Phosphorus-doped polymer as well as preparation method and application thereof
By introducing phosphorus atoms into graphite phase carbon nitride to form phosphorus doped polymers, the problems of its low specific surface area and low quantum efficiency are solved, and efficient CO2 photocatalytic reduction is achieved, especially in the formation of methane, which shows significant selectivity and efficiency improvement.
Patent Information
- Application Number
- CN202510169646.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-17
- Publication Date
- 2025-05-23
AI Technical Summary
The graphite phase carbon nitride (g-C3N4) has a low specific surface area as a photocatalyst and the photogenerated carriers are prone to recombination, resulting in low quantum efficiency, limiting its application potential in CO2 photocatalytic reduction.
By introducing phosphorus atoms as doping elements, a phosphorus-doped polymer is formed, and a stable N-P bond is formed by using nucleophilic substitution reactions to change the electron structure of the material, enhancing its electron transfer ability, and forming more active sites through high concentrations of phosphorus doping, improving photocatalytic activity and selectivity.
The photocatalytic efficiency is significantly improved, the yield of methane is improved by reducing CO2 methane, and the selectivity for methane is significantly optimized, and the yield of by-products of carbon monoxide is significantly reduced.
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Figure CN120025550A_ABST
Abstract
Description
Technical Field
[0001] The present application belongs to the technical field of organic polymer compounds, and specifically relates to a phosphorus-doped 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] Graphitic carbon nitride (gC 3 N 4 ) is a non-polluting, metal-free green catalyst with a stable structure and good performance in photocatalytic reduction of CO 2 The applicability of gC 3 N 4 It presents a two-dimensional layered structure, with nitrogen atoms connected by conjugated π bonds inside the molecule, carbon and nitrogen bound by covalent bonds, and weak interactions between molecules. This unique organization and electronic structure gives gC 3 N 4 It has extremely high stability under acid and base conditions, and it also has the advantages of narrow bandgap (2.7eV), non-toxicity, cheap raw materials, and simple preparation. 3 N 4 There are also obvious limitations, such as low specific surface area and low quantum efficiency due to easy recombination of photogenerated carriers. These problems greatly limit its application in CO 2 Potential for application in photocatalytic reduction.
[0004] To overcome these shortcomings, researchers have explored a variety of modification methods to improve gC 3 N 4 The photocatalytic performance of gC is improved by introducing dopants into the gC 3 N 4Internally, lattice defects can be generated to inhibit the recombination of photogenerated electron-hole pairs and change gC 3 N 4 The electronic structure of gC can be adjusted to adjust its energy level position and achieve energy level control. For example, Zhai Shuncheng and other researchers used the first principle to study the effect of S and O doping on gC 3 N 4 The influence of quantum dots was found that doping can significantly reduce the HOMO-LUMO energy gap, broaden the light response range, and increase the light absorption intensity. In addition, the research of Li et al. showed that S doping can more easily replace gC 3 N 4 The nitrogen atoms at the edge form hybrids with carbon atoms. Due to the larger atomic radius of S atoms (100pm), the crystal structure changes after doping. After photoexcitation, the number of free electrons increases, and the Fermi level moves up, showing typical n-type doping characteristics. Summary of the invention
[0005] The invention of this application aims to provide a novel phosphorus-doped polymer with high photocatalytic performance, which is specifically achieved through the following technical solutions:
[0006] In a first aspect, the present application provides a phosphorus-doped polymer, wherein the repeating unit of the phosphorus-doped polymer is composed of a phosphorus atom and a melamine residue directly connected thereto; the phosphorus atom is simultaneously connected to three or five amino groups of melamine. The repeating unit of the phosphorus-doped polymer is:
[0007] or,
[0008] In a second aspect, the present application provides a method for preparing a phosphorus-doped polymer, wherein the phosphorus-doped polymer is obtained by a nucleophilic substitution reaction between a melamine monomer and a phosphorus pentachloride monomer; or, the phosphorus-doped polymer is obtained by a nucleophilic substitution reaction between a melamine monomer and a phosphorus trichloride monomer.
[0009] Through the above nucleophilic substitution reaction, a stable NP bond is formed. This bonding method not only changes the chemical composition of the material, but also introduces phosphorus atoms as doping elements. Phosphorus atoms have a large electronegativity and can effectively adjust the electronic structure of the polymer and enhance its electron transfer ability. Specifically: First, the introduction of phosphorus atoms makes the polymer surface have more electron donor sites, which can adsorb and activate CO 2molecules, reducing their activation energy barriers. At the same time, the presence of phosphorus atoms can also improve the electron acceptance capacity of the material, promote the effective separation of photogenerated electron-hole pairs, reduce the recombination loss of carriers, and thus significantly improve the photocatalytic efficiency. Secondly, the number of phosphorus atoms in phosphorus pentachloride is larger, and a higher concentration of phosphorus doping can be introduced into the polymer. Compared with phosphorus trichloride, phosphorus pentachloride provides a richer phosphorus source, which not only more significantly regulates the electronic structure of the polymer, but also enhances its overall catalytic performance. High concentrations of phosphorus doping help to form more active sites, further improving the photocatalytic activity and selectivity of the material. Thirdly, the polarity of the NP bond may lead to the generation of a built-in electric field inside the material, which helps to quickly separate photogenerated electrons and holes and reduce their recombination probability. In addition, phosphorus doping may regulate the surface state of the polymer surface, optimize the distribution of electrons, and further promote the effective transfer of charges. These factors work together to make P5-AM very effective in photocatalytic CO 2 The reduction process showed excellent charge transfer ability and efficient photogenerated current density. Finally, selective adsorption and reaction path regulation of phosphorus doping may regulate CO 2 The reduction reaction path allows more electrons to flow to generate methane (CH 4 ) pathway instead of the pathway that produces carbon monoxide (CO), thereby improving the selectivity of methane. 2 During reduction, the yield of methane is as high as 908.9 μmol·g -1 The byproduct yield of carbon monoxide is less than 90 μmol·g -1 , showing a high selectivity towards methane.
[0010] Preferably, the phosphorus monomer is selected from phosphorus trichloride; and the molar ratio between the melamine monomer and phosphorus trichloride is 1:(1-3).
[0011] Preferably, the phosphorus monomer is selected from phosphorus pentachloride; the molar ratio between the melamine monomer and phosphorus pentachloride is 5:(5-7).
[0012] Preferably, the conditions of the nucleophilic substitution reaction are: temperature 180-190° C., time 22-24 h.
[0013] In a third aspect, the present application proposes the use of the above-mentioned phosphorus-doped polymer in photocatalysis.
[0014] In a fourth aspect, the present application proposes the use of the above-mentioned phosphorus-doped polymer in carbon dioxide reduction.
[0015] In a fifth aspect, the present application proposes a method for preparing methane, using carbon dioxide as a raw material and the above-mentioned phosphorus-doped polymer as a photocatalyst, wherein the phosphorus atom is connected to five amino groups of melamine; or, a phosphorus-doped polymer prepared by any of the preparation methods described above is used as a photocatalyst, wherein the phosphorus-doped polymer is obtained by a nucleophilic substitution reaction between a melamine monomer and a phosphorus pentachloride monomer.
[0016] Compared with the prior art, this application has the following beneficial effects:
[0017] This application successfully synthesized two conjugated polymers with excellent photocatalytic performance through nucleophilic substitution reaction between melamine and phosphorus pentachloride or phosphorus trichloride: P5-AM (derived from phosphorus pentachloride route) and P3-AM (derived from phosphorus trichloride route). These materials exhibit excellent photocatalytic performance and selectivity due to their unique structural characteristics, including abundant active sites. Performance test results show that under visible light irradiation, P3-AM catalyzes CO 2 Reduction to methane (CH 4 The yield of ) was 224 μmol·g -1 , and the yield of carbon monoxide (CO) is 37 μmol·g -1 ; P5-AM catalyzes CO 2 Reduction to CH 4 The rate reached 908.9 μmol·g -1 This value is 4 times higher than that of P3-AM under the same conditions, reflecting an unexpected technical effect. The byproduct yield of carbon monoxide (CO) catalyzed by P5-AM is only less than 90 μmol·g -1 , showing that the material has significantly better selectivity for methane than carbon monoxide. In addition, the present application adopts a simple supramolecular self-assembly strategy, which only requires environmentally friendly solvents and a controllable heating process, without the need for toxic reagents and cumbersome post-processing processes, making the preparation process simpler, more reliable, and easier to implement. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In order to clearly introduce the embodiments, the following is a brief introduction to the drawings:
[0019] Figure 1 Infrared spectrum for performance test 1;
[0020] Figure 2 This is the transmission electron microscopy (TEM) image of the P5-AM material in performance test 1;
[0021] Figure 3 This is a comparison chart of reduction yields in performance test 2;
[0022] Figure 4 Impedance diagram of phosphorus-doped polymer for performance test 3;
[0023] Figure 5 Photocurrent diagram of 3 phosphorus-doped polymers for performance testing. DETAILED DESCRIPTION
[0024] 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.
[0025] Example 1
[0026] This embodiment discloses a method for preparing a phosphorus-doped polymer, comprising the following steps: 600 mg of phosphorus pentachloride and 315 mg of melamine are placed in 30 mL of 4 mL of DMSO and 16 mL of CH 3 In a CN autoclave reactor, after ultrasonication at room temperature for about 30 minutes, the nanoparticles were heated in an oven at 180°C for 24 hours. The nanoparticles were collected by centrifugation and washed with N, N-dimethylformamide, tetrahydrofuran and n-hexane, respectively. Finally, they were dried overnight at 60°C in vacuum and labeled as P5-AM samples.
[0027] Example 2
[0028] This embodiment discloses a method for preparing a phosphorus-doped polymer, comprising the following steps: 600 mg of phosphorus trichloride and 315 mg of melamine are placed in 30 mL of 4 mL of DMSO and 16 mL of CH 3 In a CN autoclave reactor, after ultrasonication at room temperature for about 30 minutes, the nanoparticles were heated in an oven at 180°C for 24 hours. The nanoparticles were collected by centrifugation and washed with N, N-dimethylformamide, tetrahydrofuran and n-hexane, respectively. Finally, they were dried overnight at 60°C in vacuum and labeled as P3-AM samples.
[0029] Example 3
[0030] This embodiment discloses a method for preparing a phosphorus-doped polymer, comprising the following steps: 5 mol phosphorus pentachloride and 5 mol melamine are placed in 30 mL of 4 mL DMSO and 16 mL CH 3 In a CN autoclave reactor, after ultrasonication at room temperature for about 30 minutes, the nanoparticles were heated in an oven at 180°C for 22 hours. The nanoparticles were collected by centrifugation and washed with N, N-dimethylformamide, tetrahydrofuran and n-hexane, respectively. Finally, they were dried overnight in a vacuum at 60°C and labeled as P5-AM samples.
[0031] Example 4
[0032] This embodiment discloses a method for preparing a phosphorus-doped polymer, comprising the following steps: 7 mol phosphorus pentachloride and 5 mol melamine are placed in 30 mL of 4 mL DMSO and 16 mL CH 3 In a CN autoclave reactor, after ultrasonication at room temperature for about 30 minutes, the nanoparticles were heated in an oven at 190°C for 22 hours. The nanoparticles were collected by centrifugation and washed with N, N-dimethylformamide, tetrahydrofuran and n-hexane, respectively. Finally, they were dried overnight in a vacuum oven at 60°C and labeled as P5-AM samples.
[0033] Example 5
[0034] This embodiment discloses a method for preparing a phosphorus-doped polymer, comprising the following steps: 1 mol of phosphorus trichloride and 3 mol of melamine are placed in 30 mL of 4 mL of DMSO and 16 mL of CH 3 In a CN autoclave reactor, after ultrasonication at room temperature for about 30 minutes, the nanoparticles were heated in an oven at 180°C for 24 hours. The nanoparticles were collected by centrifugation and washed with N, N-dimethylformamide, tetrahydrofuran and n-hexane, respectively. Finally, they were dried overnight at 65°C in vacuum and labeled as P3-AM samples.
[0035] Example 6
[0036] This embodiment discloses a method for preparing a phosphorus-doped polymer, comprising the following steps: 600 mg of phosphorus trichloride and 315 mg of melamine are placed in 30 mL of 4 mL of DMSO and 16 mL of CH 3 In a CN autoclave reactor, after ultrasonication at room temperature for about 30 minutes, the nanoparticles were heated in an oven at 190°C for 24 hours. The nanoparticles were collected by centrifugation and washed with N, N-dimethylformamide, tetrahydrofuran and n-hexane, respectively. Finally, they were dried overnight at 55°C in vacuum and labeled as P3-AM samples.
[0037] Performance Test 1
[0038] This performance test was conducted on the two polymers synthesized in Example 1 and Example 2, namely, P5-AM and P3-AM samples, and their successful synthesis was further confirmed by infrared spectroscopy (FT-IR) analysis. Figure 1 The infrared spectrum of the sample shows a characteristic absorption peak corresponding to the NP bond. This result indicates that melamine successfully reacts with phosphorus trichloride or phosphorus pentachloride to form a nucleophilic substitution reaction, thereby confirming the successful synthesis of the target polymers P3-AM and P5-AM. In addition, in order to gain a deeper understanding of the microstructure of the P5-AM material, the structure of the P5-AM material prepared in Example 1 was also characterized by transmission electron microscopy in this performance test. Figure 2It can be clearly observed in the transmission electron microscope image that the prepared P5-AM presents a typical ultra-thin sheet structure with uniform thickness and neat edges. This unique morphology not only helps to increase the specific surface area of the material, but also may have a positive impact on its photocatalytic performance. Combined with the results of infrared spectroscopy, it confirms the successful preparation of phosphorus-doped polymers and their excellent structural characteristics.
[0039] Performance Test 2
[0040] In this performance test, the P5-AM and P3-AM samples of Example 1 and Example 2 were subjected to photocatalytic CO 2 Reduction test was performed to characterize its photocatalytic activity. Specifically, the 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 maintained 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 , the P5-AM sample exhibited excellent photocatalytic activity and selectivity. Specifically, under the same conditions, P5-AM catalyzed CO 2 Reduction to methane (CH 4 ) with a yield of up to 908.9 μmol·g -1 , much higher than P3-AM. At the same time, the byproduct yield of carbon monoxide (CO) was less than 90 μmol·g -1 , showing that the material's selectivity for methane is significantly better than that for carbon monoxide. This excellent performance is attributed to the unique ultra-thin sheet structure of P5-AM and the efficient photogenerated electron-hole pair separation mechanism that may exist inside it, which helps to improve the light absorption efficiency and promote CO 2 In contrast, the P3-AM sample showed a certain photocatalytic activity under the same conditions, but it was significantly lower than that of P5-AM. Specifically, P3-AM catalyzed CO 2 Reduction to methane (CH 4 The yield of ) was 224 μmol·g -1 , and the yield of carbon monoxide (CO) is 37 μmol·g -1It is particularly noteworthy that the catalytic performance of the P5-AM sample prepared by the reaction of phosphorus pentachloride and melamine is about 4 times that of P3-AM, reflecting an unexpected technical effect.
[0041] Performance Test 3
[0042] In order to further study the dynamics of photogenerated carriers of the P5-AM and P3-AM 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 5 From the electrochemical impedance spectroscopy (EIS), the radius of the semicircle in the Nyquist plot of P5-AM is significantly smaller than that of P3-AM, indicating that P5-AM has a smaller charge transfer impedance. This means that the charge transfer process of P5-AM at the interface is smoother, reducing the resistance to charge transfer. Furthermore, it can be clearly seen from the photocurrent response spectrum that P5-AM exhibits a significantly higher photogenerated current density. This phenomenon proves that in P5-AM, photogenerated charges can not only be generated efficiently, but also effectively separated and quickly transmitted, avoiding carrier recombination losses. Comprehensive analysis of the photocatalytic CO 2 The reduction test results, electrochemical impedance spectroscopy (EIS) and photocurrent response spectra show that P5-AM has significant advantages in charge transfer and photogenerated current density. These excellent properties not only verify its potential in the field of photocatalysis, but also provide important experimental basis and theoretical support for further optimizing the design of photocatalysts.
Claims
1. A phosphorus-doped polymer, characterized in that The repeating unit of the phosphorus-doped polymer is composed of a phosphorus atom and a melamine residue directly connected thereto; the phosphorus atom is simultaneously connected to three or five amino groups of melamine.
2. A method for preparing a phosphorus-doped polymer, characterized in that: The phosphorus-doped polymer is obtained by a nucleophilic substitution reaction between a melamine monomer and a phosphorus pentachloride monomer; or, the phosphorus-doped polymer is obtained by a nucleophilic substitution reaction between a melamine monomer and a phosphorus trichloride monomer.
3. The method for preparing a phosphorus-doped polymer according to claim 2, characterized in that: The phosphorus monomer is selected from phosphorus trichloride; the molar ratio between the melamine monomer and phosphorus trichloride is 1:(1-3).
4. The method for preparing a phosphorus-doped polymer according to claim 2, characterized in that: The phosphorus monomer is selected from phosphorus pentachloride; the molar ratio between the melamine monomer and phosphorus pentachloride is 5:(5-7).
5. The method for preparing a phosphorus-doped polymer according to claim 2, characterized in that: The conditions of the nucleophilic substitution reaction are: temperature 180-190° C., time 22-24 h.
6. Use of the phosphorus-doped polymer according to claim 1 or the phosphorus-doped polymer prepared by the preparation method of any one of claims 2 to 5 in photocatalysis.
7. Use of the phosphorus-doped polymer according to claim 1 or the phosphorus-doped polymer prepared by the preparation method of any one of claims 2 to 5 in carbon dioxide reduction.
8. A method for preparing methane, characterized in that: Carbon dioxide is used as a raw material, and the phosphorus-doped polymer described in claim 1 is used as a photocatalyst, wherein the phosphorus atom is connected to five amino groups of melamine; or, the phosphorus-doped polymer prepared by the preparation method described in any one of claims 2 to 5 is used as a photocatalyst, wherein the phosphorus-doped polymer is obtained by a nucleophilic substitution reaction between a melamine monomer and a phosphorus pentachloride monomer.