Modified Na-PHI carbon nitride catalyst with high photocatalytic performance, synthetic method and application of modified Na-PHI carbon nitride catalyst in photocatalytic hydrogen production

Abstract

The invention discloses a modified Na-PHI carbon nitride catalyst with high photocatalytic performance, a synthesis method and application of the modified Na-PHI carbon nitride catalyst in photocatalytic hydrogen production. Firstly, a urea raw material and multiple carbon dopants are subjected to high-temperature calcination to synthesize an intermediate product, then sodium chloride, sodium oxalate and the intermediate product in a certain proportion are mixed, calcined and treated, and finally a series of modified Na-PHI carbon nitride is obtained. The preparation method has the advantages of cheap raw materials, simple operation process and green and stable sample, and can be recycled for many times. The modified Na-PHI shows excellent photocatalytic hydrogen production efficiency in a photocatalytic water electrolysis hydrogen production reaction, wherein the hydrogen production efficiency of a modified Na-PHI sample with the most excellent activity is 20.6 times that of common carbon nitride PCN and 4.2 times that of common Na-PHI at the wavelength lambda larger than or equal to 420 nm; the hydrogen production efficiency at the wavelength lambda larger than or equal to 500 nm is 35.4 times that of common Na-PHI (common carbon nitride PCN is inactive).

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic water electrolysis for hydrogen production technology, specifically relating to a universal synthesis method of a modified Na-PHI carbon nitride catalyst with high photocatalytic performance and its application in photocatalytic hydrogen production. Background Technology

[0002] Hydrogen energy is widely recognized by the scientific community as one of the most ideal clean energy sources for the future. It boasts advantages such as high energy density (2.5 times that of natural gas, 5 times that of coal, and 3 times that of gasoline), renewable nature, and non-toxicity and pollution-free operation. It can be widely used in fuel transportation, chemical synthesis, high-temperature industries, and power generation. However, currently, 90% of industrial hydrogen production comes from the thermal reforming of traditional energy sources, such as coal gasification and natural gas reforming, with a small amount from water electrolysis. The use of traditional non-renewable energy sources is the primary cause of the energy crisis and environmental pollution. Currently, plants using photovoltaic power for water electrolysis have been built. In the solar spectrum, visible and infrared light account for approximately 95% of solar radiation energy. Therefore, directly utilizing solar energy to achieve the goal of photocatalytic water splitting to produce hydrogen is a highly promising technology for alleviating the energy crisis and can serve as one of the ideal ways to produce clean energy on a large scale.

[0003] The key to photocatalytic water splitting for hydrogen production lies in the performance of the semiconductor, among which conventional carbon nitride (PCN) is currently a research hotspot. PCN, a non-metallic organic semiconductor material, is easy to synthesize and can be directly obtained from nitrogen-rich precursors such as thermally condensed melamine, thiourea, dicyandiamine, and urea. It is environmentally friendly, possesses a suitable band gap, unique chemical and physical properties, and a controllable electronic structure, thus offering significant advantages over other semiconductor photocatalysts. However, PCN suffers from a narrow light absorption range, high carrier transport impedance, and high carrier recombination rate, hindering its ability to improve photocatalytic hydrogen production efficiency. Patent CN120169407A discloses a method for improving the crystallinity and water-decomposing performance of polyheptaazine imide-based carbon nitride photocatalysts. Melamine is used as a precursor to thermally polymerize an oligomer composed of heptaazine units called melon. Then, high-temperature molten salt calcination is carried out under a nitrogen atmosphere to obtain carbon nitride with a certain degree of crystallinity. Among them, the most active sodium polyheptaazine imide (Na-PHI) crystalline carbon nitride has an active hydrogen gas of 370 µmol / h for water decomposition under full light irradiation. Patent CN113318765A discloses a method for preparing an ultrathin, highly crystalline carbon nitride photocatalyst. Melamine is calcined in a crucible, and after natural cooling, it is ground to obtain bulk carbon nitride. This bulk carbon nitride is then placed in a ceramic boat for high-temperature air stripping, followed by natural cooling and grinding to obtain ultrathin carbon nitride. This ultrathin carbon nitride is then ground with sodium chloride and potassium chloride and calcined in a ceramic boat to obtain highly crystalline, thin carbon nitride with a partial Na-PHI structure. The resulting photocatalyst exhibits a quantum efficiency of 73.6% at 420 nm wavelength and a hydrogen production rate of 9.7 mmol / h under visible light. -1 g -1 Unfortunately, although Na-PHI shows a significant advantage in hydrogen production efficiency in the short wavelength range (λ≥420 nm), its efficiency in the long wavelength range (λ≥500 nm) remains relatively low, with almost zero activity. Therefore, broadening the light absorption range of Na-PHI crystalline carbon nitride is crucial for further improving its photocatalytic hydrogen production performance.

[0004] Therefore, exploring a universal synthesis method for modified NA-PHI with higher crystallinity, a wider light absorption range, and the introduction of special functional groups (increasing active sites) can provide significant reference for the photocatalytic splitting of water to produce hydrogen. Summary of the Invention

[0005] To overcome the problem of narrow light absorption range in existing Na-PHI crystalline carbon nitride, the present invention aims to provide a method for synthesizing modified Na-PHI with higher crystallinity, a wider light absorption range, and the introduction of special functional groups (increasing active sites). The modified Na-PHI is prepared through doping with several carbon dopants and post-treatment with sodium composite salts. This modified Na-PHI can be used for efficient photocatalytic water splitting to produce hydrogen, and can absorb and utilize light energy within a certain long wavelength range (λ≥500 nm) to activate its long-wavelength photocatalytic hydrogen production activity.

[0006] This invention prepares modified Na-PHI crystalline carbon nitride via solid-state calcination using a carbon-doped sodium salt template. This catalyst exhibits higher crystallinity and lower carrier transport impedance in the photocatalytic water splitting reaction to produce hydrogen. Furthermore, the introduction of specific functional groups (electron-donating groups hydroxyl -OH and carbonyl -C=O, and electron-withdrawing group cyano -CN) creates a strong endogenous electric field, promoting carrier separation. Additionally, the introduction of a sub-bandgap in the catalyst facilitates absorption transitions over a long wavelength range, enabling the accumulation and utilization of long-wavelength light energy, which is then converted into hydrogen production energy.

[0007] The objective of this invention can be achieved through the following technical solutions.

[0008] This invention provides a method for obtaining a modified Na-PHI carbon nitride catalyst by calcining a mixture of carbon dopant and urea, followed by a secondary calcination treatment with a sodium composite salt, comprising the following steps:

[0009] (1) Mix urea and carbon dopant in the sample bottle, and cut enough aluminum foil to tightly wrap the sample bottle; (2) Place the sample bottle wrapped in aluminum foil from step (1) into a muffle furnace and calcine it to obtain a transition sample; (3) The transition sample obtained in step (2) is wet-milled with sodium composite salt in a certain amount of anhydrous ethanol into a slurry, and the above slurry material is dried into powder in an oven. (4) Transfer the powder obtained in step (3) into a sample vial and wrap it with aluminum foil; (5) The sample bottle from step (4) is placed in a muffle furnace for calcination and treatment to obtain the modified Na-PHI carbon nitride catalyst. The obtained catalyst is washed with deionized water, filtered with water-based filter paper, and then dried.

[0010] Further, the carbon dopant in step (1) is one of 2-methylimidazole, 2,4,6-triaminopyrimidine, terephthalic acid, or succinic acid.

[0011] Furthermore, the mass ratio of urea to carbon dopant in step (1) is 10:0.05-2, depending on the type of dopant.

[0012] Further, the calcination temperature in step (2) is 500-650 ℃, preferably 550 ℃, the calcination time is 3-6 h, preferably 4 h, and the heating rate is 3-10 ℃ / min, preferably 5 ℃ / min.

[0013] Further, the sodium complex salt in step (3) is 4 g NaCl and 0.05-0.2 g Na2C2O4.

[0014] Further, the mass ratio of the transition sample to the sodium complex salt in step (3) is 1:4-10, preferably 1:8.

[0015] Further, the drying temperature in step (3) is 40-100 ℃, preferably 80 ℃, and the drying time is 0.5-2 h, preferably 1 h.

[0016] Further, the calcination temperature in step (5) is 500-650℃, preferably 600℃, the calcination time is 3-6 h, preferably 4 h, and the heating rate is 3-10 ℃ / min, preferably 5℃ / min.

[0017] Furthermore, the drying temperature in step (5) is 80 °C and the drying time is 1 h.

[0018] This invention provides a method for preparing carbon-doped modified Na-PHI carbon nitride catalysts, thus providing a universal method for Na-PHI modification. The modified Na-PHI carbon nitride catalysts exhibit highly regular crystal particle characteristics, consistent with their high crystallinity. This high crystallinity endows the catalyst with good structural order and stability, resulting in excellent photocatalytic efficiency and good photocatalytic cycle life in photocatalytic hydrogen production reactions.

[0019] The present invention provides the modified Na-PHI carbon nitride catalyst for photocatalytic water splitting to produce hydrogen.

[0020] Method: Weigh the modified Na-PHI carbon nitride catalyst and add it to 10-30 mL of 10 vol% triethanolamine aqueous solution according to the size of the reactor. Then add 300-500 μL of 2 mol / L chloroplatinic acid hexahydrate aqueous solution and ultrasonically disperse it to obtain a photocatalytic water splitting to hydrogen production reaction solution system.

[0021] Furthermore, the reaction device for the photocatalytic water splitting to produce hydrogen is the LabSolar-6A photocatalytic water splitting hydrogen production system. The reactor is evacuated for 15 minutes to remove residual air from the reaction system. The reactor rotation speed is 150-500 r / min, preferably 350 r / min.

[0022] Furthermore, the temperature of the photocatalytic water splitting reaction to produce hydrogen is 0-30℃, and 10℃ is preferred in order to have a suitable reaction rate for producing hydrogen.

[0023] Furthermore, the photocatalytic light source for the photocatalytic water splitting to produce hydrogen is a 300 W xenon lamp. The photocatalytic reaction light wavelengths obtained through the cutoff filter are 420 nm cut (λ≥420 nm) for short-wavelength light and 500 nm cut (λ≥500 nm) for long-wavelength light; the light intensity is 100 mW / cm². 2 .

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The method for synthesizing modified Na-PHI provided by the present invention can be applied to the modification of Na-PHI by various carbon dopants. It has certain universality rules, can effectively broaden the light absorption range of Na-PHI crystalline carbon nitride, and the raw materials are inexpensive, the method is simple, the reaction conditions are mild, green and environmentally friendly, and the reproducibility is high, which is conducive to scale-up production.

[0025] (2) The modified Na-PHI photocatalyst prepared by the preparation method provided by the present invention has excellent photocatalytic activity and excellent long-term stability. The catalyst does not require special protection and can be stored for a long time.

[0026] (3) The Na-PHI photocatalyst prepared by the preparation method provided by the present invention has the advantages of higher crystallinity, as well as the advantages of carbon doping to introduce a sub-band gap to broaden the light absorption range. It can absorb and utilize long-wavelength light energy. At the same time, it introduces a variety of special functional groups (electron-donating groups hydroxyl-OH and carbonyl-C=O, electron-withdrawing groups cyano-CN). On the basis of providing more photocatalytic active sites, it enhances the endogenous electric field of the photocatalyst and shows a greater advantage in the photocatalytic splitting of water to produce hydrogen. Attached Figure Description

[0027] Figure 1 The image shows the scanning electron microscope (SEM) characterization of the matrix sample UCN obtained in Comparative Example 1.

[0028] Figure 2 The image shows the scanning electron microscope (SEM) characterization of the transition sample UCN-T1.0 obtained in Example 1.

[0029] Figure 3 The image shows a scanning electron microscope (SEM) characterization of the final modified sample NUCN-T1.0 obtained in Example 1.

[0030] Figure 4The X-ray diffraction (XRD) patterns are shown for the matrix sample UCN obtained in Comparative Example 1, the control sample ordinary Na-PHI obtained in Comparative Example 2, the transition sample UCN-T1.0 obtained in Example 1, and the final modified sample NUCN-T1.0.

[0031] Figures 5(a) and 5(b) show the X-ray photoelectron spectra (XPS) of the matrix sample UCN obtained in Comparative Example 1, the transition sample UCN-T1.0 obtained in Example 1, and the final modified sample NUCN-T1.0.

[0032] Figure 6 The UV-Vis diffuse reflectance (UV-vis DRS) spectra of the matrix sample UCN obtained in Comparative Example 1, the comparative sample Na-PHI obtained in Comparative Example 2, and the final modified sample NUCN-T1.0 obtained in Example 1 are shown.

[0033] Figure 7 The graph shows the short-wavelength (λ≥420 nm) photocatalytic water splitting rate of the matrix sample UCN obtained in Comparative Example 1, the comparative sample Na-PHI obtained in Comparative Example 2, and the final modified sample NUCN-T1.0 obtained in Example 1.

[0034] Figure 8 The graph shows the long-wavelength (λ≥500 nm) photocatalytic water splitting rate for hydrogen production of the matrix sample UCN obtained in Comparative Example 1, the comparative sample Na-PHI obtained in Comparative Example 2, and the final modified sample NUCN-T1.0 obtained in Example 1.

[0035] Figure 9 The matrix samples UCN and NUCN obtained in Comparative Example 1, and a series of transition samples UCN-T obtained in Example 1. x With the final sample NUCN-T x A series of transitional samples UCN-A obtained in Example 2 x Compared with the final sample NUCN-A x A series of transitional samples UCN-P obtained in Example 3 x Compared with the final sample NUCN-P x A series of transitional samples UCN-H obtained in Example 4 x Compared with the final sample NUCN-H x The rate of hydrogen production by photocatalytic water splitting at short wavelengths (λ≥420 nm) is shown in the figure.

[0036] Figure 10 The matrix samples UCN and NUCN obtained in Comparative Example 1, and a series of transition samples UCN-T obtained in Example 1. x With the final sample NUCN-T xA series of transitional samples UCN-A obtained in Example 2 x Compared with the final sample NUCN-A x A series of transitional samples UCN-P obtained in Example 3 x Compared with the final sample NUCN-P x A series of transitional samples UCN-H obtained in Example 4 x Compared with the final sample NUCN-H x The rate of hydrogen production by photocatalytic water splitting at long wavelengths (λ≥500 nm) is shown in the figure.

[0037] Figure 11 The image shows the photocatalytic cycle performance of the final modified sample NUCN-T1.0 obtained in Example 1. Detailed Implementation

[0038] The specific implementation of the present invention will be further described below with reference to embodiments, comparative examples, and accompanying drawings. However, the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0039] Comparative Example 1 This comparison provides a method for preparing matrix samples UCN and NUCN, the preparation method comprising the following steps: (1) Transfer 10 g of urea to a 20 mL sample bottle and wrap the sample bottle with a sufficient amount of aluminum foil. (2) The sample bottle wrapped in aluminum foil in step (1) was placed in a muffle furnace for calcination at a temperature of 550°C for 4 h and a calcination rate of 5°C / min. The sample was then labeled as UCN. (3) The UCN obtained in step (2) is wet-milled with 4 g NaCl and 0.1 g Na2C2O4 with a certain amount of anhydrous ethanol into a slurry. The slurry material is then dried in an 80℃ oven for 1 h to form powder. (4) Transfer the powder obtained in step (3) into a 20 mL sample bottle and wrap it with aluminum foil; (5) The sample vial from step (4) was placed in a muffle furnace for calcination. The calcination temperature was 600℃, the calcination time was 4 h, and the calcination rate was 5℃ / min. The resulting sample was labeled NUCN.

[0040] The obtained matrix samples UCN and NUCN were used for a preliminary comparison of the photocatalytic water splitting to hydrogen production rate performance with the modified Na-PHI synthesized by this method. Figure 1This is a scanning electron microscope (SEM) characterization image of the matrix sample UCN obtained in Comparative Example 1. From... Figure 1 It is known that ordinary carbon nitride (UCN) catalysts do not have a crystalline structure and are in an amorphous state.

[0041] Comparative Example 2 This comparison provides a method for preparing a comparative sample, ordinary Na-PHI, which includes the following steps: (1) 10g of urea and 4g of NaCl were wet-ground into a slurry by passing a certain amount of anhydrous ethanol; (2) The slurry was placed in an oven and dried into powder at a temperature of 80°C for 1 hour. (3) Transfer the powder to a 20 mL sample bottle and calcine it in a muffle furnace at a temperature of 600℃ for 4 h and a calcine rate of 5℃ / min. (4) After the reaction is complete, the calcined product is washed with boiling water and repeated three times. The product is collected by vacuum filtration and then placed in an 80℃ oven to dry for 1 h to obtain the control sample ordinary Na-PHI.

[0042] The obtained comparative sample, ordinary Na-PHI, was used for a preliminary comparison of the photocatalytic water splitting to hydrogen production rate performance between it and the modified Na-PHI synthesized by this method.

[0043] Example 1 This implementation provides a transitional sample, UCN-T. x (in x (Expressed as the amount of carbon dopant 2-methylimidazole used) and the final modified Na-PHI sample NUCN-T x A preparation method comprising the following steps: (1) Mix 10 g of urea with 0.5 / 1.0 / 2.0 g of 2-methylimidazole and transfer them to 20 mL sample bottles respectively. Cut enough aluminum foil to wrap the sample bottles. (2) Place a series of sample bottles wrapped in aluminum foil in step (1) into a muffle furnace for calcination at a temperature of 550℃, a calcination time of 4 h, and a calcination rate of 5℃ / min. The resulting transition samples are labeled as UCN-T0.5, UCN-T1.0, and UCN-T2.0, respectively. (3) The UCN-T0.5, UCN-T1.0 and UCN-T2.0 obtained in step (2) are respectively wet-milled with 4 g NaCl and 0.1 g Na2C2O4 with a certain amount of anhydrous ethanol into a slurry. The above slurry materials are placed in an 80℃ oven and dried for 1 h to become powder. (4) Transfer the series of powders obtained in step (3) into a 20 mL sample bottle and wrap it with aluminum foil; (5) The series of sample bottles from step (4) were placed in a muffle furnace for calcination and post-treatment. The calcination temperature was 600℃, the calcination time was 4 h, and the calcination rate was 5℃ / min. The final modified Na-PHI samples were labeled as NUCN-T0.5, NUCN-T1.0, and NUCN-T2.0 (i.e., the samples obtained by post-treatment of UCN-T0.5, UCN-T1.0, and UCN-T2.0).

[0044] In adjusting the mass ratio of the transition sample to the sodium complex salt, combinations of 1:4, 1:8, and 1:10 were tried (the ratio of sodium chloride to sodium oxalate in the complex salt was 40:1). If the mass of sodium complex salt added was too low (1:4), the excess carbon nitride groups and dopant groups in the sample would not be fully post-treated to form a Na-PHI structure, remaining in the state of transition groups and resulting in low or even no activity. If the mass of sodium complex salt added was too high (1:10), the excess sodium complex salt would create a strongly alkaline environment during calcination, causing the carbon nitride groups and dopant groups to be over-etched, producing inactive carbon black. Therefore, a mass ratio of 1:8 for the transition sample to the sodium complex salt was ultimately chosen to synthesize the final modified sample NUCN-T. x .

[0045] Furthermore, the calcination temperature of the final synthesized sample also affects the strength of the alkaline environment formed by the sodium complex salt, thus influencing the structure and properties of the final sample. In exploring the synthesis temperature, on the one hand, the higher the synthesis temperature, the stronger the alkaline environment formed by the sodium complex salt, requiring more precise consideration of the mass ratio of the transition sample to the sodium complex salt; on the other hand, in the sodium complex salt synthesis system, a temperature of at least 600 °C is required for the formation of the Na-PHI structure by the carbon nitride groups. Therefore, the preferred synthesis temperature is 600 °C.

[0046] The obtained transition sample UCN-T x Compared with the final modified Na-PHI sample NUCN-T x The method was used to test the rate of hydrogen production from water produced by photocatalytic splitting, and the hydrogen production rate was used to confirm the general applicability of the method for synthesizing modified Na-PHI catalysts described in this invention. Figure 2 This is a scanning electron microscope (SEM) characterization image of the transition sample UCN-T1.0 obtained in Example 1. Figure 2 It can be seen that the UCN-T1.0 catalyst exhibits a more layered amorphous layered structure. Figure 3 The image shows a scanning electron microscope (SEM) characterization of the final modified Na-PHI sample NUCN-T1.0 catalyst obtained in Example 1. Figure 3It can be seen that the NUCN-T1.0 catalyst exhibits a crystalline structure, and its unit surface is smooth and flat with relatively uniform size, and the particle size is in the range of 50-300 nm.

[0047] Example 2 This implementation provides a transitional sample, UCN-A. x (in x (Expressed as the amount of carbon dopant 2,4,6-triaminopyrimidine used) and the final modified Na-PHI sample NUCN-A x A preparation method comprising the following steps: (1) Mix 10 g of urea with 0.025 / 0.050 / 0.10 g of 2,4,6-triaminopyrimidine and transfer them to 20 mL sample bottles respectively. Cut enough aluminum foil to wrap the sample bottles. (2) Place a series of sample bottles wrapped in aluminum foil in step (1) into a muffle furnace for calcination at a temperature of 550℃ for 4 h and a calcination rate of 5℃ / min. The resulting transition samples are labeled as UCN-A0.025, UCN-A0.050 and UCN-A0.10, respectively. (3) The UCN-A0.025, UCN-A0.050 and UCN-A0.10 obtained in step (2) are ground into a slurry by wet grinding with 4 g NaCl and 0.1 g Na2C2O4 with a certain amount of anhydrous ethanol. The above slurry material is placed in an 80℃ oven and dried for 1 h to become powder. (4) Transfer the series of powders obtained in step (3) into a 20 mL sample bottle and wrap it with aluminum foil; (5) The series of sample bottles from step (4) were placed in a muffle furnace for calcination and post-treatment. The calcination temperature was 600℃, the calcination time was 4 h, and the calcination rate was 5℃ / min. The final modified Na-PHI samples were labeled as NUCN-A0.025, NUCN-A0.050, and NUCN-A0.10 (i.e., the samples obtained by post-treatment of UCN-A0.025, UCN-A0.050, and UCN-A0.10).

[0048] The obtained transition sample UCN-A x Compared with the final modified Na-PHI sample NUCN-A x The method was used to test the rate of hydrogen production from water produced by photocatalytic splitting, and the hydrogen production rate was used to confirm the general applicability of the method for synthesizing modified Na-PHI catalysts described in this invention.

[0049] Example 3 This implementation provides a transitional sample, UCN-P. x (in x(Expressed as the amount of carbon dopant terephthalic acid used) and the final modified Na-PHI sample NUCN-P x A preparation method comprising the following steps: (1) Mix 10 g of urea with 0.050 / 0.10 / 0.20 g of terephthalic acid, and transfer them to 20 mL sample bottles respectively. Cut enough aluminum foil to wrap the sample bottles. (2) Place a series of sample bottles wrapped in aluminum foil in step (1) into a muffle furnace for calcination at a temperature of 550℃ for 4 h and a calcination rate of 5℃ / min. The resulting transition samples are labeled as UCN-P0.050, UCN-P0.10 and UCN-P0.20, respectively. (3) The UCN-P0.050, UCN-P0.10 and UCN-P0.20 obtained in step (2) are ground into a slurry by 4 g NaCl and 0.1 g Na2C2O4 respectively with a certain amount of anhydrous ethanol. The above slurry material is placed in an 80℃ oven and dried for 1 h to become powder. (4) Transfer the series of powders obtained in step (3) into a 20 mL sample bottle and wrap it with aluminum foil; (5) The series of sample bottles from step (4) were placed in a muffle furnace for calcination and post-treatment. The calcination temperature was 600℃, the calcination time was 4 h, and the calcination rate was 5℃ / min. The final modified Na-PHI samples were labeled as NUCN-P0.050, NUCN-P0.10, and NUCN-P0.20 (i.e., the samples obtained by post-treatment of UCN-P0.050, UCN-P0.10, and UCN-P0.20).

[0050] The obtained transition sample UCN-P x Compared with the final modified Na-PHI sample NUCN-P x The method was used to test the rate of hydrogen production from water produced by photocatalytic splitting, and the hydrogen production rate was used to confirm the general applicability of the method for synthesizing modified Na-PHI catalysts described in this invention.

[0051] Example 4 This implementation provides a transitional sample, UCN-H. x (in x (Expressed as the amount of carbon dopant succinic acid used) and the final modified Na-PHI sample NUCN-H x A preparation method comprising the following steps: (1) Mix 10 g of urea with 0.025 / 0.050 / 0.10 g of succinic acid and transfer them to 20 mL sample bottles respectively. Cut enough aluminum foil to wrap the sample bottles. (2) Place a series of sample bottles wrapped in aluminum foil in step (1) into a muffle furnace for calcination at a temperature of 550℃ for 4 h and a calcination rate of 5℃ / min. The resulting transition samples are labeled as UCN-H0.025, UCN-H0.050 and UCN-H0.10, respectively. (3) The UCN-H0.025, UCN-H0.050 and UCN-H0.10 obtained in step (2) are ground into a slurry by wet grinding with 4 g NaCl and 0.1 g Na2C2O4 with a certain amount of anhydrous ethanol. The above slurry material is placed in an 80℃ oven and dried for 1 h to become powder. (4) Transfer the series of powders obtained in step (3) into a 20 mL sample bottle and wrap it with aluminum foil; (5) The series of sample bottles from step (4) were placed in a muffle furnace for calcination and post-treatment. The calcination temperature was 600℃, the calcination time was 4 h, and the calcination rate was 5℃ / min. The final modified Na-PHI samples were labeled as NUCN-H0.025, NUCN-H0.050, and NUCN-H0.10 (i.e., the samples obtained by post-treatment of UCN-H0.025, UCN-H0.050, and UCN-H0.10).

[0052] The obtained transition sample UCN-H x Compared with the final modified Na-PHI sample NUCN-H x The method was used to test the rate of hydrogen production from water produced by photocatalytic splitting, and the hydrogen production rate was used to confirm the general applicability of the method for synthesizing modified Na-PHI catalysts described in this invention.

[0053] Figure 4 The X-ray diffraction (XRD) patterns are shown for the matrix sample UCN obtained in Comparative Example 1, the control sample ordinary Na-PHI obtained in Comparative Example 2, the transition sample UCN-T1.0 obtained in Example 1, and the final modified sample NUCN-T1.0. Figure 4 It can be seen that UCN does not have the crystal structure of Na-PHI, while ordinary Na-PHI, although it has a certain crystal structure, has poor crystallinity. The diffraction peaks of the Na-PHI crystal structure of the NUCN-T1.0 catalyst are obvious, indicating good crystallinity.

[0054] Figure 5 shows the X-ray photoelectron spectroscopy (XPS) spectra of the matrix sample UCN obtained in Comparative Example 1, the transition sample UCN-T1.0 obtained in Example 1, and the final modified sample NUCN-T1.0. As can be seen from Figure 5(a), compared with UCN and UCN-T1.0, NUCN-T1.0 has additional electron-donating groups -OH and -C=O; as can be seen from Figure 5(b), compared with UCN and UCN-T1.0, NUCN-T1.0 has a higher concentration of electron-withdrawing groups -CN.

[0055] Figure 6 The images show the UV-Vis diffuse reflectance (UV-vis DRS) spectra of the matrix sample UCN obtained in Comparative Example 1, the comparative sample Na-PHI obtained in Comparative Example 2, and the final modified sample NUCN-T1.0 obtained in Example 1. Figure 6 It can be seen that, compared with UCN, the Na-PHI structure of ordinary Na-PHI promotes its light absorption range; compared with Na-PHI, the light absorption range curve of NUCN-T1.0 shows a bulge, which is formed by the expansion of the light absorption range through the sub-bandgap introduced by carbon doping, that is, the light absorption range of Na-PHI crystalline carbon nitride is broadened.

[0056] The UCN prepared in Comparative Example 1, the ordinary Na-PHI prepared in Comparative Example 2, and the modified Na-PHI sample NUCN-T1.0 prepared in Example 1 were used for photocatalytic water splitting to produce hydrogen under short wavelength (λ≥420 nm) and long wavelength (λ≥500 nm) light sources.

[0057] from Figure 7 It can be seen that under short wavelength (λ≥420 nm) conditions, NUCN-T1.0 exhibits excellent photocatalytic hydrogen production performance, being 16.7 times that of UCN and 3.4 times that of ordinary Na-PHI; from Figure 8 It can be seen that under long wavelength (λ≥500 nm) conditions, NUCN-T1.0 has a more significant advantage in photocatalytic hydrogen production, which is 12.3 times that of ordinary Na-PHI (UCN is inactive).

[0058] The matrix samples UCN and NUCN prepared in Comparative Example 1, and a series of transition samples UCN-T prepared in Example 1. x With the final sample NUCN-T x A series of transitional samples UCN-A prepared in Example 2 x Compared with the final sample NUCN-A x A series of transitional samples UCN-P prepared in Example 3 x Compared with the final sample NUCN-P x A series of transitional samples UCN-H prepared in Example 4 x Compared with the final sample NUCN-H x It is used for photocatalytic water splitting to produce hydrogen under short wavelength (λ≥420 nm) and long wavelength (λ≥500 nm) light sources.

[0059] from Figure 9It can be seen that, under short wavelength (λ≥420 nm) conditions, the photocatalytic hydrogen production performance of each series of carbon-doped and post-treated samples is improved compared to UCN and NUCN (i.e., samples obtained by UCN post-processing); from Figure 10 It can be seen that, under long wavelength (λ≥500 nm) conditions, the photocatalytic hydrogen production performance of each series of carbon-doped and post-treated samples is significantly superior to that of UCN and NUCN. Through the comparison of the above samples, it can be confirmed that the synthesis method of the modified Na-PHI samples described in this invention has certain universality, and all methods can obtain modified samples with Na-PHI structures doped with the corresponding carbon dopant.

[0060] Among them, the NUCN-A0.025 modified Na-PHI sample exhibited the best overall performance in photocatalytic hydrogen production, with a hydrogen production efficiency of 4006.7 μmol / h at a wavelength (420 nm ≤ λ). -1 g -1 The efficiency was 20.6 times that of ordinary carbon nitride (PCN) and 4.2 times that of ordinary Na-PHI, respectively; the hydrogen production efficiency at a wavelength (500 nm ≤ λ) was 566.7 μmol h⁻¹. -1 g -1 It is 35.4 times that of ordinary Na-PHI (ordinary carbon nitride PCN is inactive).

[0061] exist Figure 9 In this study, given that doping with 2-methylimidazole can broaden the light absorption range of carbon nitride on the one hand, but may also reduce the active sites for photocatalytic activity on the other, the competitive effect of these two factors leads to a suitable doping amount of 2-methylimidazole being 1 g. Among these, UCN-T1 and NUCN-T1 exhibit the highest photocatalytic activity under visible light. Similarly, despite their different aggregation structures, UCN-A... x UCN-P x and UCN-H x There is also doped "saturation." However, alkaline sodium double salt post-treatment "cleaves" some doped carbon groups or converts them into oxygen-containing carbon groups, promoting UCN-P. x and UCN-H x With a new “volume”—more photocatalytic active sites—NUCN-P x and NUCN-H x The appropriate doping amount of carbon dopant is "lagging". Overall, despite replacing 2-methylimidazole with other carbon dopant, the synthesized series of modified Na-PHI samples still have very considerable photocatalytic hydrogen production efficiency, indicating that the process method of synthesizing modified Na-PHI by carbon doping of Na-PHI through hybrid salt-assisted crystallization has certain universality.

[0062] Figure 11 To verify the excellent photocatalytic cycling performance of NUCN-T1.0, during the photocatalytic H2 production process, the solution containing NUCN-T1.0 changed color from yellow to blue after 10 minutes of light irradiation, demonstrating the electron storage of ionic carbon nitride. As shown in the dark reaction, even without light irradiation, some H2 was still produced in the NUCN-T1.0 solution upon returning to its original state. Figure 11 (a) NUCN-T1.0 can absorb and store excess photogenerated charge carriers that do not immediately participate in the reaction to reach an excited state. In this way, these stored charge carriers are slowly released for the reaction, thereby producing hydrogen gas. Furthermore, as... Figure 11 b and Figure 11 As shown in c, NUCN-T1.0 underwent a continuous 24-hour photocatalytic H2 production test to explore its stability. Figure 11 After reacting for 24 hours under visible light (500 nm ≤ λ ≤ 780 nm) and 10 vol% TEOA conditions, the H2 production efficiency of NUCN-T1.0 remained at 78.52%. Notably, during this reaction, if 10 mL of 10 vol% TEOA was added every 8 hours, the hydrogen production efficiency of NUCN-T1.0 remained above 90%, demonstrating the excellent cycling performance of NUCN-T1.0. Figure 11 (c in the text)

[0063] Finally, it should be noted that the detailed descriptions of the above embodiments, comparative examples, and related drawings are only used to illustrate the technical solutions of the present invention and not to limit them. The present invention is not limited to the specific embodiments described above. Any modifications or equivalent substitutions made by those skilled in the art under the guidance of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for synthesizing a modified Na-PHI carbon nitride catalyst, characterized in that, Includes the following steps: (1) Mix urea and carbon dopant in a sample vial and wrap the sample vial with aluminum foil; (2) Place the sample bottle wrapped in aluminum foil from step (1) into a muffle furnace and calcine it to obtain a transition sample; (3) The transition sample obtained in step (2) is wet-milled with sodium complex salt in anhydrous ethanol into a slurry, and the above slurry material is dried into powder. (4) Transfer the powder obtained in step (3) into a sample vial and wrap it with aluminum foil; (5) The sample vial from step (4) is placed in a muffle furnace for calcination and post-treatment to obtain the modified Na-PHI carbon nitride catalyst.

2. The method for synthesizing the modified Na-PHI carbon nitride catalyst according to claim 1, characterized in that, The carbon dopant in step (1) is one of 2-methylimidazole, 2,4,6-triaminopyrimidine, terephthalic acid, or succinic acid.

3. The method for synthesizing the modified Na-PHI carbon nitride catalyst according to claim 1, characterized in that, The mass ratio of urea to carbon dopant in step (1) is 10: 0.05-2, depending on the type of dopant.

4. The method for synthesizing the modified Na-PHI carbon nitride catalyst according to claim 1, characterized in that, The calcination temperature in step (2) is 500-650 ℃, the calcination time is 3-6 h, and the heating rate is 3-10 ℃ / min.

5. The method for synthesizing the modified Na-PHI carbon nitride catalyst according to claim 1, characterized in that, The sodium complex salt in step (3) is 4 g NaCl and 0.05-0.2 g Na2C2O4.

6. The method for synthesizing the modified Na-PHI carbon nitride catalyst according to claim 1, characterized in that, The mass ratio of the transition sample to sodium complex salt in step (3) is 1:4-10.

7. The method for synthesizing the modified Na-PHI carbon nitride catalyst according to claim 1, characterized in that, The drying temperature in step (3) is 40-100 ℃ and the drying time is 0.5-2 h.

8. The method for synthesizing the modified Na-PHI carbon nitride catalyst according to claim 1, characterized in that, The calcination temperature in step (5) is 500-650 ℃, the calcination time is 3-6 h, and the heating rate is 3-10 ℃ / min.

9. A modified Na-PHI carbon nitride catalyst synthesized by the method according to any one of claims 1-8.

10. The modified Na-PHI carbon nitride catalyst according to claim 9 is used for photocatalytic water splitting to produce hydrogen.

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