Preparation of porphyrin-based covalent organic frameworks and their applications in photocatalysis

Abstract

The present invention discloses a novel porphyrin-based covalent organic framework material for its preparation and application in photocatalytic conversion of organic small molecules, belonging to the field of polymer photocatalysis. The present invention uses 5,10,15,20-tetrakis(4-aminophenyl)porphyrin and 2,5-thiophenedicarboxaldehyde to prepare the porphyrin-based covalent organic framework material by Schiff base condensation reaction under solvent thermal conditions. The obtained porphyrin-based covalent organic framework material has good light absorption capacity, high specific surface area and strong stability, can be applied to the photocatalytic conversion of various organic small molecules, and has good conversion rate, thus having good application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of polymer photocatalysis, and specifically relates to a synthesis method of a novel porphyrin-based covalent organic framework material and its application in photocatalytic conversion of organic small molecules. Background Art

[0002] With the continuous development of my country's industrial level, the use of fossil fuels such as oil has become increasingly frequent, and environmental problems have become increasingly prominent. Therefore, the search for green and clean energy has become a key to solving this problem. Solar energy has the advantages of being cheap, abundant, and clean. The conversion of light into chemical energy through catalysts has attracted widespread attention. Therefore, the development of photocatalysts with stable properties, low cost, strong light absorption capacity, and photocatalytic activity for the conversion of small organic molecules is of great application significance.

[0003] Porphyrin is a typical large π-conjugated structure and an important component of plant chlorophyll. It is often used as a photosensitizer. Porphyrin COFs are widely used in the research of photocatalysts due to their highly delocalized π-electron skeleton, flexible modification sites, efficient electron separation performance and wide absorption characteristics. Summary of the Invention

[0004] The present invention aims to provide a novel porphyrin-based covalent organic framework (COF) material. By incorporating a porphyrin unit as a photosensitizer to enhance the material's light absorption properties, the material also incorporates a thiophene unit, which exhibits excellent photoelectric properties. This results in a COF with excellent light absorption, a high specific surface area, and strong stability. When used for photocatalytic conversion of small organic molecules, it exhibits excellent conversion efficiency. Furthermore, the thiophene group can be further post-modified into a thiophene sulfone group, transforming the electron donor (D) into an electron acceptor (A), transforming the COF from a DD configuration to a DA configuration. This promotes the separation and migration of photogenerated excitons, further enhancing the photocatalytic effect.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] A porphyrin-based covalent organic framework (COF) material is prepared by a Schiff base condensation reaction of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (HP) and 2,5-thiophenedicarboxaldehyde (Th) under solvothermal conditions. The preparation method involves weighing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin and 2,5-thiophenedicarboxaldehyde in a specific stoichiometric ratio and placing them in a Pyrex tube. Benzyl alcohol and o-dichlorobenzene (the solvents) and acetic acid solution (the catalyst) are then added. The tube is then freeze-thawed in a liquid nitrogen bath three times, then flame-sealed and placed in an oven for a solvothermal reaction. The resulting reaction product is filtered, Soxhlet extracted with tetrahydrofuran (TH) overnight, and then dried in a vacuum oven overnight to yield the dark purple porphyrin-based COF material H2P-Th-COF.

[0007] Furthermore, the molar ratio of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin to 2,5-thiophenedicarboxaldehyde is 1:2.

[0008] Furthermore, the solvent thermal reaction is carried out by heating the temperature from room temperature to 120° C. and keeping the temperature for 3-7 days, preferably, keeping the temperature for 5 days.

[0009] Furthermore, the volume ratio of benzyl alcohol to o-dichlorobenzene is 1:2-6:1, preferably, the volume ratio is 1:2.

[0010] Furthermore, the concentration of the acetic acid solution is 3-6 mol / L, and the amount thereof is converted based on a molar ratio of acetic acid to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin of 15:1-15:2.

[0011] The porphyrin-based covalent organic framework material can be used for the photocatalytic conversion of organic small molecules. Specifically, the porphyrin-based covalent organic framework material is directly used as a catalyst for the photocatalytic conversion reaction of organic small molecules, or is used as a catalyst for the photocatalytic conversion reaction of organic small molecules after further oxidation modification. The organic small molecules include phenylboronic acid, benzylamine, and sulfide, which can be converted into phenol, imine, and sulfoxide accordingly.

[0012] Furthermore, the oxidative modification specifically involves mixing the porphyrin-based covalent organic framework material H2P-Th-COF with an aqueous hydrogen peroxide solution in a beaker, stirring the mixture for reaction under irradiation with a xenon lamp, washing and filtering the reaction product, and drying it in a vacuum drying oven overnight to obtain a purple-black porphyrin-based covalent organic framework material H2P-ThDo-COF with a partially oxidatively modified skeleton.

[0013] The amount ratio of the porphyrin-based covalent organic framework material to the hydrogen peroxide aqueous solution is 50-200 mg / 5 mL, preferably, the amount ratio is 100 mg / 5 mL; the volume ratio of H2O2 to H2O in the hydrogen peroxide aqueous solution is 1:8-1:2, preferably, the volume ratio is 1:4; the stirring reaction time is 15-90 min, preferably, the time is 60 min.

[0014] The beneficial effects of the present invention are:

[0015] 1) Through band structure design, the present invention uses H2P and Th to synthesize for the first time a new thiophene-containing porphyrin-based covalent organic framework material. The material has a large π-conjugated system, good response to visible light, can improve the utilization rate of solar energy, realize the photocatalytic conversion of organic small molecules, and has good chemical stability.

[0016] 2) The equipment and chemical reagents used in the present invention are easily available, the process operation is simple, the process conditions are simple, the practicability is strong, the industrial application value is high, and it is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the synthesis process of the porphyrin-based covalent organic framework material H2P-Th-COF and its subsequent modified product H2P-ThDo-COF of the present invention;

[0018] Figure 2 X-ray diffraction patterns of H2P-Th-COF prepared in Example 1 and its subsequent modified product H2P-ThDo-COF;

[0019] Figure 3 FTIR spectra of H2P-Th-COF prepared in Example 1 and its modified product H2P-ThDo-COF;

[0020] Figure 4 Scanning electron micrographs of H2P-Th-COF (a) prepared in Example 1 and its modified product H2P-ThDo-COF (b);

[0021] Figure 5 This is the N2 adsorption-desorption isotherm of H2P-Th-COF prepared in Example 1;

[0022] Figure 6 This is a comparison chart of the conversion rate and selectivity of photocatalytic benzylamine coupling to form imine at different wavelengths of H2P-Th-COF.

[0023] Figure 7The figure shows the comparison of conversion rate and selectivity of photocatalytic oxidation of sulfide to sulfoxide by H2P-Th-COF and its modified product H2P-ThDo-COF under the same conditions. DETAILED DESCRIPTION

[0024] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0025] Example 1

[0026] HP (26.7 mg, 0.04 mmol) and Th (11.2 mg, 0.08 mmol) were placed in a Pyrex tube, and o-dichlorobenzene (0.33 mL), benzyl alcohol (0.67 mL), and 6 mol / L acetic acid solution (0.1 mL) were added. The Pyrex tube was then flame-sealed under liquid nitrogen freezing and negative pressure (~10 mbar). The tube was then placed in an oven, heated to 120°C, and incubated for 5 days. The crude product was washed three times with acetone and THF, collected by filtration, and then Soxhlet extracted with THF overnight. The product was then dried under vacuum overnight to yield a dark purple HP-Th-COF.

[0027] HP-Th-COF (100 mg) was mixed with an aqueous solution of H2O2 (H2O2:H2O = 1 mL:4 mL) and stirred under xenon lamp irradiation for 60 min. The crude product was washed three times with water, collected by filtration, and vacuum-dried overnight to yield purple-black HP-ThDo-COF.

[0028] Figure 2 The XRD patterns of the prepared H2P-Th-COF and its post-modified product, H2P-ThDo-COF, are shown. The peak near 3.83° in the figure is a characteristic diffraction peak of H2P-Th-COF, confirming its successful synthesis. The peak of the post-modified H2P-ThDo-COF remains unchanged, demonstrating that the post-modification process did not destroy the crystallinity of H2P-Th-COF.

[0029] Figure 3 The Fourier transform infrared spectra of the prepared H2P-Th-COF and its modified product H2P-ThDo-COF are shown in Figure 1. -1 The stretching vibration of the carbon-oxygen double bond is at ~1610 cm -1The stretching vibration of the carbon-nitrogen double bond at 1180 cm-1 corresponds to the stretching vibration of the carbon-oxygen double bond in the synthesized COF. It can be clearly seen that the carbon-oxygen double bond in the synthesized COF has been completely reacted to form a carbon-nitrogen double bond, which further proves the successful preparation of the porphyrin-based covalent organic framework material H2P-Th-COF. In addition, after post-modification, H2P-Th-COF -1 The appearance of the stretching vibration peak of the sulfur-oxygen double bond proves that the post-modification is successful and the sulfur-oxygen double bond is generated.

[0030] Figure 4 Scanning electron micrographs of the prepared H2P-Th-COF (a) and its post-modified product, H2P-ThDo-COF (b). As can be seen, the H2P-Th-COF exhibits a square flake structure with numerous small square scale-like accumulations on its surface, while the H2P-ThDo-COF exhibits an irregular circular flake structure with numerous small scale-like accumulations on its surface. The post-modification product exhibits a significant reduction in size.

[0031] Figure 5 The nitrogen adsorption-desorption and pore size distribution of the prepared H2P-Th-COF are shown in the isotherm curve. It can be seen from the isotherm curve that when the relative pressure is low, there is a strong adsorption potential in the mesopores. As the relative pressure increases, capillary condensation occurs in the micropores, causing the desorption curve and adsorption curve to not overlap, resulting in a clear hysteresis loop. This belongs to the IV type adsorption curve with a specific surface area of ​​803 m 2 The pore size distribution diagram shows that H2P-Th-COF has a hierarchical porous structure with coexistence of micropores and mesopores.

[0032] Example 2 Photocatalytic conversion of small organic molecules:

[0033] Oxidation of phenylboronic acid to phenol: 5 mg of H2P-Th-COF was placed in a 10 mL Slack tube. 0.25 mmol of phenylboronic acid, 1.5 mL of acetonitrile, and 0.75 mmol of triethylamine were added. After sonication for 30 seconds, the balloon was evacuated and oxygen was introduced. Irradiation was performed with a 420 nm LED at room temperature for 1 hour. After the reaction was complete, 20 µL of the sample solution was mixed with 1 mL of ethyl acetate and filtered through a 0.22 µm organic filter into a gas chromatography-mass spectrometry (GC-MS) vial. The photocatalytic reaction was monitored by GC-MS.

[0034] Benzylamine coupling to imine: 5 mg of H2P-Th-COF was weighed and placed in a 10 mL Slack tube. 0.1 mmol of benzylamine and 1 mL of acetonitrile were added. After sonication for 30 seconds, the balloon was evacuated and oxygen was introduced. Irradiation was performed with a 420 nm LED for 5 minutes at room temperature. After the reaction was complete, 20 µL of the sample solution was mixed with 1 mL of ethyl acetate and filtered through a 0.22 µm organic filter into a gas chromatography-mass spectrometry (GC-MS) vial. The photocatalytic reaction was monitored by GC-MS.

[0035] Sulfide oxidation to sulfoxide: 5 mg of H2P-Th-COF was weighed and placed in a 10 mL Slack tube. 0.1 mmol of methylphenyl sulfide and 2 mL of ethanol were added. After sonication for 30 seconds, the balloon was evacuated and oxygen was introduced. Irradiation with a 420 nm LED was performed at room temperature for 2 hours. After the reaction was complete, 20 µL of the sample solution was mixed with 1 mL of ethyl acetate and filtered through a 0.22 µm organic filter into a gas chromatography-mass spectrometry (GC-MS) vial. The photocatalytic reaction was monitored by GC-MS.

[0036] Table 1 shows the conversion rate and selectivity of H2P-Th-COF and carbon nitride (PCN) for photocatalytic conversion of organic small molecules.

[0037] Table 1

[0038]

[0039] As shown in Table 1, H2P-Th-COF has the ability to photocatalyze the conversion of small molecules. Within 1 h, it can achieve a conversion rate of 96.3% and a selectivity of 99% for the oxidation of phenylboronic acid to phenol; within 5 min, the conversion rate of benzylamine coupling to imine reaches 91% and a selectivity of 99%; within 2 h, the conversion rate of sulfide oxidation to sulfoxide reaches 72.3% and a selectivity of 94%, which shows better photocatalytic potential than PCN materials.

[0040] Figure 6 The figure shows the conversion rate and selectivity comparison of H2P-Th-COF photocatalytic coupling of benzylamine to imine at different wavelengths. Figure 6 As shown in the figure, under the irradiation of 600 nm LED, the conversion rate of H2P-Th-COF to form imine reached 77% and the selectivity was 99% within 30 minutes, indicating that even with weaker light, the photocatalytic conversion can be completed efficiently, which once again shows that the obtained material has excellent performance.

[0041] Figure 7 A comparison of the conversion and selectivity of H2P-Th-COF and its modified product H2P-ThDo-COF photocatalytically oxidize sulfides to sulfoxides under the same conditions. As shown, the modified H2P-ThDo-COF photocatalytically oxidizes sulfides to sulfoxides by 3.5 times over a 1-hour reaction under the same conditions.

[0042] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. Application of a porphyrin-based covalent organic framework material in photocatalytic conversion of organic small molecules, characterized by: The porphyrin-based covalent organic framework material is further oxidatively modified and used as a catalyst for the photocatalytic conversion reaction of organic small molecules; The porphyrin-based covalent organic framework material is prepared by a Schiff base condensation reaction of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin and 2,5-thiophene dicarboxaldehyde under solvent thermal conditions; The oxidation modification specifically comprises mixing a porphyrin-based covalent organic framework material with a hydrogen peroxide solution, stirring and reacting under xenon lamp irradiation, washing and filtering the reaction product, and drying overnight to obtain a purple-black porphyrin-based covalent organic framework material H2P-ThDo-COF with a partially oxidized skeleton; The organic small molecules include phenylboronic acid, benzylamine, and thioether, which are correspondingly converted into phenol, imine, and sulfoxide.

2. The use according to claim 1, characterized in that: Specifically, 5,10,15,20-tetrakis(4-aminophenyl)porphyrin and 2,5-thiophenedicarboxaldehyde are weighed respectively according to a certain stoichiometric ratio, benzyl alcohol and o-dichlorobenzene as solvents and acetic acid solution as a catalyst are added, and the reaction is sealed for solvent thermal reaction. After filtering, the reaction product is extracted with tetrahydrofuran Soxhlet overnight and then dried overnight to obtain a dark purple porphyrin-based covalent organic framework material H2P-Th-COF.

3. The use according to claim 2, characterized in that: The molar ratio of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin to 2,5-thiophenedicarboxaldehyde was 1:

2.

4. The use according to claim 2, wherein: The solvent thermal reaction is carried out by heating the temperature from room temperature to 120° C. and keeping the temperature for 3-7 days.

5. The use according to claim 2, characterized in that: The volume ratio of benzyl alcohol and o-dichlorobenzene used is 1:2-6:

1.

6. The use according to claim 2, characterized in that: The concentration of the acetic acid solution is 3-6 mol / L, and the amount thereof is converted based on a molar ratio of acetic acid to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin of 15:1-15:

2.

7. The use according to claim 1, characterized in that: The amount ratio of the porphyrin-based covalent organic framework material to the hydrogen peroxide aqueous solution is 50-200 mg / 5 mL; the volume ratio of H2O2 to H2O in the hydrogen peroxide aqueous solution is 1:8-1:2; and the stirring reaction time is 15-90 min.

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