Conjugated polymer photocatalysts, their preparation methods and applications

Abstract

This invention discloses a conjugated polymer photocatalyst, its preparation method, and its application in the photocatalytic synthesis of nitric acid, belonging to the fields of polymer materials and photocatalysis technology. The preparation method mainly includes: firstly, synthesizing the intermediate 2CzTPN-Br via a nucleophilic substitution reaction; subsequently, synthesizing the intermediate TBBA via esterification; and finally, copolymerizing the two via coupling polymerization to obtain the target catalyst. The preparation method of this invention is process-controllable, and the resulting catalyst does not require the participation of noble metals, exhibiting broad light absorption, high specific surface area, and excellent carrier separation efficiency. When applied to the photocatalytic synthesis of nitric acid, it can directly and efficiently convert nitrogen in the air into nitric acid under mild conditions of room temperature, air atmosphere, and water as a solvent, exhibiting excellent durability. After 324 hours of continuous light irradiation, the nitric acid yield can reach 4466.2 µmol g. ‑1 cat It has broad application prospects in the field of green synthesis.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, and more specifically, to a conjugated polymer photocatalyst, its preparation method, and its application. Background Technology

[0002] Nitric acid (HNO3), a crucial basic industrial chemical, is widely used in fertilizer production, chemical intermediate synthesis, and explosives manufacturing, among other fields. Currently, the Ostwald process is the primary industrial method for large-scale synthesis of nitric acid. This process uses ammonia (NH3) as the nitrogen source, reacting it with oxygen under high temperature and pressure to produce nitric acid and water (reaction formula: NH3 + 2O2 → HNO3 + H2O). However, this method has significant drawbacks: firstly, the reaction conditions are harsh, resulting in enormous energy consumption; secondly, the entire process involves the production of large amounts of nitrogen oxides (NO3). X The emissions of these pollutants pollute the environment and fail to meet the current requirements for green, low-carbon, and sustainable development.

[0003] In recent years, some studies have attempted to construct metal-free organic polymer photocatalysts, such as the Chinese patent application CN120605765A, which obtains polymer materials containing heteroatoms through Schiff base condensation and high-temperature calcination, and uses oxygen as an oxidant in water to promote nitrogen oxidation to prepare nitric acid by generating active species such as hydrogen peroxide (H2O2) and hydroxyl radicals (•OH). However, this type of technology generally has the following shortcomings: its polymerization process usually relies on high-temperature treatment, resulting in random material structure and limited band structure control, making it difficult to achieve efficient separation of photogenerated carriers at the molecular level; at the same time, such materials have weak adsorption and activation capabilities for nitrogen molecules, mainly relying on •OH generated by O2 reduction for indirect oxidation, resulting in low selectivity and limited yield of nitric acid; and due to its irregular structure and difficulty in precisely controlling photoelectric properties, the long-term stability and durability of the system still cannot meet the needs of practical applications. Therefore, it is still necessary to develop novel pure organic photocatalysts with clear molecular design, long-range conjugated structure, excellent gas adsorption capacity, and high photoelectric conversion performance to further improve the efficiency and stability of nitric acid synthesis.

[0004] Therefore, developing a photocatalytic technology that can directly utilize atmospheric nitrogen (N2) as a nitrogen source to synthesize nitric acid under mild conditions has significant practical implications and long-term application value. Currently, there have been some exploratory studies on this technical route, but existing technologies still have significant shortcomings. First, most reported high-efficiency photocatalytic systems are based on metal-containing inorganic semiconductor materials. These metal-based catalysts may suffer from high costs, secondary pollution due to metal ion leaching, and potential toxicity to biomass. Research on N2 activation pathways using metal-free or purely organic photocatalysts is relatively scarce, and their catalytic mechanisms and performance optimization still require further investigation. More importantly, the operational stability and durability of most existing photocatalytic systems are severely lacking; their efficient catalytic lifetime is typically only a few hours to tens of hours, which greatly restricts the practical application of this technology.

[0005] Porous organic polymer materials are considered a powerful platform for constructing high-performance metal-free photocatalysts due to their advantages such as tunable band structure, broad-spectrum absorption, high specific surface area, and abundant redox active sites. In the photocatalytic oxidation of nitrogen, hydrogen peroxide (H₂O₂) is often generated in the reaction system, and studies have confirmed that the resulting hydroxyl radicals (•OH) are one of the key active species promoting the oxidation of N₂ to nitrogen-containing products. Based on this, designing and developing pure organic polymer photocatalysts that simultaneously achieve broad-spectrum absorption, efficient photogenerated carrier separation, strong gas adsorption capacity, and abundant surface reaction sites is a reasonable strategy to improve the photocatalytic N₂ activation efficiency and nitric acid selectivity. However, how to effectively synergize these properties while simultaneously obtaining excellent long-term durability remains a pressing technical challenge in this field. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a method for preparing conjugated polymer photocatalysts, so as to solve the problems of cumbersome synthesis steps, harsh reaction conditions, low product purity and difficulty in achieving stable batch preparation in the prior art.

[0007] To overcome the shortcomings of the prior art, the present invention provides a method for preparing the aforementioned conjugated polymer photocatalyst, comprising the following steps:

[0008] S1: Provides intermediate 2CzTPN-Br, which is prepared by reacting 2,5-dichloroterephthalonitrile with 3,6-dibromo-9H-carbazole under alkaline conditions and in a first organic solvent;

[0009] S2: Provides intermediate TBBA, which is prepared by reacting 4-cyanobenzonic acid with trifluoromethanesulfonic acid;

[0010] S3: In the presence of a catalyst, the intermediate 2CzTPN-Br and the intermediate TBBA are subjected to a coupling polymerization reaction under alkaline conditions and a second organic solvent to obtain the conjugated polymer photocatalyst. The structural formula of the conjugated polymer photocatalyst is as follows:

[0011] .

[0012] Compared with existing technologies, the preparation method of the conjugated polymer photocatalyst of this invention has the following advantages: The preparation method of this invention achieves the controllable synthesis of high-purity conjugated polymer photocatalysts by optimizing the reaction steps and catalytic system. In step S1, by rationally selecting the solvent and alkaline conditions, 2,5-dichloroterephthalonitrile and 3,6-dibromo-9H-carbazole are efficiently coupled to generate the intermediate 2CzTPN-Br. The alkaline system exhibits mild reaction and high selectivity, avoiding the formation of byproducts and improving the yield. In step S2, TBBA is prepared by reacting 4-cyanobenzoic acid with trifluoromethanesulfonic acid. This invention avoids the problem of easy hydrolysis and deactivation in the traditional borate ester method, and obtains intermediates with stable structure and high reactivity. In step S3, coupling polymerization is carried out under catalyst and alkaline conditions, so that the two intermediate molecules are connected by C-C bonds to form a polymeric network with a conjugated framework. The preparation method of this invention has controllable reaction conditions, high degree of polymerization, and few impurities. It has excellent solvent stability and chemical stability, and solves the problems of complex synthesis routes, poor reaction selectivity, low yield and insufficient polymeric structural stability in the prior art. It provides a reliable way for the large-scale preparation of high-performance conjugated polymer photocatalysts.

[0013] In one possible implementation, in step S1, the alkaline conditions are provided by anhydrous cesium fluoride; the first organic solvent is N,N-dimethylformamide; the reaction temperature is 80-100°C, the reaction time is 20-28 hours, and the reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the reaction product is further purified by precipitation, filtration, washing, and column chromatography, wherein the eluent for column chromatography purification is a methanol / dichloromethane solution with a volume ratio of 1:10.

[0014] Compared with existing technologies, the above-mentioned technical solution avoids side reactions caused by moisture or oxygen in the reaction system by carrying out the reaction under an inert atmosphere and anhydrous cesium fluoride, thereby improving reaction selectivity and product purity. Under the above conditions, CsF, as an alkaline reagent, can effectively promote the formation of C-C double bonds and accelerate the formation of intermediates, while DMF, as a highly polar solvent, helps to dissolve reactants and stabilize intermediates, thus significantly improving the reaction rate and product yield. By further controlling the temperature and time, the reaction can be carried out fully without causing excessive side reactions. Combined with the column chromatography purification operation in the post-processing, the target intermediate with uniform color and low impurity content can be obtained.

[0015] In one possible implementation, in step S1, the molar ratio of 2,5-dichloroterephthalonitrile, 3,6-dibromo-9H-carbazole, and anhydrous cesium fluoride is 1 : (2.0-3.0) : (12-16).

[0016] Compared with existing technologies, the above-mentioned technical solution, by reasonably controlling the ratio of raw materials to alkali, balances the reaction rate and selectivity in the reaction system. The excess carbazole monomer can effectively promote the coupling reaction and reduce the residue of unreacted monomers, while the appropriate amount of CsF provides a stable alkaline environment to activate the C–Cl bond in the substrate and generate a highly active intermediate. Within the above ratio range, the by-products are significantly reduced, and the stability of the reaction system is improved. This further improves the yield and structural integrity of the intermediate 2CzTPN-Br, making the molecular skeleton of the obtained intermediate more regular and providing an ideal precursor for subsequent polymerization reactions.

[0017] In one possible implementation, in step S2, the reaction conditions are as follows: under a nitrogen atmosphere, 4-cyanobenzoic acid and trifluoromethanesulfonic acid are placed in an ice bath and stirred for 1 hour, then stirred overnight at room temperature, and then the resulting mixture is slowly added to ice water under continuous stirring. The precipitate is collected by filtration and thoroughly washed with a large amount of water to finally obtain a light white solid product.

[0018] Compared with existing technologies, the above-mentioned technical solution effectively activates the boron center in 4-cyanobenzoic acid by introducing trifluoromethanesulfonic acid as a reaction medium at low temperature, thereby increasing the reaction rate and preventing its hydrolytic deactivation. The inert atmosphere avoids side reactions caused by oxygen or moisture in the air, ensuring the stability of the intermediate structure. Furthermore, the controllable reaction and product crystal quality are ensured by further controlling the ice bath stage. The subsequent water washing and filtration steps can thoroughly remove residual by-products and acidic impurities, resulting in high-purity and structurally stable TBBA, providing high reactivity and reproducibility for subsequent coupling polymerization reactions.

[0019] In one possible implementation, in step S2, the ratio of 4-cyanobenzoic acid to trifluoromethanesulfonic acid is 1 mmol : (0.8 - 1.2) mL.

[0020] Compared with existing technologies, the above technical solution, by controlling the ratio of 4-cyanobenzonic acid to trifluoromethanesulfonic acid, allows trifluoromethanesulfonic acid to fully activate the boric acid substrate to generate a stable intermediate, while avoiding side reactions or product decomposition caused by excessive acid. Furthermore, the acid strength and reaction rate are in equilibrium, significantly improving the crystallinity and purity of the product.

[0021] In one possible implementation, in step S3, the catalyst is tetrakis(triphenylphosphine)palladium, the alkaline conditions are provided by an aqueous potassium carbonate solution, the second organic solvent is N,N-dimethylformamide, and the coupling polymerization reaction is carried out at a temperature of 140-160°C for 60-80 hours.

[0022] Compared with existing technologies, the above technical solution can fully utilize the palladium-catalyzed coupling reaction mechanism, through Pd 0 / Pd 2+ The cycle promotes the formation of C-C bonds between aryl halides and borate groups. In the above technical solution, potassium carbonate, as a mild alkali, can effectively maintain the reaction activity and prevent side reactions. The high polarity of DMF helps to dissolve various monomers and stabilize active intermediates. By further controlling the reaction temperature and time, the degree of polymerization is further improved and the degradation of the molecular skeleton is avoided.

[0023] In one possible implementation, in step S3, the molar ratio of intermediate 2CzTPN-Br, intermediate TBBA, and tetrakis(triphenylphosphine)palladium is 1:(1.5-2.0):(0.05-0.08).

[0024] Compared with existing technologies, the above-mentioned technical solution further controls the ratio of reactants to catalysts to match the number of active centers in the system with the substrate concentration, thereby maintaining a stable catalytic cycle efficiency. In the above-mentioned technical solution, an appropriate excess of TBBA can promote the complete coupling reaction and reduce unreacted terminal groups. When the amount of catalyst is within the above-mentioned range, the reaction rate can be guaranteed, avoiding the problem of metal residue caused by over-catalysis. This further improves the yield and uniformity of the polymerization reaction, resulting in polymers with excellent photoelectric properties and structural integrity.

[0025] In one possible implementation, step S3, after the coupling polymerization reaction is completed, further includes filtering the reaction product, washing it sequentially with acid, water and an organic solvent, and purifying it by Soxhlet extraction, wherein the organic solvent includes at least one of acetone, chloroform, tetrahydrofuran and methanol; and the solvent used for Soxhlet extraction includes tetrahydrofuran and methanol.

[0026] Compared with existing technologies, the above-mentioned technical solution can further remove inorganic salts, unreacted monomers and residual catalysts in the reaction system through multi-step washing and Soxhlet extraction. Acid washing can remove residual metal ions, and polar solvent chromatography can effectively separate oligomer impurities. In this technical solution, tetrahydrofuran and methanol are used for Soxhlet extraction, which further achieves deep purification, resulting in uniform particle size, increased specific surface area and full exposure of surface active sites in the final product.

[0027] The second technical problem to be solved by the present invention is to provide a conjugated polymer photocatalyst to solve the problems of high energy consumption, high pollution, dependence on metal catalysts, low catalytic efficiency of metal-free systems and insufficient long-term durability in the existing nitric acid synthesis technology.

[0028] To overcome the shortcomings of the prior art, the present invention provides a conjugated polymer photocatalyst, wherein the conjugated polymer photocatalyst is a photocatalyst CZTB, which is prepared by the above preparation method.

[0029] Compared with existing technologies, the conjugated polymer photocatalyst of this invention has the following advantages: The conjugated polymer photocatalyst CZTB provided by this invention, by introducing units with strong electron donor and acceptor properties such as carbazole (Cz) and terephthalonitrile (TPN) into its molecular structure, forms a highly conjugated D-A type polymer framework, thereby significantly enhancing light absorption capacity and carrier separation efficiency. Through band structure modulation, the polymer of this invention allows its conduction band position to be suitable for driving the activation and oxidation reactions of nitrogen molecules, while the valence band position is conducive to the oxidation of water to generate strong oxidizing free radicals such as •OH, thus achieving a highly efficient synergistic effect between photogenerated electrons and holes. Its porous framework structure provides abundant specific surface area and reaction sites, which is conducive to gas molecule adsorption and reactant diffusion and mass transfer. Simultaneously, the presence of nitrogen heterocycles and nitrile groups in the polymer network can enhance the interaction with N2 molecules, promoting N≡N... The breaking and activation of bonds improve the selectivity and rate of photocatalytic synthesis of nitric acid. Compared with existing metal oxide or inorganic semiconductor photocatalysts, the conjugated polymer system of this invention is completely metal-free, avoiding secondary pollution caused by metal ion dissolution, and has the advantages of being green and environmentally friendly. The photocatalytic mechanism of the catalyst of this invention is as follows: under visible light irradiation, electron-hole pairs generated by CZTB excitation rapidly migrate and separate in the conjugated framework, and electrons participate in the oxidation of adsorbed N2 to NO3. - Holes promote the oxidation of H2O, providing the oxidant required for the reaction. Due to the short intramolecular charge separation path and low recombination probability, the system maintains high stability and continuous activity during long-term light irradiation. This ultimately achieves efficient direct synthesis of nitric acid under air atmosphere and room temperature conditions. Through molecular structure design, high light absorption, high charge separation efficiency, and excellent reaction stability are synergistically optimized, effectively overcoming the problems of low catalytic efficiency, short lifespan, and poor environmental adaptability of existing metal-free photocatalytic systems. This provides a novel, efficient, and sustainable photocatalytic platform for the green synthesis of nitric acid under low-carbon and metal-free conditions.

[0030] The third technical problem to be solved by the present invention is to provide a method for preparing a conjugated polymer photocatalyst, so as to solve the problems of insufficient reactivity, low nitric acid selectivity, strong dependence on light source and poor stability of catalytic system in the prior art.

[0031] To overcome the shortcomings of the prior art, the present invention provides an application of the conjugated polymer photocatalyst in the photocatalytic synthesis of nitric acid, comprising: placing the conjugated polymer photocatalyst in a reaction system containing air and water, irradiating the reaction system with a light source at room temperature, thereby catalyzing the generation of nitric acid.

[0032] Compared with existing technologies, the application of a conjugated polymer photocatalyst in the photocatalytic synthesis of nitric acid, as described in this invention, has the following advantages: This invention utilizes a conjugated polymer photocatalyst CZTB containing carbazole and aromatic nitrile structural units. Its molecular framework forms a highly extensible π-conjugated system, enabling efficient absorption of light energy in the visible light range and effective separation of electron-hole pairs. Photogenerated electrons drive the formation of oxides such as ·O2- and H2O2 from O2, while holes participate in the activation of N2 molecules, achieving a multi-electron transfer reaction via the hydroxyl radical (·OH) pathway, ultimately generating HNO3. Furthermore, the system operates under mild reaction conditions, requiring no external ammonia source or metal co-catalyst, significantly reducing energy consumption and environmental pollution. The porous structure of the catalytic material provided by this invention significantly increases the gas adsorption and reaction interface exposure area, allowing for more complete adsorption and activation of N2 in the air, thereby achieving highly selective nitric acid production. In summary, the application of this invention, through structural energy level optimization and synergistic effects of interfacial reactions, overcomes the problems of low reaction efficiency, poor selectivity, and insufficient stability in existing metal-free photocatalytic systems, achieving efficient, durable, and environmentally friendly photocatalytic synthesis of nitric acid at room temperature. Attached Figure Description

[0033] Figure 1 XPS spectra of conjugated polymer photocatalysts;

[0034] Figure 2 The image shows the FT-IR spectrum of the conjugated polymer photocatalyst.

[0035] Figure 3 The image shows the 13C NMR spectrum of the conjugated polymer photocatalyst.

[0036] Figure 4 The image shows the XRD pattern of the conjugated polymer photocatalyst.

[0037] Figure 5 SEM image of the conjugated polymer photocatalyst;

[0038] Figure 6 BET nitrogen adsorption-desorption isotherm for conjugated polymer photocatalysts;

[0039] Figure 7 The image shows the O2-TPD of the conjugated polymer photocatalyst.

[0040] Figure 8The time curve of photosynthesis of HNO3 by a conjugated polymer photocatalyst under long-term illumination in an air atmosphere with H2O as the solvent;

[0041] Figure 9 The fluorescence spectrum of the conjugated polymer photocatalyst is shown below.

[0042] Figure 10 Impedance image of a conjugated polymer photocatalyst;

[0043] Figure 11 Image of photocurrent of conjugated polymer photocatalyst;

[0044] Figure 12 The structural formula of a conjugated polymer photocatalyst;

[0045] Figure 13 This is a pore size distribution diagram of a conjugated polymer photocatalyst. Detailed Implementation

[0046] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0047] This invention provides a conjugated polymer photocatalyst, wherein the conjugated polymer photocatalyst is CZTB photocatalyst, and its specific structural formula is as follows:

[0048] .

[0049] The present invention also provides a method for preparing the conjugated polymer photocatalyst, comprising the following steps:

[0050] S1: Provides intermediate 2CzTPN-Br, which is prepared by reacting 2,5-dichloroterephthalonitrile with 3,6-dibromo-9H-carbazole under alkaline conditions and in a first organic solvent;

[0051] S2: Provides intermediate TBBA, which is prepared by reacting 4-cyanobenzonic acid with trifluoromethanesulfonic acid;

[0052] S3: In the presence of a catalyst, the intermediate 2CzTPN-Br and the intermediate TBBA are subjected to a coupling polymerization reaction under alkaline conditions and in a second organic solvent to obtain the conjugated polymer photocatalyst.

[0053] As a preferred embodiment, in step S1, the alkaline conditions are provided by anhydrous cesium fluoride; the first organic solvent is N,N-dimethylformamide; the reaction temperature is 80-100℃, the reaction time is 20-28 hours, and the reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the reaction product is further purified by precipitation, filtration, washing, and column chromatography. The eluent for column chromatography purification is a methanol / dichloromethane solution with a volume ratio of 1:10.

[0054] As a preferred embodiment, in step S1, the molar ratio of 2,5-dichloroterephthalonitrile, 3,6-dibromo-9H-carbazole, and anhydrous cesium fluoride is 1 : (2.0-3.0) : (12-16).

[0055] As a preferred embodiment, in step S2, the reaction conditions are as follows: under a nitrogen atmosphere, 4-cyanobenzoic acid and trifluoromethanesulfonic acid are placed in an ice bath and stirred for 1 hour, then stirred overnight at room temperature. Subsequently, the resulting mixture is slowly added to ice water under continuous stirring. The precipitate is collected by filtration and thoroughly washed with a large amount of water to finally obtain a light white solid product.

[0056] As a preferred embodiment, in step S2, the ratio of 4-cyanobenzoic acid to trifluoromethanesulfonic acid is 1 mmol : (0.8 - 1.2) mL.

[0057] As a preferred embodiment, in step S3, the catalyst is tetrakis(triphenylphosphine)palladium, the alkaline conditions are provided by an aqueous potassium carbonate solution, the second organic solvent is N,N-dimethylformamide, and the coupling polymerization reaction is carried out at a temperature of 140-160°C for 60-80 hours.

[0058] As a preferred embodiment, in step S3, the molar ratio of intermediate 2CzTPN-Br, intermediate TBBA, and tetrakis(triphenylphosphine)palladium is 1:(1.5-2.0):(0.05-0.08).

[0059] As a preferred embodiment, in step S3, after the coupling polymerization reaction is completed, the reaction product is further subjected to filtration, washing with acid, water and organic solvent in sequence, and purification by Soxhlet extraction, wherein the organic solvent includes at least one of acetone, chloroform, tetrahydrofuran and methanol; and the solvent used for Soxhlet extraction includes tetrahydrofuran and methanol.

[0060] The present invention also provides an application of the conjugated polymer photocatalyst in the photocatalytic synthesis of nitric acid, comprising: placing the conjugated polymer photocatalyst in a reaction system containing air and water, irradiating the reaction system with a light source at room temperature, thereby catalyzing the generation of nitric acid.

[0061] The following section, using specific data, further elaborates and explains the above-mentioned technical solution of the present invention.

[0062] Example 1

[0063] This embodiment provides a conjugated polymer photocatalyst, its preparation method, and its application. The structural formula of the conjugated polymer photocatalyst is as follows: Figure 12 As shown, the preparation method includes the following steps:

[0064] S1: Under a nitrogen atmosphere, 2,5-dichloroterephthalonitrile (1.42 mmol, 280.00 mg) and 3,6-dibromo-9H-carbazole (3.56 mmol, 1.15 g) were dissolved in 30 mL of anhydrous N,N-dimethylformamide (DMF); then anhydrous cesium fluoride (CsF) (19.75 mmol, 3 g) was added, and the mixture was stirred at 90 °C for 24 hours. After the reaction, the mixture was slowly poured into distilled water, and the precipitate was collected by filtration. The precipitate was washed with hot methanol and dried. The crude product was purified by column chromatography (eluent: methanol / dichloromethane, volume ratio 1:10) to give a yellow solid product, named 2CzTPN-Br.

[0065] S2: Under a nitrogen atmosphere, 4-cyanobenzonic acid (4.80 mmol, 700.00 mg) and trifluoromethanesulfonic acid (5 mL) were added to a 50 mL round-bottom flask, and the flask was placed in an ice bath. The reaction mixture was stirred at this temperature (ice bath temperature, approximately 0 °C) for 1 hour, and then stirred overnight at room temperature. After the reaction was completed, the resulting mixture was slowly added to ice water with continuous stirring. The precipitate was collected by filtration and washed thoroughly with plenty of water to obtain a light white solid product, named TBBA.

[0066] S3: Under a nitrogen atmosphere, 2CzTPN-Br (0.15 mmol, 100.00 mg), TBBA (0.26 mmol, 114.00 mg), and Pd(PPh3)4 (0.0097 mmol, 11.00 mg) were dispersed in 20 mL of anhydrous DMF. Then, 2 mL of K2CO3 (2 M) was added to the above solution, and the reaction mixture was stirred at 150 °C for 72 hours. After cooling to room temperature, the reaction mixture was filtered, and the obtained solid was washed successively with hydrochloric acid (2 M), water, acetone, chloroform, tetrahydrofuran, and methanol. Soxhlet extraction was performed with tetrahydrofuran and methanol (24 hours each). The collected solids were dried in a vacuum drying oven to obtain a dark green powder, named CZTB, i.e., conjugated polymer photocatalyst.

[0067] The applications include the use of the conjugated polymer photocatalyst in the photocatalytic synthesis of nitric acid, specifically including:

[0068] A mixture of 15 mg CZTB and 20 mL of water was added sequentially to 45 mL test tubes, and the photocatalytic system was then placed in air. The reaction solution was continuously irradiated with a white LED light source at room temperature for 324 hours. After the reaction, the solution was centrifuged to obtain the supernatant, and the concentration of HNO3 in the solution was quantitatively analyzed using a UV-Vis spectrophotometer; the yield of HNO3 was 4466.2 μmol g. -1 cat .

[0069] Example 2

[0070] This embodiment provides a conjugated polymer photocatalyst and its preparation method, wherein the structural formula of the conjugated polymer photocatalyst is as follows: Figure 12 As shown, the preparation method includes the following steps:

[0071] S1: Under a nitrogen atmosphere, 2,5-dichloroterephthalonitrile (1.00 mmol, 197.2 mg) and 3,6-dibromo-9H-carbazole (2.00 mmol, 646.1 mg) were dissolved in 20 mL of anhydrous N,N-dimethylformamide (DMF); then anhydrous cesium fluoride (12.00 mmol, 1.82 g) was added, and the mixture was stirred at 80 °C for 20 hours. After the reaction was completed, the mixture was slowly poured into distilled water, and the precipitate was collected by filtration. The precipitate was washed with hot methanol and dried. The crude product was purified by column chromatography (eluent was a methanol / dichloromethane solution with a volume ratio of 1:10) to finally obtain the yellow solid product 2CzTPN-Br.

[0072] S2: Under a nitrogen atmosphere, 4-cyanobenzonic acid (4.80 mmol, 700.00 mg) and trifluoromethanesulfonic acid (3.84 mL) were added to a 50 mL round-bottom flask, and the flask was placed in an ice bath. The reaction mixture was stirred at this temperature (approximately 0 °C) for 1 hour, followed by stirring overnight at room temperature. After the reaction was complete, the resulting mixture was slowly added to ice water with continuous stirring. The precipitate was collected by filtration and washed thoroughly with plenty of water to obtain the light white solid product TBBA.

[0073] S3: Under a nitrogen atmosphere, 2CzTPN-Br (0.15 mmol, 100.00 mg), TBBA (0.225 mmol, 98.7 mg), and tetrakis(triphenylphosphine)palladium (Pd(PPh3)4) (0.0075 mmol, 8.5 mg) were dispersed in 20 mL of anhydrous DMF. Then, 2 mL of potassium carbonate aqueous solution (2 M) was added to the above solution; the reaction mixture was stirred at 140 °C for 60 hours. After cooling to room temperature, the reaction mixture was filtered, and the resulting solid was washed successively with hydrochloric acid (2 M), water, acetone, chloroform, tetrahydrofuran, and methanol. Soxhlet extraction was performed with tetrahydrofuran and methanol (24 hours each), and the collected solids were dried in a vacuum drying oven to obtain a dark green powder, which is the conjugated polymer photocatalyst CZTB.

[0074] Example 3

[0075] This embodiment provides a conjugated polymer photocatalyst and its preparation method. The structural formula of the conjugated polymer photocatalyst is as follows: Figure 12 As shown, its preparation method includes the following steps:

[0076] S1: Under a nitrogen atmosphere, 2,5-dichloroterephthalonitrile (1.00 mmol, 197.2 mg) and 3,6-dibromo-9H-carbazole (3.00 mmol, 969.1 mg) were dissolved in 20 mL of anhydrous N,N-dimethylformamide (DMF). Anhydrous cesium fluoride (CsF) (16.00 mmol, 2.43 g) was then added, and the mixture was stirred at 100 °C for 28 hours. After the reaction, the mixture was slowly poured into distilled water, and the precipitate was collected by filtration. The precipitate was washed with hot methanol and dried. The crude product was purified by column chromatography (eluent: methanol / dichloromethane solution, v / v) to give a yellow solid product 2CzTPN-Br.

[0077] S2: Under a nitrogen atmosphere, 4-cyanobenzonic acid (4.80 mmol, 700.00 mg) and trifluoromethanesulfonic acid (5.76 mL) were added to a 50 mL round-bottom flask, and the flask was placed in an ice bath. The reaction mixture was stirred at this temperature (approximately 0 °C) for 1 hour, followed by stirring overnight at room temperature. After the reaction was complete, the resulting mixture was slowly added to ice water with continuous stirring. The precipitate was collected by filtration and washed thoroughly with plenty of water to obtain the pale white solid product TBBA.

[0078] S3: Under a nitrogen atmosphere, 2CzTPN-Br (0.15 mmol, 100.00 mg), TBBA (0.30 mmol, 131.6 mg), and tetrakis(triphenylphosphine)palladium (0.012 mmol, 13.6 mg) were dispersed in 20 mL of anhydrous DMF. Then, 2 mL of potassium carbonate aqueous solution (2 M) was added to the above solution; the reaction mixture was stirred at 160 °C for 80 hours. After cooling to room temperature, the reaction mixture was filtered, and the resulting solid was washed successively with hydrochloric acid (2 M), water, acetone, chloroform, tetrahydrofuran, and methanol; Soxhlet extraction was performed with tetrahydrofuran and methanol (24 hours each), and the collected solids were dried in a vacuum drying oven to obtain a dark green powder, which is the conjugated polymer photocatalyst CZTB.

[0079] The conjugated polymer photocatalyst prepared in Example 1 was characterized structurally, tested for photocatalytic performance, and its mechanism was investigated. The specific test results are as follows:

[0080] via XPS ( Figure 1 ), FT-IR ( Figure 2 ), 13 C NMR ( Figure 3 XRD Figure 4 SEM ( Figure 5 BET nitrogen adsorption ( Figure 6 ) and O2-TPD ( Figure 7 ) and the pore size distribution of conjugated polymer photocatalysts ( Figure 13 The morphology, structure, and chemical composition of the conjugated polymer photocatalyst were investigated. The results showed that 2CzTPN-Br and TBBA successfully polymerized to form the conjugated polymer photocatalyst CZTB. Furthermore, as described in Example 1, the photocatalyst CZTB prepared in this invention exhibited significantly improved photocatalytic performance under air atmosphere and H2O as solvent conditions. After 324 h of long-term illumination, its HNO3 yield was 4466.2 μmol g. -1 cat Its catalytic effect is shown in Figure 8 In addition, through fluorescence spectroscopy ( Figure 9 ),impedance( Figure 10 ) and photocurrent ( Figure 11 Tests have verified that the catalyst has significantly improved photogenerated carrier separation efficiency and good photoelectric response characteristics, which explains its high catalytic activity from a mechanistic perspective.

[0081] Compared with existing metal-free polymer photocatalysts based on Schiff base condensation and high-temperature calcination, the conjugated polymer photocatalyst CZTB provided by this invention has significant advantages. This invention constructs a well-ordered donor-acceptor (D-A) type long-range conjugated framework through precise molecular-level design of carbazole and terephthalonitrile units, enabling controllable adjustment of the band structure and efficient separation of photogenerated carriers. Prior materials, due to high-temperature carbonization, exhibit disordered structures and uncontrollable energy levels, making effective photoelectric modulation at the molecular level difficult. The polymer framework of this invention contains active sites such as carbazole nitrogen atoms and nitrile groups, enhancing the adsorption and activation capacity for nitrogen gas and making the nitrogen oxidation pathway more selective. Prior technologies mainly rely on hydrogen peroxide and •OH generated by O2 reduction. Indirect oxidation of N2 by free radicals limits the activation efficiency of nitrogen. This invention employs a controllable coupling polymerization method, resulting in a stable and reproducible material structure. This avoids the random structure and batch-to-batch differences caused by calcination. The catalytic system of this invention can achieve efficient nitric acid generation at room temperature and in air atmosphere. Its nitric acid yield is significantly higher than that of existing technologies, exhibiting excellent photocatalytic activity and long-term stability, and possessing better potential for practical applications.

[0082] In summary, the preparation method of this invention, through ingenious molecular design, constructs a donor-acceptor type conjugated polymer CZTB with carbazole as the electron donor and benzonitrile as the electron acceptor. Its unique conjugated framework effectively promotes the separation and migration of photogenerated electron-hole pairs. Simultaneously, the material's high specific surface area and abundant pore structure enhance its adsorption capacity for reactant gases, particularly its strong adsorption of oxygen, which helps generate a large number of reactive oxygen species such as hydroxyl radicals during photocatalysis. This synergistically achieves efficient activation and oxidation of nitrogen in the air at room temperature, ultimately producing nitric acid. This invention successfully develops an all-organic, metal-free catalyst that combines environmental friendliness and cost advantages. Furthermore, it exhibits excellent catalytic performance and durability in the direct synthesis of nitric acid from air. As shown in Example 1, the nitric acid yield remains as high as 4466.2 μmol g after 324 hours of continuous light irradiation. -1 cat The preparation method of this invention has mild process conditions, uses air as nitrogen source and water as medium, has low energy consumption and good safety, and its efficient carrier separation and gas adsorption capabilities have been verified from a mechanistic perspective through systematic spectral and photoelectrochemical characterization. Moreover, the preparation method of this invention has controllable process and good repeatability, and has significant potential for industrial application.

[0083] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a conjugated polymer photocatalyst, characterized in that, Includes the following steps: S1: Provides intermediate 2CzTPN-Br, which is prepared by reacting 2,5-dichloroterephthalonitrile with 3,6-dibromo-9H-carbazole under alkaline conditions and in a first organic solvent; S2: Provides intermediate TBBA, which is prepared by reacting 4-cyanobenzonic acid with trifluoromethanesulfonic acid; S3: In the presence of a catalyst, the intermediate 2CzTPN-Br and the intermediate TBBA are subjected to a coupling polymerization reaction under alkaline conditions and a second organic solvent to obtain the conjugated polymer photocatalyst. The structural formula of the conjugated polymer photocatalyst is as follows: 。 2. The method for preparing the conjugated polymer photocatalyst according to claim 1, characterized in that, In step S1, the alkaline conditions are provided by anhydrous cesium fluoride; the first organic solvent is N,N-dimethylformamide; the reaction temperature is 80-100℃, the reaction time is 20-28 hours, and the reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the reaction product is further purified by precipitation, filtration, washing, and column chromatography. The eluent for column chromatography purification is a methanol / dichloromethane solution with a volume ratio of 1:

10.

3. The method for preparing the conjugated polymer photocatalyst according to claim 2, characterized in that, In step S1, the molar ratio of 2,5-dichloroterephthalonitrile, 3,6-dibromo-9H-carbazole, and anhydrous cesium fluoride is 1:(2.0-3.0):(12-16).

4. The method for preparing the conjugated polymer photocatalyst according to claim 1, characterized in that, In step S2, the reaction conditions are as follows: under a nitrogen atmosphere, 4-cyanobenzoic acid and trifluoromethanesulfonic acid are placed in an ice bath and stirred for 1 hour, then stirred at room temperature, and the resulting mixture is slowly added to ice water under continuous stirring. The precipitate is collected by filtration and washed thoroughly with a large amount of water to finally obtain a light white solid product.

5. The method for preparing the conjugated polymer photocatalyst according to claim 1, characterized in that, In step S2, the ratio of 4-cyanobenzoic acid to trifluoromethanesulfonic acid is 1 mmol : (0.8 - 1.2) mL.

6. The method for preparing the conjugated polymer photocatalyst according to claim 1, characterized in that, In step S3, the catalyst is tetrakis(triphenylphosphine)palladium, the alkaline conditions are provided by an aqueous potassium carbonate solution, the second organic solvent is N,N-dimethylformamide, and the coupling polymerization reaction is carried out at a temperature of 140-160°C for 60-80 hours.

7. The method for preparing the conjugated polymer photocatalyst according to claim 6, characterized in that, In step S3, the molar ratio of intermediate 2CzTPN-Br, intermediate TBBA, and tetrakis(triphenylphosphine)palladium is 1:(1.5-2.0):(0.05-0.08).

8. The method for preparing the conjugated polymer photocatalyst according to claim 1, characterized in that, In step S3, after the coupling polymerization reaction is completed, the reaction product is further subjected to filtration, washing with acid, water and organic solvent in sequence, and purification by Soxhlet extraction. The organic solvent includes at least one of acetone, chloroform, tetrahydrofuran and methanol. The solvent used for Soxhlet extraction purification includes tetrahydrofuran and methanol.

9. A conjugated polymer photocatalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the conjugated polymer photocatalyst as described in claim 9 in the photocatalytic synthesis of nitric acid, characterized in that, The process includes the following steps: placing the conjugated polymer photocatalyst in a reaction system containing air and water, irradiating the reaction system with a light source at room temperature, thereby catalyzing the generation of nitric acid.

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