Dark adsorption / light degradation difunctional tetrapyrrolyl covalent organic framework material and preparation method thereof

Abstract

The invention aims to provide a dark adsorption / light degradation difunctional tetrapyrrolyl covalent organic framework material and a preparation method thereof, and belongs to the technical field of functional materials. The material has high specific surface area, high crystallinity, good stability, wide-range visible light absorption and excellent photocatalytic performance, and can efficiently adsorb organic pollutants in water in a dark state. Under the action of visible light, active oxygen species for degrading organic pollutants can be generated, rapid degradation of the organic pollutants can be realized, and meanwhile, good cycling stability is achieved. The material is obtained by carrying out Schiff base condensation on amino porphyrin and tetra (4-formyl phenyl) benzene in a reaction kettle.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a tetrapyrrole-based covalent organic framework material with dual functions of dark adsorption / photodegradation and a preparation method thereof. The material forms a porous framework structure through covalent bonding of tetrapyrrole monomers with specific linking groups, and has both the functions of efficiently dark-adsorbing organic pollutants and visible-light-driven photocatalytic degradation, and can be widely applied to fields such as sewage treatment and environmental remediation. Background Art

[0002] In recent years, covalent organic frameworks (COFs) have been widely applied to technical fields such as adsorption, catalysis, and chemical sensing because they are crystalline porous materials formed by covalent bonding of light elements (such as C, H, O, N, etc.), and have a large specific surface area, adjustable pore size, and good stability. However, the developed COF materials mostly focus on a single function (such as adsorption or catalysis), and it is difficult to simultaneously achieve the synergistic effect of efficient adsorption and degradation of pollutants. Traditional classical photocatalysts (such as TiO2, g-C3N4) are affected by problems such as a narrow visible-light absorption range, a high recombination rate of photo-generated electron-hole pairs, and weak adsorption ability, and it is difficult to achieve the synergistic removal of adsorption enrichment and rapid degradation of organic pollutants in water. In addition, most photocatalytic materials cannot continuously adsorb organic pollutants in water under dark conditions, resulting in limitations in their practical applications. Porphyrin is a conjugated macrocyclic compound formed by bridging four pyrrole rings through methylene bridges. Its unique photophysical properties and electronic structure endow it with a wide visible-light absorption range, abundant catalytic sites, and structural designability. However, traditional porphyrin small molecules have problems such as insufficient dark adsorption ability, high recombination rate of photo-generated carriers, and poor structural stability in practical applications. Based on the above analysis, there is an urgent need to develop a COF material with a high adsorption capacity, a fast mass transfer channel, and stable catalytic active sites, and through the synergistic mechanism of dark adsorption enrichment and in-situ photodegradation, achieve the efficient removal of organic pollutants in water. Therefore, the present invention proposes to construct a dual-functional COF material with a fully conjugated framework and active sites by using a tetrapyrrole group as the core building unit through topological design and dynamic covalent chemistry strategies. It can efficiently adsorb organic pollutants in water under dark conditions, and achieve the rapid removal of pollutants through the "adsorption-enrichment-in-situ degradation" synergistic mechanism under light conditions, breaking through the performance bottleneck of traditional single-functional materials and providing a new strategy for organic pollution treatment. Summary of the Invention

[0003] The present invention provides a dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material and a preparation method thereof. The material has a high specific surface area, high crystallinity, wide-range visible light absorption and excellent photocatalytic performance, and can efficiently adsorb organic pollutants in water in the dark state. Under visible light irradiation, it can generate reactive oxygen species for degrading organic pollutants, enabling rapid degradation of organic pollutants, and at the same time having good cycle stability. The material is obtained by Schiff base condensation of aminoporphyrin and tetra(4-formylphenyl)benzene in a reaction kettle, and the structural formula of the material is:

[0004] A preparation method of a dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material is as follows: First, tetraaminoporphyrin and tetra(4-formylphenyl)benzene are respectively ground using an agate mortar; then, under a nitrogen atmosphere, the powders are added into the polytetrafluoroethylene kettle core of a 20 mL reaction kettle, dissolved using a mixed solvent, sealed and ultrasonically treated for 1 min, the kettle core is placed into the reaction kettle, heated at 130 °C for 3 days, naturally cooled to room temperature after the reaction is completed, and the solid crude product is separated by centrifugation. The obtained crude product is purified and dried to finally obtain the material of the present invention.

[0005] In the above steps, the feeding ratio of tetraaminoporphyrin and tetra(4-formylphenyl)benzene is 1.1:1. The mixed solvent is N,N-dimethylacetamide, o-dichlorobenzene, n-butanol and 6 mol / L acetic acid, and the volume ratio of the solvents is 2:3:5:1. The crude product is purified by Soxhlet extraction using tetrahydrofuran, dichloromethane and acetone respectively. The purified product is dried in a vacuum drying oven at 90 °C for 24 hours. After drying, nitrogen is introduced into the vacuum drying oven, and the sample is quickly taken out and sealed for storage. Description of the Drawings

[0005] Figure 1 It is the Fourier transform infrared spectrum of the dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material.

[0006] Figure 2 It is the solid-state nuclear magnetic carbon spectrum of the dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material.

[0007] Figure 3 It is the X-ray diffraction pattern of the dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material.

[0008] Figure 4 It is the UV-Vis diffuse reflectance spectrum of the dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material.

[0009] Figure 5 It is the nitrogen adsorption / desorption isotherm of the dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material.

[0010] Figure 6 UV-Vis absorption spectra of the dark adsorption / photodegradation bifunctional tetrapyrrolic covalent organic framework material for the adsorption of low-concentration Rhodamine B at different times under dark conditions.

[0011] Figure 7 UV-Vis absorption spectra of the dark adsorption / photodegradation bifunctional tetrapyrrolic covalent organic framework material for the photodegradation of Rhodamine B at different times after saturated adsorption. Detailed implementation manner

[0012] Synthesis of the dark adsorption / photodegradation bifunctional tetrapyrrolic covalent organic framework material: Under a nitrogen atmosphere, TAPP (81.0 mg, 0.12 mmol) and TFPB (59.3 mg, 0.12 mmol) were placed in a 20 mL polytetrafluoroethylene reaction kettle. N,N-dimethylacetamide, o-dichlorobenzene, n-butanol and 6 molar acetic acid (volume ratio 2:3:5:1, 6.6 mL) were added to dissolve them. After ultrasonic treatment for 1 min, the reaction was carried out at 130 °C for 72 h. After the reaction, it was cooled to room temperature, and the solid powder was separated by centrifugation, washed with tetrahydrofuran, dichloromethane and acetone, and then dried in vacuo at 90 °C for 24 h. After drying, nitrogen was introduced into the vacuum drying oven to obtain 98 mg of dark brown powder with a yield of 70%.

[0013] The organic dye Rhodamine B was used as a pollutant model. Under dark conditions, 2 mg of the material synthesized by the above method was added to 20 mL of an aqueous Rhodamine B solution (2.0×10 -5 mol / L), and magnetic stirring was carried out at a speed of 400 rpm. By taking the suspension at different time intervals, centrifuging and taking the supernatant, the absorbance of Rhodamine B was monitored using UV-Vis absorption spectroscopy.

[0014] Under light conditions, an aqueous Rhodamine B solution (6.0×10 -5 mol / L, 40 mL) was used as the dye model, and 2 mg of the above-prepared material was used as the photocatalyst. Before illumination, in order to achieve adsorption saturation between the aqueous Rhodamine B solution and the surface of the photocatalyst, the system was stirred in the dark for 24 h. Then, the system was irradiated under visible light (λ>400 nm) and accurately timed. Every 30 min, 3 mL of the solution was taken out, the suspension was centrifuged to separate the solid catalyst, and the concentration of the supernatant was monitored using a UV-Vis spectrophotometer.

Claims

1. A dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material, characterized in that, A fully conjugated porous framework structure is formed by the Schiff base condensation reaction of tetraaminoporphyrin and tetrakis(4-formylphenyl)benzene through a dynamic covalent chemistry strategy, and its chemical structural formula is as follows:

2. The dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material according to claim 1, characterized in that, The material shows a characteristic peak of Schiff base (C=N) at δ = 150 - 160 ppm in the solid-state 13C NMR spectrum, a C=N stretching vibration peak at 1620 - 1630 cm-1 in the Fourier transform infrared spectroscopy (FT-IR), and characteristic diffraction peaks in the X-ray diffraction pattern.

3. A method for preparing the dark adsorption / photodegradation bifunctional tetrapyrrolic covalent organic framework material according to claim 1 or 2, characterized in that, It includes the following steps: (1) Grind tetraaminoporphyrin and tetrakis(4-formylphenyl)benzene into uniform powders respectively according to a molar ratio of 1.1:

1. (2) Under a nitrogen atmosphere, add the powder from step (1) into the polytetrafluoroethylene inner liner of the reaction kettle, and add a mixed solvent to dissolve it; the mixed solvent consists of N,N-dimethylacetamide, o-dichlorobenzene, n-butanol and 6 molar acetic acid, and the volume ratio is 2:3:5:

1. (3) Seal the reaction kettle and ultrasonically treat for 1 minute, then heat and react at 130 °C for 72 hours. (4) After the reaction is completed, naturally cool to room temperature, centrifuge to separate the solid product, and successively carry out Soxhlet extraction and purification using tetrahydrofuran, dichloromethane and acetone. (5) Dry the purified product in a vacuum drying oven at 90 °C for 24 hours. After drying, introduce nitrogen into the vacuum drying oven, quickly take out the sample and seal it for storage. A dual-functional tetra-pyrrole-based covalent organic framework material with dark adsorption / photodegradation is obtained.

4. The preparation method according to claim 3, characterized in that The reaction kettle is a 20 mL polytetrafluoroethylene-lined high-pressure reaction kettle, and the total volume of the mixed solvent is 6.0 - 7.0 mL.

5. Use of the dark adsorption / photodegradation bifunctional tetrapyrrole-based covalent organic framework material according to claim 1 or 2 in sewage treatment, characterized in that, It includes the following steps: (a) Under dark conditions, add the material into the water body containing organic pollutants to enrich the pollutants through adsorption. (b) Under visible light irradiation, hydroxyl radicals (·OH) and superoxide radicals (·O2 - ) are generated using the photocatalytic active sites of the material to in-situ degrade the enriched pollutants.

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