A carbon-based co monatomic photocatalyst with a co-c2n coordination structure, a preparation method and applications thereof

Abstract

The application belongs to the technical field of new materials, and provides a carbon-based Co monatomic photocatalyst with a Co-C2N coordination structure, a preparation method and application. First, urea and melamine are uniformly ground and mixed, and then calcined in an inert gas atmosphere to obtain carbon nitride, a cobalt salt and a molten salt are added thereto, and after being uniformly ground again, a Co1 / C3N4 catalyst with a specific catalytic active site structure can be accurately obtained by selecting a corresponding calcination temperature. The SACs with the Co-C2N structure loaded on the C3N4 prepared by the application exhibit excellent activity in the reaction of photocatalytic conversion of carbon dioxide to prepare methane.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, and relates to a carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure, its preparation method and application. Background Technology

[0002] With rapid industrialization and urbanization, the extensive use of fossil fuels has led to a sharp increase in CO2 emissions, becoming a major driver of global climate change. Photocatalytic CO2 reduction involves using a photocatalyst under light conditions to convert CO2 and water (or other reducing agents) into organic compounds such as carbon monoxide (CO), methanol (CH3OH), and methane (CH4). CH4 has the highest heat of combustion (55.5 MJ / kg⁻¹). -1 (Nat.Commun.2021,12,2932) and has become one of the most anticipated CO2 reduction products.

[0003] Single-atom catalysts (SACs) exhibit unique advantages in the photocatalytic reduction of CO2, specifically in the following three aspects: First, all metal atoms in SACs are in an active state, avoiding the aggregation and loss of activity of metal atoms found in traditional nanocatalysts, thus significantly improving catalytic activity and atom utilization. Second, SACs possess a unique electronic structure, allowing them to optimize reaction pathways and intermediate stability by regulating electron transfer at the metal-support interface, thereby enhancing the activity and selectivity of multi-electron reduction products. Third, the active sites of SACs are clearly defined, facilitating in-depth research into catalytic mechanisms and reaction pathways, and providing theoretical guidance for catalyst design and optimization (Adv. Mater. 2023, 35, 2208132). However, the main product of CO2 reduction catalyzed by SACs is CO, exhibiting relatively poor conversion and selectivity for the direct 8-electron reduction product CH4 via multi-proton coupled electron transfer (Angew. Chem. Int. Ed. 2024, 63, e202314384). Therefore, developing SACs with high CH4 activity and selectivity is essential.

[0004] For multi-electron catalytic processes, the precise synthesis of SACs with specific coordination structures is crucial for improving the activity and selectivity of the catalytic process. S Sheng et al. (Angew. Chem. Int. Ed. 2022, 61, e202209446) reported that Au single atoms were supported on ultrathin ZnIn2S4 nanosheets, achieving visible-light photocatalytic CO2 reduction to CH4 by forming a low-coordination Au1 / S2 structure. L Zheng et al. (Appl. Catal., B2022, 307, 121154) simultaneously introduced Ru and Cu single atoms into a C3N4 substrate, achieving a CH4 yield of 1.54 μmol under 8 h of visible light irradiation. J Wang et al. (Angew. Chem. Int. Ed. 2022, 61, e202113044) synthesized a Co2-N coordinated diatomic site catalyst to enhance the activity and selectivity of the photocatalytic CO2 reduction to CH4 reaction. Therefore, although SACs have been extensively studied in the field of CO2 reduction to CH4, there are still limitations in the precise control of active sites, especially for carbon-based non-noble metal SACs. Summary of the Invention

[0005] The purpose of this invention is to develop a carbon-based Co single-atom catalyst for the 8-electron reduction reaction of CO2. To enhance the catalyst's CO2 reduction capability, the CO2 reduction process was first simulated using DFT calculations. It was found that the Co-C2N structure is beneficial for enhancing the adsorption of the reaction intermediate *CO, thereby achieving further reduction of CO2 to CH4. Using a molten salt-assisted pyrolysis method, SACs with Co-C2N active sites were prepared within the target temperature range. Experimental results show that the catalyst with Co-C2N active sites exhibits catalytic performance for the reduction of CO2 to CH4. This result reveals the structure-activity relationship of the Co-C2N active sites, providing a new perspective for further application of SACs in the multi-electron reduction reaction of CO2.

[0006] The technical solution of this invention:

[0007] A carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure has the following structural formula:

[0008]

[0009] A method for preparing a carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure, comprising the following steps:

[0010] Step (1): Preparation of C3N4

[0011] Urea and melamine are ground and mixed evenly in a certain mass ratio and then placed in a tube furnace and calcined at 500-600℃ for 2-6 hours to obtain a yellow powder, which is C3N4.

[0012] The mass ratio of urea to melamine is between 1:1 and 1:3.

[0013] Step (2): Preparation of carbon-based Co single-atom catalysts with a coordination structure of Co-C2N

[0014] 1) Add CoCl2, KCl and LiCl to the C3N4 prepared in step (1), and grind and mix evenly to obtain mixture A;

[0015] In mixture A, the total mass of KCl and LiCl accounts for 50%-80% of the mass of mixture A, and the mass of KCl accounts for 30%-50% of the total mass of KCl and LiCl; CoCl2 accounts for 1%-10% of the mass of mixture A, and C3N4 accounts for 10%-49% of the mass of mixture A.

[0016] 2) The obtained mixture A is placed in a tube furnace and calcined at high temperature in an inert atmosphere by gradually increasing the temperature from room temperature to the target temperature.

[0017] The inert atmosphere is either Ar or N2.

[0018] The heating rate is 2–8 °C / min. -1 ;

[0019] The target temperature range is 550–600℃, and the calcination time is 2–4 hours.

[0020] 3) After the calcined powder is thoroughly ground in a mortar, it is dispersed in a dilute acid solution for acid washing. The mixture is stirred first and then sonicated. The nanoparticles sintered during the preparation process are thoroughly washed away by a combination of stirring and sonication.

[0021] The dilute acid solution is hydrochloric acid with a concentration of less than 0.5 mol / L or sulfuric acid with a concentration of less than 0.3 mol / L;

[0022] Stirring speed 200-1000 rpm, temperature 10-40℃, time 0.5-5h;

[0023] Ultrasonic power 500W, frequency 35-40kHz, duration 0.5-5h;

[0024] 4) After the sample obtained by acid washing is allowed to stand for a period of time, the sample is centrifuged and washed until neutral, vacuum dried, and the sample is recovered to obtain a carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure, denoted as Co1 / CN-550A.

[0025] The settling time is 2 to 6 hours;

[0026] The centrifugation speed is 8000-18000 rpm.

[0027] The application of a carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure in the photocatalytic reduction of CO2 to CH4 is as follows:

[0028] Step (1): Take Co-SACs catalyst and ultrasonically disperse it in a mixed solution of deionized water and hole sacrificial agent triethanolamine (TEOA). The concentration of the catalyst in the deionized water is 0.17 g / L, and the volume ratio of H2O to TEOA is 5:1. Then transfer it to a stainless steel reactor, seal it, and start introducing CO2 until the air in the reactor is exhausted.

[0029] Step (2): Use a 300W Xe lamp as the light source and 25°C condensate to maintain the temperature of the reaction system.

[0030] Step (3): After a certain reaction time, a portion of the gas in the reactor is extracted using a gas injection needle and injected into the flame ionization detector of a gas chromatograph to detect the content and type of the product.

[0031] The beneficial effects of this invention are as follows: The SACs with a Co-C2N structure supported on C3N4 prepared by this invention exhibit excellent activity in the photocatalytic conversion of CO2 to CH4. By selecting a specific calcination temperature, SACs with specific metal coordination structures are prepared, which significantly improves the adsorption capacity for the intermediate species *CO, thereby enhancing the activity and selectivity for the 8-electron reduction product CH4. Attached Figure Description

[0032] Figure 1 The images show the FT-IR spectra of Co1 / CN-550A and its comparative sample. It can be seen that the SACs still retain the characteristic peaks of C3N4, indicating that the introduction of a single Co atom does not change the crystal structure of C3N4.

[0033] Figure 2 The N2 isotherm adsorption-desorption curves are shown for Co1 / CN-550A and its comparative sample. Co1 / CN-550A exhibits a significantly increased specific surface area compared to Co1 / CN-400A and CN.

[0034] Figure 3 The image shows a comparison of the photocatalytic CO2 reduction activities of Co1 / CN-550A and its comparative samples. Co1 / CN-550A exhibits enhanced CO production and CH4 production activity, while Co1 / CN-400A and CN-550A do not possess CH4 production activity.

[0035] Figure 4The graph shows the change in CO2 reduction product yield over time for the Co1 / CN-550A sample. With the accumulation of illumination time, the yields of both CO and CH4 increase linearly, indicating that the catalyst has good stability.

[0036] Figure 5 The images show in-situ infrared spectroscopy (IR) images of Co1 / CN-550A and its comparative sample. (a) shows Co1 / CN-550A, and (b) shows Co1 / CN-400A. The presence of the key free radicals *CHO* and CH3O* in the CO2 reduction to CH4 reaction confirms that the product CH4 originates from CO2 reduction. After a period of illumination, the absorption peaks of the free radicals generated by Co1 / CN-550A completely returned to their initial state, while those of Co1 / CN-400A partially returned to their initial state, indicating that Co1 / CN-550A possesses good stability. Detailed Implementation

[0037] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0038] Example 1: Preparation of SACs (Co1 / CN-550A) with a Co-C2N coordination structure supported on C3N4.

[0039] (1) Preparation of C3N4

[0040] Urea and melamine are ground and mixed evenly at a mass ratio of 1:2, and then calcined in a tube furnace at 550°C for 2 hours to obtain a yellow powder, which is C3N4.

[0041] (2) Preparation of SACs with Co-C2N coordination structure

[0042] 1) After thoroughly grinding the C3N4 prepared in step (1) with a mortar, take 1g of C3N4 and grind it again with 2.3g of KCl, 2.1g of LiCl and 2% of CoCl2 to obtain mixture A;

[0043] 2) The obtained mixture A was placed in a tube furnace and calcined at 550°C for 2 hours in an inert Ar atmosphere, with the temperature increased from room temperature to 550°C at a rate of 5°C / min. -1 ;

[0044] 3) After the calcined powder is thoroughly ground in a mortar, it is dispersed in a 0.1M dilute hydrochloric acid solution for acid washing. First, it is stirred at room temperature for 2 hours, and then ultrasonically treated for 2 hours. The sintered nanoparticles during the preparation process are thoroughly washed away by a combination of stirring and ultrasonic treatment.

[0045] 4) After the sample obtained by the above acid washing is allowed to stand for a period of time, the sample is centrifuged and washed until neutral, vacuum dried, and the sample is recovered to obtain SACs with Co-C2N active sites that can catalyze the CO2 8-electron reduction reaction.

[0046] Comparative Example 1: Preparation of C3N4 (CN-550A) calcined at 550℃ with molten salt treatment

[0047] (1) After grinding the pure C3N4 prepared in Example 1 evenly, take 1g into another mortar, add 2.3g KCl and 2.1g LiCl, and grind evenly again to obtain mixture B;

[0048] (2) The obtained mixture B was placed in a tube furnace and calcined at 550°C for 2 hours in an inert Ar atmosphere, with the temperature increased from room temperature to 550°C at a rate of 5°C / min. -1 The powder obtained by calcination is ground again to obtain C3N4 treated with molten salt at 550℃.

[0049] Comparative Example 2: Preparation of SACs (Co1 / CN-400A) with Co-N2 coordination structure supported on C3N4.

[0050] The preparation method is basically the same as in Example 1, except that the calcination temperature in step (2) is set to 400℃.

[0051] Comparative Example 3: Preparation of SACs (Co1 / CN-700A) with Co-N2 coordination structure supported on C3N4.

[0052] The preparation method is basically the same as in Example 1, except that the calcination temperature in step (2) is set to 700℃.

[0053] Application Example 1: Activity of CN-550A in Photocatalytic CO2 Conversion

[0054] (1) Take CN-550A catalyst and ultrasonically disperse it in a mixed solution of deionized water and hole sacrificial agent triethanolamine (TEOA). The concentration of the catalyst in the deionized water is 0.17 g / L, and the volume ratio of H2O to TEOA is 5:1. Then transfer it to a stainless steel reactor, seal it, and start to introduce CO2 until the air in the reactor is exhausted.

[0055] (2) Use a 300W Xe lamp as the light source and 25℃ condensate to maintain the temperature of the reaction system;

[0056] (3) After a certain reaction time, a portion of the gas in the reactor is extracted using a gas injection needle and injected into the hydrogen flame ionization detector of the gas chromatograph to detect the content and type of the product.

[0057] Application Example 2: Activity of Co1 / CN-550A in Photocatalytic CO2 Conversion

[0058] (1) Take Co1 / CN-550A catalyst and ultrasonically disperse it in a mixed solution of deionized water and hole sacrificial agent triethanolamine (TEOA). The concentration of the catalyst in the deionized water is 0.17 g / L, and the volume ratio of H2O to TEOA is 5:1. Then transfer it to a stainless steel reactor, seal it, and start to introduce CO2 until the air in the reactor is exhausted.

[0059] (2) Use a 300W Xe lamp as the light source and 25℃ condensate to maintain the temperature of the reaction system;

[0060] (3) After a certain reaction time, a portion of the gas in the reactor is extracted using a gas injection needle and injected into the hydrogen flame ionization detector of the gas chromatograph to detect the content and type of the product.

[0061] Application Example 3: Activity of Co1 / CN-400A in Photocatalytic CO2 Conversion

[0062] (1) Take Co1 / CN-400A catalyst and ultrasonically disperse it in a mixed solution of deionized water and hole sacrificial agent triethanolamine (TEOA). The concentration of the catalyst in the deionized water is 0.17 g / L, and the volume ratio of H2O to TEOA is 5:1. Then transfer it to a stainless steel reactor, seal it, and start to introduce CO2 until the air in the reactor is exhausted.

[0063] (2) Use a 300W Xe lamp as the light source and 25℃ condensate to maintain the temperature of the reaction system;

[0064] (3) After a certain reaction time, a portion of the gas in the reactor is extracted using a gas injection needle and injected into the hydrogen flame ionization detector of the gas chromatograph to detect the content and type of the product.

[0065] Application Example 4: Activity of Co1 / CN-700A in Photocatalytic CO2 Conversion

[0066] (1) Take Co1 / CN-700A catalyst and ultrasonically disperse it in a mixed solution of deionized water and hole sacrificial agent triethanolamine (TEOA). The concentration of the catalyst in the deionized water is 0.17 g / L, and the volume ratio of H2O to TEOA is 5:1. Then transfer it to a stainless steel reactor, seal it, and start introducing CO2 until the air in the reactor is exhausted.

[0067] (2) Use a 300W Xe lamp as the light source and 25℃ condensate to maintain the temperature of the reaction system;

[0068] (3) After a certain reaction time, a portion of the gas in the reactor is extracted using a gas injection needle and injected into the hydrogen flame ionization detector of the gas chromatograph to detect the content and type of the product.

[0069] like Figure 4 , 5 As shown, Co1 / CN-550A exhibits excellent activity in the photocatalytic conversion of CO2 to CH4, with a CH4 yield of 63.26 μmol / g. -1 Furthermore, the CH4 production gradually increased with the accumulation of light exposure time, indicating that the catalyst has good stability. However, Co1 / CN-400A, Co1 / CN-700A, and CN-550A could not catalyze the reduction of CO2 to CH4. The good activity exhibited by Co1 / CN-550A in the CO2 reduction to CH4 reaction depends on its specific Co-C2N coordination structure. Compared with N coordination, the Co-C bond energy is larger, and the resulting Co single-atom active center is more stable, which is conducive to the continuous reduction of CO2. In addition, in-situ infrared results also show that the Co-C2N active site also enhances the adsorption force on reaction intermediates, enabling them to be further reduced. Simultaneously, the unsaturated coordination structure of Co-C2N also facilitates the directional separation of electrons and holes, improving the catalyst's reduction ability and achieving the reduction of CO2 to CH4.

[0070] In summary, a Co1 / C3N4 single-atom catalyst with a specific coordination structure was prepared by a simple molten salt-assisted pyrolysis method at a selected temperature. This catalyst exhibits excellent photocatalytic performance in the conversion of CO2 to CH4 and demonstrates good stability.

Claims

1. A method for preparing a carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure, characterized in that, The structural formula of this carbon-based Co single-atom photocatalyst is: ； The steps are as follows: Step (1): Preparation of C3N4 Urea and melamine are ground and mixed evenly in a certain mass ratio and then placed in a tube furnace and calcined at 500~600℃ for 2~6 h to obtain a yellow powder, which is C3N4. The mass ratio of urea to melamine is between 1:1 and 1:

3. Step (2): Preparation of carbon-based Co single-atom catalysts with a coordination structure of Co-C2N 1) Add CoCl2, KCl and LiCl to the C3N4 prepared in step (1), and grind and mix them evenly to obtain mixture A; In mixture A, the total mass of KCl and LiCl accounts for 50%-80% of the mass of mixture A, and the mass of KCl accounts for 30%-50% of the total mass of KCl and LiCl; CoCl2 accounts for 1%-10% of the mass of mixture A, and C3N4 accounts for 10%-49% of the mass of mixture A. 2) The obtained mixture A is placed in a tube furnace and calcined at high temperature in an inert atmosphere by gradually increasing the temperature from room temperature to the target temperature. The target temperature range is 550~600℃, and the calcination time is 2~4 h; 3) After the calcined powder is thoroughly ground in a mortar, it is dispersed in a dilute acid solution for acid washing. The mixture is stirred first and then sonicated. The nanoparticles sintered during the preparation process are thoroughly washed away by a combination of stirring and sonication. The dilute acid solution is hydrochloric acid with a concentration of less than 0.5 mol / L or sulfuric acid with a concentration of less than 0.3 mol / L; 4) After the sample obtained by acid washing is allowed to stand for a period of time, the sample is centrifuged and washed until neutral, vacuum dried, and the sample is recovered to obtain a carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure, denoted as Co1 / CN-550A.

2. The preparation method according to claim 1, characterized in that, In step (2), the inert atmosphere is Ar or N2; the heating rate is 2~8℃ / min. -1 .

3. The preparation method according to claim 1, characterized in that, In step (3), the combination of stirring and ultrasound is specifically as follows: Stirring speed 200~1000 rpm, temperature 10~40℃, time 0.5~5 h; Ultrasonic power 500W, frequency 35~40kHz, duration 0.5~5h.

4. The preparation method according to claim 1, characterized in that, In step (4), The settling time is 2-6 hours; The centrifugation speed is 8000~18000 rpm.

5. The application of the carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure obtained by any of the preparation methods described in claims 1-4 in the photocatalytic reduction of CO2 to CH4, characterized in that, The steps are as follows: Step (1): Take a carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure and ultrasonically disperse it in a mixed solution of deionized water and hole sacrificial agent triethanolamine. The concentration of the carbon-based Co single-atom photocatalyst with a Co-C2N coordination structure in deionized water is 0.17 g / L, and the volume ratio of H2O to triethanolamine is 5:

1. Then transfer it to a stainless steel reactor, seal it, and start introducing CO2 until the air in the reactor is exhausted. Step (2): Use a 300W Xe lamp as the light source and 25°C condensate to maintain the temperature of the reaction system; Step (3): After a certain reaction time, a portion of the gas in the reactor is extracted and injected into the hydrogen flame ionization detector of a gas chromatograph to detect the content and type of the product.

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