Metal monatomic loaded cyano carbon nitride photocatalyst as well as preparation method and application thereof
By supporting metal single atoms on the surface of cyanocarbon nitride, forming a cyanocarbon nitride photocatalyst supported by metal single atoms, the problems of high charge recombination rate, limited light absorption range and insufficient active sites in the process of photocatalytic carbon dioxide reduction to methane are solved, and efficient methane yield and selectivity are achieved.
Patent Information
- Application Number
- CN202510363569.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-26
- Publication Date
- 2025-06-27
AI Technical Summary
In the process of photocatalytic carbon dioxide reduction, existing photocatalysts have problems such as high charge recombination rate, limited absorption range and insufficient active sites, which makes methane yield and selectivity difficult to meet the actual application needs.
The cyanocarbon nitride was synthesized by a one-step molten salt method at high temperature calcination, and metal single atoms were supported on its surface by in-situ growth method to form a cyanocarbon nitride photocatalyst supported by metal single atoms.
The catalyst showed excellent reactivity and stability in the process of photocatalytic carbon dioxide reduction to methane, with methane yield reaching 18.3 μmolg-1h-1 and selectivity close to 100%, which significantly improved the photocatalytic efficiency.
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Figure CN120205212A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the fields of photochemistry and new energy material synthesis technology, and relates to a metal single-atom loaded cyanide carbon nitride photocatalyst, a preparation method thereof and an application thereof. Background Art
[0002] Methane, as an important clean energy and chemical raw material, occupies an irreplaceable position in the modern industrial system. On the one hand, its characteristics of high calorific value (55.7 MJ / kg) and low pollutant emissions make it an ideal choice to replace traditional fossil fuels, and it is widely used in fields such as power generation, heating, and transportation; on the other hand, as a key precursor for synthesizing basic chemicals such as ammonia and methanol, the global annual demand has exceeded 400 million tons. However, there are significant bottlenecks in traditional industrial methane production technologies: mainstream processes such as steam methane reforming and coal gasification highly rely on fossil energy; although the biological fermentation method is renewable, it has defects such as large seasonal fluctuations in raw materials, long reaction cycles, and low product purity. These technical routes not only exacerbate the energy-environment contradiction, but the methane escape during their production and transportation directly leads to the aggravation of the greenhouse effect.
[0003] In this context, the photocatalytic carbon dioxide (CO2) reduction to synthesize methane (CH4) technology shows unique advantages. This technology absorbs solar energy through semiconductor materials and drives the conversion of carbon dioxide and water molecules into methane. In theory, it can achieve a "negative carbon cycle": producing methane and consuming carbon dioxide, while converting dispersed solar energy into high-density chemical energy for storage. Current mainstream catalysts include metal oxides (such as TiO2), sulfides (such as CdS), carbon nitrides (C3N4), and new photocatalysts such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Although they each have advantages in aspects such as light absorption, charge separation, or CO2 adsorption, they generally have obvious defects. For example, metal oxides have a wide bandgap and low visible light utilization rate, sulfides are prone to photocorrosion, while the synthesis conditions of MOFs and COFs are harsh and their stability is insufficient. In addition, existing photocatalytic technologies generally face core challenges such as high charge recombination rate, insufficient active sites, fierce competition from side reactions (such as hydrogen evolution reaction), and poor catalyst stability, resulting in the methane yield and selectivity being difficult to meet the actual application requirements. In response to these problems, the modification and performance regulation of carbon nitride (C3N4) provide a new direction for technological breakthroughs.
[0004] C3N4 is a non-metallic semiconductor material composed of carbon and nitrogen elements. It has a layered structure and a suitable band gap (about 2.7eV). It can absorb visible light and has the advantages of low preparation cost, high chemical stability, and strong controllability. It is widely used in the field of photocatalysis. However, the C3N4 body still has problems such as high charge recombination rate, limited light absorption range, and insufficient active sites, which makes the photocatalytic efficiency of the C3N4 body often unsatisfactory, thus limiting its practical application. Researchers have found that functional group modification can construct an intramolecular donor-acceptor structure to effectively improve charge separation and transfer efficiency. For example, the introduction of a strongly electronegative cyanide (-C≡N) can destroy the Coulomb electrostatic constraint between electrons and holes and inhibit charge recombination. At the same time, the internal electric field formed by the intramolecular donor-acceptor structure can effectively drive the directional migration of electrons and holes. The introduction of metal single atoms (SACs) can introduce a large number of active sites on the C3N4 surface. By changing the type of metal and regulating the coordination environment, the catalytic reaction path can be precisely controlled at the atomic scale and the product selectivity can be optimized. Summary of the invention
[0005] In order to solve the problems of high charge recombination rate, limited light absorption range and insufficient active sites of carbon nitride photocatalytic materials, the present invention provides a metal single atom-loaded cyano carbon nitride photocatalyst, a preparation method and application thereof, which exhibits excellent reaction activity and stability in the application of photocatalytic carbon dioxide reduction to methane.
[0006] A method for preparing a metal single atom-supported cyano carbon nitride photocatalyst comprises: firstly, synthesizing cyano carbon nitride by high temperature calcination using a one-step molten salt method; secondly, supporting metal single atoms on cyano carbon nitride by an in-situ growth method. The preparation method specifically comprises the following steps:
[0007] Step 1, fully mixing a cyano carbon nitride precursor and an alkali metal chloride and grinding them to obtain a mixed powder;
[0008] Step 2, placing the mixed powder in a crucible and calcining in a muffle furnace;
[0009] Step 3, after the calcined powder is cooled to room temperature, it is uniformly dispersed in a mixed solution of water and ethanol, then washed with water and ethanol for multiple times and dried to obtain cyano carbon nitride;
[0010] Step 4, dispersing cyanocarbonitride in methanol to obtain solution A, dispersing metal chloride in methanol to obtain solution B, adding solution B dropwise to solution A, stirring continuously for 24 hours, centrifuging the obtained suspension to retain solids, and then washing and drying;
[0011] Step 5, calcining the obtained solid in an argon atmosphere to obtain metal single atom-supported cyano carbon nitride.
[0012] Further, in the step 1, the molar ratio of the cyanoguanamine precursor to the metal chloride is 7:2 - 7:4; the cyanoguanamine precursor is selected from urea, dicyandiamide or melamine, preferably dicyandiamide; the alkali metal chloride is selected from one or more of lithium chloride, sodium chloride, potassium chloride, preferably sodium chloride and potassium chloride, and the molar ratio of sodium chloride to potassium chloride is 2:1 - 1:2.
[0013] Further, in the step 2, the calcination temperature is 650 - 700 °C and the time is 30 - 60 min.
[0014] Further, in the step 3, in the water and ethanol mixed solution, the volume ratio of water to ethanol is 1:2 - 2:1.
[0015] Further, in the step 4, the concentration of cyanoguanamine in solution A is 5 - 15 mg / mL -1 , the concentration of the metal chloride in solution B calculated by the mass of the metal element is 0.2 - 0.6 mg / mL -1 , and the volume ratio of solution A to solution B is 1:2 - 2:1.
[0016] Further, in the step 4, the metal chloride is selected from one of rhodium chloride, copper chloride, iridium chloride, preferably rhodium chloride.
[0017] Further, in the step 5, the calcination temperature is 200 - 300 °C and the time is 90 - 150 min.
[0018] A metal single-atom loaded cyanoguanamine photocatalyst is prepared by the above preparation method, wherein the metal single-atom loading is 1% - 3% wt.
[0019] An application of a metal single-atom loaded cyanoguanamine photocatalyst in photocatalytic reduction of carbon dioxide to methane.
[0020] Compared with the prior art, the present invention has at least the following beneficial effects:
[0021] (1) The present invention uses the molten salt method to prepare cyanide-modified carbon nitride. Compared with the existing preparation methods, this method is simple in operation, easy to obtain raw materials, and has good repeatability; in addition, the present invention introduces metal single atoms on the surface of cyanoguanamine by a simple in-situ growth method to form a metal single-atom loaded cyanoguanamine photocatalyst. Compared with the existing preparation methods, the metal single-atom loading of this method is only 1 - 3%, the metal utilization rate is higher, and compared with the existing metal nanoparticles or clusters loaded cyanoguanamine, the cost is greatly reduced, which has important guiding significance for large-scale commercial application in the future.
[0022] (2) Compared with the carbon nitride bulk, the introduction of cyano groups in the present invention significantly expands the visible light absorption range, constructs an intramolecular donor-acceptor structure, promotes charge separation and transport, and improves the photocatalytic efficiency; after introducing metal single atoms on the basis of cyano carbon nitride, the carrier lifetime is prolonged and the charge separation efficiency is further enhanced. Moreover, the metal single atoms serve as active sites, effectively enhancing the adsorption of methane preparation intermediates and improving the methane selectivity, enabling the present invention to be applied to the catalytic reduction of carbon dioxide to methane, which can be used as an important clean energy and chemical raw material.
[0023] (3) The present invention further optimizes the performance of photocatalytic reduction of carbon dioxide to methane. Under the optimal conditions, the methane yield reaches 18.3 μmol g -1 h -1 , and the selectivity is close to 100%. Compared with existing photocatalysts, the photocatalytic methane yield and selectivity of the metal single atom-loaded cyano carbon nitride prepared by the present invention are both at a relatively high level. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 It is the X-ray diffraction pattern of the Rh-C3N4-CN photocatalyst in Example 2 and the C3N4-CN photocatalyst in Comparative Example 1.
[0025] Figure 2 It is the scanning electron microscope image and energy spectrum of the Rh-C3N4-CN photocatalyst in Example 2, where (a) is the scanning electron microscope image, (b) is the energy spectrum of C element, (c) is the energy spectrum of N element, and (d) is the energy spectrum of Rh element.
[0026] Figure 3 It is the high-resolution transmission electron microscope image of the Rh-C3N4-CN photocatalyst in Example 2.
[0027] Figure 4 It is the performance comparison diagram of photocatalytic reduction of carbon dioxide to methane of different catalysts in Example 2, Comparative Example 1, and Comparative Example 2.
[0028] Figure 5 It is the steady-state fluorescence spectrum comparison diagram of different catalysts in Example 2, Comparative Example 1, and Comparative Example 2.
[0029] Figure 6 It is the performance comparison diagram of photocatalytic reduction of carbon dioxide to methane of different catalysts in Example 2 and Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION
[0030] To further understand the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely. At the same time, the following described examples are only a part of the present invention, not all of it. The following description is only to further illustrate the advantages and features of the present invention, rather than a limitation on the claims of the present invention. Other embodiments obtained by those of ordinary skill in the art without creative efforts all fall within the scope of protection of the present invention.
[0031] The following will further illustrate the technical solutions of the present invention in conjunction with specific examples.
[0032] Example 1
[0033] A preparation method of a single-atom rhodium-loaded cyanoguanamine photocatalyst includes the following steps:
[0034] (1) Weigh 5.88 g of dicyandiamide, mix it fully with sodium chloride (0.39 g) and potassium chloride (0.99 g), and grind it with a mortar until it presents a powdery state.
[0035] (2) Place the mixed powder in a 30 mL crucible and calcine it in a muffle furnace. The calcination temperature is 650 °C, the time is 60 min, and the heating rate is 2 °C / min.
[0036] (3) After cooling to room temperature, an orange solid is obtained. Grind the solid into powder, then disperse it evenly in a mixed solution of water and ethanol, where the volume ratio of water to ethanol is 1:2. Then wash it with water and ethanol for multiple times and dry it to obtain cyanoguanamine.
[0037] (4) Weigh 25 mg of cyanoguanamine and disperse it in 5 mL of methanol to obtain solution A. Weigh 1.2 mg of iridium chloride and disperse it in 10 mL of methanol to obtain solution B. Drop solution B into solution A and continuously stir at room temperature for 24 h to obtain a suspension. Centrifuge to retain the solid, and then wash and dry it.
[0038] (5) Calcinate the dried solid in an argon atmosphere. The calcination temperature is 200 °C, the time is 150 min, and the heating rate is 5 °C / min to obtain a single-atom rhodium-loaded cyanoguanamine.
[0039] Apply the prepared single-atom iridium-loaded cyanoguanamine to photocatalytic reduction of carbon dioxide to methane. The photocatalytic methane production rate is 16.7 μmol g -1 h -1 , and the methane selectivity is 86.3%.
[0040] Example 2
[0041] A preparation method of a single-atom rhodium-loaded cyanoguanamine photocatalyst includes the following steps:
[0042] (1) Weigh 5.88 g of dicyandiamide, mix it thoroughly with sodium chloride (0.877 g) and potassium chloride (1.118 g), and grind it in a mortar until it becomes powdery.
[0043] (2) Place the mixed powder in a 30 mL crucible and calcine it in a muffle furnace at a calcination temperature of 670 °C for 45 min with a heating rate of 2 °C / min.
[0044] (3) After cooling to room temperature, an orange solid is obtained. Grind the solid into powder, then disperse it evenly in a mixed solution of water and ethanol with a volume ratio of water to ethanol of 1:1. Then wash it with water and ethanol multiple times and dry it to obtain cyano carbon nitride.
[0045] (4) Weigh 100 mg of cyano carbon nitride and disperse it in 10 mL of methanol to obtain solution A. Weigh 4.4 mg of rhodium chloride and disperse it in 5 mL of methanol to obtain solution B. Slowly add solution B dropwise to solution A and continuously stir at room temperature for 24 h to obtain a suspension. Centrifuge to retain the solid, then wash and dry it.
[0046] (5) Calcinate the dried solid in an argon atmosphere at a calcination temperature of 250 °C for 120 min with a heating rate of 5 °C / min to obtain single-atom rhodium-loaded cyano carbon nitride (Rh-C3N4-CN).
[0047] Apply the prepared single-atom rhodium-loaded cyano carbon nitride to photocatalytic reduction of carbon dioxide to methane. The photocatalytic methane yield is 18.3 μmol g -1 h -1 , and the methane selectivity is 98.5%.
[0048] Example 3
[0049] A preparation method of a single-atom rhodium-loaded cyano carbon nitride photocatalyst, comprising the following steps:
[0050] (1) Weigh 5.88 g of dicyandiamide, mix it thoroughly with lithium chloride (1.13 g) and potassium chloride (0.99 g), and grind it in a mortar until it becomes powdery.
[0051] (2) Place the mixed powder in a 30 mL crucible and calcine it in a muffle furnace at a calcination temperature of 700 °C for 30 min with a heating rate of 2 °C / min.
[0052] (3) After cooling to room temperature, an orange solid is obtained. Grind the solid into powder, then disperse it evenly in a mixed solution of water and ethanol with a volume ratio of water to ethanol of 2:1. Then wash it with water and ethanol multiple times and dry it to obtain cyano carbon nitride.
[0053] (4) Weigh 150 mg of cyano carbon nitride and disperse it in 10 mL of methanol to obtain solution A. Weigh 4.0 mg of copper chloride and disperse it in 10 mL of methanol to obtain solution B. Slowly add solution B dropwise to solution A and continue stirring at room temperature for 24 h. The obtained suspension is centrifuged to retain the solid, which is then washed and dried.
[0054] (5) The dried solid was calcined in an argon atmosphere at a temperature of 300° C. for 90 min at a heating rate of 5° C. / min to obtain single-atom rhodium-supported cyano carbon nitride.
[0055] The prepared single-atom copper-supported cyano-carbon nitride was applied to photocatalytic carbon dioxide reduction to produce methane, and the photocatalytic methane yield was 17.0 μmol g -1 h -1 , the methane selectivity is 84.4%.
[0056] Comparative Example 1
[0057] This comparative example provides a cyano carbon nitride photocatalyst, and its preparation method is as follows:
[0058] (1) Weigh 5.88 g of dicyandiamide, mix thoroughly with sodium chloride (0.877 g) and potassium chloride (1.118 g), and grind in a mortar until it becomes powdery.
[0059] (2) The mixed powder was placed in a 30 mL crucible and calcined in a muffle furnace at a temperature of 670 °C for 45 min at a heating rate of 2 °C / min.
[0060] (3) After cooling to room temperature, an orange solid is obtained, which is ground into powder and then evenly dispersed in a mixed solution of water and ethanol (volume ratio of 1:1), then washed with water and ethanol for multiple times and dried to obtain cyanocarbon nitride (C3N4-CN).
[0061] Comparative Example 2
[0062] This comparative example provides a carbon nitride photocatalyst, and its preparation method is as follows:
[0063] (1) Weigh 5.88 g of dicyandiamide and grind it in a mortar until it becomes powdery.
[0064] (2) The powder was placed in a 30 mL crucible and calcined in a muffle furnace at a temperature of 550 °C for 120 min at a heating rate of 5 °C / min.
[0065] (3) After cooling to room temperature, a yellow solid is obtained, which is ground into powder and then evenly dispersed in a mixed solution of water and ethanol (volume ratio of 1:1), then washed with water and ethanol for multiple times and dried to obtain carbon nitride (C3N4).
[0066] Comparative Example 3
[0067] This comparative example provides a carbon quantum dot-modified titanium dioxide photocatalyst, which is a catalyst commonly used for photocatalytic reduction of carbon dioxide to methane. The preparation method is as follows:
[0068] (1) Take 2 mL of the carbon quantum dot aqueous dispersion solution and dilute it to 14 mL. Slowly add 28 mL of ethanol to the carbon quantum dot aqueous solution under stirring, and adjust the solution to pH = 2.5 with dilute nitric acid.
[0069] (2) Transfer the above solution to a 250 mL round-bottom flask, heat it in a water bath at 70 °C, add 8.5 mL of tetrabutyl titanate to the round-bottom flask, and continue heating for 24 h.
[0070] (3) Wait for the reaction solution to cool to room temperature, wash it several times with deionized water and absolute ethanol, centrifuge to retain the solid, and dry it in a vacuum oven at 80 °C to obtain carbon quantum dot-modified titanium dioxide (CDQs / TiO2).
[0071] Figure 1 XRD patterns of the Rh-C3N4-CN photocatalyst in Example 2 and the C3N4-CN photocatalyst in Comparative Example 1. Characteristic peaks attributed to carbon nitride can be observed in the figure, confirming the successful synthesis of the C3N4-CN support. There is no obvious change in the spectrum after the introduction of metallic rhodium, indicating that the C3N4-CN structure is not damaged.
[0072] Figure 2 SEM image and energy spectrum of the Rh-C3N4-CN photocatalyst in Example 2. Uniformly dispersed rhodium was successfully introduced onto the surface of C3N4-CN by in-situ growth method. It can also be observed from the figure that Rh-C3N4-CN presents a two-dimensional sheet structure.
[0073] Figure 3 HRTEM image of the Rh-C3N4-CN photocatalyst in Example 2. The bright spots in the figure correspond to atomically dispersed rhodium.
[0074] Figure 4 Photocatalytic performance of different catalysts for reduction of carbon dioxide to methane in Example 2 and Comparative Examples 1 and 2. It can be seen that the Rh-C3N4-CN prepared in Example 2 has the optimal performance, and the methane yield reaches 18.3 μmol g -1 h -1, the selectivity for methane was 98.5%. For the catalysts prepared in Comparative Example 1 and Comparative Example 2, carbon dioxide could only be reduced to carbon monoxide under the same conditions, while water in the system was reduced to hydrogen, and no methane was detected. This is because the introduction of single-atom rhodium provided abundant active sites for the synthesis of methane, enhanced the adsorption of reaction intermediates, and thus regulated the reaction pathway, enabling the photoreduction of carbon dioxide to methane.
[0075] Figure 5 Figure 4 shows the steady-state fluorescence spectra of different catalysts in Example 2 and Comparative Example 1 and Comparative Example 2. It can be seen from the figure that the fluorescence intensity of C3N4 is the highest, that of C3N4-CN is the second, and the fluorescence intensity of Rh-C3N4-CN prepared in Example 2 is the lowest, indicating that the charge recombination rates of the three decrease in turn. This is because the introduction of cyano groups and the loading of metals inhibit charge recombination and improve the charge separation efficiency.
[0076] Figure 6 Figure 5 shows the photocatalytic carbon dioxide reduction to methane performance of different catalysts in Example 2 and Comparative Example 3. The photocatalytic methane yield of Rh-C3N4-CN prepared in Example 2 was 18.3 μmol g -1 h -1 , the selectivity for methane was 98.5%. The photocatalytic methane yield of CDQs / TiO2 prepared in Comparative Example 3 was 15.7 μmol g -1 h -1 , and the selectivity for methane was only 78.3%. Compared with CDQs / TiO2, Rh-C3N4-CN had a higher photocatalytic carbon dioxide reduction to methane yield and a higher methane selectivity. This is because the Rh-C3N4-CN photocatalyst has excellent charge separation and transfer efficiencies and abundant reaction active sites, and has high selectivity for methane. Therefore, compared with existing photocatalysts, the performance of the metal single-atom loaded cyano carbon nitride prepared in the present invention has been significantly improved.
[0077] The above-described embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention.
Claims
1. A method for preparing a metal single atom supported cyano carbon nitride photocatalyst, characterized in that: The preparation method firstly adopts a one-step molten salt method to calcine and synthesize cyano carbon nitride; secondly, metal single atoms are loaded on the cyano carbon nitride by an in-situ growth method.
2. The method for preparing a metal single atom supported cyano carbon nitride photocatalyst according to claim 1, characterized in that: The preparation method specifically comprises the following steps: Step 1, fully mixing a cyano carbon nitride precursor and an alkali metal chloride and grinding them to obtain a mixed powder; Step 2, placing the mixed powder in a crucible and calcining in a muffle furnace; Step 3, after the calcined powder is cooled to room temperature, it is uniformly dispersed in a mixed solution of water and ethanol, then washed with water and ethanol for multiple times and dried to obtain cyano carbon nitride; Step 4, dispersing cyanocarbonitride in methanol to obtain solution A, dispersing metal chloride in methanol to obtain solution B, adding solution B dropwise to solution A, stirring continuously for 24 hours, centrifuging the obtained suspension to retain solids, and then washing and drying; Step 5, calcining the obtained solid in an argon atmosphere to obtain metal single atom-supported cyano carbon nitride.
3. The method for preparing a metal single atom supported cyano carbon nitride photocatalyst according to claim 2, characterized in that: In the step 1, the molar ratio of the cyano carbon nitride precursor to the metal chloride is 7:2-7:4, wherein the cyano carbon nitride precursor is selected from urea, dicyandiamide or melamine, and the alkali metal chloride is selected from one or more of lithium chloride, sodium chloride and potassium chloride.
4. The method for preparing a metal single atom supported cyano carbon nitride photocatalyst according to claim 2, characterized in that: In the step 1 and the step 2, the calcination temperature is 650-700° C. and the calcination time is 30-60 min.
5. The method for preparing a metal single atom supported cyano carbon nitride photocatalyst according to claim 2, characterized in that: In the step 3, the volume ratio of water to ethanol in the mixed solution of water and ethanol is 1:2-2:
1.
6. The method for preparing a metal single atom supported cyano carbon nitride photocatalyst according to claim 2, characterized in that: In step 4, the concentration of cyano carbon nitride in solution A is 5-15 mg / mL -1 The concentration of metal chloride in solution B is calculated based on the mass of the metal element and is 0.2-0.6 mg / mL -1 , the volume ratio of solution A to solution B is 1:2-2:
1.
7. The method for preparing a metal single atom supported cyano carbon nitride photocatalyst according to claim 2 or 6, characterized in that: In the step 4, the metal chloride is selected from one of rhodium chloride, cupric chloride and iridium chloride.
8. The method for preparing a metal single atom supported cyano carbon nitride photocatalyst according to claim 2, characterized in that: In the step 5, the calcination temperature is 200-300° C. and the calcination time is 90-150 min.
9. A metal single atom supported cyano carbon nitride photocatalyst, prepared according to the preparation method according to any one of claims 1 to 8, characterized in that: The metal single atom loading is 1%-3%wt.
10. An application of the metal single atom supported cyano carbon nitride photocatalyst according to claim 9, characterized in that: Applied in photocatalytic reduction of carbon dioxide to methane.