A sugar- pyrimidine modified carbon nitride photocatalyst, and a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic materials, and relates to a sugar-pyrimidine modified carbon nitride photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: performing hydrothermal reaction on carbon nitride, 4,6-diamino-2-mercapto pyrimidine and a sugar compound to obtain the modified carbon nitride. The catalyst can be used for photocatalytic hydrogen peroxide production. Compared with the prior art, the catalyst preparation method is simple, the modified carbon nitride product obtained has a significantly enhanced visible light and near-infrared region light absorption capacity, and can realize visible light photocatalytic hydrogen peroxide production without a sacrifice agent and pH adjustment, which is 37 times that of unmodified carbon nitride.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, and relates to a sugar-pyrimidine modified carbon nitride photocatalyst, its preparation method and application, and particularly to a sugar-pyrimidine modified carbon nitride, its preparation method and its catalytic application in the photocatalytic production of hydrogen peroxide. Background Technology

[0002] Hydrogen peroxide (H2O2) is an important chemical with significant applications in the pharmaceutical industry, chemical processing, and environmental remediation. Currently, the anthraquinone process is the primary method for H2O2 production, but it suffers from high energy consumption and high pollution. In contrast, solar-powered in-situ, sacrificial-free H2O2 production technology using water and air as feedstocks has attracted considerable attention due to its low cost and lack of secondary pollution, making it a sustainable alternative to the anthraquinone process.

[0003] Carbon nitride (Cnitride) is one of the most promising photocatalysts due to its simple synthesis, high stability, and metal-free composition. However, the photocatalytic production of H₂O₂ using Cnitride has significant drawbacks, such as low activity and the need for additional sacrificial agents. These drawbacks are mainly due to its weak light absorption, rapid recombination of photogenerated electron-hole pairs, and poor electrical conductivity. To enhance the photocatalytic production of H₂O₂ from Cnitride, researchers have conducted extensive studies on its molecular structure, including elemental doping, defect engineering, and organic molecule modification. While elemental doping and defect engineering can improve its light absorption by adjusting the band gap structure, their impact on longer wavelengths remains limited. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost, simple-to-synthesize sugar-pyrimidine modified carbon nitride photocatalyst, its preparation method, and its application, to overcome the shortcomings of the current carbon nitride photocatalytic hydrogen peroxide production technology, thereby achieving efficient H2O2 production under simple reaction conditions of visible light and pure water.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] The best way to improve light absorption is to develop narrow bandgap catalysts. Organic small molecule modification is an effective method that can easily tune the molecular and electronic structures of carbon nitride. Since carbon nitride has a small number of terminal -NH2 sites, the bandgap structure can be optimized by substituting terminal amino groups to maintain the activity of the main active sites, thereby promoting the directional transfer of electrons and holes.

[0007] The pyrimidine ring is a six-membered aromatic heterocycle that enhances electrical conductivity and is therefore present in various optically active compounds. 4,6-Diamino-2-mercaptopyrimidine is a typical polyaminopyrimidine organic compound. Under hydrothermal conditions, the dimer formed from 4,6-diamino-2-mercaptopyrimidine can be adsorbed onto the surface of carbon nitride via hydrogen bonding, increasing the number of amino groups on the modified carbon nitride surface. Since organic semiconductors have narrow band gaps, modifying carbon nitride with organic molecules presents a potential improvement strategy. Hydrothermal carbonaceous carbon (HTCC) is a carbon-based material with semiconductor properties obtained through hydrothermal treatment of biomass such as sugars, and can be used for photocatalysis. Studies have shown that this semiconductor property can be attributed to the conjugated structure of sp2-hybridized polyfurans in HTCC. The sp2-hybridized polyfuran structure can bridge with amino groups, altering the band gap structure of carbon nitride.

[0008] Based on the above technical concept, this invention provides a highly efficient sugar-pyrimidine modified carbon nitride photocatalyst, its preparation method, and its application.

[0009] The first aspect of the present invention provides a method for preparing a sugar-pyrimidine modified carbon nitride photocatalyst. This method utilizes hydrogen bonding to adsorb 4,6-diamino-2-mercaptopyrimidine onto carbon nitride to increase the number of amino groups on the surface. Then, sugars are used as crosslinking agents to react with carbon nitride and the 4,6-diamino-2-mercaptopyrimidine adsorbed on the surface of carbon nitride via a Schiff base reaction to obtain the modified carbon nitride product photocatalyst.

[0010] Specifically, this involves a hydrothermal reaction of carbon nitride, 4,6-diamino-2-mercaptopyrimidine, and a carbohydrate compound to obtain the desired product.

[0011] The carbohydrate-pyrimidine modified carbon nitride photocatalyst obtained by the preparation method of the present invention exhibits a layered stacked structure of carbon nitride, mainly manifested as a carbon nitride structure.

[0012] In this invention, the sugar-pyrimidine modified carbon nitride photocatalyst is characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and EDS-mapping. Its composition is a cross-linked polymer structure of sugar and carbon nitride adsorbed with 4,6-diamino-2-mercaptopyrimidine, and the structure is stable.

[0013] Furthermore, the carbohydrate compound is selected from at least one of glucose, sucrose, or raffinose.

[0014] Furthermore, the mass ratio of the carbon nitride, 4,6-diamino-2-mercaptopyrimidine, and sugar compound is 20:10:1-10.

[0015] Furthermore, in the hydrothermal reaction, the reaction temperature is 200-240℃, and the stirring time is preferably 12h.

[0016] Furthermore, the carbon nitride is obtained by thermal polymerization of melamine.

[0017] Furthermore, in the thermal polymerization method, carbon nitride is obtained by heating to 550-600°C in air at a rate of 5°C / min and holding at that temperature for 2 hours. There are various methods for preparing carbon nitride, including but not limited to carbon nitride prepared by this method.

[0018] A second aspect of the present invention provides a sugar-pyrimidine modified carbon nitride photocatalyst, which is prepared by the method described above.

[0019] A third aspect of the present invention provides an application of a glyco-pyrimidine modified carbon nitride photocatalyst, comprising using the glyco-pyrimidine modified carbon nitride photocatalyst for the photocatalytic production of hydrogen peroxide from water. In particular, it can catalyze the production of H2O2 from water under visible light irradiation without the presence of sacrificial agents.

[0020] Furthermore, in the reaction system, the ratio of catalyst to water is 8-12 mg: 50 mL.

[0021] Furthermore, in the reaction system, the reaction temperature is room temperature, and the light irradiation wavelength is 400-450 nm.

[0022] Furthermore, the pH of the reaction system is 3-11.

[0023] The catalyst preparation method of this invention is simple, and the modified carbon nitride product obtained has significantly enhanced light absorption capacity in the visible and near-infrared regions. Under the condition of pure water without sacrificial agents and pH adjustment, it can achieve photocatalytic production of hydrogen peroxide under visible light conditions, which is 37 times that of unmodified carbon nitride.

[0024] Compared with the prior art, the present invention has the following characteristics:

[0025] 1) The sugar-pyrimidine modified carbon nitride photocatalyst of the present invention is the first to be discovered and reported, and applied to the field of photocatalytic hydrogen peroxide production. Its precursor raw materials, sugar, 4,6-diamino-2-mercaptopyrimidine, and carbon nitride are inexpensive, the synthesis method is simple, and the reaction process is stable and does not release metal pollution.

[0026] 2) The sugar-pyrimidine modified carbon nitride photocatalyst of this invention overcomes the shortcomings of traditional carbon nitride, such as narrow absorption range and the need to add additional sacrificial agents. Its synthesis of H2O2 is simple, requiring only visible light and water.

[0027] 3) The sugar-pyrimidine modified carbon nitride photocatalyst of this invention has a wide applicable pH range for photocatalysis, and performs very well in the range of 3 to 11;

[0028] 4) The catalyst also exhibits excellent stability and can generate H2O2 in multiple cycles. Attached Figure Description

[0029] Figure 1 Examples 1-3 compare the H2O2 production performance of photocatalysts and carbon nitride under visible light and pure water conditions; where ◆ represents carbon nitride, ▲ represents pyrimidine-modified carbon nitride, ● represents glucose-modified carbon nitride, and ■ represents glucose-pyrimidine-modified carbon nitride.

[0030] Figure 2 The ultraviolet absorption spectra of the photocatalysts and carbon nitride in Examples 1-3 are shown.

[0031] Figure 3 The effect of glucose dosage on Examples 3-5 is shown; where ■ represents 10 mg of glucose, ● represents 50 mg of glucose, and ▲ represents 100 mg of glucose.

[0032] Figure 4 This is a comparison of the H2O2 production performance of different sugars on modified carbon nitride in Examples 3 and 6-7.

[0033] Figure 5 Example 3: Recycling performance of glucose-pyrimidine modified carbon nitride;

[0034] Figure 6 The recycling performance of sucrose and raffinose pyrimidine-modified carbon nitride in Examples 6-7;

[0035] Figure 7 The effect of pH conditions on the H2O2 production performance of glucose-pyrimidine modified carbon nitride in Example 3. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0037] A sugar-pyrimidine modified carbon nitride photocatalyst is prepared by subjecting carbon nitride, 4,6-diamino-2-mercaptopyrimidine, and a sugar compound to a hydrothermal reaction.

[0038] The carbohydrate compound is selected from at least one of glucose, sucrose, or raffinose.

[0039] In some specific embodiments, the mass ratio of carbon nitride, 4,6-diamino-2-mercaptopyrimidine, and sugar compound is 20:10:1-10.

[0040] In some specific embodiments, the hydrothermal reaction is carried out at a temperature of 200-240°C, and the stirring time is preferably 12 hours.

[0041] In some specific embodiments, the carbon nitride is obtained from melamine via thermal polymerization. There are various methods for preparing carbon nitride, including but not limited to those used in this method.

[0042] In some specific embodiments, the thermal polymerization method involves heating the material in air at a rate of 5°C / min to 550-600°C and holding it at that temperature for 2 hours.

[0043] An application of a glyco-pyrimidine modified carbon nitride photocatalyst includes using the glyco-pyrimidine modified carbon nitride photocatalyst for the photocatalytic production of hydrogen peroxide in aquaculture. Specifically, it can catalyze the production of H2O2 from aquaculture under visible light irradiation without the presence of sacrificial agents.

[0044] In some specific embodiments, the reaction conditions include at least one of the following:

[0045] A. The catalyst to water ratio is 8-12 mg: 50 mL.

[0046] B. The reaction temperature is room temperature, and the light wavelength is 400-450nm.

[0047] C. The pH of the reaction system is 3-11.

[0048] This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0049] The following are more detailed implementation examples, which further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0050] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0051] In the following examples, carbon nitride was prepared by thermal polymerization: it was heated to 600°C in air at a rate of 5°C / min and held for 2 hours.

[0052] Example 1

[0053] A method for preparing a pyrimidine-modified carbon nitride photocatalyst, the method comprising the following steps:

[0054] 200 mg of carbon nitride and 100 mg of 4,6-diamino-2-mercaptopyrimidine were dispersed in 30 mL of water and stirred for 30 min. The mixture was then transferred to a hydrothermal reactor, sealed, and heat-treated at 200 °C for 12 h. The precipitate was collected, washed, and dried to obtain the pyrimidine-modified carbon nitride photocatalyst.

[0055] Example 2

[0056] A method for preparing a glucose-modified carbon nitride photocatalyst, the method comprising the following steps:

[0057] 200 mg of carbon nitride and 50 mg of glucose were dispersed in 30 mL of water and stirred for 30 min. The mixture was then transferred to a hydrothermal reactor, sealed, and heat-treated at 200 °C for 12 h. The precipitate was collected, washed, and dried to obtain glucose-modified carbon nitride photocatalyst.

[0058] Example 3

[0059] A method for preparing a glucose-pyrimidine modified carbon nitride photocatalyst, the method comprising the following steps:

[0060] 200 mg of carbon nitride, 100 mg of 4,6-diamino-2-mercaptopyrimidine, and 50 mg of glucose were dispersed in 30 mL of water and stirred for 30 min. The mixture was then transferred to a hydrothermal reactor, sealed, and heat-treated at 200 °C for 12 h. The precipitate was collected, washed, and dried to obtain glucose-pyrimidine modified carbon nitride photocatalyst.

[0061] Example 4

[0062] A method for preparing a glucose-pyrimidine modified carbon nitride photocatalyst differs from Example 3 only in that the amount of glucose added is 10 mg. The rest is the same as in Example 3.

[0063] Example 5

[0064] A method for preparing a glucose-pyrimidine modified carbon nitride photocatalyst differs from Example 3 only in that the amount of glucose added is 100 mg. The rest is the same as in Example 3.

[0065] Example 6

[0066] A method for preparing a sucrose-pyrimidine modified carbon nitride photocatalyst differs from Example 3 only in that glucose is replaced with sucrose. The rest is the same as in Example 3.

[0067] Example 7

[0068] A method for preparing a raffinose-pyrimidine modified carbon nitride photocatalyst differs from Example 3 in that glucose is replaced with raffinose. The rest is the same as in Example 3.

[0069] Performance characterization:

[0070] I. Performance of visible light photocatalytic hydrogen peroxide production

[0071] Add 10 mg of carbon nitride or the catalyst prepared in Examples 1-7, along with 50 mL of ultrapure water, to an open beaker and ultrasonically disperse for 15 min. Start timing from the time of irradiation with a xenon lamp (300 W, with a 420 nm cutoff filter), take samples at the set time points for filtration, and analyze the hydrogen peroxide concentration in the filtrate using ultraviolet light.

[0072] The photocatalytic hydrogen peroxide production effect of all samples Figure 1 , 3 As shown in -4.

[0073] Figure 1 This indicates that unmodified carbon nitride has a very weak ability to produce H2O2 under pure water and visible light conditions, with an H2O2 yield of only 2.7 μmol L. -1 h -1 4,6-Diamino-2-mercaptopyrimidine and glucose both enhance the photocatalytic effect of carbon nitride. Notably, the simultaneous addition of both results in the optimal photocatalytic H₂O₂ production, reaching 56.8 μmol L⁻¹ h⁻¹, which is 21 times that of unmodified carbon nitride. This is mainly due to the surface modification of the surface by the hybrid structure formed by the reaction of the hydrothermal formation of glucose (polyfuran) with carbon nitride and the Schiff base of 4,6-diamino-2-mercaptopyrimidine, providing a narrower band gap. Figure 2 As shown, this gives carbon nitride a strong ability to absorb visible light. Analysis of the band gap structure indicates that glucose-pyrimidine modified carbon nitride mainly produces H₂O₂ through the oxygen reduction reaction.

[0074] Figure 3 The effect of different glucose dosages on the photocatalytic performance of the catalyst was investigated. It can be seen that the H2O2 production capacity increases with increasing glucose dosage, but the overall effect is not significant. Therefore, 50 mg was selected as the optimal dosage.

[0075] Figure 4 This indicates that different sugars can react with carbon nitride and 4,6-diamino-2-mercaptopyrimidine Schiff bases to modify carbon nitride. After modification with sucrose and raffinose as precursors, carbon nitride showed better results than glucose-pyrimidine modification, with photocatalytic H2O2 production reaching 63.9 μmol L⁻¹h⁻¹ and 99.2 μmol L⁻¹h⁻¹, respectively, which are 24 and 37 times that of unmodified carbon nitride.

[0076] II. Cyclic catalytic performance (multiple reuses of photocatalytic hydrogen peroxide production)

[0077] 1. Glucose-pyrimidine modified carbon nitride photocatalyst

[0078] The catalyst prepared in Example 3 and 50 mL of ultrapure water were added to an open beaker, ultrasonically dispersed for 15 min, and then stirred for 15 min in the dark to reach adsorption-desorption equilibrium. Starting from the time of irradiation by a xenon lamp (300W, with a 420 nm cutoff filter), samples were taken and filtered at the set time points, and the concentration of hydrogen peroxide in the filtrate was obtained by ultraviolet testing and analysis.

[0079] After reacting for 1 hour, the catalyst was filtered and washed three times with ethanol, then dried at 60°C for 6 hours to obtain a reusable catalyst. The above steps were repeated 6 times.

[0080] Experimental results are as follows Figure 5 As shown, after six cycles, the glucose-pyrimidine modified carbon nitride still exhibited a high photocatalytic H2O2 yield without significant decrease. This indicates that the copolymerization of glucose on pyrimidine and carbon nitride enhances the stability of the composite sample.

[0081] 2. Sucrose / raffinose-pyrimidine modified carbon nitride photocatalyst

[0082] Add 10 mg of the catalyst from Examples 6-7 and 50 mL of ultrapure water to an open beaker. Sonicate the dispersion for 15 min, then stir for 15 min in the dark to reach adsorption-desorption equilibrium. Starting from the time of irradiation with a xenon lamp (300 W, with a 420 nm cutoff filter), samples were taken and filtered at the set time points. The concentration of hydrogen peroxide in the filtrate was obtained by UV testing and analysis.

[0083] After reacting for 1 hour, the catalyst obtained was filtered and washed three times with ethanol, and dried at 60°C for 6 hours to obtain a reusable catalyst. The above steps were repeated 5 times.

[0084] Experimental results are as follows Figure 6 As shown, after five cycles of testing, the active sites of the sucrose-pyrimidine modified and raffinose-pyrimidine modified samples were 40.1 and 52.5 μmol L, respectively. -1 h -1 Although raffinose-modified carbon nitride exhibited higher initial photocatalytic activity, its activity decreased significantly after the first use, but remained relatively stable from the second to the fifth cycle. XRD characterization before and after the reaction revealed impurity peaks in the raffinose-pyrimidine-modified carbon nitride before the reaction, possibly due to unbonded raffinose on the carbon nitride surface. However, these impurity peaks disappeared after the reaction, indicating that the raffinose no longer existed on the catalyst surface. Compared to sucrose and raffinose as sugar precursors, glucose-pyrimidine-modified carbon nitride demonstrated better stability.

[0085] III. Effect of Acidity / Alkalinity of the Reaction System (Effect of Different pH Conditions on the Photocatalytic Production of Hydrogen Peroxide by Glucose-Pyrimidine Modified Carbon Nitride)

[0086] 10 mg of the catalyst from Example 3 and 50 mL of ultrapure water were added to an open beaker. The initial pH of the dispersion was adjusted to 3–11 using sulfuric acid and sodium hydroxide. The dispersion was sonicated for 15 min and then stirred for 15 min in the dark to reach adsorption-desorption equilibrium. Starting from the time of irradiation by a xenon lamp (300 W, with a 420 nm cutoff filter), samples were taken and filtered at the set time points. The concentration of hydrogen peroxide in the filtrate was obtained by ultraviolet testing and analysis.

[0087] Photocatalytic performance diagram as shown Figure 7As shown, the results indicate that the catalyst exhibits excellent pH stability, maintaining a good hydrogen peroxide yield even at a pH of 11.

[0088] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a sugar-pyrimidine modified carbon nitride photocatalyst, characterized in that, include: Carbon nitride, 4,6-diamino-2-mercaptopyrimidine, and a sugar compound were subjected to a hydrothermal reaction at 200-240°C to obtain the following: The carbohydrate compound is selected from at least one of glucose, sucrose, or raffinose.

2. The method for preparing the sugar-pyrimidine modified carbon nitride photocatalyst according to claim 1, characterized in that, The mass ratio of carbon nitride, 4,6-diamino-2-mercaptopyrimidine, and sugar compounds is 20:10:1-10.

3. A sugar-pyrimidine modified carbon nitride photocatalyst, characterized in that, It is prepared by the method described in claim 1 or 2.

4. The application of the sugar-pyrimidine modified carbon nitride photocatalyst as described in claim 3, characterized in that, The aforementioned sugar-pyrimidine modified carbon nitride photocatalyst is used for the photocatalytic production of hydrogen peroxide from water.

5. The application of the sugar-pyrimidine modified carbon nitride photocatalyst according to claim 4, characterized in that, In the reaction system, the reaction temperature is room temperature and the light wavelength is 400-450 nm.

6. The application of the sugar-pyrimidine modified carbon nitride photocatalyst according to claim 5, characterized in that, The pH of the reaction system is 3-11.

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