Covalent triazine framework / alkali bismuth salt complexes and use for electrocatalytic production of hydrogen peroxide

Abstract

The application provides a preparation method of a covalent triazine framework / alkali bismuth salt composite for electrocatalytic production of hydrogen peroxide. A porous covalent triazine framework of 2,2'-dipyridyl and a soluble bismuth salt are dispersed in a non-water polar solvent in sequence, then a certain amount of weak acid is added to adjust the pH value of the system, chelation and bismuth salt hydrolysis reaction are carried out at a certain temperature, and finally after filtration, washing and drying, the target product of the chelated alkali bismuth salt in the inner hole of the covalent triazine framework is obtained. The preparation process of the covalent triazine framework / alkali bismuth salt composite is simple, the pollution to the environment is small, the covalent triazine framework / alkali bismuth salt composite has excellent electrocatalytic performance of oxygen reduction to hydrogen peroxide. It shows 90~95% two-electron selectivity and high reaction activity.

Description

Technical Field

[0001] This invention relates to the preparation of electrocatalysts and its application in fields such as green industrial synthesis, exemplified by the electrocatalytic production of hydrogen peroxide. Background Technology

[0002] Hydrogen peroxide (H2O2) is an important chemical product with advantages such as a high proportion of reactive oxygen species, strong oxidizing power, and environmental friendliness. It has wide applications in chemical synthesis, paper bleaching, wastewater treatment, disinfection, and fuel cells. Currently, the industrial production of hydrogen peroxide generally uses the anthraquinone process, which has disadvantages such as high energy consumption and high pollution, and requires hydrogen as a hydrogen source, failing to meet the requirements of green and sustainable development. In contrast, the electrocatalytic two-electron oxygen reduction reaction (2e... - ORR (Organic Hydrogen Peroxide Synthesis) can use protons in water as a hydrogen source to synthesize hydrogen peroxide under the drive of electricity. It is energy-saving and environmentally friendly, and has great development potential. Therefore, 2e - The electrosynthesis of hydrogen peroxide by ORR has received widespread attention. (In 2e) - In the ORR reaction, the catalyst plays a crucial role. An efficient catalyst can effectively reduce the overpotential of the reaction and improve its activity and selectivity. Covalent triazine frameworks (CTFs) are nitrogen-containing aromatic polymer frameworks with triazine rings. Their highly porous nature gives them a sufficiently large specific surface area, providing numerous adsorption sites for bismuth salts. Their excellent stability endows CTFs with great potential as substrate materials for ORR electrocatalysts. It has been reported that metallic bismuth nanoparticles are effective against 2e⁻. - ORR exhibits high selectivity (greater than 96%) and extremely high kinetic current density (3.8 mA cm⁻¹ at 0.65 V). -2 While the catalyst exhibits good stability (Joule, 2023, 7, 1–13), the reported method uses a pyrolysis strategy to prepare the catalyst, which involves a complex preparation process and harsh reaction conditions. In contrast, this invention selects a solvothermal method, which not only has a simple preparation process and mild preparation conditions, but also allows for the one-step acquisition of the target product. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for preparing hydrogen peroxide via electrocatalysis using a covalent triazine framework (CTF) / basic bismuth salt complex, comprising the following steps:

[0004] Step 1: The covalent triazine framework CTF and soluble bismuth salt are uniformly dispersed in a non-aqueous polar solvent to obtain a dispersion. A non-aqueous polar solvent is chosen because the soluble bismuth salt rapidly precipitates in aqueous solution, hindering its recombination with CTF. This problem is effectively avoided in a non-aqueous polar solvent. Non-aqueous polar solvents include methanol, tetrahydrofuran, and N,N-dimethylformamide (DMF).

[0005] In some embodiments, the mass ratio of CTF to soluble bismuth salt is 1:0.5 to 1:2, and the dispersibility of CTF in a non-aqueous polar solvent is 1 to 3 mg / mL. -1 .

[0006] The CTF is [2,2'-bipyridyl]-5,5'-dimethylmethanol, which is obtained by mixing benzene monomer biphenyl-4,4'-dimethylamidine or terephthalamide, adding cesium carbonate, precipitating, and then washing and freeze-drying the resulting solid product.

[0007] In some embodiments, the molar ratio of [2,2'-bipyridyl]-5,5'-dimethylmethanol to benzene monomer biphenyl-4,4'-dimethylamidine or terephthalamide is 1:2-5.

[0008] The soluble bismuth salts mentioned include bismuth nitrate pentahydrate, bismuth acetate, bismuth sulfate, and bismuth chloride.

[0009] Step 2: Add the above dispersion to the pH adjuster (chelating agent), sonicate until homogeneous, and then heat and stir to react.

[0010] The dispersion has a pH of 3-6, and the pH adjuster (also known as a chelating agent) used is a weak acid such as acetic acid, malonic acid, or oxalic acid, with a concentration of 1-10 mol / L. -1 .

[0011] In this invention, the pH adjuster and the chelating agent are the same thing. The purpose of adding the pH adjuster (chelating agent) is to create a weakly acidic reaction environment. At the same time, it has negatively charged properties, and CTF contains a large number of N binding sites, so the whole environment is negatively charged. Therefore, as a positively charged soluble bismuth salt, it can be well combined with CTF and the chelating agent.

[0012] The heating temperature is 30~100 ℃, and the time is 6~24 h.

[0013] Step 3: After filtration, washing, and drying, the catalyst is obtained.

[0014] In some embodiments, one or more non-aqueous polar solvents such as methanol, tetrahydrofuran, and N,N-dimethylformamide (DMF) are selected and washed repeatedly at least three times. After filtration, the sample is placed in a vacuum drying oven and dried for 6 to 24 hours to obtain the catalyst.

[0015] The covalent triazine framework / basic bismuth salt complex prepared by the described method is used as a catalyst for the electrocatalytic production of hydrogen peroxide. This preparation method is simple and has low environmental pollution. The covalent triazine framework / basic bismuth salt complex exhibits excellent electrocatalytic performance in reducing oxygen to hydrogen peroxide, demonstrating 90-95% two-electron selectivity and high reactivity. Attached Figure Description

[0016] Figure 1 a is the ORR curve of the sample in Example 1, b is the tafeline curve of the sample in Example 1, c is the hydrogen peroxide selectivity of the sample in Example 1, and d is the number of transferred electrons of the sample in Example 1.

[0017] Figure 2 a is the ORR curve of the sample in Example 2, b is the tafeline curve of the sample in Example 2, c is the hydrogen peroxide selectivity of the sample in Example 2, and d is the number of transferred electrons of the sample in Example 2.

[0018] Figure 3 a is the ORR curve of the sample in Example 3, b is the tafeline curve of the sample in Example 3, c is the hydrogen peroxide selectivity of the sample in Example 3, and d is the number of transferred electrons of the sample in Example 3.

[0019] Figure 4 a is the ORR curve of sample 4, b is the tafeline curve of sample 4, c is the hydrogen peroxide selectivity of sample 4, and d is the number of transferred electrons of sample 4.

[0020] Figure 5 a is the ORR curve of the sample in Example 5, b is the tafeline curve of the sample in Example 5, c is the hydrogen peroxide selectivity of the sample in Example 5, and d is the number of transferred electrons of the sample in Example 5.

[0021] Figure 6 a is the ORR curve of the sample in Example 6, b is the tafeline curve of the sample in Example 6, c is the hydrogen peroxide selectivity of the sample in Example 6, and d is the number of transferred electrons of the sample in Example 6.

[0022] Figure 7 a is the ORR curve of the sample in Example 7, b is the tafeline curve of the sample in Example 7, c is the hydrogen peroxide selectivity of the sample in Example 7, and d is the number of transferred electrons of the sample in Example 7.

[0023] Figure 8 a is the ORR curve of the sample in Example 8, b is the tafeline curve of the sample in Example 8, c is the hydrogen peroxide selectivity of the sample in Example 8, and d is the number of transferred electrons of the sample in Example 8.

[0024] Figure 9The XRD pattern of Example 3, combined with the standard card, shows the presence of basic bismuth salt and bismuth oxide, proving the successful preparation of the CTF / basic bismuth nitrate complex.

[0025] Figure 10 TEM images of Example 5, with Figure a magnification of 150,000x and Figure b magnification of 300,000x.

[0026] Figure 11 The mapping diagram of Example 5 shows that the CTF / basic bismuth nitrate complex is uniformly distributed. Detailed Implementation

[0027] Characterization conditions:

[0028] The ORR test method in this embodiment of the invention is as follows: Take 980 μL of water, 980 μL of ethanol, and 40 μL of Nafion, mix them thoroughly, then take 1 mg of sample and add it to the solution, sonicate for 2 h to disperse it evenly. Then drop the resulting slurry onto a rotating ring electrode with a loading of 0.02 mg cm⁻¹. -2 The test was then conducted using a three-electrode system consisting of a reference electrode (mercuric oxide), a counter electrode (carbon rod), and a working electrode in an oxygen-saturated 0.1 M KOH solution.

[0029] Preparation of covalent triazine framework (CTF):

[0030] In a round-bottom flask (100 mL), [2,2'-bipyridyl]-5,5'-dimethylmethanol (0.4 mmol), benzene monomer biphenyl-4,4'-dimethylamidine (0.8 mmol), and cesium carbonate (1.0 mmol) were added to a dimethyl sulfoxide solution (25.0 mL). The precipitate in the yellow suspension was thoroughly washed with dilute hydrochloric acid (1 M, 50 mL) to remove residual cesium carbonate, and then washed several times with water, ethanol, and tetrahydrofuran. The filtered solid was freeze-dried for 24 h to obtain yellow CTF.

[0031] Example 1

[0032] Add Bi(NO3)3·5H2O, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of Bi(NO3)3·5H2O and CTF in methanol is 0.33 g / L. -1 Then, acetic acid was added to adjust the pH of the solution to 3-6, and the dispersion of acetic acid in the system was 0.04 mol / L. -1After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove the residual Bi(NO3)3·5H2O in the precipitate. Finally, it was placed in a vacuum drying oven and dried for 12 hours to obtain a covalent triazine framework / basic bismuth nitrate complex. Figure 1 a shows the ORR curve of the sample from Example 1, with an initial potential of 0.673 V vs RHE and a limiting current density of 1.18 mA cm⁻¹. -2 The half-wave potential is 0.60 V vs RHE. Figure 1 b is the tafeline curve for sample 1 in Example 1, showing a tafeline slope of 62.7 mV dec. -1 , Figure 1 c represents the hydrogen peroxide selectivity of the sample from Example 1, which shows a selectivity of 87%. Figure 1 d represents the number of transferred electrons in the sample of Example 1, which can be calculated to be 2.23.

[0033] Example 2

[0034] Add Bi(NO3)3·5H2O, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of Bi(NO3)3·5H2O and CTF in methanol is 0.67 g / L. -1 Then, acetic acid was added to adjust the pH of the solution to 3-6, and the dispersion of acetic acid in the system was 0.04 mol / L. -1 After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove the residual Bi(NO3)3·5H2O in the precipitate. Finally, it was placed in a vacuum drying oven and dried for 12 hours to obtain a covalent triazine framework / basic bismuth nitrate complex. Figure 2 a shows the ORR curve of the sample from Example 2, with an initial potential of 0.66 V vs RHE and a limiting current density of 1 mA cm⁻¹. -2 The half-wave potential is 0.58 V vs RHE. Figure 2 b is the tafeline curve for the sample in Example 2, showing a tafeline slope of 69.7 mV dec. -1 , Figure 2 c represents the hydrogen peroxide selectivity of the sample from Example 2, which shows a selectivity of 92%. Figure 2 d represents the number of transferred electrons in the sample of Example 2, which can be calculated to be 2.15.

[0035] Example 3

[0036] Add Bi(NO3)3·5H2O, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of Bi(NO3)3·5H2O and CTF in methanol is 1 g / L. -1 Then, acetic acid was added to adjust the pH of the solution to 3-6, and the dispersion of acetic acid in the system was 0.04 mol / L. -1 After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove the residual Bi(NO3)3·5H2O in the precipitate. Finally, it was placed in a vacuum drying oven and dried for 12 hours to obtain a covalent triazine framework / basic bismuth nitrate complex. Figure 3 a shows the ORR curve of the sample from Example 3, with an initial potential of 0.65 V vs RHE and a limiting current density of 1.15 mA cm⁻¹. -2 The half-wave potential is 0.6 V vs RHE. Figure 3 b is the tafeline curve for sample 3 of Example 3, showing a tafeline slope of 69.6 mV dec. -1 , Figure 3 c represents the hydrogen peroxide selectivity of the sample in Example 3, which shows a selectivity of 97%. Figure 3 d represents the number of transferred electrons in the sample of Example 3, which can be calculated to be 2.04. Figure 9 The XRD pattern of the sample in Example 3, combined with the standard card, shows the presence of basic bismuth salt and bismuth oxide, proving the successful preparation of the CTF / basic bismuth nitrate complex.

[0037] Example 4

[0038] Add Bi(NO3)3·5H2O, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of Bi(NO3)3·5H2O and CTF in methanol is 1.5 g / L. -1 Then, acetic acid was added to adjust the pH of the solution to 3-6, and the dispersion of acetic acid in the system was 0.04 mol / L. -1 After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove the residual Bi(NO3)3·5H2O in the precipitate. Finally, it was placed in a vacuum drying oven and dried for 12 hours to obtain a covalent triazine framework / basic bismuth nitrate complex. Figure 4 a shows the ORR curve for sample 4, with an initial potential of 0.66 V vs RHE and a limiting current density of 1.11 mA cm⁻¹. -2 The half-wave potential is 0.6V vs RHE. Figure 4 b is the tafeline curve for sample 4 in Example 4, showing a tafeline slope of 75.5 mV dec.-1 , Figure 4 c represents the hydrogen peroxide selectivity of the sample in Example 4, which shows a selectivity of 98%. Figure 4 d represents the number of transferred electrons in the sample of Example 4, which can be calculated to be 2.02.

[0039] Example 5

[0040] Add Bi(NO3)3·5H2O, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of Bi(NO3)3·5H2O and CTF in methanol is 1 g / L. -1 Then, malonic acid was added to adjust the pH of the solution to 3-6, and the dispersion of malonic acid in the system was 0.04 mol / L. -1 After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove the residual Bi(NO3)3·5H2O in the precipitate. Finally, it was placed in a vacuum drying oven and dried for 12 hours to obtain a covalent triazine framework / basic bismuth nitrate complex. Figure 5 a shows the ORR curve for sample 5 of Example 5, with an initial potential of 0.7V vs. RHE and a limiting current density of 2.1mA / cm². -2 The half-wave potential is 0.60 V vs RHE. Figure 5 b is the tafeline curve for sample 5 of Example 5, showing a tafeline slope of 68.6 mV dec. -1 , Figure 5 c represents the hydrogen peroxide selectivity of the sample from Example 5, which shows a selectivity of 90%. Figure 5 d represents the number of transferred electrons in the sample of Example 5, which can be calculated to be 2.19. Figure 10 This is a TEM image of the sample from Example 5. Figure 11 The image shows the mapping diagram of the sample in Example 5, where the percentage of Bi atoms is 33.52%, the percentage of C atoms is 43.35%, and the percentage of O atoms is 20.77%.

[0041] Example 6

[0042] Add Bi(C2H2O2)3, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of Bi(C2H3O2)3 and CTF in methanol is 1 g / L. -1 Then, malonic acid was added to adjust the pH of the solution to 3-6, and the dispersion of malonic acid in the system was 0.04 mol / L. -1After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove the residual Bi(C2H3O2)3 in the precipitate. Finally, it was placed in a vacuum drying oven and dried for 12 hours to obtain a covalent triazine framework / basic bismuth acetate complex. Figure 6 a shows the ORR curve of the sample from Example 6, with an initial potential of 0.67 V vsRHE and a limiting current density of 1.36 mA cm⁻¹. -2 The half-wave potential is 0.6 V vs RHE. Figure 6 b is the tafeline curve for sample 6 of Example 6, showing a tafeline slope of 80 mV dec. -1 , Figure 6 c represents the hydrogen peroxide selectivity of the sample from Example 6, which shows a selectivity of 78%. Figure 6 d represents the number of transferred electrons in the sample of Example 6, which can be calculated to be 2.4.

[0043] Example 7

[0044] Add Bi(SO4)3, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of Bi(SO4)3 and CTF in methanol is 1 g / L. -1 Then, malonic acid was added to adjust the pH of the solution to 3-6, and the dispersion of malonic acid in the system was 0.04 mol / L. -1 After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove the residual Bi(SO4)3 in the precipitate. Finally, it was placed in a vacuum drying oven and dried for 12 hours to obtain a covalent triazine framework / basic bismuth sulfate complex. Figure 7 a shows the ORR curve for sample 7, with an initial potential of 0.63 V vs. RHE and a limiting current density of 1.3 mA cm⁻¹. -2 The half-wave potential is 0.57 V vs RHE. Figure 7 b is the tafeline curve for sample 7 in Example 7, showing a tafeline slope of 99.8 mV dec. -1 , Figure 7 c represents the hydrogen peroxide selectivity of the sample from Example 7, which shows a selectivity of 85%. Figure 7 d represents the number of transferred electrons in the sample of Example 7, which can be calculated to be 2.3.

[0045] Example 8

[0046] Add BiCl3, CTF, and methanol to a round-bottom flask (50 mL), ensuring that the dispersion of BiCl3 and CTF in methanol is 1 g / L. -1Then, malonic acid was added to adjust the pH of the solution to 3-6, and the dispersion of malonic acid in the system was 0.04 mol / L. -1 After the mixture was sonicated to homogenize, it was heated and stirred at 65°C for 8 hours. After the reaction was completed, the precipitate was obtained by filtration. The precipitate was washed several times with methanol to remove residual BiCl3. Finally, it was dried in a vacuum drying oven for 12 hours to obtain a covalent triazine framework / basic bismuth chloride complex. Figure 8 a shows the ORR curve for sample 8 of Example 8, with an initial potential of 0.67 V vs RHE and a limiting current density of 1.3 mA cm⁻¹. -2 The half-wave potential is 0.61 V vs RHE. Figure 8 b is the tafeline curve for sample 8 in Example 8, showing a tafeline slope of 82.5 mV dec. -1 , Figure 8 c represents the hydrogen peroxide selectivity of the sample from Example 8, which shows a selectivity of 84%. Figure 8 d represents the number of transferred electrons in the sample of Example 8, which can be calculated to be 2.29.

Claims

1. A method for preparing a covalent triazine framework / basic bismuth salt complex, characterized in that, The preparation steps include the following: S1. A covalent triazine framework CTF and a soluble bismuth salt are uniformly dispersed in a non-aqueous polar solvent to obtain a dispersion; the CTF is [2,2'-bipyridyl]-5,5'-dimethylmethanol, and benzene monomer biphenyl-4,4'-dimethylamidine or terephthalamide is mixed, cesium carbonate is added, and after precipitation, the resulting solid product is washed and freeze-dried. S2. Add a pH adjuster to the dispersion described in S1. The pH adjuster also acts as a chelating agent. After ultrasonic homogenization, heat and stir the mixture to react. The pH value of the dispersion is 3 to 6. The pH adjuster used is selected from any one of acetic acid, malonic acid, and oxalic acid. S3. After filtration, washing, and drying, the catalyst is obtained.

2. The preparation method according to claim 1, characterized in that, The mass ratio of CTF to soluble bismuth salt in S1 is 1:0.5 to 1:2, and the dispersibility of CTF in a non-aqueous polar solvent is 1 to 3 mg / mL. -1 .

3. The preparation method according to claim 1, characterized in that, The soluble bismuth salts include one or more of bismuth nitrate pentahydrate, bismuth acetate, bismuth sulfate, or bismuth chloride.

4. The preparation method according to claim 1, characterized in that, Non-aqueous polar solvents include one or more of methanol, tetrahydrofuran, or N,N-dimethylformamide.

5. The preparation method according to claim 1, characterized in that, The concentration of the pH adjuster is 1-10 mol·L⁻¹ -1 .

6. The preparation method according to claim 1, characterized in that, In S2, the heating temperature is 30~100 ℃ and the time is 6~24 h.

7. The application of the covalent triazine framework / basic bismuth salt complex prepared by the preparation method according to any one of claims 1-6 as a catalyst for electrocatalytic hydrogen peroxide production.

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