COFs-based photocatalytic material with improved structure as well as preparation method and application of COFs-based photocatalytic material

Abstract

The invention discloses a COFs (Covalent Organic Frameworks)-based photocatalytic material with an improved structure as well as a preparation method and application of the COFs-based photocatalytic material. The covalent organic framework-based photocatalytic material with the anti-protein structure is obtained by taking silicon dioxide photonic crystal microbeads as a template and 4, 4 '-biphenyl dinitrile as a template, carrying out in-situ polymerization on the 4, 4'-biphenyl dinitrile in confinement pores in the silicon dioxide photonic crystal microbeads and then etching silicon dioxide. The preparation method comprises the following steps: (1) adding a catalyst into a 4, 4 '-biphenyl dinitrile monomer, then adding silicon dioxide photonic crystal microbeads, and carrying out a polymerization reaction; and (2) etching the silicon dioxide to obtain the covalent organic framework-based photocatalytic material with the inverse opal structure. The COFs material and the inverse opal structure are combined, so that the photocatalytic activity of the material is remarkably enhanced, and efficient and selective conversion of CO2 is promoted.

Description

Technical Field

[0001] The present invention relates to a photocatalytic material and a preparation method and application thereof, and in particular to a COFs-based photocatalytic material with an improved structure and a preparation method and application thereof. Background Art

[0002] The continuous increase in atmospheric CO2 concentration has brought severe challenges to the environment and energy, such as global warming and the depletion of fossil fuel reserves. These problems urgently require effective carbon capture, utilization and storage strategies. Among many methods, photocatalytic CO2 reduction uses solar energy to convert CO2 into valuable chemicals under mild conditions without secondary pollution, making it a green and sustainable solution. The development of efficient photocatalytic CO2 reduction catalysts requires strong light absorption ability, effective charge separation efficiency and abundant active sites. Covalent organic frameworks (COFs) are a class of crystalline porous materials composed of organic structural units through covalent bonding. They have attracted widespread attention due to their excellent chemical and structural stability, tunable porosity and extensive π-conjugated systems. These properties make COFs ideal materials for CO2 capture and photocatalytic reduction. Covalent triazine frameworks (CTFs) are a subclass of COFs. Due to their nitrogen-rich structure and ability to interact with CO2 molecules, they are particularly suitable for photocatalytic reduction of CO2. However, traditional CTF materials usually suffer from low light utilization, poor charge separation efficiency and limited active surface area, which seriously restrict their photocatalytic performance. Summary of the invention

[0003] Purpose of the invention: The first purpose of the present invention is to provide a COFs-based photocatalytic material with an improved structure, so as to solve the problems of low visible light utilization rate, easy recombination of photogenerated electrons, low catalytic reduction CO2 yield and poor selectivity in existing COFs-based photocatalytic materials; the second purpose of the present invention is to provide a method for preparing the COFs-based photocatalytic material with an improved structure; the third purpose of the present invention is to provide the application of the COFs-based photocatalytic material with an improved structure.

[0004] Technical solution: The COFs-based photocatalytic material with improved structure described in the present invention has an organic structural unit of 4,4'-biphenyl dinitrile. 4,4'-biphenyl dinitrile is polymerized in situ in the confined pores within silica photonic crystal microbeads, and then the silica is etched to obtain a covalent organic framework-based photocatalytic material with an anti-protein structure.

[0005] The present invention mixes silica photonic crystal microbeads with 4,4'-biphenyl dicarbonitrile (BPCN) monomer solution, and fills the monomer solution into the ordered pores of the photonic crystal by means of capillary action. Then, under the action of CF3SO3H catalyst, the reaction is carried out at room temperature to form composite microbeads. Next, ammonium bifluoride (NH4HF2) is used to remove the silica template, thereby obtaining a covalent organic framework (COFs)-based photocatalyst with an inverse opal structure.

[0006] Preferably, the covalent organic framework-based photocatalytic material is a spherical structure with an ordered hexagonal porous array inside.

[0007] Preferably, the particle size of the raw material silica nanoparticles of the silica photonic crystal microbeads is 180 to 500 nm. As the size of the silica particles increases, the performance of the COFs-based photocatalyst is enhanced. When the silica particle size is 240 nm, the catalytic performance reaches the best effect, and the yield of photocatalytic CO2 reduction to CO is the highest, while when the silica particle size is 500 nm, the photocatalytic performance is the weakest.

[0008] The method for preparing the COFs-based photocatalytic material with improved structure described in the present invention comprises the following steps:

[0009] (1) adding a catalyst to a 4,4'-biphenyl dinitrile monomer, and then adding silica photonic crystal microbeads to carry out a polymerization reaction;

[0010] (2) Etching silica to obtain a covalent organic framework-based photocatalytic material with an inverse opal structure.

[0011] Preferably, the polymerization reaction is carried out at a temperature of 20 to 30° C. for 1.5 to 3 hours.

[0012] Preferably, the catalyst is CF3SO3H, and the volume mass ratio of CF3SO3H to 4,4'-biphenyl dicarbonitrile is 2-4 mL: 0.1-0.3 g.

[0013] Preferably, ammonium bifluoride is used to etch silicon dioxide.

[0014] Preferably, the preparation method of the silica photonic crystal microbeads is: using silica nanoparticles as a hard template, preparing an aqueous dispersion, forming droplets in silicone oil through a microfluidic device, and drying in an oven at 45 to 60° C. for 12 to 24 hours to complete the curing process to obtain dried microbeads; finally, calcining the dried microbeads to obtain silica photonic crystal microbeads.

[0015] Preferably, the concentration of the aqueous dispersion is 15-20 wt %.

[0016] The microbeads are calcined at a temperature of 750 to 900° C. for 2 to 4 hours.

[0017] The COFs-based photocatalytic material with improved structure described in the present invention is used in catalytic reduction of CO2 to generate CO.

[0018] Invention mechanism:

[0019] The present invention proposes an innovative method to prepare inverse opal structure COFs-based photocatalysts by combining microfluidics with pore-confined polymerization. The polymerization reaction occurs in the pores of the photonic crystal formed by the assembly of silica nanoparticles, and the spatial confinement of the pores effectively controls the arrangement and growth of COFs. This method can precisely control the periodicity and pore characteristics of the inverse opal structure, thereby forming a strong and highly ordered structure.

[0020] The present invention improves the light absorption performance, charge transfer speed, and photocatalytic CO2 reduction yield and selectivity of the material by combining COFs material with inverse opal structure. Inverse opal structure is a three-dimensional ordered macroporous material. Its unique optical effects (such as slow photon effect, photon band gap and Bragg reflection) improve the light utilization rate of COFs material. This structure can not only extend the propagation path of light and enhance the interaction between photons and substances, but also significantly promote efficient charge transfer; in addition, its highly porous structure provides efficient mass transfer channels and abundant catalytic active sites, which improves the adsorption capacity of CO2 and the photocatalytic reduction yield.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By combining COFs material and inverse opal structure, the photocatalytic activity of the material is significantly enhanced, promoting the efficient and selective conversion of CO2; (2) The COFs-based photocatalytic material with improved structure has a CO yield of 118.69 μmol g-1h-1 without using sacrificial agents or co-catalysts, and the product selectivity is as high as 97.25%; (3) The preparation method is simple and the reaction conditions are mild. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Optical microscope photo and SEM image of the photocatalytic material prepared in Example 1;

[0023] Figure 2 The UV-visible absorption spectra of the photocatalytic materials prepared in Examples 1 to 5 and Comparative Example 1;

[0024] Figure 3 Photoluminescence images of the photocatalytic materials prepared in Examples 1 to 5 and Comparative Example 1;

[0025] Figure 4 The transient photocurrent response diagram of the photocatalytic materials prepared in Examples 1 to 5 and Comparative Example 1;

[0026] Figure 5 The electrochemical impedance spectra of the photocatalytic materials prepared in Examples 1 to 5 and Comparative Example 1;

[0027] Figure 6 The performance diagram of photocatalytic CO2 reduction prepared by Example 1 and the comparison diagram of the effect of active substances on catalytic activity;

[0028] Figure 7 This is a data chart showing the CO yield from the catalytic reduction of CO2 by the catalytic materials of Examples 1 to 5 and Comparative 1. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below in conjunction with embodiments.

[0030] Example 1

[0031] The COFs-based photocatalytic material with improved structure of the present invention comprises the following steps:

[0032] (1) Using silica nanoparticles with a particle size of 240 nm as a hard template, a 20 wt% aqueous dispersion is prepared, and through a microfluidic device, the 20 wt% silica aqueous dispersion is used as a dispersed phase, and dimethyl silicone oil is used as a continuous phase to generate droplets, which are then collected in a polypropylene container pre-filled with dimethyl silicone oil, and dried in an oven at 60° C. for 12 hours to solidify them, thereby obtaining dried microbeads; then, the dried microbeads are calcined at 900° C. for 2 hours to obtain silica photonic crystal microbeads;

[0033] (2) In an ice-salt bath, 2.5 mL of CF3SO3H was slowly added to 0.2 g of 4,4'-biphenyl dicarbonitrile (BPCN) monomer to obtain a red viscous solution. Subsequently, 1.0 g of the silica photonic crystal microbeads prepared in step (1) was added to the red viscous solution and reacted at 25° C. for 1.5 h. After the reaction, the product was washed with deionized water and ammonia water in sequence;

[0034] (3) Finally, the silica photonic crystal microbeads treated in step (2) are immersed in 4 mol / L ammonium bifluoride (NH4HF2) to etch the silica to obtain a covalent organic framework (COF)-based photocatalytic material with an inverse opal structure.

[0035] Example 2

[0036] On the basis of Example 1, the particle size of the silicon dioxide nanoparticles was changed to 180 nm, and the other conditions remained unchanged.

[0037] Example 3

[0038] On the basis of Example 1, the particle size of the silicon dioxide nanoparticles was changed to 330 nm, and the other conditions remained unchanged.

[0039] Example 4

[0040] On the basis of Example 1, the particle size of the silicon dioxide nanoparticles was changed to 430 nm, and the other conditions remained unchanged.

[0041] Example 5

[0042] On the basis of Example 1, the particle size of the silicon dioxide nanoparticles was changed to 500 nm, and the other conditions remained unchanged.

[0043] Comparative Example 1

[0044] Based on Example 1, steps (1) and (3) are not performed, and silica photonic crystal microbeads are not added during the reaction of step (2), and the reaction obtains a bulk covalent organic framework (COF)-based photocatalytic material.

[0045] Structural characterization

[0046] Figure 1 The optical microscope photograph and SEM image of the inverse opal structure COF microbeads obtained in Example 1 show that the synthesized COF has a spherical morphology, a bright green appearance, and a hexagonal ordered porous array inside, with an average pore size of about 220 nm.

[0047] Performance Characterization

[0048] 1. Optical performance

[0049] The optical properties of the inverse opal structured covalent organic framework (COFs)-based photocatalytic materials prepared in Examples 1 to 5 and the bulk covalent organic framework (COF)-based photocatalytic material of Comparative Example 1 were tested. The results are as follows: Figures 2 to 5 shown.

[0050] Figure 2 The figure is a UV-visible absorption spectrum of the catalytic material. Compared with the catalytic material prepared in Comparative Example 1, the catalytic materials prepared in Examples 1 to 5 show a more obvious light absorption effect. As the silica particle size increases, the light absorption intensity of the catalytic materials prepared in Examples 1 to 5 gradually increases. When the particle size increases to 500nm, the absorption intensity decreases, but it is still higher than the bulk catalytic material in Comparative Example 1, indicating that the inverse opal pore structure is conducive to improving the light capture ability.

[0051] Figure 3The photoluminescence graph of the catalytic material shows that the catalytic materials of Examples 1 to 5 and Comparative Example 1 have a fluorescence emission peak at a wavelength of 480 nm, and the emission peak intensity of the catalytic materials of Examples 1 to 5 is weaker, indicating that the number of photogenerated charge carriers increases, thereby improving the catalytic activity. The fluorescence emission intensity of the catalytic materials prepared in Examples 1 to 5 decreases as the silica particle size increases. When the particle size increases to 500 nm, the fluorescence emission intensity increases, but is weaker than that of the bulk catalytic material in Comparative Example 1. When the particle size is 240 nm, the fluorescence intensity is the weakest, indicating that the number of photogenerated charges increases.

[0052] Figure 4 The transient photocurrent response diagram of the catalytic material shows that the catalytic materials of Examples 1 to 5 have a higher response current density, proving that the inverse opal structure can more effectively separate photogenerated charge carriers. The catalytic materials prepared in Examples 1 to 5 gradually increase in response current density as the silica particle size increases, indicating that the photogenerated charges are effectively transferred. When the particle size increases to 500nm, the current density decreases slightly, but is still higher than the bulk catalytic material in Comparative Example 1, indicating that the three-dimensional ordered pore structure is conducive to alleviating the recombination of photogenerated charge-hole pairs.

[0053] Figure 5 The electrochemical impedance spectrum of the catalytic material is shown in the figure. As shown in the figure, compared with the bulk CTF of Comparative Example 1, the impedance spectra of the inverse opal COF microbeads of Examples 1 to 5 have a smaller semicircle radius, which indicates that the three-dimensional inverse opal structure is beneficial to reducing resistance and promoting electron transfer. As the silica particle size increases, the semicircle radius of the Nernst curve of the catalytic materials prepared in Examples 1 to 5 decreases, indicating that compared with the bulk catalytic material of Comparative Example 1, the inverse opal structure can reduce the material resistance and promote electron transfer.

[0054] 2. Catalytic CO2 reduction performance

[0055] The catalytic CO2 reduction performance of the inverse opal structured covalent organic framework (COFs)-based photocatalytic materials prepared in Examples 1 to 5 and the blocky covalent organic framework (COF)-based photocatalytic materials of Comparative Example 1 was tested.

[0056] Test method: 10 mg of photocatalytic material was dispersed in 4 mL of deionized water and ultrasonicated for 5 min. The resulting suspension was then transferred to a sealed quartz reactor and high-purity carbon dioxide was introduced into the reactor for 30 min to remove residual air. A 300 W xenon lamp (150 mW cm -2 ) was used as the light source, and a circulating water condenser was used to maintain the reaction temperature at room temperature. After the reaction was completed, 1 mL of gas sample was drawn with a syringe and analyzed by gas chromatography (GC-7900) to determine the composition of the gaseous product. The test results are shown in Figure 6 shown.

[0057] Figure 6 The photocatalytic CO2 reduction performance of the covalent organic framework (COF)-based photocatalytic material with an inverse opal structure obtained in Example 1 is shown in the figure. As can be seen from the figure, CO is the main product with a yield of 118.69 μmol g -1 h -1 , the selectivity is as high as 97.25%. In contrast, the generation of CH4 and O2 is negligible. Free radical scavenging experiments show that the addition of quenchers leads to a significant decrease in the catalytic activity of COF, indicating that ·OH, ·O2 - and h + It is the key to drive the photocatalytic process.

[0058] Depend on Figure 7 It can be seen that the CO yields of the catalytic materials prepared in Examples 2 to 5 and Comparative Example 1 are 62 μmol g -1 h -1 , 92 μmol g -1 h -1 , 78 μmol g -1 h -1 , 58 μmol g -1 h -1 , 2 μmol g -1 h -1 The CO yield of the block catalytic material of Comparative Example 1 is the lowest, and the CO yield of the catalytic material of Example 1 is the highest.

Claims

1. A COFs-based photocatalytic material with improved structure, characterized in that: The organic structural unit of the material is 4,4'-biphenyl dicarbonitrile. 4,4'-biphenyl dicarbonitrile is in situ polymerized in the confined pores within silica photonic crystal microbeads, and then the silica is etched to obtain a covalent organic framework-based photocatalytic material with an anti-protein structure.

2. The COFs-based photocatalytic material with improved structure according to claim 1, characterized in that: The covalent organic framework-based photocatalytic material is a spherical structure, and the interior thereof presents a hexagonal ordered porous array.

3. The COFs-based photocatalytic material with improved structure according to claim 1, characterized in that: The particle size of the raw material silicon dioxide nanoparticles of the silicon dioxide photonic crystal microbeads is 180-500nm.

4. A method for preparing a COFs-based photocatalytic material with improved structure according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) adding a catalyst to a 4,4'-biphenyl dinitrile monomer, and then adding silica photonic crystal microbeads to carry out a polymerization reaction; (2) Etching silica to obtain a covalent organic framework-based photocatalytic material with an inverse opal structure.

5. The method for preparing the COFs-based photocatalytic material with improved structure according to claim 4, characterized in that: The polymerization reaction is carried out at a temperature of 20 to 30° C. for 1.5 to 3 hours.

6. The method for preparing the COFs-based photocatalytic material with improved structure according to claim 4, characterized in that: The catalyst is CF3SO3H, and the volume mass ratio of CF3SO3H to 4,4'-biphenyl dinitrile is 2-4 mL: 0.1-0.3 g.

7. The method for preparing the COFs-based photocatalytic material with improved structure according to claim 4, characterized in that: The preparation method of the silica photonic crystal microbeads is as follows: using silica nanoparticles as a hard template, preparing a water dispersion, forming droplets in silicone oil through a microfluidic device, and drying in an oven at 45 to 60° C. for 12 to 24 hours to complete the curing process to obtain dried microbeads; finally, calcining the dried microbeads to obtain silica photonic crystal microbeads.

8. The method for preparing the COFs-based photocatalytic material with improved structure according to claim 7, characterized in that: The concentration of the aqueous dispersion is 15-20 wt %.

9. The method for preparing the COFs-based photocatalytic material with improved structure according to claim 7, characterized in that: The microbeads are calcined at a temperature of 750 to 900° C. for 2 to 4 hours.

10. Use of the COFs-based photocatalytic material with improved structure as claimed in any one of claims 1 to 3 in catalytic reduction of CO2 to generate CO.

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