Method for high-temperature solid-phase preparation of amido bond bridged organic polymer oxygen-producing photocatalyst

Abstract

The invention relates to a method for high-temperature solid-phase preparation of an amido bond bridged organic polymer oxygen-producing photocatalyst, which comprises the following steps: mixing an aromatic polyamine monomer and an aromatic polyacyl chloride monomer, and then carrying out high-temperature treatment and cooling to obtain the amido bond bridged organic polymer oxygen-producing photocatalyst, the temperature T of the high-temperature treatment is greater than or equal to T1 and less than or equal to T2, the time of the high-temperature treatment is 10-60 minutes, T1 is a temperature higher than the melting point of the aromatic polyacyl chloride monomer and not lower than 260 DEG C, and T2 is a temperature lower than the initial decomposition temperature of the aromatic polyamine monomer by more than 20 DEG C. According to the invention, a one-step high-temperature solid-phase method is adopted, the reaction temperature is regulated between T1 and T2, and the aromatic multi-element acyl chloride monomer is fused to form a solvent as a reaction medium, so that amino and acyl chloride groups are directly and quickly condensed to generate amido bonds, and the synthesis period is short; meanwhile, sufficient energy can be provided for molecular chain movement and ordered arrangement under the reaction temperature condition, a high-crystallinity polymer network is formed, and therefore the good performance of producing oxygen through water photolysis is shown.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic water splitting for oxygen production, and more particularly to a method for high-temperature solid-phase preparation of an amide-bridged organic polymer photocatalyst for oxygen production. Background Technology

[0002] Covalent organic polymers (COPs) have shown great potential in photocatalysis due to their advantages such as highly designable molecular structures and tunable light absorption ranges. Current research mainly focuses on reduction half-reactions such as photocatalytic water splitting for hydrogen production and carbon dioxide reduction. However, there are still few reports on high-performance COPs materials for the more challenging photocatalytic water splitting for oxygen production. This is mainly attributed to the insufficient chemical stability of most COPs materials under the continuous accumulation of strong oxidizing holes, and the difficulty in their band structure simultaneously meeting the thermodynamic requirements of light absorption and oxygen production reactions.

[0003] In the construction of organic polymers, the chemical stability and electronic properties of the linking units are crucial. Among numerous linking units such as imine bonds, carbon-carbon double bonds, borate ester bonds, and amide bonds, amide bonds exhibit unique comprehensive advantages due to their strong polarity and high chemical stability: their strong polarity helps optimize the hydrophilicity of the material, promoting water molecule adsorption and mass transfer; their abundant hydrogen bond network significantly enhances skeletal stability, enabling them to withstand a wider range of pH environments; simultaneously, the coordination sites provided by the nitrogen and oxygen atoms in the amide bond can efficiently adsorb and activate intermediate species in water oxidation reactions. Theoretical calculations and previous experiments have shown that, compared to imine bonds, amide-bridged organic polymers can effectively reduce the activation energy of water oxidation reactions, demonstrating great potential in photocatalytic water splitting for oxygen production.

[0004] However, existing methods for synthesizing amide-bridged organic polymers have significant limitations. The mainstream two-step method requires first synthesizing an imine-linked intermediate via a solvothermal process, and then oxidizing it to an amide bond using a strong oxidizing agent. Another widely used method is the sol-gel method, which prepares the target polymer by directly condensing amino and acyl chloride groups in an organic solvent. Both the two-step method and the sol-gel method heavily rely on organic solvents as a medium, which not only leads to complex and time-consuming processes (several days), but also makes the complete removal of organic solvents difficult, thus limiting the effective improvement of the material's crystallinity.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for high-temperature solid-phase preparation of amide-bridged organic polymer oxygen-generating photocatalysts.

[0007] The technical solution adopted in this invention is as follows: The application provides a method for preparing an amide bond bridged organic polymer oxygen-producing photocatalyst by high-temperature solid phase, comprising the following steps: mixing aromatic polyamine monomers and aromatic polyacyl chloride monomers, and then performing high-temperature treatment, and cooling to obtain the product. The temperature T of the high-temperature treatment satisfies T1≤T≤T2, and the time of the high-temperature treatment is 10-60 min, wherein T1 is a temperature higher than the melting point of the aromatic polyacyl chloride monomers and not lower than 260 DEG C, and T2 is a temperature 20 DEG C lower than the initial decomposition temperature of the aromatic polyamine monomers.

[0008] The method for preparing an amide bond bridged organic polymer oxygen-producing photocatalyst by high-temperature solid phase provided by the application adopts one-step high-temperature solid phase method, the reaction temperature is controlled between T1 and T2, the aromatic polyacyl chloride monomers are used as reaction medium by virtue of the characteristic of self-forming solvent in melting, the amino group and the acyl chloride group are directly and quickly condensed to generate amide bond, the synthesis efficiency is greatly improved (the period is shortened from dozens of hours in the traditional process to within one hour), and the adverse influence of residual organic solvent is avoided; meanwhile, the reaction temperature condition can provide sufficient energy for molecular chain movement and ordered arrangement, so that a polymer network with high crystallinity is constructed. The amide bond bridged organic polymer prepared by the method has regular molecular arrangement and stable energy band structure, can effectively promote the separation and migration of photo-generated electron-hole pairs, and thus has good water splitting oxygen production performance.

[0009] Preferably, the aromatic polyamine monomers are melamine. The aromatic polyacyl chloride monomers are one or a combination of two or more of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride.

[0010] Preferably, the molar ratio of the aromatic polyamine monomers to the aromatic polyacyl chloride monomers is 2:1-1:5.

[0011] Preferably, T2 is a temperature 30-40 DEG C lower than the initial decomposition temperature of the aromatic polyamine monomers.

[0012] Preferably, the heating rate of the high-temperature treatment is 5-80 DEG C / min.

[0013] Preferably, the high-temperature treatment adopts microwave heating treatment.

[0014] Preferably, the reaction atmosphere adopted by the high-temperature treatment is air atmosphere and / or inert atmosphere. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The Fourier transform infrared spectrum of the amide bond bridged organic polymer oxygen-producing photocatalyst prepared in Examples 1-3 is shown in the following figure. Figure 2Solid state carbon nuclear magnetic resonance spectrum of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 1; Figure 3 X-ray diffraction spectrum of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 1, Example 4 and Example 5; Figure 4 X-ray diffraction spectrum of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 2 and Comparative Example 1; Figure 5 High resolution transmission electron microscope image of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 1; Figure 6 Scanning electron microscope image of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 1; Figure 7 Nitrogen adsorption-desorption isotherm graph of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 1; Figure 8 Pore size distribution graph of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 1; Figure 9 Solid state ultraviolet-visible diffuse reflectance spectrum of the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Example 1-3. DETAILED DESCRIPTION

[0016] In order to better understand the above technical solutions, the exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present application can be more clearly, thoroughly understood and the scope of the present application can be completely conveyed to those skilled in the art.

[0017] The present application provides a method for preparing an amide bond bridged organic polymer oxygen evolution photocatalyst by high temperature solid phase, comprising the following steps: mixing aromatic polyamine monomers and aromatic polyacyl chloride monomers, then performing high temperature treatment, and cooling to obtain the product. The temperature T of the high temperature treatment satisfies T1≤T≤T2, and the time of the high temperature treatment is 10-60 min, wherein T1 is a temperature higher than the melting point of the aromatic polyacyl chloride monomers and not lower than 260℃, and T2 is a temperature 20℃ lower than the initial decomposition temperature of the aromatic polyamine monomers.

[0018] The present application defines the temperature T of high-temperature treatment as T1 and T2, aiming to simultaneously achieve efficient reaction and high crystallinity product formation under solvent-free condition. The present application selects T1 as the lower limit, on the one hand, the high-temperature treatment temperature needs to be higher than the melting point of the used aromatic polyacyl chloride monomer to ensure its sufficient melting, improve mass transfer and reaction efficiency, on the other hand, the temperature not less than 260℃ provides sufficient thermodynamic driving force for the condensation reaction of amino group and acyl chloride group, ensuring that the reaction can proceed quickly and fully, thereby forming a stable polymer network; and T2 is selected as the upper limit, on the one hand, it provides sufficient energy for the movement and ordered arrangement of polymer molecular chains to induce the formation of high crystallinity structure; on the other hand, it is to avoid the decomposition of reactants or the destruction of polymer structure due to overheating. In addition, the present application does not make special limitation to the mixing method of raw materials and the method of high-temperature treatment, for example, the mixing method can be direct grinding mixing, layered coating, etc., and the high-temperature treatment can use muffle furnace, high-temperature tube furnace, etc.

[0019] In a preferred embodiment, the aromatic polyamine monomer is melamine; The aromatic polyacyl chloride monomer is one or a combination of two or more of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride.

[0020] In the present application, melamine is selected as the aromatic polyamine monomer, which has higher thermal stability, and the initial temperature of thermal decomposition is usually 300-350℃, accordingly the upper limit of reaction temperature T2≤330℃ is set; at the same time, trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride are selected as the aromatic polyacyl chloride monomer, all of which have lower melting points (<100℃), accordingly the lower limit of temperature T1≥260℃ is set. Based on this, the high-temperature treatment temperature T can be selected in the range of 260-330℃, for example, T can be any value in 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, etc. In addition, during the high-temperature treatment process, melamine can be in a controllable gaseous phase (the sublimation temperature at normal pressure is 250-300℃) to rapidly and uniformly contact and react with the molten aromatic polyacyl chloride monomer (while there is a gas-liquid-solid three-phase cooperative mass transfer network), thereby significantly improving the efficiency of synthesizing amide bond bridged organic polymers.

[0021] In a preferred embodiment, the molar ratio of aromatic polyamine monomer to aromatic polyacyl chloride monomer is 2:1-1:5. The present application is beneficial to efficient polymerization and crystallization by adjusting the amount ratio of aromatic polyamine monomer to aromatic polyacyl chloride monomer, for example, the molar ratio of the two can be any value in 0.2:1, 0.5:1, 1:1, 1.5:1, 2:1, etc.

[0022] In a preferred embodiment, T2 is a temperature 30-40°C lower than the initial decomposition temperature of the aromatic polyamine monomer. The present application further selects the range of the upper limit of the reaction temperature T2, which can provide sufficient energy for the movement and ordered arrangement of the polymer molecular chain to induce crystallization, and can more limit the risk of degradation caused by overheating, and is more conducive to obtaining an amide bond bridged organic polymer with excellent water-splitting oxygen production performance and high crystallinity. For example, when the aromatic polyamine monomer is melamine (T2≤320°C) and the aromatic polyacyl chloride monomer is terephthaloyl chloride (T1≥260°C), the high-temperature treatment temperature T can be any one of 260°C, 280°C, 300°C, 320°C, etc.

[0023] In a preferred embodiment, the heating rate of the high-temperature treatment is 5-80°C / min. For example, the heating rate of the high-temperature treatment can be any one of 5°C / min, 10°C / min, 20°C / min, 30°C / min, 40°C / min, 50°C / min, 60°C / min, 70°C / min, 80°C / min, etc.

[0024] In a preferred embodiment, the high-temperature treatment adopts microwave heating treatment. In the present application, the bulk heating and selective heating characteristics of microwaves can not only achieve rapid and uniform heating of the reactants and efficient reaction, but also promote the directional arrangement at the molecular level, thereby significantly inducing the ordered crystallization of the polymer. Compared with conventional calcination, the amide bond bridged organic polymer prepared by microwave heating shows obvious improvement in crystallinity and water-splitting oxygen production performance.

[0025] In a preferred embodiment, the high-temperature treatment adopts an air atmosphere and / or an inert atmosphere. For example, the inert atmosphere can be nitrogen, argon, etc., and is not particularly limited.

[0026] Example 1 A method for preparing an amide bond bridged organic polymer oxygen-producing photocatalyst by high-temperature solid phase, comprising the following steps: weighing melamine and terephthaloyl chloride in a molar ratio of 1:3 and placing them in a wave-absorbing reaction boat (the lower layer is terephthaloyl chloride and the upper layer is melamine), covering with a quartz glass cover plate, and then placing the whole in a microwave tube furnace, under an air atmosphere, heating at a rate of 20°C / min to 280°C, maintaining for 10 min, after the reaction is completed, cooling, and grinding to obtain the product.

[0027] Example 2 A method for preparing an amide bond bridged organic polymer oxygen evolution photocatalyst by high temperature solid phase, comprising the following steps: weighing melamine and trimesoyl chloride in a molar ratio of 3:5 and placing them in a wave-absorbing reaction boat (trimesoyl chloride at the bottom and melamine at the top), covering with a quartz glass cover plate, and then placing the whole in a microwave tube furnace, heating to 280℃ at a rate of 20℃ / min under air atmosphere, and keeping the temperature for 10 min. After the reaction is completed, cool and grind to obtain the product.

[0028] Example 3 A method for preparing an amide bond bridged organic polymer oxygen evolution photocatalyst by high temperature solid phase, comprising the following steps: weighing melamine and isophthaloyl chloride in a molar ratio of 1:3 and placing them in a wave-absorbing reaction boat (isophthaloyl chloride at the bottom and melamine at the top), covering with a quartz glass cover plate, and then placing the whole in a microwave tube furnace, heating to 280℃ at a rate of 20℃ / min under air atmosphere, and keeping the temperature for 10 min. After the reaction is completed, cool and grind to obtain the product.

[0029] Example 4 The difference between this example and Example 1 is that a conventional heating method is used, specifically a muffle furnace is used instead of a microwave tube furnace, and the reactor vessel is replaced by a crucible. The remaining steps remain unchanged.

[0030] Example 5 The difference between this example and Example 1 is that a conventional heating method is used, specifically a high-temperature tube furnace is used instead of a microwave tube furnace, and the reactor vessel is replaced by an arc-bottom corundum boat. The remaining steps remain unchanged.

[0031] Example 6 A method for preparing an amide bond bridged organic polymer oxygen evolution photocatalyst by high temperature solid phase, comprising the following steps: weighing 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and terephthaloyl chloride in a molar ratio of 1:1, mixing by grinding, and then placing them in a wave-absorbing reaction boat, covering with a quartz glass cover plate, and then placing the whole in a microwave tube furnace, heating to 310℃ at a rate of 10℃ / min under nitrogen atmosphere (nitrogen flow rate is 100 mL / min), and keeping the temperature for 30 min. After the reaction is completed, cool and grind to obtain the product.

[0032] Example 7 A method for preparing an amide bond bridged organic polymer oxygen evolution photocatalyst by high temperature solid phase, comprising the following steps: weighing melamine and trimesoyl chloride in a molar ratio of 1:1 and placing them in a wave-absorbing reaction boat (trimesoyl chloride at the bottom and melamine at the top), covering with a quartz glass cover plate, and then placing the whole in a microwave tube furnace, heating to 300℃ at a rate of 30℃ / min under nitrogen atmosphere (nitrogen flow rate is 100 mL / min), and keeping the temperature for 40 min. After the reaction is completed, cool and grind to obtain the product.

[0033] Comparative Example 1 The difference between this comparative example and Example 2 is that the traditional sol-gel method is used for preparation, which comprises the following steps: 3 mmol of melamine was dissolved in 18 mL of dimethyl sulfoxide and 2 mL of N-methyl-2-pyrrolidone to form solution A, 5 mmol of trimesoyl chloride was dissolved in the same dimethyl sulfoxide / N-methyl-2-pyrrolidone mixture to form solution B, which was stirred at room temperature for 30 min, solution B was added to solution A, and then heated to 60°C, and continued to stir for 15 min to form a sol. The sol was placed in a sealed container, heated at 85°C for 24 h to form a wet gel, and aged at 60°C for 24 h. The aged gel was purified by anhydrous ethanol solvent exchange method, freeze-dried for 48 h to remove the solvent, and ground to obtain the sample.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that the microwave heating temperature is adjusted from 280°C to 250°C. The remaining steps remain unchanged.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that the microwave heating temperature is adjusted from 280°C to 340°C. The remaining steps remain unchanged.

[0036] Examples 1-7 and Comparative Examples 1-3 were tested for performance, and the results are recorded in Figures 1-8 and Table 1.

[0037] The water photolysis oxygen production performance test method is as follows: 50 mg of the synthesized sample is added to 100 mL of water, ultrasonicated, and then added to a water photolysis reaction system, followed by the addition of 0.2 g of lanthanum oxide, 0.17 g of silver nitrate, and 1 wt.% of cobalt ions (cobalt nitrate). The reaction temperature is controlled at 10°C using a circulating condensate water device, the air in the reaction system is removed using a vacuum system, and a xenon lamp is used to simulate sunlight. The reaction product gas is analyzed online by gas chromatography.

[0038] Figure 1 The Fourier transform infrared spectrum of the sample shows that the amide bond bridged organic polymer oxygen evolution photocatalyst prepared in Examples 1-3 has a molecular structure containing benzene ring, triazine ring, amino group, carbonyl group and other core groups, which meets the molecular characteristics of the target polymer after polymerization of melamine and acyl chloride-containing monomer. Further, the solid-state nuclear magnetic carbon spectrum of the sample shows three carbon peaks corresponding to the benzene ring, amide bond and triazine ring in the structure, indicating the successful polymerization of the two raw material monomers. Figure 2

[0039] Figure 3 ​The XRD pattern of the sample obtained by the high-temperature solid-phase method of the application shows that, compared with the samples obtained by example 1, example 4 and example 5, the sharp characteristic diffraction peaks corresponding to the raw material terephthaloyl chloride and melamine disappear obviously, and new characteristic diffraction peaks appear, which shows that the high-temperature solid-phase method of the application can obtain an organic polymer material with a certain degree of crystallinity; compared with example 4 and example 5 of the traditional heating mode, the diffraction peak of example 1 is more sharp due to the use of microwave heating, which shows that the crystallinity of example 1 is higher. Figure 4 The XRD pattern shows that, compared with the amorphous material prepared by the traditional sol-gel method, the high-temperature solid-phase method of the application can obviously improve the crystallinity of the material.

[0040] Further, the amide bond bridged organic polymer oxygen evolution photocatalyst prepared by example 1 is observed by electron microscope. Figure 5 The high-resolution transmission electron microscope image shows that there are clear crystal lattice fringes in the sample of example 1, which provides intuitive morphological evidence for the high crystallinity of the material; and Figure 6 The SEM image shows that the micro-morphology of the sample is blocky material, and the whole is relatively dense.

[0041] Figure 7 and Figure 8 respectively are the nitrogen adsorption-desorption isotherm graph and the pore size distribution graph of the sample synthesized by example 1. As shown in Figure 7 , the adsorption amount slowly rises in the medium pressure region with P / Po value between 0.2 and 0.5, and significantly increases in the high pressure region with P / Po value between 0.8 and 1.0, and the hysteresis loop appears in the range of 0.5-1.0, which belongs to the IV type of nitrogen adsorption-desorption isotherm. The specific surface area is 2.4 m 2 / g by BET test, the value is small, which is consistent with the scanning electron microscope observation of Figure 6 . The pore size distribution of the catalyst is analyzed by Barrett-Joyner-Halenda (BJH) method, as shown in Figure 8 , the pore size is mainly concentrated around 10 nm, which shows that the sample is a mesoporous material.

[0042] As can be seen from Figure 9 , the samples obtained by examples 1-3 all have obvious semiconductor characteristics, and the absorption band edges of the three samples are 540, 530 and 525 nm respectively, which shows that the samples can absorb visible light.

[0043] Table 1

[0044] The samples prepared in each embodiment and comparative examples were subjected to the test of the water photolysis oxygen production performance, and it can be seen from Table 1 that (1) the catalytic activity of the embodiments (such as embodiments 1-3 and 6-7) using microwave heating is better than that of the embodiments 4-5 using conventional heating, which proves the unique advantage of microwave heating in improving the intrinsic catalytic activity of the material; (2) the comparison results of embodiment 1 and comparative examples 2-3 show that when the high-temperature treatment temperature is too high or too low, it is not conducive to the photocatalytic oxygen production performance of the material; (3) the comparison results of embodiment 2 and comparative example 1 show (in combination with Figure 4 ), the method of the present application can prepare a catalyst with a water photolysis oxygen production rate close to the level of the traditional sol-gel method (about 75%) in a very short time without complex post-treatment; although the sol-gel method may have higher initial photocatalytic activity due to the advantages of specific surface area, the high crystallinity material obtained by the present application has a more superior energy band structure, charge separation ability and long-term stability potential, which also provides a reference for further optimizing the photocatalytic performance by means of morphology engineering and other means.

[0045] Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for high-temperature solid-phase preparation of amide-bridged organic polymer oxygen-generating photocatalysts, characterized in that, Includes the following steps: The aromatic polyamine monomer and the aromatic polyacryl chloride monomer are mixed and subjected to high temperature treatment, followed by cooling to obtain the product. The high-temperature treatment temperature T satisfies T1≤T≤T2, and the high-temperature treatment time is 10~60min, wherein T1 is a temperature higher than the melting point of the aromatic polyacrylamide monomer and not lower than 260℃, and T2 is a temperature more than 20℃ lower than the initial decomposition temperature of the aromatic polyamine monomer.

2. The method for preparing amide-bridged organic polymer oxygen-generating photocatalysts at high temperature solid phase as described in claim 1, characterized in that, The aromatic polyamine monomer is melamine; The aromatic polyacryl chloride monomer is one or a combination of two or more of pyromellitic trichloroisocyanurate, terephthaloyl chloride and isophthaloyl chloride.

3. The method for preparing amide-bridged organic polymer oxygen-generating photocatalysts at high temperature solid phase as described in claim 1 or 2, characterized in that, The molar ratio of the aromatic polyamine monomer to the aromatic polyacrylamide monomer is 2:1 to 1:

5.

4. The method for preparing amide-bridged organic polymer oxygen-generating photocatalysts at high temperature solid phase as described in claim 1, characterized in that, T2 is a temperature 30-40°C lower than the initial decomposition temperature of the aromatic polyamine monomer.

5. The method for preparing amide-bridged organic polymer oxygen-generating photocatalysts at high temperature solid phase as described in claim 1, characterized in that, The heating rate of the high-temperature treatment is 5~80℃ / min.

6. The method for preparing amide-bridged organic polymer oxygen-generating photocatalysts at high temperature solid phase as described in claim 1, characterized in that, The high-temperature treatment employs microwave heating.

7. The method for preparing amide-bridged organic polymer oxygen-generating photocatalysts at high temperature solid phase as described in claim 1, characterized in that, The high-temperature treatment uses an air atmosphere and / or an inert atmosphere as the reaction atmosphere.

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