Conjugated polymer as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of organic high-molecular compounds, and particularly relates to a conjugated polymer as well as a preparation method and application thereof. According to the application, two conjugated polymers with excellent photocatalytic performance, namely a naphthalene ring-phosphazene conjugated polymer (TCOP) and a pyrene ring-phosphazene conjugated polymer (FCOP), are successfully synthesized through a nucleophilic substitution reaction between hexachlorocyclotriphosphazene and 2, 7-diacetylene pyrene or 2, 6-diacetylene naphthalene. The materials show excellent photocatalytic performance due to unique structural characteristics. Performance tests show that TCOP has excellent performance in the aspect of catalyzing CO2 reduction, CO2 can be efficiently converted into CH4, and FCOP is good at efficiently reducing CO2 into CO. The two polymers not only maintain efficient activity and selectivity in respective catalytic processes, but also show good application potential.

Description

Technical Field

[0001] The present application belongs to the technical field of organic polymer compounds, and specifically relates to a conjugated polymer and a preparation method and application thereof. Background Art

[0002] As carbon dioxide (CO 2 ) content has increased exponentially, and a series of environmental and social challenges have also arisen. To meet these challenges, it is necessary to develop efficient catalytic conversion technologies to convert CO 2 Converting CO into chemical products with high economic value has become a key strategy to solve environmental problems and alleviate energy shortages. Among the many catalytic methods including thermal catalysis, electrocatalysis, photocatalysis and biocatalysis, photocatalysis technology is the most popular because it can make full use of renewable solar energy to convert CO 2 Converting CO into methane, carbon monoxide and other energy sources is considered one of the most promising solutions. In view of this, the development of efficient photocatalysts to achieve CO 2 The efficient conversion into high value-added chemicals is an important task in the current scientific research field.

[0003] Currently, CO 2 Research in the field of photocatalytic reduction has developed a variety of inorganic semiconductor catalysts, including transition metal complexes, metal oxides, metal sulfides, and organic-inorganic hybrid materials. 2 It has shown significant potential in converting organic photocatalysts into high value-added chemicals. However, most reported inorganic semiconductor photocatalysts contain metal components, which not only increases the cost of catalytic materials, but also may introduce environmental problems such as heavy metal pollution, limiting their large-scale application and long-term sustainability. For this reason, organic semiconductor catalysts have emerged. This type of catalyst is represented by conjugated polymers and other organic materials, which have the advantages of wide sources, low cost, and environmental friendliness. However, compared with inorganic semiconductor materials, organic semiconductor materials have a major technical bottleneck: the strong Coulomb interaction between excited electrons and holes hinders the dissociation of excitons into carriers, thereby inhibiting the improvement of the catalytic efficiency of photocatalysts. Therefore, designing and synthesizing organic semiconductor photocatalysts with efficient charge separation is an important way to promote the improvement of their photocatalytic performance.

[0004] In 2019, Wang and his team revealed that in linear conjugated polymers, by modulating the donor-acceptor (DA) unit, the exciton binding energy can be effectively reduced and the energy loss of the charge transfer state can be reduced. This optimization not only enhances the separation efficiency of photogenerated charges, but also enables the improved photocatalyst to exhibit high photocatalytic H 2 O-H 2However, to date, there is little research on the use of DA units in two-dimensional conjugated polymers to achieve efficient CO 2 There are relatively few studies on photocatalytic reduction, and the anthraquinone-functionalized donor-acceptor conjugated polymer catalysts prepared by Sonogashira coupling reaction of 2,6-dibromoanthraquinone and tri(4-ethynylphenyl)amine have not been studied in CO 2 A certain catalytic activity was shown during the reduction process, but overall, the yield was still relatively low, indicating that its photocatalytic efficiency needs to be improved. Summary of the invention

[0005] The invention of this application aims to provide a novel conjugated polymer with high photocatalytic performance, which is specifically achieved through the following technical solutions: In the first aspect, the present application provides a conjugated polymer, wherein the repeating unit of the conjugated polymer is composed of a cyclotriphosphazene and a conjugated unit directly connected to its phosphorus atom; the conjugated unit includes a residue of 2,6-diethynylnaphthalene or 2,7-diethynylpyrene; the phosphorus atom of the cyclotriphosphazene is connected to two conjugated units. The repeating unit of the conjugated polymer is: The R is selected from the residue of 2,6-diethynylnaphthalene or 2,7-diethynylpyrene.

[0006] In a second aspect, the present application provides a method for preparing a conjugated polymer, wherein the conjugated polymer is obtained by a nucleophilic substitution reaction between a hexachlorocyclotriphosphazene monomer and a diacetylene aromatic monomer, wherein the diacetylene aromatic monomer is selected from 2,7-diethynylpyrene or 2,6-diethynylnaphthalene.

[0007] In the present application, hexachlorocyclotriphosphazene (HCCP) is used as a multifunctional precursor. HCCP provides a stable nitrogen heterocyclic skeleton during the polymerization process, which can effectively react with the acetylenic group in the aromatic monomer to form a conjugated system. The diacetylene aromatic monomer contains two acetylene groups (-C≡C-), which act as a π bridge structure to connect the donor and acceptor parts to form a highly conjugated main chain. Specifically, the phenyl group in the diacetylene aromatic monomer acts as a donor part to provide electron cloud density, while the cyclotriphosphazene acts as an acceptor part to accept electrons, thereby forming a typical D-π-A structure. This structure can effectively promote the transfer of electrons from the donor part to the acceptor part to form a stable charge separation state. This efficient charge separation helps to improve the efficiency of the photocatalytic reaction. Furthermore, by controlling the number of benzene rings in the phenyl part, the two products obtained in the present application both show good photocatalytic ability and product selectivity.

[0008] Preferably, the molar ratio of the hexachlorocyclotriphosphazene monomer to the diacetylene aromatic monomer is 1:(2-4).

[0009] Preferably, the conditions of the nucleophilic substitution reaction are: temperature 180-190° C., time 22-24 h.

[0010] In a third aspect, the present application proposes the use of the above-mentioned conjugated polymer in photocatalysis.

[0011] In a fourth aspect, the present application proposes the use of the above-mentioned conjugated polymer in carbon dioxide reduction.

[0012] In a fifth aspect, the present application proposes a method for preparing methane, using carbon dioxide as a raw material and the above-mentioned conjugated polymer as a photocatalyst, wherein the conjugated unit is selected from 2,6-diethynylnaphthalene.

[0013] In a sixth aspect, the present application proposes a method for preparing carbon monoxide, using carbon dioxide as a raw material and the above-mentioned conjugated polymer as a photocatalyst; the conjugated unit is selected from 2,7-diethynylpyrene.

[0014] Compared with the prior art, this application has the following beneficial effects: This application successfully synthesized two conjugated polymers with excellent photocatalytic performance: naphthalene ring-phosphazene conjugated polymer (TCOP) and pyrene ring-phosphazene conjugated polymer (FCOP) through nucleophilic substitution reaction between hexachlorocyclotriphosphazene and 2,7-diethynylpyrene or 2,6-diethynylnaphthalene. These materials exhibit excellent photocatalytic performance due to their unique structural characteristics. Performance tests show that under visible light irradiation, TCOP samples catalyze CO 2 Reduction to CH 4 The yield was 550.9 μmol·g -1 The yield of carbon monoxide (CO) was 149.1 μmol·g -1 , showing significant photocatalytic activity. In contrast, the FCOP sample catalyzed CO 2 Reduction to CH 4 The yield was only 16.0 μmol·g -1 , and the yield of CO was as high as 543.7 μmol·g -1 , also showing excellent photocatalytic activity. In addition, TCOP and FCOP showed significantly different product selectivities: TCOP tended to efficiently generate CH 4 , while FCOP prefers to generate CO. This difference in selectivity may be due to the difference in their structure or composition, which affects the electronic properties and surface active sites of the materials, thereby determining their respective catalytic reaction pathways. It shows good application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to clearly introduce the embodiments, the following is a brief introduction to the drawings: Figure 1 Infrared spectrum for performance test 1; Figure 2 Mapping image of conjugated organic polymer for performance test 1; Figure 3 This is a comparison chart of reduction yields in performance test 2; Figure 4 Impedance diagram of conjugated polymer for performance test 3; Figure 5 Photocurrent graphs of 3 conjugated polymers for performance testing. DETAILED DESCRIPTION

[0016] The present application will be further described below in the form of specific embodiments. Those of ordinary skill in the art will be able to implement the present application based on these descriptions. In addition, the embodiments of the present application involved in the following description are generally only embodiments of a part of the present application, rather than all embodiments. Therefore, based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present application.

[0017] In the following examples, the preparation method of 2,6-diethynylnaphthalene monomer is as follows: 2,6-dibromonaphthalene (570 mg, 2 mmol), cuprous iodide (7.6 mg, 0.04 mmol), tetrakistriphenylphosphine palladium (462 mg, 0.4 mmol) are placed together in a mixed solvent of trimethylsilylacetylene (2 mL), triethylamine (20 mL), and tetrahydrofuran (30 mL). The mixture is heated to reflux at 75° C. for 24 to 48 h, cooled naturally, purified by column chromatography, and added to 30 mL of tetrahydrofuran together with 2 to 3 mL of tetramethylsilane, stirred for 12 to 24 h, and the solvent is dried by spin drying and subjected to column chromatography (PE:EA=10:1) to obtain 2,6-diethynylnaphthalene monomer product.

[0018] In the following examples, the preparation method of 2,7-diethynylpyrene monomer is as follows: 2,7-dibromopyrene (720 mg, 2 mmol), cuprous iodide (7.6 mg, 0.04 mmol), tetrakistriphenylphosphine palladium (462 mg, 0.4 mmol) are placed together in a mixed solvent of trimethylsilylacetylene (2 mL), triethylamine (15 mL), and tetrahydrofuran (30 mL). The mixture is heated to reflux at 75° C. for 24 to 48 h, cooled naturally, purified by column chromatography, and added to 30 mL of tetrahydrofuran together with 2 to 3 mL of tetramethylsilane, stirred for 12 to 24 h, and the solvent is dried by spin drying and subjected to column chromatography (PE:EA=10:1) to obtain 2,7-diethynylpyrene monomer product.

[0019] Example 1 This embodiment discloses a method for preparing a conjugated polymer, comprising the following steps: adding 2,6-diethynylnaphthalene (229 mg, 1.3 mol) and hexachlorocyclotriphosphazene (173.5 mg, 0.5 mol) to a reaction tube, and then adding a mixed solvent of dimethyl sulfoxide (4 mL) and acetonitrile (16 mL). Heating at 180°C for 24 h and cooling naturally. The product was washed with pure water and ethanol several times, and dried in a vacuum oven overnight to obtain a naphthalene ring-phosphazene conjugated polymer (TCOP).

[0020] Example 2 This embodiment discloses a method for preparing a conjugated polymer, comprising the following steps: adding 2,7-diethynylpyrene (229 mg, 1.3 mol) and hexachlorocyclotriphosphazene (173.5 mg, 0.5 mol) to a reaction tube, and then adding a mixed solvent of dimethyl sulfoxide (4 mL) and acetonitrile (16 mL). Heating at 180°C for 24 h and cooling naturally. The product was washed with pure water and ethanol several times, and dried in a vacuum oven overnight to obtain a pyrene ring-phosphazene conjugated polymer (FCOP).

[0021] Example 3 This embodiment discloses a method for preparing a conjugated polymer, comprising the following steps: adding 2,6-diethynylnaphthalene (264 mg, 1.3 mol) and hexachlorocyclotriphosphazene (173.5 mg, 0.5 mol) to a reaction tube, and then adding a mixed solvent of dimethyl sulfoxide (4 mL) and acetonitrile (16 mL). Heating at 190° C. for 22 h and cooling naturally. The product is washed with pure water and ethanol several times, and dried in a vacuum oven overnight to obtain a naphthalene ring-phosphazene conjugated polymer (TCOP).

[0022] Example 4 This embodiment discloses a method for preparing a conjugated polymer, comprising the following steps: adding 2,6-diethynylnaphthalene (264 mg, 1.3 mol) and hexachlorocyclotriphosphazene (173.5 mg, 0.5 mol) to a reaction tube, and then adding a mixed solvent of dimethyl sulfoxide (4 mL) and acetonitrile (16 mL). Heating at 185°C for 23 h and cooling naturally. The product was washed with pure water and ethanol several times, and dried in a vacuum oven overnight to obtain a naphthalene ring-phosphazene conjugated polymer (TCOP).

[0023] Example 5 This embodiment discloses a method for preparing a conjugated polymer, comprising the following steps: adding 2,6-diethynylnaphthalene (352 mg, 2 mol) and hexachlorocyclotriphosphazene (173.5 mg, 0.5 mol) to a reaction tube, and then adding a mixed solvent of dimethyl sulfoxide (4 mL) and acetonitrile (16 mL). Heating at 190°C for 23 h and cooling naturally. The product was washed with pure water and ethanol several times, and dried in a vacuum oven overnight to obtain a naphthalene ring-phosphazene conjugated polymer (TCOP).

[0024] Example 6 This embodiment discloses a method for preparing a conjugated polymer, comprising the following steps: adding 2,6-diethynylnaphthalene (176 mg, 1 mol) and hexachlorocyclotriphosphazene (173.5 mg, 0.5 mol) to a reaction tube, and then adding a mixed solvent of dimethyl sulfoxide (4 mL) and acetonitrile (16 mL). Heating at 180° C. for 23 h and cooling naturally. The product is washed with pure water and ethanol several times, and dried in a vacuum oven overnight to obtain a naphthalene ring-phosphazene conjugated polymer (TCOP).

[0025] Performance Test 1 This performance test is to perform infrared characterization on the two conjugated polymers synthesized in Example 1 and Example 2, namely, naphthalene ring-phosphazene conjugated polymer (TCOP) and pyrene ring-phosphazene conjugated polymer (FCOP), and further confirm their successful synthesis through infrared spectroscopy (FT-IR) analysis. Figure 1 The infrared spectrum of the product shows a characteristic absorption peak corresponding to the CP bond. This result indicates that hexachlorocyclotriphosphazene successfully undergoes a nucleophilic substitution reaction with 2,7-diethynylpyrene or 2,6-diethynylnaphthalene to form a CP bond, thus confirming the successful synthesis of the target polymers TCOP and FCOP.

[0026] This performance test also conducts element mapping analysis on the two conjugated polymers synthesized in Example 1 and Example 2, namely, naphthalene ring-phosphazene conjugated polymer (TCOP) and pyrene ring-phosphazene conjugated polymer (FCOP), to obtain their microstructure information. Figure 2 , it can be seen that carbon (C), nitrogen (N) and phosphorus (P) elements are evenly distributed in the two polymers. This phenomenon not only further confirms the nucleophilic substitution reaction between hexachlorocyclotriphosphazene and 2,7-diethynylpyrene or 2,6-diethynylnaphthalene, but also shows that the uniform dispersion of active elements (such as phosphorus) indicates that these polymers may have higher catalytic activity and selectivity in photocatalytic applications. The evenly distributed active sites help improve the reaction efficiency and provide strong support for the potential application of these materials in the field of photocatalysis.

[0027] Performance Test 2 This performance test was performed on the conjugated polymer samples of Example 1 and Example 2 to perform photocatalytic CO 2 Reduction test was performed to characterize its photocatalytic activity. Specifically, the conjugated polymer catalyst (5 mg), pure water (2 mL), acetonitrile (3 mL) and triethanolamine (1 mL) were added to a 100 mL photoreactor. The mixture was ultrasonically dispersed for 20 min to obtain a uniform suspension. Before illumination, the reactor was evacuated and replaced with high-purity CO 2 (99.99%) and maintain for 1 hour, so that CO 2 The adsorption / desorption equilibrium is reached in the reaction solution. A 300W Xe lamp with a 420nm cutoff filter is used as the light source to simulate visible light. The light is placed 1cm above the reactor and the light reaction is carried out. The reactor is kept at room temperature and pressure and maintained at 25℃ using circulating water. After 5 hours of light exposure, 1mL of gas mixture is sampled from the photoreactor and gas phase analysis is performed using a gas chromatograph equipped with TCD and FID detectors using Ar as the carrier gas. Please refer to Figure 3 , under visible light irradiation, TCOP samples catalyzed CO 2 Reduction to methane (CH 4 The yield of ) was 550.9 μmol·g -1 The yield of carbon monoxide (CO) was 149.1 μmol·g -1 , showing significant photocatalytic activity. In contrast, the FCOP sample catalyzed CO 2 Reduction to methane (CH 4 The yield of ) was only 16.0 μmol·g -1 , and the yield of carbon monoxide (CO) is as high as 543.7 μmol·g -1 , also showed excellent photocatalytic activity. TCOP and FCOP showed significantly different product selectivities: TCOP tended to efficiently generate methane (CH 4 ), while FCOP prefers to produce carbon monoxide (CO). This difference in selectivity may be due to differences in their structures or compositions, which affect the electronic properties and surface active sites of the materials and thus determine their respective catalytic reaction pathways.

[0028] Performance Test 3 In order to further study the dynamics of photogenerated carriers in the conjugated polymer photocatalytic materials of Example 1 and Example 2, this performance test explored the electrochemical impedance spectroscopy and photocurrent spectrum of the two materials. Figure 4 and Figure 5From the electrochemical impedance spectroscopy (EIS), the radius of the semicircle in the Nyquist plot of TCOP is significantly smaller than that of FCOP, indicating that TCOP has a smaller charge transfer impedance. This means that the charge transfer process of TCOP at the interface is smoother, reducing the resistance to charge transfer. Further, it can be clearly seen from the photocurrent response spectrum that TCOP exhibits a significantly higher photogenerated current density. This phenomenon proves that in TCOP, photogenerated charges can not only be generated efficiently, but also effectively separated and quickly transmitted, avoiding the recombination loss of carriers. Based on the above results, it can be inferred that the introduction of strong electron-donating and electron-accepting groups (such as strong electron-donating or electron-withdrawing substituents) into the conjugated polymer structure in this application can effectively reduce its electrochemical impedance and enhance the conductivity of the material. This structural modification can optimize the energy level matching of the polymer, promote the effective separation of photogenerated electron-hole pairs, and accelerate their transmission path, thereby improving the overall photocatalytic performance and efficiency. In addition, the stronger electron-donating and electron-accepting interaction may also improve the optical absorption characteristics of the material, enabling it to respond in a wider spectral range, further improving the light utilization rate, so the conjugated polymer has good photocatalytic performance.

Claims

1. A conjugated polymer, characterized in that The repeating unit of the conjugated polymer is composed of cyclotriphosphazene and a conjugated unit directly connected to the phosphorus atom of the cyclotriphosphazene; the conjugated unit includes the residue of 2,6-diethynylnaphthalene or 2,7-diethynylpyrene; and the phosphorus atom of the cyclotriphosphazene is connected to two conjugated units.

2. A method for preparing a conjugated polymer, characterized in that: The conjugated polymer is obtained by a nucleophilic substitution reaction between a hexachlorocyclotriphosphazene monomer and a diacetylene aromatic monomer, wherein the diacetylene aromatic monomer is selected from 2,7-diethynylpyrene or 2,6-diethynylnaphthalene.

3. The method for preparing a conjugated polymer according to claim 2, characterized in that: The molar ratio between the hexachlorocyclotriphosphazene monomer and the diacetylene aromatic monomer is 1:(2-4).

4. The method for preparing a conjugated polymer according to claim 2, characterized in that: The conditions of the nucleophilic substitution reaction are: temperature 180-190° C., time 22-24 h.

5. Use of a conjugated polymer according to claim 1 or a conjugated polymer prepared by the preparation method of any one of claims 2 to 4 in photocatalysis.

6. Use of a conjugated polymer according to claim 1 or a conjugated polymer prepared by the preparation method of any one of claims 2 to 4 in carbon dioxide reduction.

7. A method for preparing methane, characterized in that: Carbon dioxide is used as a raw material, and the conjugated polymer according to claim 1 is used as a photocatalyst; the conjugated unit is selected from 2,6-diethynylnaphthalene.

8. A method for preparing carbon monoxide, characterized in that: Carbon dioxide is used as a raw material, and the conjugated polymer according to claim 1 is used as a photocatalyst; the conjugated unit is selected from 2,7-diethynylpyrene.

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