Graphite phase carbon nitride photocatalyst based on supercritical carbon dioxide induced delaminated supramolecular precursor modification as well as preparation method and application thereof

Abstract

The invention discloses a preparation method and application of a graphite phase carbon nitride photocatalyst based on supercritical carbon dioxide induced delaminated supramolecular precursor modification, and belongs to the technical field of photocatalytic hydrogen production. Comprising the following steps: by taking melamine, cyanuric acid and hexamethylenetetramine as raw materials, carrying out hydrothermal reaction to prepare a supramolecular precursor; carrying out supercritical carbon dioxide induced delamination treatment on the supramolecular precursor; and calcining the precursor subjected to supercritical carbon dioxide induced delamination treatment to prepare the graphite phase carbon nitride photocatalyst. The graphite phase carbon nitride photocatalyst with excellent visible light catalytic hydrogen production performance is prepared by performing supercritical carbon dioxide induced delamination treatment and calcination on the prepared supramolecular precursor, the solvent is green and environment-friendly in the preparation process, the yield is high, and the method is suitable for industrial production. The graphite-phase carbon nitride photocatalyst prepared by the invention has the advantages of large specific surface area, high photon-generated carrier transfer speed and high photocatalytic hydrogen production activity.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic hydrogen production technology, specifically relating to a graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor, its preparation method, and its application. Background Technology

[0002] Developing efficient, stable, and environmentally friendly visible light photocatalysts is crucial for advancing the large-scale application of photocatalytic water splitting for hydrogen production. Graphitic carbon nitride (g-C3N4), as a metal-free organic semiconductor photocatalyst, possesses advantages such as low cost, high thermal stability, and good chemical stability, making it one of the most promising visible light photocatalysts. However, bulk g-C3N4 synthesized through traditional thermal polymerization processes typically suffers from drawbacks such as small specific surface area and severe recombination of photogenerated carriers, significantly limiting its visible light photocatalytic hydrogen production performance.

[0003] Researchers have proposed a series of corresponding g-C3N4 modification strategies to improve its photocatalytic activity, including crystallinity regulation, microstructure regulation, co-catalyst loading, and heterojunction construction with other semiconductors. Among these, microstructure regulation can effectively increase the specific surface area of ​​g-C3N4 photocatalysts and shorten the migration distance of photogenerated carriers, thereby increasing its reactive sites, improving the separation and migration efficiency of photogenerated carriers, and broadening the light absorption capacity. This is an effective strategy to improve the photocatalytic hydrogen production efficiency of g-C3N4. However, the traditional template method for morphology regulation of g-C3N4 has drawbacks such as complex preparation process, low yield, and the need for etching with highly corrosive hydrofluoric acid or strong alkali for template removal. Therefore, developing efficient, template-free, and solvent-friendly g-C3N4 photocatalyst morphology regulation strategies is an important and highly challenging research direction.

[0004] Supercritical carbon dioxide (SCCO) possesses unique advantages in delamination of layered materials due to its excellent properties such as low viscosity, zero surface tension, and high diffusivity. SCCO can effectively penetrate the interlayer spaces of layered materials, expanding the interlayer spacing. When carbon dioxide is released through a decompression process, the supercritical carbon dioxide expands between the layers, successfully overcoming the van der Waals forces and achieving delamination. Simultaneously, high pressure effectively raises the free energy barrier, reduces interlayer attraction, and improves the colloidal stability of the delamination sheets during dispersion. Furthermore, the delamination of layered materials using SCCO can achieve separation from the material through decompression, eliminating the need for complex subsequent separation steps and drying processes, and leaving no solvent residue. This greatly simplifies the reaction process and offers broad application prospects.

[0005] It is evident that the synthesis and modification of materials based on supercritical carbon dioxide systems holds great promise. For example, Chinese invention patent CN119114133A discloses a graphitic carbon nitride photocatalyst for photocatalytic hydrogen production and its preparation method. Specifically, it discloses the following: preparing a hexamethylenetetramine-doped melamine precursor based on a supercritical carbon dioxide solvothermal method to modify the graphitic carbon nitride photocatalyst. However, this method only uses melamine as the main component of the precursor, and its effect on modifying the morphology of calcined graphitic carbon nitride is limited. Therefore, the obtained graphitic carbon nitride photocatalyst has a small specific surface area, and the visible light photocatalytic hydrogen production activity of the modified graphitic carbon nitride is only 501 μmol h⁻¹. -1 g -1 The improvement in photocatalytic hydrogen production activity is relatively low compared to the unmodified form. Summary of the Invention

[0006] To address the drawbacks of traditional thermal polymerization processes in preparing graphitic carbon nitride photocatalysts, such as small specific surface area and severe recombination of photogenerated carriers, this invention proposes a method and application for preparing graphitic carbon nitride photocatalysts modified with supercritical carbon dioxide-induced exfoliation supramolecular precursors. By subjecting the prepared supramolecular precursors to supercritical carbon dioxide-induced exfoliation and calcination, a graphitic carbon nitride photocatalyst with excellent visible light photocatalytic hydrogen production performance is prepared. Furthermore, the preparation process utilizes environmentally friendly solvents, achieves high yields, and has a wide range of applications.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor, comprising: preparing a supramolecular precursor by hydrothermal reaction using melamine, cyanuric acid and hexamethylenetetramine as raw materials; subjecting the supramolecular precursor to supercritical carbon dioxide-induced exfoliation treatment; and calcining the supercritical carbon dioxide-induced exfoliated precursor to obtain the graphitic carbon nitride photocatalyst.

[0008] Specifically, it includes the following steps: 1) Melamine, cyanuric acid and hexamethylenetetramine are mixed and subjected to a hydrothermal reaction to prepare a supramolecular precursor; 2) The supramolecular precursor is subjected to supercritical carbon dioxide-induced delamination treatment; 3) The precursor treated with supercritical carbon dioxide-induced exfoliation was calcined to obtain a graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor.

[0009] Preferably, in step 1), the mass ratio of melamine, cyanuric acid and hexamethylenetetramine is (0.80~0.90):(3.00~4.00):(0.40~0.60).

[0010] Preferably, in step 1), the hydrothermal reaction involves mixing melamine, cyanuric acid, and hexamethylenetetramine and dissolving them in water, stirring thoroughly, treating at 100-120 °C for 20-24 h, and then washing, drying, and grinding to obtain the supramolecular precursor.

[0011] Preferably, in step 2), the reaction temperature for the supercritical carbon dioxide-induced delamination treatment is 40~140°C. o C, reaction pressure is 14~20 MPa, treatment time is 12~24 h.

[0012] Preferably, in step 3), the calcination treatment involves heating from room temperature to 520~550 ℃ at a rate of 5 ℃ / min, holding at that temperature for 4~6 h, and then allowing it to cool naturally.

[0013] More specifically, it includes the following steps: Step 1: Preparation of supramolecular precursor. Weigh 0.80–0.90 g of melamine, 3.00–4.00 g of cyanuric acid, and 0.40–0.60 g of hexamethylenetetramine, dissolve them in 30–60 mL of deionized water, and stir for 10–30 min to obtain a uniformly dispersed mixed solution. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor and carry out a hydrothermal reaction at 100–120 °C for 20–24 h. Wash the obtained product three times with deionized water, then dry it at 60–80 °C for 8–12 h, and grind it to obtain the supramolecular precursor.

[0014] Step 2: Supercritical carbon dioxide-induced delamination treatment of the supramolecular precursor. Add 2.00–3.00 g of the supramolecular precursor to an 11 mL supercritical carbon dioxide high-pressure reactor (made of Hastelloy C276 stainless steel). After sealing, pump in 5–10 MPa of carbon dioxide, maintain for 5–10 min, check the airtightness, and then purge the air from the reactor. Then, pump in a certain amount of CO2 again and heat the supercritical carbon dioxide high-pressure reactor to 40–140 °C, achieving a pressure of 14–20 MPa. Stabilize the reaction for 12–24 h. After cooling to room temperature, rapidly release CO2 through a pressure relief valve to reduce pressure, and collect the precursor after supercritical carbon dioxide-induced delamination treatment.

[0015] Step 3: Preparation of graphitic carbon nitride photocatalyst by calcining the precursor. The precursor treated with supercritical carbon dioxide-induced exfoliation was placed in a covered crucible, and then the crucible was placed in a muffle furnace for calcination. The temperature was increased to 520~550 ℃ at a rate of 5 ℃ / min, and held at that temperature for 4~6 h. After natural cooling, it was ground and collected to obtain the graphitic carbon nitride photocatalyst modified based on the supercritical carbon dioxide-induced exfoliated supramolecular precursor.

[0016] This invention also discloses a graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor, prepared by the above-described method. The visible light catalytic hydrogen production activity of this graphitic carbon nitride photocatalyst is 7104 μmol h⁻¹. -1 g -1 .

[0017] This invention also discloses the application of the above-mentioned graphitic carbon nitride photocatalyst modified with supercritical carbon dioxide-induced exfoliated supramolecular precursor in photocatalytic water splitting for hydrogen production.

[0018] This invention also discloses a method for photocatalytic water splitting to produce hydrogen, comprising: The above-mentioned graphitic carbon nitride photocatalyst modified by supercritical carbon dioxide-induced exfoliated supramolecular precursor was dispersed in a reaction solution, and platinum was loaded onto the surface of the graphitic carbon nitride photocatalyst by in-situ photodeposition. Under an argon atmosphere and at a temperature of 30-40°C, the reaction solution is thoroughly stirred and homogenized. The reaction solution is then irradiated with visible light using a 300 W xenon lamp to produce hydrogen gas.

[0019] Preferably, a graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor is dispersed in a 10% triethanolamine aqueous solution. Using an aqueous solution of chloroplatinic acid hexahydrate as a precursor, platinum is loaded onto the surface of the photocatalyst by in-situ photodeposition to prepare a reaction solution. The platinum content in the added chloroplatinic acid hexahydrate aqueous solution is 3% of the added graphitic carbon nitride content.

[0020] Preferably, argon gas is introduced into the reactor for 10-15 minutes before illumination to remove oxygen from the system; visible light irradiation is performed using a 300 W xenon lamp equipped with a cutoff filter with λ>400 nm.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This invention first considers that supramolecular self-assembly is a bottom-up approach that can synthesize graphitic carbon nitride with superior morphological characteristics and high specific surface area. Therefore, it chooses to achieve the self-arrangement of monomer units through hydrogen bonding between melamine, cyanuric acid, and hexamethylenetetramine, thereby forming a high-order supramolecular precursor with unique physical and chemical properties. Secondly, it utilizes the low viscosity, zero surface tension, and high diffusivity of supercritical carbon dioxide to induce exfoliation of the supramolecular precursor. Supercritical carbon dioxide, with its strong exfoliation and shearing effects, effectively... By breaking the interlayer van der Waals forces and in-plane hydrogen bonds of the layered supramolecular precursor, a graphitic carbon nitride photocatalyst with a fluffy three-dimensional silver ear-like structure was prepared during subsequent thermal polymerization. This allowed for further control over the microstructure of the graphitic carbon nitride, effectively shortening the migration distance of photogenerated carriers, improving their separation efficiency, and significantly increasing the specific surface area. This provided abundant reactive sites for photocatalytic hydrogen production, resulting in a graphitic carbon nitride photocatalyst with superior morphology, high specific surface area, and high photocatalytic hydrogen production activity. This invention utilizes supercritical carbon dioxide to induce the exfoliation of supramolecular precursors and subsequent thermal polymerization to modify the morphology of the graphitic carbon nitride photocatalyst. It avoids the use of harmful organic solvents, resulting in a green and environmentally friendly solvent, high yield, and broad application value.

[0022] This invention, through photocatalytic hydrogen production testing, revealed that the visible light photocatalytic hydrogen production activity of the graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor prepared according to this invention is 7104 μmol h⁻¹. - 1 g -1 (Significantly higher than the hydrogen production activity of catalysts prepared by existing technologies), it is 23.8 times that of unmodified graphitic carbon nitride photocatalysts. Attached Figure Description

[0023] Figure 1 The bar chart shows the visible light hydrogen production rates of the graphitic carbon nitride photocatalysts synthesized in Examples 1-4 and Comparative Examples 1 and 2. Figure 2 The stability diagram of photocatalytic hydrogen production of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 is shown. Figure 3The images show scanning electron microscope (SEM) images of the precursors and synthesized graphitic carbon nitride photocatalysts in Examples 1 and Comparative Examples 1 and 2. (a) is an SEM image of the original precursor M in Comparative Example 1; (b) is an SEM image of the precursor MCA-HMTA in Comparative Example 2; (c) is an SEM image of the supercritical carbon dioxide-induced exfoliated supramolecular precursor MCA-HMTA-scCO2-100 in Example 1; (d) is an SEM image of the graphitic carbon nitride photocatalyst CN synthesized in Comparative Example 1; (e) is an SEM image of the graphitic carbon nitride photocatalyst CN-MCA-HMTA synthesized in Comparative Example 2; and (f) is an SEM image of the graphitic carbon nitride photocatalyst CN-MCA-HMTA-scCO2-100 modified based on the supercritical carbon dioxide-induced exfoliated supramolecular precursor in Example 1. Figure 4 Transmission electron microscope (TEM) images of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2; wherein, (a) is a TEM image of the graphitic carbon nitride photocatalyst CN synthesized in Comparative Example 1; (b) is a TEM image of the graphitic carbon nitride photocatalyst CN-MCA-HMTA synthesized in Comparative Example 2; and (c) is a TEM image of the graphitic carbon nitride photocatalyst CN-MCA-HMTA-scCO2-100 synthesized in Example 1. Figure 5 The N2 adsorption-desorption isotherms of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 are shown. Figure 6 The electron paramagnetic resonance spectra of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 are shown below. Figure 7 The transient photocurrent spectra of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 are shown. Figure 8 Electrochemical impedance spectroscopy (EIS) of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2; Figure 9 The steady-state fluorescence spectra of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 are shown. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0025] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0026] The present invention will now be described in further detail with reference to the accompanying drawings: Example 1 This embodiment provides a method for preparing a graphitic carbon nitride photocatalyst modified based on a supercritical carbon dioxide-induced exfoliated supramolecular precursor, mainly including the following steps: Step 1: Preparation of the supramolecular precursor. Weigh 0.84 g of melamine, 3.36 g of cyanuric acid, and 0.50 g of hexamethylenetetramine, dissolve them in 30 mL of deionized water, and stir for 30 min to obtain a uniformly dispersed mixed solution. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor and carry out a hydrothermal reaction at 100 °C for 20 h. Wash the obtained product three times with deionized water, then dry it at 60 °C for 12 h, and grind it to obtain the supramolecular precursor, denoted as MCA-HMTA.

[0027] Step 2: Supercritical carbon dioxide-induced delamination treatment of the supramolecular precursor. 2.50 g of the supramolecular precursor was added to an 11 mL supercritical carbon dioxide high-pressure reactor. After sealing, 5 MPa CO2 was pumped in and maintained for 5 min. The airtightness was checked, and the air inside the reactor was purged. Then, a certain amount of CO2 was pumped in again, and the supercritical carbon dioxide high-pressure reactor was heated to 100℃, reaching a pressure of 16 MPa. The reaction was stabilized for 20 h. After cooling to room temperature, CO2 was rapidly released through a pressure relief valve to reduce the pressure. The precursor after supercritical carbon dioxide-induced delamination treatment was collected and designated as MCA-HMTA-scCO2-100.

[0028] Step 3: Preparation of graphitic carbon nitride photocatalyst by calcining the precursor. 2.00 g of the precursor treated with supercritical carbon dioxide-induced exfoliation was weighed and placed in a covered crucible. The crucible was then placed in a muffle furnace for calcination, with the temperature increased to 520 °C at a rate of 5 °C / min and held for 4 h. After natural cooling, the mixture was ground, and the resulting graphitic carbon nitride photocatalyst modified with the supercritical carbon dioxide-induced exfoliated supramolecular precursor was collected and named CN-MCA-HMTA-scCO2-100.

[0029] Example 2 The difference between this embodiment and Example 1 is that, during the supercritical carbon dioxide-induced exfoliation treatment of the supramolecular precursor, the supercritical carbon dioxide high-pressure reactor was heated to 40 °C to obtain the precursor after supercritical carbon dioxide-induced exfoliation treatment, denoted as MCA-HMTA-scCO2-40. After calcination, a graphitic carbon nitride photocatalyst modified based on the supercritical carbon dioxide-induced exfoliated supramolecular precursor was obtained, named CN-MCA-HMTA-scCO2-40.

[0030] Example 3 The difference between this embodiment and Example 1 is that, during the supercritical carbon dioxide-induced exfoliation treatment of the supramolecular precursor, the supercritical carbon dioxide high-pressure reactor was heated to 80 °C to obtain the precursor after supercritical carbon dioxide-induced exfoliation treatment, denoted as MCA-HMTA-scCO2-80. After calcination, a graphitic carbon nitride photocatalyst modified based on the supercritical carbon dioxide-induced exfoliated supramolecular precursor was obtained, named CN-MCA-HMTA-scCO2-80.

[0031] Example 4 The difference between this embodiment and Example 1 is that, during the supercritical carbon dioxide-induced exfoliation treatment of the supramolecular precursor, the supercritical carbon dioxide high-pressure reactor was heated to 140 °C to obtain the precursor after supercritical carbon dioxide-induced exfoliation treatment, denoted as MCA-HMTA-scCO2-140. After calcination, a graphitic carbon nitride photocatalyst modified based on the supercritical carbon dioxide-induced exfoliated supramolecular precursor was obtained, named CN-MCA-HMTA-scCO2-140.

[0032] Example 5 The difference between this embodiment and Embodiment 1 is that the reaction pressure during the supercritical carbon dioxide-induced exfoliation supramolecular precursor treatment is 14 MPa.

[0033] Example 6 The difference between this embodiment and Embodiment 1 is that the reaction pressure during the supercritical carbon dioxide-induced exfoliation supramolecular precursor treatment is 18 MPa.

[0034] Example 7 The difference between this embodiment and Embodiment 1 is that the reaction pressure during the supercritical carbon dioxide-induced exfoliation supramolecular precursor treatment is 20 MPa.

[0035] Example 8 The difference between this embodiment and Embodiment 1 is that the reaction time during the supercritical carbon dioxide-induced exfoliation supramolecular precursor treatment is 12 h.

[0036] Example 9 The difference between this embodiment and Embodiment 1 is that the reaction time during the supercritical carbon dioxide-induced exfoliation supramolecular precursor treatment is 16 h.

[0037] Example 10 The difference between this embodiment and Embodiment 1 is that the reaction time during the supercritical carbon dioxide-induced exfoliation supramolecular precursor treatment is 24 h.

[0038] Comparative Example 1 Weigh 2.00 g of melamine (M) and place it in a covered crucible. Then place the crucible in a muffle furnace for calcination. The temperature is increased to 520 °C at a rate of 5 °C / min and held for 4 h. After natural cooling, grind to obtain a graphitic carbon nitride photocatalyst, denoted as CN.

[0039] Comparative Example 2 Step 1: Weigh 0.84 g of melamine, 3.36 g of cyanuric acid, and 0.50 g of hexamethylenetetramine, dissolve them in 30 mL of deionized water, and stir for 30 min to obtain a uniformly dispersed mixed solution. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor and carry out a hydrothermal reaction at 100 °C for 20 h. Wash the obtained product three times with deionized water, then dry it at 60 °C for 12 h, and grind it to obtain a supramolecular precursor, denoted as MCA-HMTA.

[0040] Step 2: Weigh 2.00 g of MCA-HMTA precursor and place it in a covered crucible. Then, place the crucible in a muffle furnace for calcination. The temperature is increased to 520 °C at a rate of 5 °C / min and held for 4 h. After natural cooling, grind and collect the graphitic carbon nitride photocatalyst, which is named CN-MCA-HMTA.

[0041] The performance of photocatalytic hydrogen production was evaluated below using the above-described examples and comparative examples: The photocatalytic hydrogen production test method is as follows: 0.02 g of graphitic carbon nitride photocatalyst was dispersed in a 10% (v / v) triethanolamine aqueous solution. Using chloroplatinic acid hexahydrate aqueous solution as a precursor, platinum was loaded onto the surface of the photocatalyst via in-situ photodeposition (the platinum content in the added chloroplatinic acid hexahydrate aqueous solution was 3% of the added graphitic carbon nitride content). Before irradiation, argon gas was introduced into the reactor for 10–15 min to remove oxygen from the system. The reactor temperature was maintained at 30–40 °C using circulating water. A magnetic stirrer was turned on, and visible light irradiation was performed using a 300 W xenon lamp equipped with a cutoff filter (λ>400 nm) to obtain hydrogen gas. The activity of the synthesized graphitic carbon nitride photocatalytic hydrogen production was evaluated by detecting the amount of hydrogen produced in the photocatalytic system.

[0042] Figure 1 The bar chart shows the visible light hydrogen production rates of the graphitic carbon nitride photocatalysts synthesized in Examples 1-4 and Comparative Examples 1 and 2. According to... Figure 1 It can be seen that the graphitic carbon nitride photocatalysts obtained in Examples 1-4 of this invention, after treatment with supercritical carbon dioxide-induced exfoliated supramolecular precursors at reaction temperatures of 40 ℃, 80 ℃, 100 ℃, and 140 ℃, all exhibit higher photocatalytic hydrogen production activities than the graphitic carbon nitride photocatalysts synthesized in Comparative Examples 1 and 2. Among them, the graphitic carbon nitride photocatalyst synthesized in Example 1 exhibits the highest photocatalytic hydrogen production activity (7104 μmol h⁻¹). -1 g -1 The graphitic carbon nitride photocatalyst synthesized in Example 1 is 23.8 times stronger than that synthesized in Example 1, indicating that the present invention is an effective means to improve the photocatalytic performance of graphitic carbon nitride photocatalysts by using a supercritical carbon dioxide-induced exfoliated supramolecular precursor modification method.

[0043] Figure 2 This is a photocatalytic hydrogen production stability diagram of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2. According to... Figure 2 It can be seen that, within a 15-hour reaction time, the graphitic carbon nitride photocatalyst modified by supercritical carbon dioxide-induced exfoliated supramolecular precursor synthesized in Example 1 of this invention exhibits good photocatalytic hydrogen production stability.

[0044] Figure 3 These are scanning electron microscope (SEM) images of the precursors and synthesized graphitic carbon nitride photocatalysts used in Example 1 and Comparative Examples 1 and 2. Figure 3As can be observed, the original precursor M exhibits a micron-sized blocky morphology with a smooth surface. MCA-HMTA is composed of aggregated thick sheets, exhibiting more pores compared to the original M, while MCA-HMTA-scCO2-100 exhibits a dispersed, fragmented sheet morphology. The graphitic carbon nitride photocatalyst CN synthesized in Comparative Example 1 is composed of aggregated thick nanosheets. The graphitic carbon nitride photocatalyst CN-MCA-HMTA synthesized in Comparative Example 2 exhibits an aggregated structure of smaller nanosheets. The graphitic carbon nitride photocatalyst CN-MCA-HMTA-scCO2-100 synthesized in Example 3 exhibits a fluffy three-dimensional silver ear-like microstructure, with significantly more wrinkles and pores than the above samples. This indicates that the supercritical carbon dioxide-induced exfoliation supramolecular precursor treatment of the present invention has a significant modifying effect on the microstructure of graphitic carbon nitride.

[0045] Figure 4 Transmission electron microscopy (TEM) images of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2. From... Figure 4 As can be observed, the graphitic carbon nitride photocatalyst modified by supercritical carbon dioxide-induced exfoliated supramolecular precursor synthesized in Example 3 of this invention becomes thinner and has more wrinkles and pores, consistent with the scanning electron microscope images.

[0046] Figure 5 The N2 adsorption-desorption isotherms of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 are shown. The results indicate that all samples exhibit type IV N2 adsorption-desorption isotherms, with the graphitic carbon nitride photocatalyst CN-MCA-HMTA-scCO2-100 synthesized in Example 3 of this invention showing the highest N2 adsorption-desorption isotherm at high relative pressure (…). P / P At a specific surface area (0>0.8), it exhibited significantly better adsorption capacity than the graphitic carbon nitride photocatalysts CN and CN-MCA-HMTA synthesized in Comparative Examples 1 and 2. Furthermore, compared to the specific surface areas of the graphitic carbon nitride photocatalysts CN and CN-MCA-HMTA synthesized in Comparative Examples 1 and 2 (8.0 m² and 0.8 m² respectively), it showed significantly better adsorption capacity. 2 g -1 109.8 m 2 g -1 The specific surface area of ​​the graphitic carbon nitride CN-MCA-HMTA-scCO2-100 synthesized in Example 1 is 166.6 m². 2 g -1 The significant improvement indicates that the graphitic carbon nitride photocatalyst modified by supercritical carbon dioxide-induced exfoliation supramolecular precursor has generated more abundant mesopores and macropores, thus obtaining a larger specific surface area, which can provide more reaction sites for photocatalytic reactions.

[0047] Figure 6The electron paramagnetic resonance spectra of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 are shown. Figure 6 It can be seen that the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 all possess a characteristic single Lorentz line and the same... g The value (2.0041) is due to the sp in the π-conjugated aromatic ring. 2 This is caused by the unpaired electrons of hybridized carbon atoms. Furthermore, the graphitic carbon nitride photocatalyst synthesized in Example 3 of this invention exhibits a significantly stronger spin characteristic peak than the graphitic carbon nitride photocatalysts synthesized in Comparative Examples 1 and 2, proving that the graphitic carbon nitride photocatalyst synthesized in Example 3, based on supercritical carbon dioxide-induced exfoliated supramolecular precursor modification, has more unpaired electrons, which is beneficial for the separation and migration of photogenerated carriers.

[0048] Figure 7 The transient photocurrent spectra of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2 are shown. Figure 7 As can be observed, the photocurrent density of the graphitic carbon nitride photocatalyst synthesized in Example 3 of this invention is significantly higher than that of the graphitic carbon nitride photocatalysts synthesized in Comparative Examples 1 and 2, indicating that the separation and migration efficiency of photogenerated carriers in the graphitic carbon nitride photocatalyst modified based on supercritical carbon dioxide-induced exfoliated supramolecular precursor is higher.

[0049] Figure 8 The images show the electrochemical impedance spectroscopy (EIS) spectra of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2. Based on... Figure 8 It can be seen that the graphitic carbon nitride synthesized in Example 3 of the present invention has a smaller impedance radius than the graphitic carbon nitride photocatalysts synthesized in Comparative Examples 1 and 2, indicating that the charge transfer impedance of the graphitic carbon nitride photocatalyst modified based on supercritical carbon dioxide-induced exfoliated supramolecular precursor is lower and the interfacial migration ability of photogenerated carriers is stronger.

[0050] Figure 9 The images show the steady-state fluorescence spectra of the graphitic carbon nitride photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2. According to... Figure 9 It can be seen that the graphitic carbon nitride photocatalysts synthesized in Comparative Examples 1 and 2 both exhibit strong characteristic peaks, indicating severe recombination of photogenerated carriers within them. However, the characteristic peak intensities of the graphitic carbon nitride photocatalyst synthesized in Example 3 of this invention are significantly weakened, indicating that the recombination of photogenerated carriers in the graphitic carbon nitride photocatalyst modified by supercritical carbon dioxide-induced exfoliation supramolecular precursor is significantly suppressed, and the separation and migration efficiency are higher.

[0051] In summary, this invention utilizes supercritical carbon dioxide-induced exfoliation of supramolecular precursors to modify graphitic carbon nitride photocatalysts. Supercritical carbon dioxide, with its strong exfoliation and shearing effects, effectively breaks the interlayer van der Waals forces and in-plane hydrogen bonds of the layered supramolecular precursors. During subsequent thermal polymerization, a graphitic carbon nitride photocatalyst with a fluffy three-dimensional silver ear-like structure is prepared, effectively shortening the migration distance of photogenerated carriers, improving the separation efficiency of photogenerated carriers, and significantly increasing the specific surface area, providing abundant reactive sites for photocatalytic hydrogen production. The preparation method involved in this invention has the advantages of using environmentally friendly reaction solvents, producing graphitic carbon nitride photocatalysts with large specific surface area, fast photogenerated carrier transfer speed, and high photocatalytic hydrogen production activity. The above description only illustrates the preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of this invention are also within the scope of protection of this invention. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a graphitic carbon nitride photocatalyst modified based on a supercritical carbon dioxide-induced exfoliated supramolecular precursor, characterized in that, Includes the following steps: 1) Melamine, cyanuric acid and hexamethylenetetramine are mixed and subjected to a hydrothermal reaction to prepare a supramolecular precursor; 2) The supramolecular precursor is subjected to supercritical carbon dioxide-induced delamination treatment; 3) The precursor treated with supercritical carbon dioxide-induced exfoliation was calcined to obtain a graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor.

2. The preparation method of graphitic carbon nitride photocatalyst modified based on supercritical carbon dioxide-induced exfoliated supramolecular precursor according to claim 1, characterized in that, In step 1), the mass ratio of melamine, cyanuric acid and hexamethylenetetramine is (0.80~0.90):(3.00~4.00):(0.40~0.60).

3. The preparation method of the graphitic carbon nitride photocatalyst modified based on supercritical carbon dioxide-induced exfoliated supramolecular precursor according to claim 1, characterized in that, In step 1), the hydrothermal reaction involves mixing melamine, cyanuric acid, and hexamethylenetetramine and dissolving them in water, stirring thoroughly, treating at 100-120 °C for 20-24 h, and then washing, drying, and grinding to obtain the supramolecular precursor.

4. The preparation method of the graphitic carbon nitride photocatalyst modified based on supercritical carbon dioxide-induced exfoliated supramolecular precursor according to claim 1, characterized in that, In step 2), the reaction temperature for the supercritical carbon dioxide-induced delamination treatment is 40~140°C. o C, reaction pressure is 14~20 MPa, treatment time is 12~24 h.

5. The method for preparing the graphitic carbon nitride photocatalyst modified based on supercritical carbon dioxide-induced exfoliated supramolecular precursor according to claim 1, characterized in that, In step 3), the calcination treatment involves heating from room temperature to 520~550 ℃ at a rate of 5 ℃ / min, holding at that temperature for 4~6 h, and then cooling naturally.

6. A graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor, prepared by the preparation method according to any one of claims 1-5, characterized in that, The visible light catalytic hydrogen production activity of this graphitic carbon nitride photocatalyst is 7104 μmol h⁻¹. -1 g -1 .

7. The application of the graphitic carbon nitride photocatalyst modified with supercritical carbon dioxide-induced exfoliated supramolecular precursor as described in claim 6 in photocatalytic water splitting for hydrogen production.

8. A method for photocatalytic water splitting to produce hydrogen, characterized in that, include: The graphitic carbon nitride photocatalyst modified by supercritical carbon dioxide-induced exfoliated supramolecular precursor as described in claim 6 is dispersed in a reaction solution, and platinum is loaded onto the surface of the graphitic carbon nitride photocatalyst by in-situ photodeposition. Under an argon atmosphere and at a temperature of 30-40°C, the reaction solution is thoroughly stirred and homogenized. The reaction solution is then irradiated with visible light using a 300 W xenon lamp to produce hydrogen gas.

9. The photocatalytic water splitting method for hydrogen production according to claim 8, characterized in that, A graphitic carbon nitride photocatalyst modified with a supercritical carbon dioxide-induced exfoliated supramolecular precursor was dispersed in a 10% (v / v) triethanolamine aqueous solution. Platinum was loaded onto the surface of the photocatalyst using an aqueous solution of chloroplatinic acid hexahydrate as a precursor via in-situ photodeposition to prepare a reaction solution. The platinum content in the added chloroplatinic acid hexahydrate aqueous solution was 3% of the content of the added graphitic carbon nitride.

10. The photocatalytic water splitting method for hydrogen production according to claim 8, characterized in that, Argon gas was introduced into the reactor for 10-15 minutes before illumination to remove oxygen from the system; visible light irradiation was performed using a 300 W xenon lamp equipped with a cutoff filter with λ > 400 nm.

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