G-C3N4 photocatalyst, preparation method thereof and application of g-C3N4 photocatalyst in urea production
By using g-C3N4 photocatalysts doped with metal elements, the problem of low efficiency in the photocatalytic preparation of urea in existing technologies has been solved. It has achieved efficient catalytic co-reduction of CO2 and NO to produce urea under mild conditions, which improves the yield and selectivity of urea and simplifies the preparation process.
Patent Information
- Application Number
- CN202511185829.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-22
- Publication Date
- 2025-12-12
AI Technical Summary
In the existing technology, the method of preparing urea by photocatalytic reduction using NO and CO2 as raw materials has problems such as high overpotential and low catalytic efficiency, and the activation of N2 is difficult, which limits the production of urea.
The g-C3N4 photocatalyst, doped with metal elements such as K, Li, Na, Zn, Co, Fe, Ni, Mn, Cu, Sn and Bi, is used to activate CO2 and NO to produce urea through photocatalytic activation. The metal atoms are used as adsorption and activation sites, and the defect structure of the catalyst is combined to improve the catalytic activity and selectivity.
This method efficiently catalyzes the co-reduction of CO2 and NO to produce urea under mild conditions, improving urea yield and selectivity, reducing byproduct formation, and employing a simple preparation process that is easy to industrialize.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of photocatalysts, in particular to a g-C3N4 photocatalyst, a preparation method thereof and an application thereof in urea production. BACKGROUND
[0002] Urea (CO(NH2)2) is an essential nitrogen fertilizer for human society and is also used as a chemical raw material in various industries. The industrial urea synthesis process path is composed of the Haber-Bosch process for producing ammonia and the subsequent Bosch-Meiser process for producing urea. The synthesis of ammonia based on the Haber-Bosch process requires severe reaction conditions, and the energy consumption for synthesizing ammonia accounts for about 2% of the world's energy consumption every year. Therefore, it has broad application prospects to use renewable energy to carry out nitrogen fixation under mild conditions.
[0003] Considering the high energy consumption of industrial ammonia synthesis (Haber-Bosch), it is imperative to develop alternative nitrogen-containing reactants for urea electro-synthesis. Since the 1990s, people have begun to use nitrate and nitrite (NO3 - / NO2 - ) as a nitrogen source to couple with CO2 for urea electro-synthesis. However, the conversion of nitrate to urea requires a complex 16-electron reduction process, and the instability of nitrite limits the development and application potential of this technology. In addition, the trade-off relationship between Faraday efficiency and current density also hinders the output of urea synthesis using nitrate / nitrite as a nitrogen source.
[0004] In recent years, some researchers have creatively used nitrogen (N2) and CO2 to achieve urea electro-synthesis. However, the activation of N2 is difficult (activation energy is as high as 940.95 kJ / mol), the solubility of N2 is low (K H = 6.24 x 10 -4 mol / L / atm), and it competes with the hydrogen evolution reaction (HER), which hinders the output of urea. Therefore, it is necessary to have an active nitrogen source that is more easily available and has a considerable yield.
[0005] NO in flue gas nitrogen oxides is a key intermediate for the electro-reduction of nitrate / nitrite, and the electro-synthesis of urea by coupling CO2 with a nitrogen source provided by NO is a promising new technology. However, the electro-synthesis method still has problems such as high overpotential and low catalytic efficiency.
[0006] Photocatalysis is a process that uses sunlight to directly excite a semiconductor catalyst to produce photo-generated electrons and holes, and the photo-generated electrons can reduce the reaction substrate to obtain the target product. Photocatalysis has many advantages such as mild reaction conditions and simple process. There are few reports on the preparation of urea by photocatalytic reduction using NO and CO2 as raw materials, and further research is needed. SUMMARY
[0007] The present application aims to at least partially solve the technical problems existing in the prior art. To this end, the present application proposes a g-C3N4 photocatalyst, a preparation method thereof, an application thereof in the production of urea, and a method for producing urea. The g-C3N4 photocatalyst of the present application has high photocatalytic activity and can be controlled and adjusted, can efficiently catalyze CO2 and NO to produce urea, and can improve the yield and selectivity of urea. Under mild conditions (without external heating or electricity), the effects of carbon sequestration and nitrogen fixation can be achieved simultaneously. Moreover, the preparation process is simple, the energy consumption is low, and industrialization is easy to realize.
[0008] In one aspect of the present application, the present application proposes a g-C3N4 photocatalyst. According to an embodiment of the present application, the g-C3N4 photocatalyst comprises a g-C3N4 matrix and a doping element, and the doping element comprises at least five of K, Li, Na, Zn, Co, Fe, Ni, Mn, Cu, Sn and Bi.
[0009] The g-C3N4 photocatalyst of the present application is doped with at least five metal elements, providing abundant active catalytic sites. Alkali metal atoms such as K, Li and Na can act as an electronic bridge between the g-C3N4 layers, accelerating the interlayer charge transfer; metal atoms such as Zn, Co, Fe, Ni, Mn, Cu, Sn and Bi can act as adsorption sites and activation sites for CO2 and NO. Thus, the photocatalytic activity can be effectively improved, so that the co-reduction of NO and CO2 can be effectively photocatalyzed to produce urea, the yield and selectivity of urea can be improved, and the generation of by-products can be reduced.
[0010] According to an embodiment of the present application, the g-C3N4 photocatalyst described above can also have the following additional technical features: According to an embodiment of the present application, the molar ratio of each of the doping elements is the same.
[0011] According to an embodiment of the present application, the g-C3N4 matrix contains defects, and the defects include at least one of C defects and N defects.
[0012] In another aspect of the present application, the present application proposes a method for preparing the aforementioned g-C3N4 photocatalyst. According to an embodiment of the present application, the method comprises: performing a first calcination treatment on a g-C3N4 precursor in a defect atmosphere to obtain a g-C3N4 containing defects; mixing the g-C3N4 containing defects, a metal precursor and a solvent, evaporating and drying to obtain a mixture precursor, and the metal precursor comprises a metal soluble salt containing the at least five doping elements; performing a second calcination treatment on the mixture precursor to obtain the g-C3N4 photocatalyst.
[0013] According to embodiments of the present application, the metal-soluble salt comprises at least one of hydrochloride, nitrate, sulfate, and acetate.
[0014] According to embodiments of the present application, the mass ratio of the g-C3N4 precursor to the metal precursor is 100: (0.5-10).
[0015] According to embodiments of the present application, the concentration of the metal precursor in the mixture of the metal precursor and the solvent is 0.1 mg / L-100 mg / L.
[0016] According to embodiments of the present application, the calcination atmosphere of the first calcination treatment and the second calcination treatment is independently at least one of air, ammonia, hydrogen, and hydrogen-argon mixture; the calcination temperature is independently 400°C-600°C; and the calcination time is independently 0.5 h-3 h.
[0017] According to embodiments of the present application, after the first calcination treatment, the obtained calcination product is cooled to room temperature, ground, and washed by centrifugation with deionized water and an organic solvent, and dried to obtain the g-C3N4 containing defects.
[0018] According to embodiments of the present application, after the second calcination treatment, the obtained calcination product is cooled to room temperature, ground, and washed by centrifugation with deionized water and an organic solvent, and dried to obtain the g-C3N4 photocatalyst.
[0019] According to embodiments of the present application, the organic solvent comprises anhydrous ethanol.
[0020] In another aspect of the present application, the present application provides an application of the above-mentioned g-C3N4 photocatalyst or the g-C3N4 photocatalyst prepared by the above-mentioned method for preparing a g-C3N4 photocatalyst in the production of urea. The g-C3N4 photocatalyst of the present application has high photocatalytic activity and controllable adjustment, and can efficiently catalyze the production of urea from CO2 and NO, thereby improving the yield and selectivity of urea.
[0021] According to embodiments of the present application, the urea is prepared by photocatalytic co-reduction of NO and CO2.
[0022] In another aspect of the present application, the present application provides a method for producing urea. According to embodiments of the present application, the method comprises: using the above-mentioned g-C3N4 photocatalyst or the g-C3N4 photocatalyst prepared by the above-mentioned method for preparing a g-C3N4 photocatalyst to photocatalyze the co-reduction of NO and CO2, thereby obtaining urea. The g-C3N4 photocatalyst of the present application has high photocatalytic activity and controllable adjustment, and can efficiently catalyze the production of urea from CO2 and NO, thereby improving the yield and selectivity of urea.
[0023] According to the embodiment of the present application, the method comprises: placing the g-C3N4 photocatalyst, the sacrificial agent and water in a reactor, mixing uniformly; introducing CO2 into the reactor, exhausting air, introducing NO again, and maintaining a preset pressure of the reactor, and performing light treatment to obtain urea.
[0024] According to the embodiment of the present application, the sacrificial agent is selected from compounds that can dissociate protons; and the sacrificial agent comprises at least one of methanol, ethanol, isopropanol, ethylene glycol and benzyl alcohol.
[0025] According to the embodiment of the present application, the volume ratio of the sacrificial agent to water is (1:9)~(9:1).
[0026] According to the embodiment of the present application, the flow ratio of CO2 to NO is (10:1)~(1:10).
[0027] According to the embodiment of the present application, the preset pressure is 1~5 atm.
[0028] According to the embodiment of the present application, the light treatment adopts natural light or simulated sunlight.
[0029] According to the embodiment of the present application, the light treatment time is 4~12 h.
[0030] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS
[0031] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings. Figure 1 SEM images of the high-entropy doped g-C3N4 containing defects prepared for Example 1, (a) scale 5 μm, (b) scale 500 nm; Figure 2 XRD images of the high-entropy doped g-C3N4 containing defects prepared for Example 1. DETAILED DESCRIPTION
[0032] It should be noted that the terms "first", "second" are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. Further, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.
[0033] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the application. Any numeric range recited is intended to include all values from the lower value to the upper value, inclusive of both values, and to sub-ranges falling within the specified range. In this context, individual points within a range should not be discounted as they can be used in combination with other points to define a new range. The endpoints of the ranges and any value are not limited to the precise value recited as the exact dimensions are not critical to the application.
[0034] The present application provides a g-C3N4 photocatalyst, a preparation method and application thereof, and a method for producing urea. The g-C3N4 photocatalyst, the preparation method and application thereof, and the method for producing urea will be described in detail below.
[0035] g-C3N4 photocatalyst In one aspect of the present application, the present application provides a g-C3N4 photocatalyst. According to an embodiment of the present application, the g-C3N4 photocatalyst comprises a g-C3N4 matrix and a doping element, and the doping element comprises at least five of K, Li, Na, Zn, Co, Fe, Ni, Mn, Cu, Sn and Bi.
[0036] The g-C3N4 photocatalyst of the present application is doped with at least five metal elements, providing abundant active catalytic sites. Alkali metal atoms such as K, Li and Na can act as an electronic bridge between the g-C3N4 layers, accelerating the interlayer charge transfer. Metal atoms such as Zn, Co, Fe, Ni, Mn, Cu, Sn and Bi can act as adsorption sites and activation sites for CO2 and NO. Thus, the photocatalytic activity can be effectively improved, and the co-reduction of NO and CO2 to produce urea can be effectively photocatalyzed, the yield and selectivity of urea can be improved, and the generation of by-products can be reduced.
[0037] According to an embodiment of the present application, the molar ratio of each of the doping elements is the same. Thus, a high-entropy doped g-C3N4 is obtained, which can effectively improve the photocatalytic activity.
[0038] According to an embodiment of the present application, the g-C3N4 matrix contains defects, and the defects comprise at least one of C defects and N defects. Due to the lack of atoms at the defects, the charge distribution is unbalanced, which can firmly adsorb NO and CO2 on the surface of the catalyst, stretch and weaken the N=O and C=O bonds in NO and CO2, and reduce the reaction energy barrier. C defects and N defects can enhance light absorption, adjust the band gap structure, enhance the separation of photo-generated electron / hole pairs, and accelerate electron transfer. Metal atoms and C / N defects act as active sites for CO2 and NO, which can improve the photocatalytic performance and efficiently catalyze the co-reduction of NO and CO2 to generate urea. Furthermore, by adjusting the types / contents of metal atoms and defects, the band gap structure of carbon nitride can be adjusted to achieve the adjustment of photocatalytic performance.
[0039] Method for preparing g-C3N4 photocatalyst In another aspect of the present application, the present application provides a method for preparing the above-mentioned g-C3N4 photocatalyst. According to an embodiment of the present application, the method comprises: subjecting a g-C3N4 precursor to a first calcination treatment in a defect atmosphere to obtain a g-C3N4 containing defects; mixing the g-C3N4 containing defects, a metal precursor and a solvent, evaporating and drying to obtain a mixture precursor, the metal precursor comprising a metal soluble salt containing the at least five kinds of doping elements; and subjecting the mixture precursor to a second calcination treatment to obtain the g-C3N4 photocatalyst.
[0040] During the first calcination treatment, under the action of heat driving, the C or N atoms constituting the g-C3N4 skeleton react to form vacancies, i.e. defects. The defects lack atoms, the charge distribution is unbalanced, and can firmly adsorb NO and CO2 on the surface of the catalyst, and stretch and weaken the N=O and C=O bonds in NO and CO2, thereby reducing the reaction energy barrier. Thus, the photocatalytic performance can be improved, and NO and CO2 can be efficiently co-reduced to generate urea. During the second calcination treatment, the metal elements can be doped into the precursor to form the g-C3N4 photocatalyst.
[0041] According to an embodiment of the present application, the metal soluble salt comprises at least one of hydrochloride, nitrate, sulfate and acetate.
[0042] According to an embodiment of the present application, the mass ratio of the g-C3N4 precursor to the metal precursor is 100: (0.5-10). In some embodiments, the mass ratio of the g-C3N4 precursor to the metal precursor is 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10. Thus, the obtained photocatalyst has better photocatalytic activity.
[0043] According to an embodiment of the present application, the concentration of the metal precursor in the mixed solution of the metal precursor and the solvent is 0.1 mg / L-100 mg / L. In some embodiments, the concentration of the metal precursor is 0.1 mg / L, 1 mg / L, 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L.
[0044] According to an embodiment of the present application, the calcination atmosphere of the first calcination treatment and the second calcination treatment is independently at least one of air, ammonia, hydrogen and hydrogen-argon mixed gas.
[0045] According to embodiments of the present application, the calcination temperature is independently 400-600°C, exemplarily 400°C, 420°C, 450°C, 460°C, 500°C, 520°C, 550°C, 560°C, 600°C; the calcination time is independently 0.5-3h, exemplarily 0.5h, 1h, 1.5h, 2h, 2.5h, 3h. Thus, the obtained photocatalyst has better photocatalytic activity.
[0046] According to embodiments of the present application, after the first calcination treatment, the obtained calcination product is cooled to room temperature, grinded and washed with deionized water and organic solvent by centrifugation, dried to obtain the g-C3N4 containing defects. Thus, the unreacted precursors, soluble impurities and weakly adsorbed particles are thoroughly washed away, improving the purity of g-C3N4 containing defects.
[0047] According to embodiments of the present application, after the second calcination treatment, the obtained calcination product is cooled to room temperature, grinded and washed with deionized water and organic solvent by centrifugation, dried to obtain the g-C3N4 photocatalyst. Thus, the unreacted precursors, soluble impurities and weakly adsorbed particles are thoroughly washed away, improving the purity of g-C3N4 photocatalyst.
[0048] According to embodiments of the present application, the organic solvent includes anhydrous ethanol. Thus, in order to fully remove unreacted substances, impurities and particles, and avoid damaging the performance of g-C3N4 containing defects and g-C3N4 photocatalyst.
[0049] It should be noted that the features and advantages described above for the g-C3N4 photocatalyst also apply to the method, which will not be repeated here.
[0050] Application In another aspect of the present application, the present application provides an application of the above-mentioned g-C3N4 photocatalyst or the g-C3N4 photocatalyst prepared by the above-mentioned method for producing urea. The g-C3N4 photocatalyst of the present application has high and controllable photocatalytic activity, can efficiently catalyze the production of urea from CO2 and NO, and improve the yield and selectivity of urea.
[0051] According to embodiments of the present application, the urea is prepared by photocatalytic co-reduction of NO and CO2.
[0052] It should be noted that the features and advantages described above for the g-C3N4 photocatalyst and its preparation method also apply to the application, which will not be repeated here.
[0053] Method for producing urea In another aspect of the present application, a method for producing urea is provided. According to an embodiment of the present application, the method comprises: using the g-C3N4 photocatalyst described above or the g-C3N4 photocatalyst prepared by the method described above, photocatalyzing the co-reduction of NO and CO2 to obtain urea. The g-C3N4 photocatalyst of the present application has high photocatalytic activity and can be controlled and adjusted, and can efficiently catalyze the production of urea from CO2 and NO, thereby improving the yield and selectivity of urea.
[0054] According to an embodiment of the present application, the method comprises: placing the g-C3N4 photocatalyst, a sacrificial agent and water in a reactor, mixing uniformly; introducing CO2 into the reactor, exhausting air, introducing NO, and maintaining a predetermined pressure in the reactor, and performing light treatment to obtain urea.
[0055] According to an embodiment of the present application, the sacrificial agent is selected from a compound that can dissociate protons; and the sacrificial agent comprises at least one of methanol, ethanol, isopropanol, ethylene glycol, and benzyl alcohol. The use of the sacrificial agent can improve the solubility of NO, and the sacrificial agent can be oxidized by photo-generated holes to generate protons required in the synthesis of urea, thereby improving the yield of urea.
[0056] According to an embodiment of the present application, the flow ratio of CO2 to NO is (10:1)~(1:10). Thereby, the reaction can be fully carried out to achieve high urea yield.
[0057] According to an embodiment of the present application, the volume ratio of the sacrificial agent to water is (1:9)~(9:1). In some embodiments, the volume ratio of the sacrificial agent to water is 1:9, 1:8, 1:5, 1:2, 1:1, 2:1, 4:1, 5:1, 6:1, 8:1, or 9:1. Thereby, the solubility of NO can be better improved, and the yield of urea can be improved.
[0058] According to an embodiment of the present application, the predetermined pressure is 1~5 atm. In some embodiments, the predetermined pressure is 1 atm, 1.5 atm, 2 atm, 2.5 atm, 3 atm, 3.5 atm, 4 atm, 4.5 atm, or 5 atm. Thereby, the reaction can be fully carried out to achieve high urea yield.
[0059] According to an embodiment of the present application, the light treatment uses natural light or simulated sunlight.
[0060] According to an embodiment of the present application, the light treatment is performed for 4~12 h. In some embodiments, the light treatment is performed for 4 h, 5 h, 6 h, 8 h, 10 h, or 12 h. Thereby, the co-reduction of NO and CO2 under the action of the g-C3N4 photocatalyst can be fully carried out, thereby improving the yield of urea.
[0061] It should be noted that the features and advantages described above for the g-C3N4 photocatalyst and the preparation method thereof are also applicable to the method, which will not be repeated here.
[0062] The scheme of the present application will be explained below in conjunction with examples. Those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific technology or condition is not specified in the examples, it is carried out according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase in the market.
[0063] Example 1 A preparation method of high-entropy doped g-C3N4, comprising the following steps: S1, a certain amount of melamine is weighed, calcined in air atmosphere at 405℃ for 0.5h, then cooled to room temperature, washed repeatedly with deionized water and anhydrous ethanol by centrifugation, and dried to obtain N-deficient g-C3N4; S2, 10mg of N-deficient g-C3N4 obtained in step S1 is immersed in 10mL of aqueous solution containing Zn, Co, Fe, Ni, Cu nitrate with a concentration of 10mg / L, fully stirred, evaporated, dried, and ground to form a mixture precursor; S3, the mixture precursor obtained in step S2 is calcined in air atmosphere at 550℃ for 3h, then cooled to room temperature, ground, washed repeatedly with deionized water and anhydrous ethanol by centrifugation, and dried to obtain N-deficient Zn, Co, Fe, Ni, Cu co-doped g-C3N4.
[0064] Example 2 A preparation method of high-entropy doped g-C3N4, comprising the following steps: S1, a certain amount of melamine is weighed, calcined in air atmosphere at 405℃ for 2h, then cooled to room temperature, washed repeatedly with deionized water and anhydrous ethanol by centrifugation, and dried to obtain N-deficient g-C3N4; S2, 10mg of N-deficient g-C3N4 obtained in step S1 is immersed in 10mL of aqueous solution containing Zn, Co, Fe, Ni, Cu acetate with a concentration of 5mg / L, fully stirred, evaporated, dried, and ground to form a mixture precursor; S3, the mixture precursor obtained in step S2 is calcined in air atmosphere at 550℃ for 2h, then cooled to room temperature, ground, washed repeatedly with deionized water and anhydrous ethanol by centrifugation, and dried to obtain N-deficient Zn, Co, Fe, Ni, Cu co-doped g-C3N4.
[0065] Example 3 A preparation method of high-entropy doped g-C3N4, comprising the following steps: S1, a certain amount of melamine is weighed, calcined in hydrogen atmosphere at 550°C for 3h, then cooled to room temperature, ground and washed repeatedly with deionized water and anhydrous ethanol by centrifugation, and dried to obtain N-deficient g-C3N4; S2, 10mg of N-deficient g-C3N4 obtained in step S1 is immersed in 10mL of aqueous solution of Zn, Co, Fe, Ni, Cu and Mn nitrate with a concentration of 10mg / L, fully stirred, evaporated, dried, ground and formed into a mixture precursor; S3, the mixture precursor obtained in step S2 is calcined in air atmosphere at 550°C for 0.5h, then cooled to room temperature, ground and washed repeatedly with deionized water and anhydrous ethanol by centrifugation, and dried to obtain Zn, Co, Fe, Ni, Cu and Mn co-doped g-C3N4 containing N defects.
[0066] Example 4 A preparation method of high-entropy doped g-C3N4, comprising the following steps: S1, a certain amount of melamine is weighed, calcined in ammonia atmosphere at 500°C for 1h, then cooled to room temperature, and ground to obtain C-deficient and N-deficient g-C3N4; S2, 10mg of C-deficient and N-deficient g-C3N4 obtained in step S1 is immersed in 10mL of aqueous solution of K, Zn, Co, Fe and Bi hydrochloride with a concentration of 0.1mg / L, fully stirred, evaporated, dried, ground and formed into a mixture precursor; S3, the mixture precursor obtained in step S2 is calcined in air atmosphere at 550°C for 1h, then cooled to room temperature, ground and washed repeatedly with deionized water and anhydrous ethanol by centrifugation, and dried to obtain K, Zn, Co, Fe and Bi co-doped g-C3N4 containing C defects and N defects.
[0067] Example 5 A preparation method of high-entropy doped g-C3N4, comprising the following steps: S1, a certain amount of melamine is weighed, calcined in 10% H2 / Ar mixed gas atmosphere (hydrogen accounts for 10% of the volume of hydrogen and argon mixed gas) at 600°C for 3h, then cooled to room temperature, and ground to obtain N-deficient g-C3N4; S2, 10mg of N-deficient g-C3N4 obtained in the above step is immersed in 10mL of aqueous solution of Li, Na, K, Sn and Mn sulfate with a concentration of 100mg / L, fully stirred, evaporated, dried, ground and formed into a mixture precursor; S3, the mixture precursor obtained in step S2 was calcined in air atmosphere at 550℃ for 0.5h, then cooled to room temperature, washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and dried to obtain N-defect-containing Li, Na, K, Sn, Mn co-doped g-C3N4.
[0068] Comparative Example 1 A certain amount of melamine was weighed, calcined in air atmosphere at 405℃ for 2h, then cooled to room temperature, washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and dried to obtain N-defect-containing g-C3N4.
[0069] Comparative Example 2 S1, a certain amount of melamine was weighed, calcined in air atmosphere at 405℃ for 2h, then cooled to room temperature, washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and dried to obtain N-defect-containing g-C3N4; S2, 10g of N-defect-containing g-C3N4 obtained in step S1 was immersed in 10mL of aqueous solution containing potassium nitrate with a concentration of 10mg / L, stirred thoroughly, evaporated, dried, and ground to form a mixture precursor; S3, the mixture precursor obtained in step S2 was calcined in air atmosphere at 550℃ for 3h, then cooled to room temperature, washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and dried to obtain N-defect-containing K-doped g-C3N4.
[0070] Comparative Example 3 S1, a certain amount of melamine was weighed, calcined in air atmosphere at 405℃ for 2h, then cooled to room temperature, washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and dried to obtain N-defect-containing g-C3N4; S2, 10g of N-defect-containing g-C3N4 obtained in step S1 was immersed in 10mL of aqueous solution containing K, Bi nitrate with a concentration of 10mg / L, stirred thoroughly, evaporated, dried, and ground to form a mixture precursor; S3, the mixture precursor obtained in step S2 was calcined in air atmosphere at 550℃ for 3h, then cooled to room temperature, washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and dried to obtain N-defect-containing K, Bi co-doped g-C3N4.
[0071] Comparative Example 4 S1, a certain amount of melamine was weighed, calcined in air atmosphere at 405℃ for 2h, then cooled to room temperature, washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and dried to obtain N-defect-containing g-C3N4; S2, 10 g of N-defect g-C3N4 obtained in step S1 was dipped in 10 mL of an aqueous solution containing K, Bi, and Zn nitrate with a concentration of 10 mg / L, and was fully stirred. After evaporation, drying, and grinding, a mixture precursor was formed. S3, the mixture precursor obtained in step S2 was calcined in an air atmosphere at 550°C for 3 h, and then cooled to room temperature. After grinding, the product was repeatedly washed by centrifugation with deionized water and anhydrous ethanol, and was dried to obtain N-defect K, Bi, and Zn co-doped g-C3N4.
[0072] Test Example 1 The high-entropy doped g-C3N4 prepared in Examples 1-5 was subjected to scanning electron microscope and X-ray diffraction detection, respectively. The SEM image of Example 1 is shown in FIG. 1, and the XRD image is shown in FIG. 2. As can be seen from FIG. 1, the high-entropy doped N-defect g-C3N4 prepared has an irregular porous structure. As can be seen from FIG. 2, the high-entropy doped N-defect g-C3N4 prepared has characteristic peaks of graphite phase carbon nitride at 2θ of 13.3°, 27.4°, and 44.3°, and no other impurity peaks exist, indicating that the metal elements may be doped into the crystal lattice of carbon nitride. Figure 1 Figure 2 Figure 2
[0073] Test Example 2 The high-entropy doped g-C3N4 prepared in Examples 1-5 and Comparative Examples 1-4 was used as a photocatalyst to produce urea, and the specific steps were as follows: 50 mg of g-C3N4 photocatalyst was added to a quartz reactor containing 100 mL of a methanol / water (volume ratio 1:1) mixed solvent, and was continuously stirred. The reactor was purged with CO2 for 30 min, and air was discharged. Subsequently, NO was introduced, and the flow ratio of CO2 / NO was 1:1. The reactor was maintained at a pressure of 1 atm, and then a 300 W xenon lamp was used to simulate sunlight for 4 h to perform a photocatalytic reaction to prepare urea.
[0074] The urea yield and selectivity are shown in Table 1. Compared with N-defect g-C3N4, N-defect K-doped g-C3N4, N-defect K and Bi co-doped g-C3N4, and N-defect K, Bi, and Zn co-doped g-C3N4, the high-entropy doped N-defect g-C3N4 showed significantly enhanced catalytic activity and significantly improved urea yield and selectivity, which may be attributed to the synergistic effect of multi-metal doping, rich defects, and developed pore structure.
[0075] Table 1: Urea yield and selectivity
[0076] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that changes, modifications, substitutions and variations can be made by those skilled in the art without departing from the scope of the present application.
Claims
1. A g-C3N4 photocatalyst, characterized by, The g-C3N4 substrate and the doping elements, the doping elements including at least five of K, Li, Na, Zn, Co, Fe, Ni, Mn, Cu, Sn and Bi.
2. The g-C3N4 photocatalyst according to claim 1, characterized in that, The molar ratio of each of the doping elements is the same.
3. The g-C3N4 photocatalyst according to claim 1, characterized in that, The g-C3N4 substrate contains defects, the defects including at least one of C defects and N defects.
4. A method for preparing the g-C3N4 photocatalyst according to any one of claims 1 to 3, characterized in that, The g-C3N4 substrate and the doping elements, the doping elements including at least five of K, Li, Na, Zn, Co, Fe, Ni, Mn, Cu, Sn and Bi. The g-C3N4 precursor is subjected to a first calcination treatment in a defect atmosphere to obtain a g-C3N4 containing defects; The g-C3N4 containing defects, a metal precursor and a solvent are mixed, evaporated and dried to obtain a mixture precursor, the metal precursor including a metal soluble salt containing the at least five doping elements; The mixture precursor is subjected to a second calcination treatment to obtain the g-C3N4 photocatalyst.
5. The method of claim 4, wherein, The metal soluble salt includes at least one of hydrochloride, nitrate, sulfate and acetate; The mass ratio of the g-C3N4 precursor to the metal precursor is 100: (0.5-10); The concentration of the metal precursor in the mixture of the metal precursor and the solvent is 0.1 mg / L-100 mg / L.
6. The method of claim 4, wherein, The calcination atmosphere of the first calcination treatment and the second calcination treatment is independently at least one of air, ammonia, hydrogen and hydrogen-argon mixture; the calcination temperature is independently 400°C-600°C; and the calcination time is independently 0.5 h-3 h. After the first calcination treatment, the obtained calcination product is cooled to room temperature, ground, washed by centrifugation with deionized water and an organic solvent, and dried to obtain the g-C3N4 containing defects; After the second calcination treatment, the obtained calcination product is cooled to room temperature, ground, washed by centrifugation with deionized water and an organic solvent, and dried to obtain the g-C3N4 photocatalyst, wherein the organic solvent includes anhydrous ethanol.
7. Use of the g-C3N4 photocatalyst of any one of claims 1-3 or the g-C3N4 photocatalyst prepared by the method of any one of claims 4-6 in the production of urea. Preferably, the urea is prepared by photocatalytic co-reduction of NO and CO2.
8. A method of producing urea, characterized by, The g-C3N4 photocatalyst of any one of claims 1-3 or the g-C3N4 photocatalyst prepared by the method of any one of claims 4-6 is used to photocatalyze the co-reduction of NO and CO2 to obtain urea. The g-C3N4 photocatalyst, a sacrificial agent and water are placed in a reactor and mixed uniformly; 9. The method according to claim 8, characterized in that, CO2 is introduced into the reactor, air is exhausted, NO is introduced, and the reactor is maintained at a preset pressure, and light treatment is performed to obtain urea. The sacrificial agent is selected from compounds that can dissociate protons; the sacrificial agent includes at least one of methanol, ethanol, isopropanol, ethylene glycol and benzyl alcohol; The volume ratio of the sacrificial agent to water is (1:9)-(9:1); 10. The method according to claim 9, characterized in that, The flow ratio of CO2 to NO is (10:1)-(1:10); The preset pressure is 1-5 atm; The light treatment adopts natural light or simulated sunlight. The time of the light treatment is 4-12 hours.