Preparation method and application of organic molecular network modified bismuth nanoparticles

Abstract

The application discloses a preparation method and application of an organic molecular network modified nano-bismuth, and aims to solve the problem of instability of a traditional carbon dioxide electrocatalyst at a gas-liquid-solid three-phase interface. A fluorocarbon crosslinking network is used to wrap a Bi-based precursor, and after wet chemical co-reduction, superfine Bi nanoparticles modified by the organic molecular network are obtained. The Bi-based catalyst obtained through the method can ensure high active sites, realize long-term stable three-phase reaction interface precise construction, and has good application prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing bismuth nanoparticles modified with an organic molecular network, which can be used for the electrocatalytic reduction of carbon dioxide to formic acid, and belongs to the fields of materials science and electrocatalysis. Background Technology

[0002] The ever-increasing carbon dioxide emissions have become a serious environmental problem, exacerbating global warming and climate change. Humanity urgently needs to explore effective industrial routes for the resource utilization of carbon dioxide. Besides the traditional high-temperature, high-pressure catalytic hydrogenation conversion method, utilizing renewable energy to electrochemically reduce carbon dioxide into high-value-added carbon molecules (such as formic acid, carbon monoxide, methane, and ethanol) is an effective and feasible approach. Among these, formic acid (or formate esters) is one of the most promising products for industrialization due to its liquid nature, ease of storage and transportation, suitability for use as a power source in fuel cells, and widespread application as a basic raw material in organic synthesis industries such as dyes, food, and leather.

[0003] To date, indium, mercury, bismuth, and tin are recognized as effective metal catalysts for the electrochemical conversion of carbon dioxide to formic acid. Among them, bismuth-based electrocatalysts possess advantages such as high selectivity, low cost, and low toxicity, making them potentially suitable for industrial application in the electroreduction of carbon dioxide to formic acid. However, at industrial-level current densities, the gas-liquid-solid three-phase interface at the catalyst becomes extremely unstable and may even be disrupted. Therefore, currently reported bismuth-based catalysts suffer from the following problems: the optimal operating current density for most bismuth-based catalysts is only 100-200 mA / cm², making it difficult to maintain stable operation for extended periods at excessively high current densities. The reactivity and stability are mutually restrictive, resulting in high economic costs for this technical route. Therefore, the development of bismuth-based catalysts that operate stably at high industrial-level current densities is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing an organic molecular network modified bismuth nanocatalyst for electrocatalytic carbon dioxide reduction and its application in formic acid synthesis. By chemically bonding a rich fluorocarbon organic network to the active sites of Bi, a stable and controllable hydrophobic gas-liquid-solid three-phase interface is formed, solving the problems of poor stability, low formic acid yield, and severe competitive hydrogen evolution reaction in existing electrocatalytic carbon dioxide reduction processes. This method achieves the electrocatalytic reduction of carbon dioxide to formic acid at an industrial current density (>800 mA / cm²), and has the advantages of simple synthesis process, strong electrocatalytic activity, and good stability.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing bismuth nanoparticles modified with an organic molecular network, the method comprising the following steps:

[0006] 1) Dissolve the bismuth salt in an organic solvent, stir until homogeneous, and then heat at the first heating temperature to accelerate dissolution while maintaining a constant temperature;

[0007] 2) The Bi precursor is obtained by heating the solution at a second heating temperature to precipitate the precipitate, centrifuging, washing, and drying. The second heating temperature is greater than the first heating temperature.

[0008] 3) Mix the Bi precursor obtained in step 2) with liquid hydrophobic organic molecules to obtain a mixture;

[0009] 4) Add borohydride solution to the mixture obtained in step 3), centrifuge and wash after precipitation, and dry to obtain organic molecular network modified bismuth nanoparticles.

[0010] Furthermore, the bismuth salt is one of bismuth nitrate, bismuth chloride, and bismuth sulfate, and the dosage is 100-1000 mg.

[0011] Furthermore, the organic solvent is a mixed solvent of propylene glycol methyl ether acetate (PMA) and dimethylformamide (DMF), with a mass ratio of 10:1 to 20:1 and a total mass of 400-4000 mg.

[0012] Furthermore, the first heating temperature is 50–80°C, and the heating method is oil bath or water bath heating.

[0013] Furthermore, the second heating temperature is 110-150℃, and the heating method is oil bath heating.

[0014] Furthermore, the washing sequence in steps 2) and 4) is repeated washing with DMF at 70°C, deionized water, and ethanol.

[0015] Furthermore, the hydrophobic organic molecule is heptadecafluorodecyltrimethoxysilane (PD).

[0016] Furthermore, the borohydride solution is a 0.05–0.2 mol / L sodium borohydride (NaBH4) solution.

[0017] Furthermore, the drying in steps 2) and 4) must be carried out under vacuum conditions at 50–80°C.

[0018] On the other hand, the present invention also provides an application of organic molecular network modified bismuth nanoparticles in electrocatalytic carbon dioxide reduction.

[0019] The advantages of this invention are:

[0020] (1) The method is simple. The method for preparing organic molecular network modified bismuth nanoparticles provided by this invention does not involve high temperature and high pressure synthesis conditions. It is simple, convenient and easy to operate, does not require large-scale equipment, and the raw materials are readily available, which is conducive to large-scale production.

[0021] (2) Excellent catalytic performance. The organic molecular network modified nano-bismuth provided by this invention achieves a formic acid partial current density of over 800 mA / cm² and a stability of over 12 hours in the electrocatalytic reduction of carbon dioxide to formic acid, which is of great significance for the industrial promotion of carbon dioxide reduction to formic acid.

[0022] (3) High versatility. The method for preparing nano-bismuth modified by organic molecular network provided by this invention can be extended to the development of other catalysts. By adjusting the type of metal in the active center, catalysts for various carbon products can be developed. Alternatively, the hydrophilicity and hydrophobicity of the interface can be controlled by adjusting the organic molecular network to achieve compatibility with various chemical reactions, thus having broad application prospects. Attached Figure Description

[0023] Figure 1 This is a transmission electron microscope image of bismuth nanoparticles modified with an organic molecular network;

[0024] Figure 2 This is an X-ray diffraction pattern of bismuth nanoparticles modified with an organic molecular network;

[0025] Figure 3 This is a transmission electron microscope image of ordinary nano-bismuth;

[0026] Figure 4 This is an X-ray diffraction pattern of ordinary nano-bismuth;

[0027] Figure 5 This is a Faraday efficiency diagram of organic molecular network modified bismuth nanoparticles at different current densities;

[0028] Figure 6 This is a Faraday efficiency diagram of ordinary nano-bismuth at different current densities;

[0029] Figure 7 This is a comparison of the formic acid partial current density between iR-compensated organic molecular network modified bismuth nanoparticles and ordinary bismuth nanoparticles.

[0030] Figure 8 This is a graph showing the electrocatalytic stability test of bismuth nanoparticles modified with organic molecular networks; Detailed Implementation

[0031] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1:

[0033] Add 600 mg of bismuth nitrate pentahydrate to 2034 mg PMA + 120 mL DMF solvent, stir for 40 min, then heat in an oil bath to 70 °C and maintain the temperature until all chemicals are dissolved. Then heat the solution to 120 °C and keep it at that temperature for 30 min. After the precipitate appears, collect it and centrifuge it. Wash it repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry it overnight at 70 °C. Take 150 mg of the obtained precursor and mix it with 10 μL of PD and dissolve it in 5 mL of ethanol. Dissolve 50 mg of sodium borohydride in 15 mL of deionized water and pour it into the mixed solution. Centrifuge to collect the precipitate and wash it repeatedly with deionized water and ethanol. Dry it under vacuum at 70 °C for 12 h to obtain organic molecular network modified bismuth nanoparticles.

[0034] Example 2:

[0035] Add 100 mg of bismuth nitrate pentahydrate to 500 mg PMA + 30 mL DMF solvent, stir for 40 min, then heat in an oil bath to 50 °C and maintain the temperature until all chemicals are dissolved. Then heat the solution to 110 °C and keep it at that temperature for 30 min. After the precipitate appears, collect it and centrifuge it. Wash it repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry it overnight at 70 °C. Take 150 mg of the obtained precursor and mix it with 10 μL of PD and dissolve it in 5 mL of ethanol. Dissolve 30 mg of sodium borohydride in 15 mL of deionized water and pour it into the mixed solution. Centrifuge to collect the precipitate and wash it repeatedly with deionized water and ethanol. Dry it under vacuum at 50 °C for 12 hours to obtain organic molecular network modified bismuth nanoparticles.

[0036] Example 3:

[0037] 1000 mg of bismuth nitrate pentahydrate was added to 3000 mg PMA + 180 mL DMF solvent. After stirring for 40 min, the solution was heated to 80 °C in an oil bath and kept at a constant temperature until all chemicals were dissolved. The solution was then heated to 150 °C and kept at that temperature for 30 min. After precipitation occurred, the solution was collected and centrifuged. The solution was washed repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dried overnight at 70 °C. 150 mg of the precursor was mixed with 10 μL of PD and dissolved in 5 mL of ethanol. 50 mg of sodium borohydride was dissolved in 15 mL of deionized water and poured into the mixed solution. The precipitate was collected by centrifugation and washed repeatedly with deionized water and ethanol. The solution was then vacuum dried at 80 °C for 12 h to obtain organic molecular network modified bismuth nanoparticles.

[0038] Example 4:

[0039] Add 600 mg of bismuth nitrate pentahydrate to 2034 mg PMA + 120 mL DMF solvent, stir for 40 min, then heat in an oil bath to 70 °C and maintain the temperature until all chemicals are dissolved. Then heat the solution to 120 °C and keep it at that temperature for 30 min. After the precipitate appears, collect it and centrifuge it. Wash it repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry it overnight at 70 °C. Take 150 mg of the obtained precursor and mix it with 10 μL of PD and dissolve it in 5 mL of ethanol. Dissolve 50 mg of sodium borohydride in 15 mL of deionized water and pour it into the mixed solution. Centrifuge to collect the precipitate and wash it repeatedly with deionized water and ethanol. Dry it under vacuum at 70 °C for 12 h to obtain organic molecular network modified bismuth nanoparticles.

[0040] The microstructure of the obtained organic molecular network modified bismuth nanoparticles was characterized using transmission electron microscopy, such as... Figure 1 As shown, the lattice spacing of the nanoparticles is 0.327 nm, belonging to the lattice fringes of Bi metal, corresponding to the Bi(012) principal crystal plane, which is consistent with the diffraction pattern of the Bi(012) crystal plane in the selected area electron diffraction (SAED) pattern. In addition, an amorphous layer is also encapsulated on the surface of metallic Bi. The phase is characterized using X-ray diffraction, such as... Figure 2 As shown, the corresponding Bi(012) principal crystal plane is consistent with the transmission electron microscopy results, and the diffraction peak intensity is weak, which is related to the amorphous layer surrounding the metallic Bi.

[0041] Example 5:

[0042] Add 600 mg of bismuth nitrate pentahydrate to 2034 mg PMA + 120 mL DMF solvent, stir for 40 min, then heat in an oil bath to 70 °C and maintain the temperature until all chemicals are dissolved. Then heat the solution to 120 °C and keep it at that temperature for 30 min. After the precipitate appears, collect it and centrifuge it. Wash it repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry it overnight at 70 °C. Take 150 mg of the obtained precursor and dissolve it in 5 mL of ethanol. Dissolve 120 mg of sodium borohydride in 15 mL of deionized water and pour it into the mixed solution. Centrifuge to collect the precipitate and wash it repeatedly with deionized water and ethanol. Dry it under vacuum at 70 °C for 12 hours to obtain ordinary nano-bismuth.

[0043] The microstructure of the obtained ordinary bismuth nanoparticles was characterized by transmission electron microscopy, such as... Figure 3 As shown, the lattice spacing of the nanoparticles is 0.329 nm, belonging to the lattice fringes of Bi metal, corresponding to the Bi(012) principal crystal plane, which is consistent with the diffraction pattern of the Bi(012) crystal plane in the selected area electron diffraction (SAED) pattern. Furthermore, ordinary nano-bismuth exhibits better crystallinity than organic molecular network-modified nano-bismuth. The phase was characterized using X-ray diffraction, such as... Figure 4As shown, the corresponding Bi(012) principal crystal plane is consistent with the transmission electron microscopy results, and the stronger diffraction peaks of the bismuth nanoparticles modified with organic molecular network are consistent with the better crystallinity results in the transmission electron microscopy results.

[0044] Example 6:

[0045] Add 600 mg of bismuth nitrate pentahydrate to 2034 mg PMA + 120 mL DMF solvent, stir for 40 min, then heat in an oil bath to 70 °C and maintain the temperature until all chemicals are dissolved. Then heat the solution to 120 °C and keep it at that temperature for 30 min. After the precipitate appears, collect it and centrifuge it. Wash it repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry it overnight at 70 °C. Take 150 mg of the obtained precursor and mix it with 10 μL of PD and dissolve it in 5 mL of ethanol. Dissolve 50 mg of sodium borohydride in 15 mL of deionized water and pour it into the mixed solution. Centrifuge to collect the precipitate and wash it repeatedly with deionized water and ethanol. Dry it under vacuum at 70 °C for 12 h to obtain organic molecular network modified bismuth nanoparticles.

[0046] Six milligrams of organic molecular network-modified bismuth nanoparticles were dispersed in a mixed solution of 15 μL Nafion and 345 μL ethanol, and then sprayed onto carbon paper to form an electrode. The performance was evaluated using a flow cell three-electrode system. Under conditions of continuous introduction of carbon dioxide at a flow rate of 40 sccm in 1 M KHCO3 electrolyte, different currents were applied to the system, and the Faradaic efficiency (FE) of each product (formic acid, hydrogen, carbon monoxide, etc.) at the corresponding current densities was measured. Figure 5 As shown in the figure. The results show that the organic molecular network modified bismuth nanoparticles achieved extremely high formic acid product selectivity (over 95%) over a wide voltage range (2.51V), and also had a certain effect of inhibiting competitive hydrogen evolution reaction even at high current densities.

[0047] Example 7:

[0048] Add 600 mg of bismuth nitrate pentahydrate to 2034 mg PMA + 120 mL DMF solvent, stir for 40 min, then heat in an oil bath to 70 °C and maintain the temperature until all chemicals are dissolved. Then heat the solution to 120 °C and keep it at that temperature for 30 min. After the precipitate appears, collect it and centrifuge it. Wash it repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry it overnight at 70 °C. Take 150 mg of the obtained precursor and dissolve it in 5 mL of ethanol. Dissolve 50 mg of sodium borohydride in 15 mL of deionized water and pour it into the mixed solution. Centrifuge to collect the precipitate and wash it repeatedly with deionized water and ethanol. Dry it under vacuum at 70 °C for 12 hours to obtain ordinary nano-bismuth.

[0049] Six milligrams of ordinary bismuth nanoparticles were dispersed in a mixed solution of 15 μL Nafion and 345 μL ethanol, and then sprayed onto carbon paper to form an electrode. The performance was evaluated using a flow cell three-electrode system. Under conditions of continuous introduction of carbon dioxide at a flow rate of 40 sccm in 1 M KHCO3 electrolyte, different currents were applied to the system, and the Faradaic efficiency (FE) of each product (formic acid, hydrogen, carbon monoxide, etc.) at the corresponding current densities was measured. Figure 6 As shown in the figure. The results show that ordinary nano-bismuth has only a narrow high-selectivity voltage window (0.53V), and the competitive hydrogen evolution reaction is severe under high current density.

[0050] Example 8:

[0051] Add 600 mg of bismuth nitrate pentahydrate to 2034 mg PMA + 120 mL DMF solvent, stir for 40 min, then heat in an oil bath to 70 °C, maintain the temperature until all chemicals dissolve, then heat the solution to 120 °C and hold for 30 min. Collect the precipitate and centrifuge. Wash repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry overnight at 70 °C. Dissolve 150 mg of the obtained precursor in 10 μL of PD in 5 mL of ethanol. Dissolve 50 mg of sodium borohydride in 15 mL of deionized water and add to the mixed solution. Centrifuge to collect the precipitate and wash repeatedly with deionized water and ethanol. Vacuum dry at 70 °C for 12 h to obtain organic molecular network modified bismuth nanoparticles. Following the same procedure, ordinary bismuth nanoparticles were prepared without the addition of PD. Sprayed onto carbon paper to form an electrode, its performance was evaluated using a flow cell three-electrode system. The polarization curve of the system under iR compensation was measured under conditions of 1 M KHCO3 electrolyte and a continuous flow of carbon dioxide at a flow rate of 40 sccm. Figure 7 As shown in the figure. The results show that organic molecular network modified bismuth nanoparticles exhibit lower reaction overpotentials than ordinary bismuth nanoparticles at various current densities, demonstrating good catalytic performance.

[0052] Example 9:

[0053] Add 600 mg of bismuth nitrate pentahydrate to 2034 mg PMA + 120 mL DMF solvent. After stirring for 40 min, heat in an oil bath to 70 °C and maintain the temperature until all chemicals dissolve. Then heat the solution to 120 °C and hold for 30 min. After precipitation, collect and centrifuge. Wash repeatedly with hot DMF at 70 °C, deionized water, and ethanol, and dry overnight at 70 °C. Take 150 mg of the obtained precursor and mix it with 10 μL of PD and dissolve in 5 mL of ethanol. Dissolve 50 mg of sodium borohydride in 15 mL of deionized water and pour it into the mixed solution. Centrifuge to collect the precipitate and wash it repeatedly with deionized water and ethanol. Vacuum dry at 70 °C for 12 h to obtain organic molecular network modified bismuth nanoparticles. The performance of the nanoparticles was evaluated using a flow cell three-electrode system. The stability of the system was measured under the conditions of 1 M KHCO3 electrolyte and continuous carbon dioxide flow at a flow rate of 40 sccm. Figure 8 As shown, the organic molecular network modified bismuth nanoparticles maintained extremely high formic acid selectivity for 12 hours as the reaction progressed, and the surface morphology of the catalyst after long-term operation was similar to that at the beginning, exhibiting good stability.

[0054] Experimental results

[0055] Through the operational trials and performance comparisons of the above embodiments, the organic molecular network modified bismuth nanoparticles exhibit excellent electrochemical stability in maintaining the gas-liquid-solid three-phase interface due to the hydrophobic coating on their surface. Their excellent catalytic performance achieves over 95% formic acid selectivity within a wide potential window of 2.51V, stability exceeding 12 hours, and an optimal partial current density exceeding 800 mA / cm², demonstrating promising prospects for industrial application.

[0056] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing bismuth nanoparticles modified with an organic molecular network, characterized in that, The method includes the following steps: 1) Dissolve the bismuth salt in an organic solvent, stir until homogeneous, and then heat at the first heating temperature to accelerate dissolution while maintaining a constant temperature; 2) The Bi precursor is obtained by heating the solution at a second heating temperature to precipitate the precipitate, centrifuging, washing, and drying. The second heating temperature is greater than the first heating temperature. 3) Mix the Bi precursor obtained in step 2) with the liquid hydrophobic organic molecule heptadecafluorodecyltrimethoxysilane to obtain a mixture; 4) Add borohydride solution to the mixture obtained in step 3), centrifuge and wash after precipitation, and dry to obtain organic molecular network modified bismuth nanoparticles.

2. The method for preparing bismuth nanoparticles modified with an organic molecular network according to claim 1, characterized in that, The bismuth salt is one of bismuth nitrate, bismuth chloride, or bismuth sulfate, and the dosage is 100-1000 mg.

3. The method for preparing bismuth nanoparticles modified with an organic molecular network according to claim 1, characterized in that, The organic solvent is a mixture of propylene glycol methyl ether acetate (PMA) and dimethylformamide (DMF) in a mass ratio of 10:1 to 20:1, with a total mass of 400-4000 mg.

4. The method for preparing bismuth nanoparticles modified with an organic molecular network according to claim 1, characterized in that, The first heating temperature is 50~80℃, and the heating method is oil bath or water bath heating.

5. The method for preparing bismuth nanoparticles modified with an organic molecular network according to claim 1, characterized in that, The second heating temperature is 110-150℃, and the heating method is oil bath heating.

6. The method for preparing bismuth nanoparticles modified with an organic molecular network according to claim 1, characterized in that, The washing sequence for steps 2) and 4) is repeated washing with DMF at 70°C, deionized water, and ethanol.

7. The method for preparing bismuth nanoparticles modified with an organic molecular network according to claim 1, characterized in that, The borohydride solution is a 0.05~0.2 mol / L sodium borohydride (NaBH4) solution.

8. The method for preparing bismuth nanoparticles modified with an organic molecular network according to claim 1, characterized in that, The drying in steps 2) and 4) must be carried out under vacuum at 50~80℃.

9. The application of an organic molecular network modified bismuth nanoparticle prepared by any one of claims 1 to 8 in the electrocatalytic reduction of carbon dioxide.

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