Carbon nitride photocatalyst based on multiple asymmetric active sites in hydrogen peroxide production applications

Abstract

The application discloses a kind of carbon nitride photocatalyst based on multiple asymmetric active sites in hydrogen peroxide production application. Sulfur-doped carbon nitride nanotubes are synthesized by thermal polymerization method, and then a photocatalytic material S-CNT-Zn is obtained by impregnation-calcination method, in which zinc monatomic atoms are loaded on the sulfur-doped carbon nitride nanotubes. The preparation process is simple, and the preparation process is simple. The carbon nitride photocatalyst with multiple asymmetric active sites can break the symmetry of carbon nitride material, form a gradient charge distribution, realize multi-path charge transfer, and promote the migration and separation of carriers. And zinc monatomic atoms as oxygen adsorption sites can promote the adsorption of oxygen and reduce the formation energy barrier of intermediates. In the visible light driven oxygen reduction synthesis of hydrogen peroxide, the carbon nitride photocatalyst with multiple asymmetric active sites maintains the stability of the catalyst and high hydrogen peroxide yield, thereby realizing clean, stable and efficient photocatalytic reduction of oxygen to synthesize hydrogen peroxide.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials, specifically relating to a modified carbon nitride photocatalyst with multiple asymmetric active sites, and its application in solar-driven hydrogen peroxide synthesis. Background Technology

[0002] Hydrogen peroxide, as a multifunctional green oxidant, plays a crucial role in environmental remediation, chemical synthesis, and energy conversion. However, the traditional anthraquinone process for industrial hydrogen peroxide production suffers from high energy consumption, harmful byproducts, and complex infrastructure, severely limiting its sustainability. Photocatalytic synthesis of hydrogen peroxide via solar-driven oxygen reduction reaction has emerged as a promising alternative, providing a renewable and environmentally friendly pathway for utilizing solar energy to produce chemical fuels.

[0003] Generally, an ideal catalyst for the photocatalytic synthesis of hydrogen peroxide via oxygen reduction should possess the following characteristics: (1) The photocatalytic material has a suitable band gap to absorb sunlight and generate electron-hole pairs. (2) Photogenerated electrons should be effectively separated and reach the material surface to participate in the reduction reaction. (3) The photocatalyst should provide a large number of active sites, generating numerous adsorption sites and photocatalytic reaction centers. (4) The reduction reaction between reactants and photogenerated electrons requires that the negative potential at the bottom of the conduction band of the photocatalytic material be lower than the reduction potential.

[0004] Compared to conventional metal catalysts (such as TiO2 semiconductors), carbon nitride's band structure spans the potentials for both oxygen reduction and water oxidation, and its attractive electronic structure and narrow band gap (2.7 eV) allow for more efficient utilization of visible light. Furthermore, carbon nitride exhibits excellent physicochemical stability, convenient synthesis, and functionalization properties. Therefore, since its pioneering work in photocatalysis in 2009, carbon nitride has opened up new prospects for the direct in-situ photocatalytic production of hydrogen peroxide. It is undeniable that the practical application of carbon nitride in photocatalytic hydrogen peroxide production is still hindered by the following factors: (I) The medium band gap of carbon nitride determines that it cannot effectively absorb photons in visible light with wavelengths beyond 460 nm, limiting the generation of charge carriers; (II) The repeating Mellem structures in carbon nitride (including tris-triazine and triazine structures) hinder the separation of charge carriers; and (III) The stacked structure of bulk carbon nitride not only increases the migration distance of charge carriers but also masks the reaction sites of oxygen, leading to poor utilization of reactants and a reduction in selective redox reactions.

[0005] In recent years, research on improving the photocatalytic performance of carbon nitride has mainly focused on heteroatom doping (such as B, S, P) and metal single-atom engineering. These methods can tune electronic properties and break the symmetry structure of carbon nitride, but the local unit point asymmetry usually leads to limited electron delocalization, which in turn causes slow separation and rapid recombination of photogenerated carriers, weakening the photoreduction reaction. Summary of the Invention

[0006] This invention addresses the shortcomings of existing carbon nitride-based catalysts for the photosynthesis of hydrogen peroxide by providing a carbon nitride photocatalyst based on multiple asymmetric active sites, its preparation method, and its application in hydrogen peroxide production. Introducing multiple asymmetric sites into the triazine repeating unit generates a highly asymmetric electronic structure, expands electron delocalization, and promotes spatial separation of charge carriers in carbon nitride, thereby improving the performance of photocatalytic synthesis of hydrogen peroxide via oxygen reduction. This invention uses thermal polymerization and impregnation-calcination methods to load non-metallic sulfur atoms, oxygen atoms, and metallic zinc single atoms onto carbon nitride nanotubes, breaking the highly symmetric charge distribution of the carbon nitride nanotubes. The multiple asymmetric catalytic site characteristics of this catalyst promote spatial separation of charge carriers by expanding electron delocalization and achieving charge gradient distribution. The multi-active-site configuration optimizes the adsorption behavior of oxygen on zinc single atoms and reduces the activation barrier of intermediates during the reaction process, overcoming the rate-limiting step limitation in the oxygen-adsorbed oxygen conversion process while maintaining stable and efficient hydrogen peroxide synthesis.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A carbon nitride photocatalyst based on multiple asymmetric active sites is disclosed. The catalyst possesses four asymmetric active sites (nitrogen, oxygen, sulfur, and zinc) within a repeating unit of carbon nitride, maximally disrupting the electron cloud uniformity of carbon nitride. The spatial distribution of these four sites creates multiple atomic-level charge transfer channels, promoting the transfer and separation of photogenerated carriers. Zinc single atoms, acting as oxygen adsorption sites, lower the energy barrier in oxygen activation and intermediate formation processes, overcoming the rate-limiting step limitation in the oxygen-adsorbed oxygen conversion process. During the reaction, the photocatalyst with atomically dispersed multiple asymmetric catalytic sites maintains highly efficient and stable hydrogen peroxide synthesis performance.

[0009] This invention also provides a method for preparing the aforementioned carbon nitride photocatalyst based on multiple asymmetric active sites, the preparation steps of which are as follows:

[0010] (1) Urea, melamine and sodium bisulfite were ground into powder in a mortar and then transferred to an alumina rectangular boat for thermal polymerization to synthesize carbon nitride nanotubes.

[0011] (2) The sulfur-doped carbon nitride nanotubes obtained in step (1) are uniformly dispersed in ethanol and added to a zinc acetate solution with N,N-dimethylformamide as solvent, and stirred and mixed evenly.

[0012] (3) After filtering, washing and drying the composite material obtained in step (3), the impregnated composite material is placed in an alumina rectangular boat and calcined to obtain S-CNT-Zn with uniform dispersion of zinc single atoms and sulfur doping; wherein the raw material mass ratio of S:Zn is 40:1.

[0013] (4) The S-CNT-Zn photocatalyst prepared in step (3) is used for hydrogen peroxide production.

[0014] Further, in step (1), 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite were uniformly ground into powder in a mortar and then transferred to an alumina rectangular boat. The mixture was thermally polymerized under a nitrogen atmosphere at a heating rate of 3°C per minute, heated to 570°C and maintained for 90 minutes. After cooling to room temperature, sulfur-doped carbon nitride nanotubes (S-CNTs) were obtained.

[0015] Furthermore, in step (1), the mass ratio of urea, melamine, and sodium bisulfite is 150~350: 10~40:1.

[0016] In step (1), urea, melamine, and sodium bisulfite are thermally polymerized under a nitrogen atmosphere throughout the process. The heating rate is 2-5°C per minute. The temperature is raised to 400-700°C and maintained for 60-120 minutes. After cooling to room temperature, the mixture is removed and the nitrogen atmosphere is removed.

[0017] In step (2), the concentration of sulfur-doped carbon nitride nanotubes dispersed in anhydrous ethanol is 2.0~8.0 mg / mL, the concentration of zinc acetate dihydrate dispersed in N,N-dimethylformamide is 0.01~0.04 mg / mL, and the mass ratio of carbon nitride nanotubes to N,N-dimethylformamide is 2~5:1.

[0018] In step (2), the mixture is stirred at 50-90°C for 1-3 hours.

[0019] In step (3), the mixture is filtered, washed multiple times with anhydrous ethanol, and dried overnight at 50-100°C.

[0020] In step (3), the calcination atmosphere is argon atmosphere, the heating rate is 2~8℃ per minute to 300~500℃, maintained for 30~90 minutes, and then removed after cooling to room temperature and the argon atmosphere is removed.

[0021] Steps (2) and (3) are impregnation-calcination methods, in which the precursor of zinc species is impregnated on the matrix and uniformly dispersed in atomic form on sulfur-doped carbon nitride under an argon atmosphere.

[0022] In the photocatalyst S-CNT-Zn obtained in step (3), sulfur, oxygen, and zinc atoms are introduced into the tubular carbon nitride matrix to form multiple asymmetric catalytic sites together with the matrix nitrogen, and the molar ratio of zinc to oxygen is 1:1~3.

[0023] The photosynthesis of hydrogen peroxide specifically includes the following steps:

[0024] The photocatalyst S-CNT-Zn obtained in step (3) was dispersed in an ethanol-water solution and stirred in the dark to allow the ethanol-water solution and the catalytic material to reach an adsorption-desorption equilibrium. The resulting suspension was then used to catalyze the synthesis of hydrogen peroxide under visible light with a wavelength greater than 420 nm.

[0025] The method for preparing carbon nitride photocatalyst based on multiple asymmetric active sites is characterized in that: the volume ratio of ethanol to water in the ethanol-water solution is 0.20-0.30:1, the mass ratio of the catalytic material to the ethanol-water solution is 0.00005-0.0001:1, the stirring time in the dark is 10-20 min, and the catalytic process temperature is room temperature.

[0026] Beneficial effects:

[0027] The catalyst of this invention is based on a carbon nitride photocatalyst with multiple asymmetric active sites. The introduction of sulfur, oxygen, and zinc atoms in the carbon nitride matrix breaks the symmetry and forms multiple asymmetric active sites in a spatially distributed manner. The highly asymmetric structure enables charge gradient distribution and promotes spatial separation of charge carriers. The multi-active-site configuration optimizes the adsorption behavior of oxygen on zinc single atoms and reduces the activation barrier of intermediates in the reaction process, breaking through the rate-limiting step limitation in the oxygen-adsorbed oxygen conversion process. During the reaction, the catalyst maintains a high efficiency in hydrogen peroxide synthesis and exhibits high stability.

[0028] (1) The present invention synthesizes carbon nitride photocatalysts with multiple asymmetric active sites, such as non-metallic sulfur, oxygen and supported metal single-atom zinc, in two steps by thermal polymerization and impregnation-calcination. The preparation process is simple, the process is easy to control, and it is less affected by environmental factors.

[0029] (2) This invention breaks the uniformity of the original carbon nitride electronic structure to the greatest extent. Compared with the traditional single active site modification, multiple active sites in this invention can form multiple carrier transfer paths, and the highly asymmetric structure formed can realize charge gradient distribution and promote the spatial separation of carriers.

[0030] (3) The zinc metal provided by this invention is in the form of a single atom within a carbon nitride framework, coordinated with nitrogen and oxygen atoms in the carbon nitride structure. The presence of zinc single atoms optimizes the oxygen adsorption pathway, lowers the activation energy barrier of oxygen and intermediates, and breaks the limitation of the oxygen-adsorbed oxygen rate-limiting step in the reaction process; at the same time, in the visible light-driven oxygen reduction synthesis of hydrogen peroxide, the carbon nitride photocatalyst with multiple asymmetric active sites maintains catalyst stability and a high hydrogen peroxide yield, thereby achieving clean, stable, and efficient photocatalytic reduction of oxygen to synthesize hydrogen peroxide.

[0031] (4) Through integrated material innovation, this invention maximizes the utilization of catalyst active sites in the catalytic synthesis of hydrogen peroxide, far exceeding the hydrogen peroxide yield of single-site modified carbon nitride in most current studies, such as nitrogen-deficient carbon nitride at 1620 μmol g. -1 h -1 567 μmol g of sulfur-doped carbon nitride -1 h -1 486 μmol g of phosphorus-doped carbon nitride -1 h -1 574 μmol g of boron-doped carbon nitride -1 h -1 730 μmol g of tungsten oxide supported on carbon nitride -1 h -1 710 μmol g of cadmium sulfide loaded on carbon nitride -1 h -1 wait.

[0032] (5) When using catalyst S-CNT-Zn-1 with a S:Zn ratio of 40:1, the hydrogen peroxide yield is the highest, reaching 2711 μmol g. -1 h -1 Compared to the CNTs prepared in Example 9 (154 μmol g), -1 h -1 ) and S-CNT (1155 μmol g) prepared in Example 10 -1 h -1 This represents an increase of at least 17.6 and 2.4 times. From Figure 8 This indicates that the catalyst has good stability; its performance did not decline after five cycles of use. Figure 9 It can be concluded that the catalyst has the ability to produce hydrogen peroxide stably for a long period of time, up to 18 hours or more. Attached Figure Description

[0033] Figure 1This is a schematic diagram of the synthesis route of the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in Examples 1-6 of the present invention.

[0034] Figure 2 In the image, (a) is a SEM image of the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in Example 1 of the present invention; (b) is a TEM image of the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in the present invention; and (c) is a high-resolution attenuated full sampling electron tomography (HAADFS) image of the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in the present invention.

[0035] Figure 3 This is a SEM-EDS image of the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in Example 1 of the present invention.

[0036] Figure 4 This is the X-ray diffraction pattern of the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in Example 1 of the present invention.

[0037] Figure 5 The ZnK-edge fitting results are for the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in Example 1 of this invention.

[0038] Figure 6 These are the effect diagrams of photocatalytic reduction of oxygen to hydrogen peroxide using the materials described in Examples 1-6 and Example 10 of the present invention.

[0039] Figure 7 These are the effect diagrams of the photocatalytic reduction of oxygen to hydrogen peroxide by the materials described in Examples 1 and 9-10 of this invention.

[0040] Figure 8 This is a cycle effect diagram of the photocatalytic reduction of oxygen to hydrogen peroxide by the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in Example 1 of the present invention.

[0041] Figure 9 This is a long-term effect diagram of the photocatalytic reduction of oxygen to hydrogen peroxide by the carbon nitride photocatalyst S-CNT-Zn with multiple asymmetric active sites in Example 1 of the present invention. Detailed Implementation

[0042] The present invention is further illustrated below by way of examples. It should be understood that these examples are illustrations and examples of the present invention and do not limit the scope of the present invention in any way.

[0043] Example 1

[0044] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0045] (2) Add 1.1 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h.

[0046] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-1 (S:Zn=40:1) was obtained.

[0047] The S-CNT-Zn material prepared in Example 1 was characterized. First, its morphology was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results are as follows. Figure 2 The catalysts shown in (a) and 2(b) are nanotube-like materials with uniform diameter. High-resolution attenuated full-sample electron tomography images, i.e. Figure 2 (c) Clearly shows that metallic zinc is uniformly distributed in single-atom form on the surface of carbon nitride nanotubes. Next, EDS testing was performed, and the results are as follows... Figure 3 As shown, the various elements are uniformly distributed on the carbon nitride nanotubes. Next, XRD tests were performed on the S-CNT-Zn material prepared in Example 1, and the XRD results are as follows. Figure 4 As shown, a typical carbon nitride crystal structure is observed, with two distinct diffraction peaks at 27.4° and 13.1°, corresponding to the (1 0 0) and (0 0 2) crystal planes of tubular carbon nitride, respectively. No diffraction peaks of metal oxides are present, indicating that metallic zinc has not formed metal particles or agglomerated. Finally, Figure 5 The Zn K-edge fitting results of S-CNT-Zn in Example 1 are shown. It was found that the fitting effect was best when the Zn single atom was coordinated with 3 N and 1 O.

[0048] Example 2

[0049] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0050] (2) Add 0.6 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h.

[0051] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-2 (S:Zn=80:1) was obtained.

[0052] Example 3

[0053] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0054] (2) Add 2.1 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h.

[0055] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-3 (S:Zn=20:1) was obtained.

[0056] Example 4

[0057] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0058] (2) Add 5.4 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h.

[0059] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and then dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-4 (S:Zn=8:1) was obtained.

[0060] Example 5

[0061] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0062] (2) Add 8.6 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h.

[0063] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-5 (S:Zn=5:1) was obtained.

[0064] Example 6

[0065] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0066] (2) Add 11 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h.

[0067] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and then dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-6 (S:Zn=4:1) was obtained.

[0068] in, Figure 1 The flowcharts show the preparation process of the catalyst materials in Examples 1-6.

[0069] Example 7

[0070] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0071] (2) Add 1.1 mg of zinc acetate dihydrate to 50 mL of anhydrous ethanol to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h.

[0072] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-1 (S:Zn=40:1) was obtained.

[0073] Example 8

[0074] (1) Grind 10 g of urea, 1 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 3°C per minute. The temperature is raised to 570°C and maintained for 90 minutes, and then cooled to room temperature.

[0075] (2) Add 1.1 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and sonicate at 70°C for 2 h.

[0076] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn-1 (S:Zn=40:1) was obtained.

[0077] Example 9

[0078] 10 g of urea and 1 g of melamine were ground into powder in a mortar and then transferred to an alumina rectangular boat. The mixture was then thermally polymerized under a nitrogen atmosphere at a heating rate of 3°C per minute, reaching 570°C and maintaining the temperature for 90 minutes. After cooling to room temperature, carbon nitride nanotubes (CNTs) were obtained.

[0079] Example 10

[0080] 10 g of urea, 1 g of melamine, and 40 mg of sodium bisulfite (250:25:1) were ground into powder in a mortar and then transferred to an alumina rectangular boat. The mixture was thermally polymerized under a nitrogen atmosphere at a heating rate of 3 °C per minute, and the temperature was raised to 570 °C and maintained for 90 minutes. After cooling to room temperature, sulfur-doped carbon nitride nanotubes (S-CNTs) were obtained.

[0081] 10 g of urea, 1 g of melamine, and 20 mg of sodium bisulfite (500:50:1) were ground into powder in a mortar and then transferred to an alumina rectangular boat. The mixture was thermally polymerized under a nitrogen atmosphere at a heating rate of 3 °C per minute, and the temperature was raised to 570 °C and maintained for 90 minutes. After cooling to room temperature, sulfur-doped carbon nitride nanotubes S-CNT-1 were obtained.

[0082] 10 g of urea, 1 g of melamine, and 80 mg of sodium bisulfite (250:25:2) were ground into powder in a mortar and then transferred to an alumina rectangular boat. The mixture was then thermally polymerized under a nitrogen atmosphere at a heating rate of 3 °C per minute, reaching 570 °C and maintaining the temperature for 90 minutes. After cooling to room temperature, sulfur-doped carbon nitride nanotubes S-CNT-2 were obtained.

[0083] 10 g of urea, 1 g of melamine, and 160 mg of sodium bisulfite (250:25:4) were ground into powder in a mortar and then transferred to an alumina rectangular boat. The mixture was then thermally polymerized under a nitrogen atmosphere at a heating rate of 3 °C per minute, reaching 570 °C and maintaining the temperature for 90 minutes. After cooling to room temperature, sulfur-doped carbon nitride nanotubes S-CNT-3 were obtained.

[0084] Among the four S-CNTs prepared with different sulfur doping ratios, the one with the mass ratio of urea:melamine:sodium bisulfite = 250:25:1 exhibited the best performance in photosynthetic hydrogen peroxide, being 1.18 times that of S-CNT-1, 1.05 times that of S-CNT-2, and 1.22 times that of S-CNT-3. This is the most suitable matrix for the subsequent impregnation-calcination process.

[0085] Example 11

[0086] (1) Grind 6 g of urea, 0.4 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 2°C per minute. The temperature is raised to 400°C and maintained for 120 minutes, and then cooled to room temperature.

[0087] (2) Add 0.5 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 20 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 50°C for 3 h.

[0088] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and then dried at 100°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 300°C at a rate of 2°C per minute under an argon atmosphere, maintained for 90 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn (S:Zn=40:1) was obtained.

[0089] Example 12

[0090] (1) Grind 14 g of urea, 1.6 g of melamine and 40 mg of sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them under a nitrogen atmosphere at a heating rate of 5°C per minute. The temperature is raised to 700°C and maintained for 60 minutes, and then cooled to room temperature.

[0091] (2) Add 2 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 80 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 90°C for 1 h.

[0092] (3) The composite material obtained in step (3) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 500°C at a rate of 8°C per minute under an argon atmosphere, maintained for 30 minutes, cooled to room temperature, removed, and the argon atmosphere was removed. Zinc single-atom uniformly dispersed and sulfur-doped S-CNT-Zn (S:Zn=40:1) was obtained.

[0093] Example 13

[0094] Performance testing of catalytic synthesis of hydrogen peroxide: 0.005 g of the prepared catalyst powder was weighed and dispersed in 100 mL of 20% (v / v) ethanol-water solution. The solution was magnetically stirred for 15 min in the dark to allow the ethanol-water solution and powder particles to reach adsorption-desorption equilibrium. The suspension was then placed in a reaction apparatus, and the photocatalytic reaction to synthesize hydrogen peroxide was carried out under visible light with a wavelength greater than 420 nm. The absorbance of the characteristic absorption peak of hydrogen peroxide at a wavelength of 350 nm was measured using iodometric titration and a UV-Vis spectrophotometer. The results are shown below. Figure 6 and 7 As shown in the figure. The results indicate that when using the catalyst prepared in Example 1 with an S:Zn ratio of 40:1, the hydrogen peroxide yield is the highest, reaching 2711 μmol g. -1 h -1 Compared to the CNTs prepared in Example 9 (154 μmol g), -1 h -1 ) and S-CNT (1155 μmol g) prepared in Example 10 -1 h -1The efficiency was increased by at least 17.6 and 2.4 times, respectively. The S-CNT-Zn prepared in Example 7 showed similar performance in the oxygen reduction photosynthesis of hydrogen peroxide as the S-CNT-Zn prepared in Example 1, with the solvent used in the impregnation process having minimal impact on the catalytic effect. The S-CNT-Zn prepared in Example 8 showed weaker performance in the oxygen reduction photosynthesis of hydrogen peroxide than the S-CNT-Zn prepared in Example 1, possibly because the ultrasonic process affected the form of zinc during impregnation, causing it to transform into zinc oxide, thus reducing the efficiency of the oxygen reduction photosynthesis of hydrogen peroxide. The S-CNT-Zn prepared in Examples 11 and 12 showed slightly weaker performance in the oxygen reduction photosynthesis of hydrogen peroxide than the S-CNT-Zn prepared in Example 1, with the temperature during thermal polymerization and calcination having little effect on the results.

[0095] Example 14

[0096] The stability of the S-CNT-Zn material prepared in Example 1 was tested. 0.0025 g of the catalyst powder prepared in Example 1 was weighed and dispersed in 50 mL of a 20% (v / v) ethanol-water solution. The solution was magnetically stirred for 15 min in the dark to allow the ethanol-water solution and powder particles to reach adsorption-desorption equilibrium. The suspension was then placed in a reaction apparatus and subjected to photocatalytic reaction to synthesize hydrogen peroxide under visible light with a wavelength greater than 420 nm. The absorbance of the characteristic absorption peak of hydrogen peroxide at a wavelength of 350 nm was measured using iodometric titration and a UV-Vis spectrophotometer. The material was then collected, washed several times with ethanol, filtered, dried, and subjected to the next cycle test. The test results are shown below. Figure 8 As shown. From Figure 8 The results show that the catalyst has good stability, and its performance did not decline after being recycled five times.

[0097] Example 15

[0098] The S-CNT-Zn material prepared in Example 1 underwent a long-term performance test for 18 hours. 0.0025 g of the catalyst powder prepared in Example 1 was weighed and dispersed in 50 mL of a 20% (v / v) ethanol-water solution. The solution was magnetically stirred for 15 min in the dark to allow the ethanol-water solution and powder particles to reach adsorption-desorption equilibrium. The suspension was then placed in a reaction apparatus, and a photocatalytic reaction to synthesize hydrogen peroxide was carried out under visible light with a wavelength greater than 420 nm. The absorbance of the characteristic absorption peak of hydrogen peroxide at a wavelength of 350 nm was measured using iodometric titration and a UV-Vis spectrophotometer. The test results are as follows: Figure 9 As shown. From Figure 9 This indicates that the catalyst has the ability to produce hydrogen peroxide stably over a long period of time.

Claims

1. A carbon nitride photocatalyst based on multiple asymmetric active sites for hydrogen peroxide production, characterized in that: Includes the following steps: (1) Grind 10 g urea, 1 g melamine and 40 mg sodium bisulfite evenly in a mortar until they are in powder form, then transfer them to an alumina rectangular boat and thermally polymerize them in a nitrogen atmosphere at a heating rate of 3°C per minute. Heat the mixture to 570°C and maintain it for 90 minutes, then cool it to room temperature. (2) Add 1.1 mg of zinc acetate dihydrate to 50 mL of N,N-dimethylformamide to form solution A. Then, uniformly disperse 40 mg of sulfur-doped carbon nitride nanotubes obtained in step (1) in 10 mL of ethanol to form mixture B. Slowly pour mixture B into solution A and stir at 70°C for 2 h. (3) The composite material obtained in step (2) was filtered, washed three times with anhydrous ethanol, and dried at 50°C overnight. The dried composite material was placed in an alumina rectangular boat, heated to 400°C at a rate of 5°C per minute under an argon atmosphere, maintained for 60 minutes, cooled to room temperature, removed and the argon atmosphere was removed. Zinc single atoms uniformly dispersed and sulfur doped S-CNT-Zn-1 were obtained, wherein the mass ratio of S:Zn was 40:

1. The prepared S-CNT-Zn photocatalyst is used in hydrogen peroxide production.

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