Preparation method of novel secondary amine covalent organic framework material and photocatalytic application of novel secondary amine covalent organic framework material

Abstract

The invention belongs to the field of photocatalytic preparation of hydrogen peroxide, and relates to a novel secondary amine linked covalent organic framework material (AR-COF) as well as a preparation method and application thereof. According to the material, tetraaldehyde phenyl porphyrin and 2, 5-diamino-1, 4-benzenediol dihydrochloride are subjected to a Schiff base reaction to synthesize an imine bond connected porphyrinyl covalent organic framework (IM-COF), and then synthesis post-modification (PSM) is performed on the imine bond connected porphyrinyl covalent organic framework (IM-COF) so that the imine bond connected porphyrinyl covalent organic framework (IM-COF) and sodium borohydride can be subjected to a reduction reaction to generate AR-COF. The photocatalytic stability of the material is maintained through modification after synthesis, the catalytic activity is improved, and the original crystal structure is not damaged. A photocatalytic hydrogen peroxide production experiment shows that the catalytic activity of AR-COF under 420 nm monochromatic light is superior to that of IM-COF, the yield under an oxygen condition reaches 7.79 mmol.g <-1 >. H <-1 >, and hydrogen peroxide can be stably produced. The method utilizes solar energy for green synthesis under mild conditions, and provides a safe and efficient method for hydrogen peroxide production.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a method for preparing a novel porphyrin-based secondary amine-linked covalent organic framework material and its application in photocatalytic hydrogen peroxide production. Background Technology

[0002] Hydrogen peroxide (H2O2), as an important green oxidant, plays a vital role in many fields such as chemical synthesis, wastewater treatment, and medical and health applications due to its high reactive oxygen species content and the fact that its reaction products are only water and oxygen. However, the global production of H2O2 is still dominated by the anthraquinone oxidation method, which suffers from high energy consumption, cumbersome processes, and the emission of hazardous waste, resulting in a heavy environmental burden and contradicting the principles of green chemistry and low-carbon emission goals. Therefore, the technology route of converting H2O or O2 into H2O2 in pure water using solar energy is widely recognized as an ideal strategy that is green, energy-saving, low-consumption, and safe. This process uses sunlight as an energy source and can be carried out under mild natural environmental and pressure conditions, meeting the needs of sustainable development and demonstrating great potential to replace traditional anthraquinone processes due to its advantages of low energy consumption, no pollution, and high safety.

[0003] Covalent organic frameworks (COFs) are a class of multifunctional materials possessing both well-defined crystal structures and inherent porosity. Their frameworks can be customized by introducing diverse functionalities, which play a central role in various COF applications. Imine-linked COFs have been widely prepared due to their reversible synthesis and controllable structure, but compared to chemically bonded COFs, they suffer from drawbacks such as lower catalytic activity. To address these issues, researchers have been exploring the preparation and application of other types of COFs in recent years. However, direct synthesis methods often face challenges in practical preparation: some functional groups may be incompatible with reaction conditions or compete with other monomers for reaction; simultaneously, the pre-synthesis of bulk components in COFs can adversely affect crystal formation. To circumvent these problems, post-synthetic modification (PSM) methods for imine COFs have emerged—this strategy not only enhances their photocatalytic activity but also maintains material stability without significantly affecting the crystal structure, becoming an effective means of optimizing COF performance. Summary of the Invention

[0004] To address the shortcomings of existing technologies and the needs of research and application in this field, a method is provided for producing hydrogen peroxide by using hydrogenation reduction modification of imine bonds during the in-situ synthesis of COF to obtain a novel covalent organic framework photocatalyst.

[0005] The preparation method of the photocatalyst involves first selecting a tetraaldehyde phenylporphyrin with photocatalytic activity, then selecting a hydroxyl-modified diamine monomer—2,5-diamino-1,4-benzenediol dihydrochloride—and constructing a porphyrin-based covalent organic framework material (IM-COF) linked by imine bonds via a Schiff base reaction. This material is then reacted with sodium borohydride to generate a porphyrin-based covalent organic framework material (AR-COF) linked by secondary amine bonds, which is then used as the photocatalyst. Post-synthetic modification (PSM) enhances the photocatalytic activity of the material while maintaining long-term structural and performance stability. Simultaneously, this improved stability does not significantly affect the crystal structure of the material, ensuring that the photocatalytic active sites and crystal order imparted by the COF are fully preserved, guaranteeing the efficient performance of the material's core functions. The catalyst exhibits stable and efficient photocatalytic hydrogen peroxide production performance, achieving a dual improvement in structural stability and catalytic activity, and can be applied in the field of photocatalytic hydrogen peroxide production.

[0006] A method for preparing a porphyrin-based covalent organic framework material AR-COF photocatalyst includes the following steps:

[0007] Weigh 42.6 mg (0.02 mmol) of 2,5-diamino-1,4-benzenediol dihydrochloride and 72 mg (0.1 mmol) of tetraaldehyde phenylporphyrin, and add them together to a Schlenk tube. Then, add a mixed solution consisting of 2 mL of o-dichlorobenzene, 2 mL of mesitylene, and 0.2 mL of 6M acetic acid, and sonicate for 10 minutes. Perform three freeze-evacuation-thawing cycles to complete the degassing process. Afterward, place the Schlenk tube in a sand bath and react at 120 °C for 72 hours. After the reaction, wash the precipitate three times by centrifugation, first with N,N-dimethylformamide (DMF), then with anhydrous ethanol, until the supernatant is colorless. After centrifugation, the product was extracted using a Soxhlet extractor with dichloromethane as the solvent for three days. Finally, the product was dried in a vacuum oven at 60°C for 6 hours to obtain the catalyst IM-COF. Terephthalic acid (49.8 mg, 0.3 mmol) and IM-COF (50 mg) were added to 25 mL of methanol (MeOH). Before adding NaBH4 (431.25 mg, 11.4 mmol), the mixture was stirred in an ice bath for 10 minutes. After stirring in the ice bath for 2 hours, the product was collected by centrifugation and washed three times with methanol. The obtained product was dried in a vacuum oven at 60°C for 12 hours to obtain the AR-COF photocatalyst.

[0008] The transient photocurrent response and electrochemical impedance spectroscopy of AR-COF and IM-COF photocatalysts were tested, including the following steps:

[0009] 5 mg of completely ground sample was mixed with 1 mL of ethanol under ultrasonic treatment for 30 minutes to completely disperse the sample. The resulting slurry was dropped onto an ITO-coated glass plate and heated to 80 °C until completely dry. The FTO glass plated with the prepared sample, platinum wire, and calomel electrode were used as the working electrode, counter electrode, and reference electrode, respectively. A 300 W xenon lamp was used as the light source, and a 0.5 M Na₂SO₄ aqueous solution was used as the electrolyte throughout the measurement process. Electrochemical impedance spectroscopy (EIS) and photocurrent response measurements were performed using a CHI660E electrochemical workstation (CHII Instruments, Shanghai, China).

[0010] A comparison of AR-COF and IM-COF photocatalysts for hydrogen peroxide production includes the following steps:

[0011] 3 mg of the photocatalyst AR-COF was weighed and added to a mixture of 8 mL deionized water and 8 mL benzyl alcohol. The catalyst was then fully dispersed by ultrasonic treatment. A stir bar was then added to the system, and the mixture was transferred to a reaction vessel, which was then ventilated. Reactions were conducted under oxygen, air, and nitrogen conditions, respectively, with 420 nm monochromatic light as the light source, and the photocatalytic reaction was initiated at a stirring speed of 500 rpm. After the reaction, the aqueous and organic phases were separated to obtain a pure hydrogen peroxide solution. The amount of hydrogen peroxide produced was determined spectrophotometrically. The colorimetric reagents used in the determination were peroxidase (POD) and N,N-diethyl-p-phenylenediamine sulfate (DPD), and a 0.5 M phosphate solution at pH 6 was used as a buffer to ensure the stability of the colorimetric reaction and detection process.

[0012] The beneficial effects of this invention are as follows: This invention utilizes post-synthetic modification (PSM) to improve a covalent organic framework material (IM-COF) to synthesize a novel covalent organic framework material (AR-COF) with high crystallinity and order. This catalyst exhibits high efficiency in the photocatalytic hydrogen peroxide production reaction, not only effectively driving the reaction to generate hydrogen peroxide, but also providing stable catalytic effects, thus providing a green, efficient, and safe method for hydrogen peroxide production. Attached Figure Description

[0013] Appendix Figure 1 This is a synthetic route diagram of the AR-COF prepared in Example 1;

[0014] Appendix Figure 2 This is a scanning electron microscope image of the AR-COF photocatalyst;

[0015] Appendix Figure 3 This is a transmission electron microscope image of the AR-COF photocatalyst;

[0016] Appendix Figure 4 This is the powder X-ray diffraction pattern of the AR-COF photocatalyst;

[0017] Appendix Figure 5 This is the photocurrent diagram of the AR-COF photocatalyst;

[0018] Appendix Figure 6 This is the electrochemical impedance spectroscopy diagram of the AR-COF photocatalyst;

[0019] Appendix Figure 7 This is the infrared spectrum of the AR-COF photocatalyst;

[0020] Appendix Figure 8 This is the Raman spectrum of the AR-COF photocatalyst;

[0021] Appendix Figure 9 This is a comparison chart of hydrogen peroxide yield between AR-COF photocatalyst and IM-COF under oxygen, air, and nitrogen conditions;

[0022] Appendix Figure 10 This is a graph showing the cycle stability of hydrogen peroxide production for AR-COF photocatalysts. Detailed Implementation

[0023] Example 1

[0024] (I) Preparation of AR-COF:

[0025] Weigh 42.6 mg (0.02 mmol) of 2,5-diamino-1,4-benzenediol dihydrochloride and 72 mg (0.1 mmol) of tetraaldehyde phenylporphyrin, and add them together to a Schlenk tube. Then, add a mixed solution consisting of 2 mL of o-dichlorobenzene, 2 mL of mesitylene, and 0.2 mL of 6M acetic acid, and sonicate for 10 minutes. Perform three freeze-evacuation-thawing cycles to complete the degassing process. Afterward, place the Schlenk tube in a sand bath and react at 120 °C for 72 hours. After the reaction, wash the precipitate three times by centrifugation, first with N,N-dimethylformamide (DMF), then with anhydrous ethanol, until the supernatant is colorless. After centrifugation, the product was extracted using a Soxhlet extractor with dichloromethane as the solvent for three days. Finally, the product was dried in a vacuum oven at 60°C for 6 hours to obtain the catalyst IM-COF. Terephthalic acid (49.8 mg, 0.3 mmol) and IM-COF (50 mg) were added to 25 mL of methanol (MeOH). Before adding NaBH4 (431.25 mg, 11.4 mmol), the mixture was stirred in an ice bath for 10 minutes. After stirring in the ice bath for 2 hours, the product was collected by centrifugation and washed three times with methanol. The obtained product was dried in a vacuum oven at 60°C for 12 hours to obtain the AR-COF photocatalyst. Figure 1This is a schematic diagram of the synthetic route for the prepared AR-COF.

[0026] (II) Test Results:

[0027] Figure 2 This is a scanning electron microscope image of the AR-COF photocatalyst.

[0028] Figure 3 This is a transmission electron microscope image of the AR-COF photocatalyst. From... Figure 3 As can be seen, AR-COF is a non-uniform nanosheet structure.

[0029] Figure 4 This is the powder X-ray diffraction pattern of the AR-COF photocatalyst. Figure 4 It can be seen that obvious and sharp diffraction peaks appear around 5°, reflecting a regular pore structure, indicating that AR-COF has good crystallinity and order.

[0030] Figure 5 This is the transient photocurrent response diagram of the AR-COF photocatalyst. AR-COF exhibits a higher photocurrent density, indicating that secondary amine linkage facilitates more efficient charge separation.

[0031] Figure 6 These are electrochemical impedance spectroscopy (EIS) plots of the AR-COF and IM-COF catalyst-modified electrodes. AR-COF exhibits a smaller charge transfer resistance compared to IM-COF, indicating that AR-COF has higher charge-mass transfer efficiency, thereby significantly improving its catalytic activity.

[0032] Figure 7 This is the infrared spectrum of the AR-COF photocatalyst. The CN peak is enhanced (1328 cm⁻¹). -1 This confirms that the product AR-COF forms a CN connection mode.

[0033] Figure 8 This is the Raman spectrum of the AR-COF photocatalyst. The CN peak is enhanced (1276 cm⁻¹). -1 This confirms that the product AR-COF forms a CN connection mode.

[0034] Example 2

[0035] Application of AR-COF and IM-COF photocatalysts in photocatalytic production of hydrogen peroxide

[0036] The method is as follows: The reaction is carried out in a photocatalytic reactor, with 420 nm monochromatic light as the light source, under oxygen, air, and nitrogen conditions respectively. 3 mg of photocatalysts AR-COF and IM-COF are weighed and added to a mixture of 8 mL deionized water and 8 mL benzyl alcohol, respectively. The catalysts are fully dispersed by ultrasonic treatment. A stir bar is placed in the system, and the mixture is transferred to the reactor and aerated. The photocatalytic reaction is initiated with 420 nm monochromatic light as the light source and a stirring speed of 500 rpm. After the reaction, the aqueous and organic phases are separated to obtain a pure hydrogen peroxide solution.

[0037] After reacting for 1 hour, the supernatant, which was a hydrogen peroxide solution, was collected from the reaction vessel. The amount of hydrogen peroxide generated was determined spectrophotometrically. The amount of hydrogen peroxide generated was determined spectrophotometrically using peroxidase (POD) and N,N-diethyl-p-phenylenediamine sulfate (DPD) as colorimetric reagents, and 0.5 M phosphate solution at pH 6 as buffer. A UV spectrophotometer was used to detect the amount of hydrogen peroxide generated.

[0038] Experimental results are as follows Figure 9 Under oxygen conditions, the amount of hydrogen peroxide produced by AR-COF was 7.79 mmol·g. -1 The hydrogen peroxide production of IM-COF was 3.86 mmol·g. -1 The amount of hydrogen peroxide produced by AR-COF under air conditions was 5.63 mmol·g. -1 The hydrogen peroxide production of IM-COF was 2.74 mmol·g. -1 Under nitrogen conditions, the amount of hydrogen peroxide produced by AR-COF was 2.48 mmol·g. -1 The hydrogen peroxide production of IM-COF was 1.68 mmol·g. -1 Under oxygen conditions, AR-COF showed approximately a two-fold increase in photocatalytic hydrogen peroxide yield compared to IM-COF, demonstrating the effectiveness of the post-synthetic modification strategy. The yields of both AR-COF and IM-COF for hydrogen peroxide synthesis were significantly higher in oxygen environments than in nitrogen environments, with both showing a marked decrease in yield under a nitrogen atmosphere. This phenomenon indicates that these two covalent organic framework materials primarily rely on the oxygen reduction pathway to produce hydrogen peroxide during photocatalysis.

[0039] During the reaction under oxygen conditions, a supernatant, which was a hydrogen peroxide solution, was drawn from the reactor every 30 minutes. The amount of hydrogen peroxide generated was determined spectrophotometrically. The colorimetric reagents were peroxidase (POD) and N,N-diethyl-p-phenylenediamine sulfate (DPD), with a pH=6, 0.5M phosphate solution as the buffer. The amount of hydrogen peroxide generated was detected using a UV spectrophotometer.

[0040] The results of the cyclic stability test are as follows: Figure 10 As a photocatalyst, AR-COF showed a uniform increase in hydrogen peroxide production within 2 hours with increasing reaction time, exhibiting stronger catalytic ability than IM-COF and good stability after 5 cycles.

[0041] It is evident that the AR-COF photocatalyst exhibits higher activity and better catalytic performance, enabling stable production of hydrogen peroxide. It boasts significant advantages such as low energy consumption, low cost, and safety without pollution, and has promising application prospects in the field of photocatalytic hydrogen peroxide production.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any equivalent changes, alterations, and variations made to the above embodiments based on the implementation techniques of the present invention are within the protection scope of the present invention.

Claims

1. A porphyrin-based covalent organic framework material AR-COF photocatalyst, characterized in that, The AR-COF photocatalyst is a covalent organic framework material linked by secondary amine bonds.

2. The method for preparing a porphyrin-based covalent organic framework material AR-COF photocatalyst according to claim 1, characterized by the following steps: (1) Weigh 42.6 mg (0.02 mmol) of 2,5-diamino-1,4-benzenediol dihydrochloride and 72 mg (0.1 mmol) of tetraaldehyde phenylporphyrin and add them together into a Schlenk tube; (2) Add a mixed solution consisting of 2 mL of o-dichlorobenzene, 2 mL of mesitylene and 0.2 mL of 6M acetic acid into the tube, sonicate for 10 minutes, and perform three freeze-evacuation-thawing cycles to complete the degassing operation; (3) Place the Schlenk tube in a sand bath and react at 120°C for 72 hours; (4) After the reaction is complete, the precipitate is first washed three times by centrifugation with N,N-dimethylformamide (DMF) and then with anhydrous ethanol until the supernatant is colorless. (5) After centrifugation, the product was placed in a Soxhlet extractor and extracted with dichloromethane as solvent for three days. Finally, the product was placed in a vacuum oven at 60°C and dried for 6 hours to obtain the catalyst IM-COF. (6) Add terephthalic acid (49.8 mg, 0.3 mmol) and IM-COF (50 mg) to 25 mL of methanol (MeOH), stir the mixture in an ice bath for 10 minutes, and then add NaBH4 (431.25 mg, 11.4 mmol); (7) After stirring in an ice bath for 2 hours, centrifuge to collect the product and wash it with methanol 3 times. (8) The product was dried in a vacuum oven at 60°C for 12 hours to obtain the photocatalyst AR-COF.

3. The novel secondary amine covalent organic framework material AR-COF catalyst as described in claim 1, characterized in that: (1) AR-COF can maintain photocatalytic stability through structural optimization without significantly affecting the crystal structure, thus ensuring its continued function. (2) AR-COF can regulate surface functional groups, which is beneficial to improve the activity of the material in photocatalytic reactions.

4. The AR-COF according to claim 1, applied to photocatalytic production of hydrogen peroxide, characterized by the following steps: (1) Weigh 3 mg of photocatalyst AR-COF and add it to a mixture of 8 mL of deionized water and 8 mL of benzyl alcohol. Use sonication to fully disperse the catalyst. (2) Add a stir bar to the system, transfer the mixture to the reactor, and ventilate the photocatalytic reactor under oxygen conditions. (3) Set 420nm monochromatic light as the light source and start the photocatalytic reaction at a stirring speed of 500rpm. (4) After the reaction is complete, the aqueous phase and organic phase in the system are separated to obtain a pure hydrogen peroxide solution. (5) The amount of hydrogen peroxide generated was determined by spectrophotometry. The colorimetric reagents used in the determination were peroxidase (POD) and N,N-diethyl-p-phenylenediamine sulfate (DPD), and a 0.5M phosphate solution with pH=6 was used as a buffer to ensure the stability of the colorimetric reaction and detection process.

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