CN115521441B - Conjugated microporous polymer and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the field of photocatalysis CO ₂, and particularly relates to a conjugated microporous polymer, a preparation method and application thereof. The narrow band gap conjugated microporous polymer designed and synthesized for the first time can be used for selectively reducing CO ₂ to CO and CH ₄ under the irradiation of red light. By introducing electron donating pyrene and electron deficient fluorenone derivatives into the polymer backbone, the resulting polymer has an optical band gap between 1.61 and 1.74eV, exhibits broad optical absorption, and covers the entire visible region. Under visible light, the catalyst shows good visible light reduction activity, and the precipitation rates of CH ₄ and CO are respectively as high as 943.4 and 932.9 mu mol h ^‑1g^‑1. More importantly, under the irradiation of red light, the generation rates of CH ₄ and CO can still reach 293.7 and 282.6 mu mol h ^‑1g^‑1 respectively, and the reaction selectivity is about 100%.

Description

Conjugated microporous polymer and preparation method and application thereof

Technical Field

The invention belongs to the field of photocatalysis CO ₂, and particularly relates to a conjugated microporous polymer, a preparation method and application thereof.

Background

In recent years, the use of a large amount of fossil fuels in industrial production has not only continuously increased the global CO ₂ gas emissions, but also accelerated the progress of global energy shortage. Currently, the reduction of CO ₂ into fuels with increased added values such as CO, CH ₄ and CH ₃ OH by a photocatalysis technology by using inexhaustible solar energy as an energy input source is widely paid attention to researchers in various countries worldwide, and is considered to be one of effective ways for solving the current energy crisis and environmental pollution problems.

It is well known that in the solar radiation spectrum, visible light (wavelengths 380-760 nm) accounts for about 50%, while the remaining 7% and 43% consist of ultraviolet (< 380 nm) and Infrared (IR, >760 nm) light, respectively. However, to date, most catalysts for photocatalytic CO ₂ reduction are effective only for the visible region of sunlight, while red light with a wavelength greater than 600 nm, although accounting for over 50% of the solar radiation spectrum, are rarely used for photocatalysis. At present, few materials with red light/near infrared light activity are reported, and few examples of the materials comprise an Os (II) -Re (I) supermolecular complex, oxygen vacancy modified Bi ₂O₃ -x, carbon dots/Bi ₂WO₆, zn/carbon dots, csPbBr ₃/WO₃ and the like, wherein the materials are too many inorganic composite materials, the preparation process is complex, and the heavy metals contained in the materials possibly cause certain toxic risks to the environment. Therefore, it is still very challenging to develop a stable, low-cost and environmentally friendly photocatalyst to efficiently utilize sunlight above 600 nm for photocatalytic CO ₂, which requires a reasonable design of the catalyst.

Disclosure of Invention

The invention aims to solve the defects in the prior art, and provides a conjugated microporous polymer and a preparation method and application thereof, and the following technical scheme is adopted:

A conjugated microporous polymer, the structural schematic formula of the constituent units of which is shown as follows:

；

wherein, For/>（P1）、/>(P2) or/>（P3）。

The inventor takes 1,3,6, 8-tetraethynyl pyrene as an electron donor (donor), fluorenone derivatives as an electron acceptor (receptor), and synthesizes a series of narrow band gap polymers P1, P2 and P3 with D-A structures through triple bond connection. Based on the "donor-acceptor" interaction between pyrene and fluorene derivatives, the band gap of the polymer can be effectively tuned to 1.61-1.74 eV by internal charge transfer. All polymers exhibit a broad optical absorption, covering a range from 350 nm to 1000 nm, which is very unusual for organic polymers. Furthermore, it was found that the incorporation of carbonyl groups containing structural units significantly enhanced photogenerated charge transfer.

The conjugated microporous polymer is applied to photocatalytic reduction of CO ₂, and under the irradiation condition of lambda >420 nm, the yield of CH ₄ is 403.8 mu mol h ^-1g^-1-932.9 μmol h^-1g^-1, and the yield of CO is 545.1 mu mol h ^-1g^-1-943.4 μmol h^-1g^-1. Under irradiation conditions of λ >600 nm, the yield of CH ₄ was 259.5 μmol h ^-1g^-1-378.1 μmol h^-1g^-1 and the yield of CO was 278.8 μmol h ^-1g^-1-366.9 μmol h^-1g^-1.

The conjugated microporous polymer has a pore size of less than 2 nm and a BET surface area of 371: 371 cm ²g^-1-837 cm²g^-1. The optical band gap is 1.61 eV-1.74 eV.

The invention also provides a preparation method of the conjugated microporous polymer, which comprises the following steps: dissolving 1,3,6, 8-tetraethynyl pyrene, dibromo-substituted comonomer and a catalyst in a solvent, stirring and reacting 48 h under the conditions of 100 ℃ and inert gas atmosphere, cooling to room temperature, filtering, and washing, purifying and drying the precipitate in sequence to obtain the conjugated microporous polymer;

The dibromo-substituted comonomer is 2, 7-dibromo-9H-fluorene, 2, 7-dibromo-9 fluorenone or 2, 7-dibromophenanthrene-9, 10-dione; the catalyst was Pd (PPh ₃)₄ and CuI; the solvent was a mixture of DMF and Et ₃ N.

In some preferred embodiments, the ratio of 1,3,6, 8-tetraethynylpyrene, dibromo-substituted comonomer, pd (PPh ₃)₄, cuI, DMF and Et ₃ N is 1 mmol:1 mmol:0.03 mmol:0.03 mmol:15 mL:3 mL.

In some preferred embodiments, the washing is specifically: the washing was performed sequentially with CH ₂Cl₂, THF, water and methanol. The inert gas is nitrogen.

The beneficial effects of the invention are as follows: for the fact that the optical band gap of most photocatalysts is relatively wide at present, sunlight with the wavelength exceeding 600 nm cannot be effectively absorbed, and the utilization rate of sunlight and the photocatalytic conversion efficiency of the photocatalysts can be greatly limited. The present invention first designed and synthesized three narrow band gap conjugated microporous polymers for the selective reduction of CO ₂ to CO and CH ₄ under red light illumination (> 600 nm). By introducing electron donating pyrene and electron deficient fluorenone derivatives into the polymer backbone, the three polymers all exhibit broad optical absorption with an optical band gap between 1.61 and 1.74 eV, covering the entire visible region. Under visible light (lambda >420 nm), good visible light reduction activity is shown, and the precipitation rates of CH ₄ and CO are up to 943.4 and 932.9 mu mol h ^-1g^-1 respectively. More importantly, under the irradiation of red light (lambda >600 nm), the generation rates of CH ₄ and CO can still reach 293.7 and 282.6 mu mol h ^-1g^-1 respectively, and the reaction selectivity is about 100%.

Drawings

FIG. 1 shows a CPMAS ¹³ C NMR spectrum of P1;

FIG. 2 shows a CPMAS ¹³ C NMR spectrum of P2;

FIG. 3 shows a CPMAS ¹³ C NMR spectrum of P3;

FIG. 4 shows FTIR spectra of P1, P2 and P3; (a) FTIR spectrum for P1; (b) FTIR spectrum for P2; (c) FTIR spectrum for P3

FIG. 5 shows SEM images of P1, P2 and P3;

FIG. 6 shows XRD patterns of P1, P2 and P3;

FIG. 7 shows thermogravimetric analysis curves for P1, P2 and P3;

FIG. 8 shows pore sizes and gas adsorption results for P1, P2, and P3; (a) Adsorption (solid curve) and desorption (open curve) isotherms for N ₂ measured at 77K; (b) is a pore size distribution map; (c) Adsorption isotherms for CO ₂ at 273K and 298K; (d) is a heat of adsorption map;

FIG. 9 is a graph showing the results of the photophysical, electrochemical and photoelectrochemical properties of P1, P2 and P3; (a) is an ultraviolet visible near infrared diffuse reflection absorption spectrum; (b) The fluorescence spectrum of the polymer solid at 450 nm is P2, P1 and P3 from top to bottom; (c) A band gap structure (at ph=0, potential versus standard hydrogen electrode) that is a porous polymer; (d) A photocurrent density versus time (I-t) curve for a polymer electrode in an aqueous Na ₂SO₄ solution at a concentration of 0.5M;

FIG. 10 is a graph showing fluorescence lifetime of P1, P2, and P3 measured by time-dependent single photon counting;

FIG. 11 shows the EIS Nyquist plot of a polymer electrode in 0.5M Na ₂SO₄ aqueous solution;

FIG. 12 shows a reduction cyclic voltammogram of a polymer modified glassy carbon electrode;

FIG. 13 is a graph showing the results of photocatalytic CO ₂ reduction activities for P1, P2, and P3; (a) Photocatalytic CO ₂ reduction activity for polymers under visible light (> 420 nm) irradiation; (b) Photocatalytic CO ₂ reduction activity under red light (> 600 nm) irradiation; (c) Results of gas chromatography-mass spectrometry (GC-MS) for CO and CH ₄ generated using ¹³CO₂ as starting materials; (d) The photocatalytic stability results of the repeated measurement of P3 under red light irradiation are shown;

FIG. 14 is a schematic diagram showing a possible mechanism of P1, P2 and P3 photo-reduction of CO ₂;

FIG. 15 shows the CP MAS ¹³ C NMR spectrum of P3 after the same light irradiation in a cyclic experiment.

Detailed Description

The conception and the technical effects produced by the present invention will be clearly and completely described below with reference to the embodiments and the drawings to fully understand the objects, aspects and effects of the present invention.

In the following examples, all solvents and reagents were analytically pure, purchased from Ananaresistant Ji chemical priority Co., ltd., or Tokyo chemical industry Co., japan. The solid state CP/MAS ¹³ C NMR spectrum of the polymer was determined by a Bruker AVANCE III 500 spectrometer. The palladium and copper content of the polymer network was measured by inductively coupled plasma on a PerkinElmer 8300 ICP-OES spectrometer (united states). The C, H, N elemental analysis of the polymer was performed on ELEMENTAR VARIO MICRO CUBE. Fourier transform infrared spectroscopy (FTIR) was scanned in the 4000-400 cm ^-1 range using a aNicolet-iS10 FTIR spectrometer (Thermo Scientific, usa). The morphology of the polymer aggregates was tested by field emission scanning electron microscopy (Zeiss Gemini 300, germany). The crystallinity of the samples was analyzed by X-ray diffraction (XRD) on a Bruker D8X-ray diffractometer. N ₂ and CO ₂ adsorption isotherms were collected on a Micromeritics ASAP 2460 volume adsorption analyzer. The samples were degassed in vacuo at 100 ℃ for 10 hours, and then the adsorbed amounts of N ₂ and CO ₂ were measured at 77K and 273K/298K, respectively. Ultraviolet visible Diffuse Reflectance Spectroscopy (DRS) was obtained using a Shimazu UV 3600 spectrometer equipped with an integrating sphere, baSO ₄ as an absorption reference. Fluorescence spectra were tested at Edinburgh Analytical Instruments FLS980,980 and combined with a time-dependent single light counting system at room temperature. Thermogravimetric analysis (TGA) was measured on Netzsch TG209F1 using an automatic vertical overhead thermal balance under nitrogen flow, at a ramp rate of 10 ℃ min ^-1 from 50 ℃ to 800 ℃.

Example 1:

The preparation of the conjugated microporous polymer comprises the following steps:

1,3,6, 8-Tetraethynylpyrene (1 mmol), dibromo-substituted comonomer (1 mmol), pd (PPh ₃)₄ (0.03 mmol) and CuI (0.03 mmol) were dissolved in 15 mL degassed mixture of DMF and 3 mL Et ₃ N the reaction mixture was stirred at 100deg.C under nitrogen atmosphere for 48 h, cooled to room temperature and filtered, the precipitate was washed with CH ₂Cl₂, THF, water and methanol in order to remove any unreacted monomer or catalyst residues, and the obtained solid was purified in order with CH ₂Cl₂ and THF using a Soxhlet apparatus and dried in vacuo to give the final product.

The dibromo-substituted comonomer adopts 2, 7-dibromo-9H-fluorene, 2, 7-dibromo-9 fluorenone and 2, 7-dibromophenanthrene-9, 10-dione respectively; the conjugated microporous polymers P1, P2 and P3 are respectively prepared.

P1-red powder. Yield rate ：94%. Anal. Calcd for (C₇₆H₄₂)_n:C, 95.57; H, 4.43; Found C, 93.43; H, 6.57%;Pd, 0.35%; Cu, 0.042%.

P2. red powder. Yield rate ：90%. Anal. Calcd for (C₇₆H₃₄O₄)_n: C, 90.28; H, 3.39; Found C, 92.13; H, 4.23; Pd, 0.31%; Cu, 0.012%.

P3. red powder. Yield rate ：91%. Anal. Calcd for (C₈₀H₃₄O₈)_n:C, 85.55; H, 3.05%; Found C, 87.12; H, 2.95%; Pd, 0.40%; Cu, 0.015%.

The structural schematic formulas of the constituent units of the conjugated microporous polymers P1, P2, P3 are as follows:

the structural formulas of 1,3,6, 8-tetraethynyl pyrene, 2, 7-dibromo-9H-fluorene, 2, 7-dibromo-9 fluorenone and 2, 7-dibromophenanthrene-9, 10-dione are shown below respectively:

、/>、/>、/>。

Example 2:

the conjugated microporous polymers P1, P2, P3 prepared in example 1 were characterized as follows:

As shown in the solid-state ¹³ C NMR spectra of FIGS. 1-3, all polymers exhibited characteristic peaks of sp ² hybridized carbon at 120-140: 140 ppm, with a chemical shift of about 90 ppm due to C.ident.C formed by coupling.

As shown in the FT-IR spectrum of FIG. 4, a stretching vibration of C.ident.C was observed around 2180 cm ^-1, which indicates that efficient coupling between monomers was established. For P2 and P3, 190.69 ppm and 180.05 ppm peaks can be attributed to the presence of c=o, with the carbonyl carbon atom being displaced to the high field due to the larger conjugated system of P3.

As shown in the SEM image of FIG. 5 (a and b are P1; c and d are P2; e and f are P3), it is shown that the polymer is built up from nano-scale irregular spherical solids.

As shown in the powder X-ray diffraction pattern of fig. 6, the structure without long range order in all three polymers is amorphous.

As shown in the thermogravimetric analysis (TGA) curve of FIG. 7, thermogravimetric analysis under an atmosphere of N ₂ shows that all three polymers have good thermal stability. At a mass loss of 5%, the decomposition temperatures are above 350 ℃.

Example 3:

The conjugated microporous polymers P1, P2, P3 prepared in example 1 were subjected to performance test, and the results were as follows:

(1) Pore size and gas adsorption

The polymers were tested for porosity by adsorption and desorption experiments with nitrogen at 77K, and as shown in fig. 8 (a) (P1, P3, P2 from top to bottom), all three polymers exhibited typical type I adsorption isotherms, with a dramatic increase in adsorption capacity at lower relative pressures, indicating that all three polymers had microporous properties.

The pore size distribution of the polymers did also show that the pore size of all three polymers was <2 nm and that the pore peaks were mainly located in the microporous region, as shown in fig. 8 (b).

The calculated total pore volume of the polymer at P/P ₀ = 0.99 was 0.82, 0.50 and 0.55 cm ³g^-1, respectively (results are shown in table 1). As calculated, P1 has the highest BET surface area, 837 cm ²g^-1. The surface area was 580 cm ²g^-1 times P3. However, the surface area of P2 was the lowest, 371 cm ²g^-1 (table 1). The lower specific surface area means fewer active sites for CO ₂, which may have some effect on its photocatalytic reaction performance.

In addition, the adsorption behavior of three polymers on CO ₂ was studied at 273K and 298K (as shown in fig. 8 (c)). At 273K, P1, P2 and P3 showed CO ₂ adsorption of 46.5, 34.3 and 38.7 cm ³g^-1, respectively (table 1). 298 At K, the adsorption of the three polymers was reduced to 29.3, 19.8 and 24.7 cm ³g^-1, respectively. At different temperatures, the adsorption capacity of CO ₂ of P1 and P3 is equivalent, and the adsorption capacity of P2 is lower. The specific surface area and the CO ₂ adsorption capacity have a great influence on the reduction performance of photocatalytic CO ₂. It is speculated that the photocatalytic performance of P2 may be limited accordingly. In addition, in order to compare the strength of the interaction between the polymer and the CO ₂ molecules, the heat of adsorption of CO ₂ of the polymer was calculated (as shown in fig. 8 (d)). Qst for P1, P2 and P3 were 23.2, 26.9 and 25.8 kJmol ^-1, respectively (Table 1). The effect of the three polymers and CO ₂ all belongs to the physical adsorption process.

(2) Photophysical, electrochemical and photoelectrochemical properties

The specific method for electrochemical testing comprises the following steps:

cyclic voltammetry testing of the polymer was performed in a deoxygenated anhydrous acetonitrile solution containing 0.1M tetrabutylammonium hexafluorophosphate (Bu ₄NPF₆) as electrolyte. Testing was performed at 298K using a platinum wire as the counter electrode, glassy carbon as the working electrode, and an Ag/AgNO ₃ electrode (in acetonitrile solution containing 0.1M Bu ₄NPF₆ and 0.01M AgNO ₃). The potential for ferrocene/ferrocene (Fc/Fc ⁺) is recorded. The Fc/Fc ⁺ redox couple was converted to a common hydrogen electrode (NHE) using equation E _NHE= E_Fc/Fc+ + 0.63V.

The specific method for photoelectrochemical testing comprises the following steps:

Under ultrasonic treatment, the 5mg polymer was well dispersed in a mixed solution of 0.5 mL acetonitrile and 10 μl of 5 wt% Nafion. The resulting polymer suspension was drop coated onto the FTO glass surface and air dried at room temperature in air. The photocurrent response was measured in a three electrode system, with the photoelectrode being the working electrode, the platinum wire being the counter electrode, and Ag/AgCl being the reference electrode. Measurements were made using a 0.5M Na ₂SO₄ (ph=7) solution with a bias voltage of +0.6V. 300W xenon lamp cut-off 420 nm was used as a light source, and the EIS diagram was obtained in the dark. The bias potential applied for both measurements was +0.6V (vs. Ag/AgCl). EIS spectra were recorded by applying a 10 mV AC signal in the frequency range of 100 kHz to 0.01 Hz.

The optical properties of solid state polymers were investigated by uv-vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. The absorption spectrum of the polymer showed a broad absorption at 400-800 nm (as shown in fig. 9 (a)). The optical bandgaps of P1, P2 and P3 were estimated to be 1.61,1.74 and 1.64 eV, respectively, based on the absorption edge (as shown in (c) of fig. 9 and table 1). The narrow band gap of the polymer can be attributed to intramolecular charge transfer from the donor to the acceptor. The broad optical absorption of polymers makes them well suited for photocatalytic studies in long wavelength sunlight. Under excitation of 450 nm, P2 produced a strong emission peak centered at 773 nm. In contrast, P1 and P3 exhibited significantly weaker fluorescence with emission peaks at 749 and 764 nm, respectively (as shown in (a) of fig. 9). The stronger fluorescence of P2 compared to P1 and P3 is attributable to the unique stacking of planar units. The fluorescence lifetime spectrum of the polymer shows (as shown in fig. 10) that the average lifetimes of P1, P2 and P3 after fitting are 1.41,1.57 and 1.78 ns in this order.

In addition, transient photocurrent experiments were performed to investigate the separation and transport behavior of the photo-generated charges of the polymers. As can be seen from (d) in fig. 9, the photocurrent of P3 is significantly higher than P1 and P2. Indicating that it has better electron mobility. And as the number of carbonyl groups in the center of the monomer increases, the photocurrent also increases. Electrochemical impedance spectroscopy studies have consistent results, with the radius of the semicircle in the nyquist plot (fig. 11) showing that P3 exhibits a smaller radius under illumination, with a significant decrease in charge transfer resistance, indicating a faster charge separation.

The redox properties of the polymers were studied by cyclic voltammetry (fig. 12, reduction cyclic voltammetry curves of polymer modified glassy carbon electrode (0.1 Mn-Bu ₄NPF₆ as supporting electrolyte relative to Ag/Ag ⁺ in acetonitrile solution.) all polymers showed reversible reduction potentials, starting reduction potentials of P1, P2 and P3 were-1.12, -1.13 and-1.14V, respectively, whereby the Lowest Unoccupied Molecular Orbital (LUMO)/Highest Occupied Molecular Orbital (HOMO) energy levels of polymer molecules P1, P2 and P3 were estimated to be-0.49/1.12 (vs.nhe), -0.50/1.24 (vs.nhe) and-0.51/1.13 (vs.nhe), respectively.

TABLE 1

^a) The absorption band edge is calculated by the DRS according to the formula E _g,opt=1240/λ_onset; ^b) A scan rate of 50 mV s ^-1 compared to Fc/Fc ⁺ in acetonitrile solution. ^c)E_HOMO=E_LUMO−E_g,opt.^d) Calculated in the pressure range of P/P ₀ =0.01-0.05. ^e)V_total Total pore volume calculated at P/P ₀ = 0.99.

(3) Photocatalytic CO ₂ reduction Activity

The specific method comprises the following steps:

in a 20mL glass reactor, 0.5 mg photocatalyst was dispersed under sonication in a mixture containing 5mL anhydrous acetonitrile (CH ₃ CN), 1mL Triethanolamine (TEOA), 0.1M 1-benzyl-1, 4-dihydronicotinamide (BNAH). The reactor was bubbled with high purity CO ₂ (99.999%) for 15 minutes and then irradiated using a 300W xenon lamp with a 420 or 600 nm cutoff filter. The temperature of the reaction system was maintained at 30 ℃. During the photocatalysis, the reaction system is vigorously stirred by a magnetic stirrer. After the reaction, the gaseous reaction product evolved was quantified by Panna a60 gas chromatograph with FID and TCD detectors and Ar carrier gas.

Three polymers were tested for CO ₂ reduction performance under lambda >420 nm and 600 nm irradiation. The reaction was carried out in a 20 mL glass bottle using a mixed solution of acetonitrile and triethanolamine (5:1 by volume) as solvent, BNAH as sacrificial agent. Fig. 13 (a) shows that under irradiation with lambda >420 nm, both CH ₄ and CO can be produced simultaneously by all three polymers with a trace of hydrogen production. The CH ₄ yields of P1, P2 and P3 were 735.8, 403.8 and 932.9 μmolh ^-1g^-1, respectively. The yields of CO were 745.6, 545.1 and 943.4. Mu. Mol h ^-1g^-1, respectively. Consistent with the previous discussion, P3 exhibited the best differential photocatalytic performance from whichever product. Furthermore, when irradiated with red light, the yields of P3 photocatalytic CO ₂ to CH ₄ and CO remain highest, reaching 293.7 and 282.6 μmol h ^-1g^-1, significantly higher than P2 (135.4 and 121.7 μmol h ^-1g^-1) (as shown in fig. 13 (b)). P1 also performed well with yields of CH ₄ and CO of 193.3 and 188.7. Mu. Mol h ^-1g^-1, respectively.

To verify the source of the photocatalytic product, we performed an isotopic labeling experiment using ¹³CO₂. The specific method comprises the following steps:

The MeCN/TEOA (5:1, v/v) 6.0 mL mixed solution in the reaction cell containing BNAH (0.1M) and P3 (1 mg) was purged with ¹³CO₂(99 atom%¹³C, 99.93 atom%¹⁶ O for 10 minutes instead of ¹²CO₂. The suspension was then irradiated for 4 hours using a 300W Xe light source equipped with a lambda >420 nm filter. The evolved CO and CH ₄ gases were analyzed by GC/MS.

As shown in fig. 13 (c), the MS peaks at m/z=17 and 29 can be attributed to ¹³CH₄ and ¹³ CO. This indicates that the photocatalytic product is derived from the reduction of ¹³CO₂. Based on the above results, we infer a possible photocatalytic mechanism (as shown in fig. 14). CO ₂ molecules are firstly adsorbed by polymer molecules, photo-generated charges generated by photo-excitation are quickly transferred to the surfaces of the polymer molecules, photo-generated electrons reduce CO ₂ into CH ₄ and CO, and BNAH is oxidized by holes to generate BNAH ^+*. In addition, a 4-hour continuous photocatalytic cycle experiment was performed with the recovered photocatalyst under red light irradiation to verify the stability of the photocatalyst P3. As shown in fig. 13 (d), the yields of CH ₄ and CO remained stable, indicating excellent reusability and stability of P3. Furthermore, we have also further examined the durability of P3 by testing its nuclear magnetism after operation. The results showed that there was no significant change in the nuclear magnetic pattern of P3 before and after the catalytic reaction, confirming that P3 had good stability (as shown in fig. 15).

In conclusion, the invention reasonably designs and prepares the narrow band gap conjugated microporous polymer (P1, P2 and P3) with the D-A structure, which is used for producing CH ₄ and CO by photocatalytic CO ₂ reduction. All polymers showed broad optical absorption at 400-1000 nm and optical band gaps between 1.61-1.74 eV. Experimental results show that P3 has good CO ₂ capturing and excellent charge carrier separation performance. Under irradiation with lambda >420 nm, the yields of CH ₄ and CO reached 932.9 and 943.4 μmolh ^-1g^-1. In addition, P3 also had the highest photocatalytic efficiency of CO ₂ under red light, with yields of CH ₄ and CO of 293.7 and 282.6. Mu. Mol h ^-1g^-1, respectively, with a selectivity of about 100%. This work lays a good foundation for designing a polymer photocatalyst with a broad spectral response.

The present invention is not limited to the above embodiments, but is merely preferred embodiments of the present invention, and the present invention should be construed as being limited to the above embodiments as long as the technical effects of the present invention are achieved by the same means. Various modifications and variations are possible in the technical solution and/or in the embodiments within the scope of the invention.

Claims (8)

1. A conjugated microporous polymer, characterized in that the structural schematic formula of the constituent units of the conjugated microporous polymer is as follows:

；

wherein, For/>、/>Or/>；

The pore diameter of the conjugated microporous polymer is less than 2 nm, and the BET surface area of the conjugated microporous polymer is 371 cm ² g^-1-837 cm² g^-1;

The optical band gap of the conjugated microporous polymer is 1.61 eV-1.74 eV.

2. A method of preparing the conjugated microporous polymer of claim 1, comprising the steps of: dissolving 1,3,6, 8-tetraethynyl pyrene, dibromo-substituted comonomer and a catalyst in a solvent, stirring and reacting 48 h under the conditions of 100 ℃ and inert gas atmosphere, cooling to room temperature, filtering, and washing, purifying and drying the precipitate in sequence to obtain the conjugated microporous polymer;

The dibromo-substituted comonomer is 2, 7-dibromo-9H-fluorene, 2, 7-dibromo-9 fluorenone or 2, 7-dibromophenanthrene-9, 10-dione; the catalyst was Pd (PPh ₃)₄ and CuI; the solvent was a mixture of DMF and Et ₃ N.

3. The method according to claim 2, wherein the ratio of 1,3,6, 8-tetraethynylpyrene, dibromo-substituted comonomer, pd (PPh ₃)₄, cuI, DMF and Et ₃ N is 1 mmol:1 mmol:0.03 mmol:0.03 mmol:15 mL:3 mL.

4. The method according to claim 2, characterized in that the washing is in particular: the washing was performed sequentially with CH ₂Cl₂, THF, water and methanol.

5. The method of claim 2, wherein the inert gas is nitrogen.

6. Use of the conjugated microporous polymer of claim 1 for photocatalytic reduction of CO ₂.

7. The use according to claim 6, wherein the conjugated microporous polymer is subjected to photocatalytic reduction of CO ₂ under irradiation conditions of λ > 420 nm with a yield of CH ₄ of 403.8 μmol h ^-1 g^-1-932.9 μmol h^-1 g^-1 and a yield of CO of 545.1 μmol h ^-1 g^-1-943.4 μmol h^-1 g^-1.

8. The use according to claim 6, wherein the conjugated microporous polymer is subjected to photocatalytic reduction of CO ₂ under irradiation conditions of λ > 600 nm with a yield of CH ₄ of 259.5 μmol h ^-1 g^-1-378.1 μmol h^-1 g^-1 and a yield of CO of 278.8 μmol h ^-1 g^-1-366.9 μmol h^-1 g^-1.