.7° corresponds to the interlayer stacking between adjacent carbon and nitrogen layers. For the CN / CoNC-5 sample, both peaks of CN are retained, while the peak intensity decreases slightly. This result indicates that CoNC is successfully combined with CN while maintaining the CN framework.

[0080] Figure 2 Fourier transform infrared (FTIR) spectra of CN, CoNC and CN / CoNC-5 photocatalysts, as shown in Figure 2 As shown, the FTIR spectrum of pure CN is at 814 cm -1 、1220-1644cm -1 and 3000-3600cm -1 Representative bands are shown at the 400 nm region, attributed to triazine ring vibration, CN stretching vibration, and -NH / -OH groups. The CN / CoNC-5 nanocomposite retains these characteristic peaks, but exhibits a decrease in transmittance and a slight shift in peak position. This indicates successful bonding of CoNC and CN.

[0081] Figure 3The UV-visible diffuse reflectance spectra (UV-vis DRS) of CN and CN / CoNC-5 are shown in Figure 2. Figure 3 As shown, the UV-vis DRS of CN and CN / CoNC-5 photocatalysts revealed that the optimal CN / CoNC-5 displayed better light absorption performance than pure CN, elucidating the important role of CoNC loading in promoting visible light absorption and facilitating the formation of more photoexcited electron-hole pairs, thereby enhancing the photocatalytic H2 production performance.

[0082] Figure 4 Figure 2 is the photoluminescence spectra (PL) of CN and CN / CoNC-5 photocatalysts. Figure 4 As shown, the photoluminescence intensity of CN / CoNC-5 is lower than that of bare CN, indicating reduced recombination of photoexcited electron-hole pairs. This improvement in carrier separation is attributed to the synergistic effect of Co single atoms, which provide efficient electron-trapping sites, and the enhanced charge transport provided by the NC support. In summary, the combination of CoNC and CN promotes more efficient charge separation and transport.

[0083] Figure 5 The figure is a comparison of the photocatalytic hydrogen production rates of CN and CN / CoNC photocatalysts prepared in the examples. Figure 5 As shown, all CN / CoNC samples exhibited significantly higher hydrogen production rates than pure CN. The maximum activity of the CN / CoNC photocatalyst is attributed to the combined effects of Co single atoms and the NC support, which serve as active sites for proton reduction and charge transfer, respectively. This strategy facilitates more efficient separation and utilization, leading to enhanced photocatalytic hydrogen production activity.

[0084] Figure 6 This is the cyclic stability test diagram of CN / CoNC-5 nanocomposite photocatalyst. Figure 6 As shown, the CN / CoNC-5 nanocomposite photocatalyst maintained excellent hydrogen production stability over four consecutive reaction cycles. This result indicates that the combination of CoNC and CN not only improves the photocatalytic performance, but also makes it highly stable and recyclable due to the strong interaction between CoNC and the CN network, thus avoiding the decomposition of the photocatalyst during repeated use.

[0085] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a CN / CoNC nanocomposite photocatalyst, characterized in that: The following steps are involved: S1, respectively preparing methanol solutions of cobalt salt and 2-methylimidazole; The methanol solution of the cobalt salt is evenly added to the methanol solution of 2-methylimidazole, and the mixture is ultrasonically mixed. The mixed solution is subjected to a solvent thermal reaction and then dried to obtain ZIF-67. S2, mixing ZIF-67 and urea in a set ratio and grinding them, and calcining them under inert atmosphere to obtain a CN / CoNC nanocomposite photocatalyst; In step S1, the solvent thermal treatment is maintained at 110-120°C for 3-5 hours; In the step S2, the mass ratio of ZIF-67 to urea is 3-7:10000; In the step S2, the calcination operation is to raise the temperature to 550-600°C at a rate of 4-6°C / min and keep the temperature for 3-5 hours; Cobalt single atoms derived from metal organic frameworks are embedded in NC, called CoNC, and introduced into CN to prepare a CN / CoNC nanocomposite photocatalyst, which improves the photocatalytic activity while maintaining the high stability of the material. The NC is carbonized nitrogen and the CN is polymerized graphite phase carbon nitride.

2. The preparation method according to claim 1, wherein In step S1, the cobalt salt is selected from any one of cobalt nitrate, cobalt chloride, and cobalt sulfate, and the mass ratio of the cobalt salt to 2-methylimidazole is 1:1-1.

3.

3. The preparation method according to claim 1, wherein In step S1, the drying operation is performed in a vacuum oven at 70-90° C. for 20-24 hours.

4. The preparation method according to claim 1, wherein In step S1, ultrasonic treatment was performed for 20-40 minutes.

5. The preparation method according to claim 1, wherein In step S2, the inert atmosphere is argon or nitrogen. 6 . A CN / CoNC nanocomposite photocatalyst prepared by the preparation method according to any one of claims 1 to 5 .

7. Use of the CN / CoNC nanocomposite photocatalyst according to claim 6 in photocatalytic water decomposition to produce hydrogen.

8. A method for producing hydrogen by photocatalytic water decomposition, characterized in that: The following steps are involved: (1) Mixing the CN / CoNC nanocomposite photocatalyst according to claim 6, a sacrificial agent, and water to obtain a suspension; (2) depositing Pt on the CN / CoNC nanocomposite photocatalyst to obtain a mixed solution; (3) applying a light source to the mixed solution to perform photocatalytic hydrolysis under visible light to generate hydrogen.

9. The method according to claim 8, wherein In step (1), the sacrificial agent is triethanolamine, and the mass volume ratio of the CN / CoNC nanocomposite photocatalyst to the sacrificial agent is 4-6:1 mg / mL; in step (2), the Pt loading amount is 1-3% of the weight of the photocatalyst.

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