An all-organic polymer s-type heterojunction photocatalytic material, a preparation method and application thereof

Abstract

The application discloses a kind of all-organic polymer S-type heterojunction photocatalytic material and its preparation method and application, the material includes carrier and organic polymer polymerized on the surface of carrier, organic monomer is polymerized on the surface of carbon nitride and constitutes all-organic polymer S-type heterojunction, the organic monomer is 1,4-diethynylbenzene, 2,5-diethynylpyridine or 3,6-diethynylpyridazine;Its preparation method is: (1) carbon nitride and catalyst are added in polar base solution, and mix evenly;(2) organic monomer is placed in mixed solution, polymerization reaction occurs, and all-organic polymer S-type heterojunction photocatalytic material is generated in situ.The application selects carbon nitride as carrier and organic conjugated polymer composite, wherein organic conjugated polymer can be matched with the energy band position of carbon nitride by changing molecular structure, to form all-organic polymer S-type heterojunction, so that intramolecular charge transfer rate is faster, and photocatalytic performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor photocatalytic materials, in particular to a full-organic polymer S-type heterojunction photocatalytic material and a preparation method and application thereof. BACKGROUND

[0002] With the increasing energy shortage and environmental crisis, photocatalysis using sunlight as green energy can directly realize the conversion of solar energy to chemical energy, which is an efficient and sustainable energy conversion method. However, the single semiconductor material used for photocatalytic production is often affected by the serious recombination of photo-generated electrons and holes and the slow kinetics of the transfer speed. At the same time, due to the limitation of fixed energy band structure, it cannot guarantee that the photo-generated carriers have strong oxidation and reduction ability. It is still challenging to obtain a high-efficiency photocatalytic system with the advantages of wide visible light response, efficient photo-generated carrier separation / transport separation, and strong oxidation and reduction ability. Therefore, building a suitable heterojunction is one of the most promising ways to solve such challenges. Unlike the previously reported type II heterojunction photocatalysts, the newly developed S-type heterojunction is mainly composed of a reduction-type photocatalyst and an oxidation-type photocatalyst in a closely contacted manner. The unique S-type charge transfer path allows the meaningless electrons and holes to recombine, and the meaningful electrons and holes to effectively separate. Not only can the separation efficiency of the carriers be enhanced, but also the catalyst has strong oxidation and reduction ability, effectively improving the photocatalytic performance.

[0003] In recent years, the application of S-type heterojunction materials in the field of photocatalysis has gradually become a research hotspot. Compared with traditional full-inorganic heterojunctions, a series of inorganic / organic semiconductor S-type heterojunctions have been reported in recent years to improve the carrier separation efficiency and optimize the photocatalytic performance. However, the fixed energy band position of inorganic semiconductors makes it a time-consuming step to screen materials with matching energy band positions. Therefore, the rational design and efficient screening of semiconductors with suitable energy band positions are a huge challenge in constructing S-type heterojunction photocatalytic materials. SUMMARY

[0004] The first object of the present application is to provide a full-organic polymer S-type heterojunction photocatalytic material constructed by an organic polymer and a carbon nitride carrier to improve the catalytic activity. The second object of the present application is to provide a preparation method of the full-organic polymer S-type heterojunction photocatalytic material. The third object of the present application is to provide the application of the full-organic polymer S-type heterojunction photocatalytic material.

[0005] Technical solution: The full organic polymer S-type heterojunction photocatalytic material provided by the application comprises a carrier and an organic polymer grown on the surface of the carrier, and the organic monomer is polymerized on the surface of carbon nitride to form the full organic polymer S-type heterojunction, wherein the organic monomer is 1,4-diethynylbenzene (DEB), 2,5-diethynylpyridine (DEP) or 3,6-diethynylpyridazine (DED).

[0006] Preferably, the mass ratio of the organic monomer to the carrier carbon nitride is 3:1 to 5:1. With the increase of the proportion of the organic monomer, the photocatalytic performance of the full organic polymer S-type heterojunction photocatalytic material in producing hydrogen peroxide increases first and then decreases.

[0007] Preferably, the carbon nitride is porous carbon nitride. The porous carbon nitride is distributed with many pore structures, and the continuous pores can greatly increase the specific surface area of the material, which is beneficial to the in-situ polymerization of the organic monomer on the porous carbon nitride, and the more pores are beneficial to obtain more active sites, which can promote the effective improvement of the photocatalytic performance.

[0008] The preparation method of the full organic polymer S-type heterojunction photocatalytic material provided by the application comprises the following steps:

[0009] (1) adding carbon nitride and a catalyst into a polar base solution and mixing uniformly;

[0010] (2) placing the organic monomer in the mixed solution prepared in step (1) to generate a polymerization reaction and generate the full organic polymer S-type heterojunction photocatalytic material in-situ.

[0011] Preferably, the catalyst is cuprous chloride.

[0012] Preferably, the temperature of the polymerization reaction is 40 to 80 DEG C.

[0013] Preferably, the polymerization reaction time is 4 to 8 hours.

[0014] Preferably, the polar solvent in the polar base solution is pyridine.

[0015] Preferably, the polar base in the polar base solution is piperidine.

[0016] The full organic polymer S-type heterojunction photocatalytic material provided by the application is applied to the photocatalytic production of hydrogen peroxide.

[0017] Inventive mechanism: The application uses carbon nitride (CN) as a carrier and cuprous chloride as a catalyst to catalyze the in-situ polymerization of organic monomers on the surface of carbon nitride to generate a full-organic polymer heterojunction material. The selected organic monomers are 1,4-diethynylbenzene (DEB), 2,5-diethynylpyridine (DEP) or 3,6-diethynylpyridazine (DED). The application uses the Cu + and Cu 2+ produced by cuprous chloride in a polar alkaline solution to catalyze the Glaser coupling reaction between the alkynyl groups to obtain a uniform and stable organic conjugated polymer film on the surface of carbon nitride.

[0018] The carbon nitride and the organic conjugated polymer are selected to be combined, and the energy band position of the organic conjugated polymer can be adjusted to match the energy band position of the carbon nitride by changing the molecular structure to form a full-organic polymer S-type heterojunction, so that the charge separation efficiency in the molecule is higher.

[0019] The organic conjugated polymer material is directly grown in-situ on the carbon nitride to form a closely contacted heterojunction interface with the carbon nitride, greatly promoting the migration rate of the photo-generated carriers; secondly, the carbon nitride and the organic conjugated polymer form an S-type heterojunction material through an interlaced energy band structure, effectively improving the carrier separation efficiency; finally, the ratio of the carbon nitride and the organic conjugated polymer can be optimized to make it have the optimal catalytic performance in the photocatalytic reaction.

[0020] Advantages: Compared with the prior art, the application has the following significant advantages: (1) carbon nitride is selected as a carrier and an organic conjugated polymer is combined, and the energy band position of the organic conjugated polymer can be adjusted to match the energy band position of the carbon nitride by changing the molecular structure to form a full-organic polymer S-type heterojunction, so that the charge transfer rate in the molecule is faster; (2) the ratio of the carbon nitride and the organic conjugated polymer can be optimized to make it have the optimal catalytic performance in the photocatalytic reaction; (3) the preparation method has mild process conditions, simple operation and low cost, and can be used for large-scale production; (4) compared with traditional carbon nitride, the in-situ grown full-organic polymer S-type heterojunction photocatalytic material produced by the application has an efficiency of producing hydrogen peroxide that is about 3 times higher. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a catalyst preparation flowchart of the application;

[0022] Figure 2 It is a scanning electron microscope image of porous carbon nitride;

[0023] Figure 3 It is a scanning electron microscope image of poly(1,4-diethynylbenzene);

[0024] Figure 4Scanning electron microscope image of pDEB-CN-4 in Example 2;

[0025] Figure 5 Transmission electron microscope image of pDEB-CN-4 in Example 2;

[0026] Figure 6 EDX spectrogram of pDEB-CN-4 in Example 2;

[0027] Figure 7 X-ray diffraction spectrum (XRD) of Examples 1-3 and Comparative Examples 1 and 2;

[0028] Figure 8 Photocatalytic activity test of composite materials of different proportions of DEB monomers;

[0029] Figure 9 Photocatalytic activity test of composite materials of different proportions of DEP monomers;

[0030] Figure 10 Photocatalytic activity test of composite materials of different proportions of DED monomers;

[0031] Figure 11 Photocatalytic activity test of composite materials of different organic monomers;

[0032] Figure 12 In Table 1, a is the photocurrent response test of the samples prepared in Example 2 and Comparative Examples 1 and 2; b is the electrochemical impedance test of the corresponding samples. DETAILED DESCRIPTION

[0033] The technical solutions of the present application are further described below in conjunction with examples.

[0034] Example 1

[0035] The preparation method of the all-organic polymer S-type heterojunction photocatalytic material of the present application comprises the following steps:

[0036] (1) Preparation of porous carbon nitride

[0037] 5 g of urea was weighed into a 20 mL porcelain boat with a cover, the cover was closed, and it was placed in a tube furnace, which was heated from room temperature to 550℃ at a rate of 5℃ / min, and kept at 550℃ for 4 h. After the reaction was completed, it was naturally cooled to room temperature, taken out, and ground uniformly in a quartz mortar to obtain a porous carbon nitride powder;

[0038] (2) 20 mg of the porous carbon nitride powder obtained in step (1) and 250 mg of cuprous chloride were weighed into a glass reaction bottle, 50 μL of piperidine and 5 mL of pyridine were weighed into the glass reaction bottle, and ultrasonic dispersion was performed to obtain a mixture;

[0039] (3) Again take 60mg of DEB and add it to the mixture obtained in step (2), and place the reaction system in an oven and react at 60℃ for 6h; after the reaction is completed, cool the reaction system to room temperature, then wash the obtained product with pyridine, dichloromethane and methanol in sequence, and finally dry the product to obtain the pDEB-CN-3 all-organic polymer photocatalytic material.

[0040] Example 2

[0041] The all-organic polymer S-type heterojunction photocatalytic material of the present application has a preparation method comprising the following steps:

[0042] Steps (1) and (2) are the same as in Example 1.

[0043] (3) Again take 80mg of DEB and add it to the mixture obtained in step (2), and place the reaction system in an oven and react at 60℃ for 6h; after the reaction is completed, cool the reaction system to room temperature, then wash the obtained product with pyridine, dichloromethane and methanol in sequence, and finally dry the product to obtain the pDEB-CN-4 all-organic polymer photocatalytic material.

[0044] Example 3

[0045] The all-organic polymer S-type heterojunction photocatalytic material of the present application has a preparation method comprising the following steps:

[0046] Steps (1) and (2) are the same as in Example 1.

[0047] (3) Again take 100mg of DEB and add it to the mixture obtained in step (2), and place the reaction system in an oven and react at 60℃ for 6h; after the reaction is completed, cool the reaction system to room temperature, then wash the obtained product with pyridine, dichloromethane and methanol in sequence, and finally dry the product to obtain the pDEB-CN-5 all-organic polymer photocatalytic material.

[0048] Example 4

[0049] The all-organic polymer S-type heterojunction photocatalytic material of the present application has a preparation method comprising the following steps:

[0050] Steps (1) and (2) are the same as in Example 1.

[0051] (3) Again take 60mg of DEP and add it to the mixture obtained in step (2), and place the reaction system in an oven and react at 60℃ for 6h; after the reaction is completed, cool the reaction system to room temperature, then wash the obtained product with pyridine, dichloromethane and methanol in sequence, and finally dry the product to obtain the pDEP-CN-3 all-organic polymer photocatalytic material.

[0052] Example 5

[0053] The preparation method of the full-organic polymer S-type heterojunction photocatalytic material of the present application comprises the following steps:

[0054] Steps (1) and (2) are the same as those in Example 1.

[0055] (3) 80 mg of DEP is weighed again and added into the mixed solution obtained in step (2), and the reaction system is placed in an oven for reaction at 60℃ for 6 h; after the reaction is completed, the reaction system is cooled to room temperature, and then the obtained product is sequentially washed with pyridine, dichloromethane and methanol, and finally the product is dried to obtain the pDEP-CN-4 full-organic polymer photocatalytic material.

[0056] Example 6

[0057] The preparation method of the full-organic polymer S-type heterojunction photocatalytic material of the present application comprises the following steps:

[0058] Steps (1) and (2) are the same as those in Example 1.

[0059] (3) 100 mg of DEP is weighed again and added into the mixed solution obtained in step (2), and the reaction system is placed in an oven for reaction at 60℃ for 6 h; after the reaction is completed, the reaction system is cooled to room temperature, and then the obtained product is sequentially washed with pyridine, dichloromethane and methanol, and finally the product is dried to obtain the pDEP-CN-5 full-organic polymer photocatalytic material.

[0060] Example 7

[0061] The preparation method of the full-organic polymer S-type heterojunction photocatalytic material of the present application comprises the following steps:

[0062] Steps (1) and (2) are the same as those in Example 1.

[0063] (3) 60 mg of DED is weighed again and added into the mixed solution obtained in step (2), and the reaction system is placed in an oven for reaction at 60℃ for 6 h; after the reaction is completed, the reaction system is cooled to room temperature, and then the obtained product is sequentially washed with pyridine, dichloromethane and methanol, and finally the product is dried to obtain the pDED-CN-3 full-organic polymer photocatalytic material.

[0064] Example 8

[0065] The preparation method of the full-organic polymer S-type heterojunction photocatalytic material of the present application comprises the following steps:

[0066] Steps (1) and (2) are the same as those in Example 1.

[0067] (3) Weighing 80 mg of DED and adding it to the mixed solution obtained in step (2), the reaction system was placed in an oven at 60° C. for 6 h; after the reaction, the reaction system was cooled to room temperature, and the obtained product was washed with pyridine, dichloromethane, and methanol in sequence, and finally the product was dried to obtain the pDED-CN-4 all-organic polymer photocatalytic material.

[0068] Example 9

[0069] The preparation method of the all-organic polymer S-type heterojunction photocatalytic material of the present invention comprises the following steps:

[0070] Step (1) and step (2) are the same as in Example 1.

[0071] (3) Weighing 100 mg of DED and adding it to the mixed solution obtained in step (2), the reaction system was placed in an oven at 60° C. for 6 h; after the reaction, the reaction system was cooled to room temperature, and the obtained product was washed with pyridine, dichloromethane, and methanol in sequence, and finally the product was dried to obtain the pDED-CN-5 all-organic polymer photocatalytic material.

[0072] Comparative Example 1

[0073] Comparative Example 1 is different from Example 1 in that only step (1) is completed to obtain the ground powder, which is marked as CN.

[0074] Comparative Example 2

[0075] Comparative Example 2 is different from Example 1 in that the powder obtained in step (1) is not added in step (2). The remaining steps are the same as those in Example 1, and the obtained product is labeled as pDEB.

[0076] Comparative Example 3

[0077] Comparative Example 3 is different from Example 4 in that the powder obtained in step (1) is not added in step (2). The remaining steps are the same as those in Example 4, and the obtained product is labeled as pDEP.

[0078] Comparative Example 4

[0079] Comparative Example 4 is different from Example 7 in that the powder obtained in step (1) is not added in step (2). The remaining steps are the same as those in Example 1, and the obtained product is labeled as pDED.

[0080] Morphological characterization

[0081] (1) Physical characterization of the samples prepared in Examples 1 to 3, Comparative Example 1 and Comparative Example 2 was performed. The results are as follows: Figures 2 to 7 shown.

[0082] Depend on Figure 2It can be seen that the porous carbon nitride prepared in Comparative Example 1 is a nanosheet layered and uniformly stacked, and an obvious pore structure can be observed on the nanosheet.

[0083] Depend on Figure 3 It can be seen that the poly(1,4-diethynylbenzene) prepared in Comparative Example 2 exhibits irregular fibrous distribution.

[0084] Depend on Figure 4 It can be seen that the prepared pDEB conjugated polymer grows uniformly on the porous carbon nitride.

[0085] Depend on Figure 5 Under high-resolution transmission electron microscopy, it was clearly observed that the surface of the porous carbon nitride nanosheets was covered with continuous and uniform fibrous poly(1,4-diethynylbenzene).

[0086] Figure 6 The medium energy dispersive X-ray spectroscopy element mapping diagram shows that C and N elements are evenly distributed in the pDEB-CN-4 all-organic polymer S-type heterojunction material in Example 2.

[0087] Figure 7 The porous carbon nitride, poly (1,4-diethynylbenzene) and pDEB-CN-3 / 4 / 5 in Examples 1 to 3 can be seen. It can be seen that the original conjugated polymer has no obvious diffraction peak, while the composite material in the example has a diffraction peak corresponding to the 002 crystal plane of carbon nitride at 27.4°, which indicates that the pDEB-CN-3 / 4 / 5 all-organic polymer composite material was successfully synthesized.

[0088] Performance Characterization

[0089] (1) Catalytic activity test of different ratios of DEB monomers

[0090] Under xenon lamp irradiation (λ≥420nm, 60mW cm -2 ) conditions, 15 mg of the materials synthesized in Example 1, Example 2, Example 3 and Comparative Example 2 were taken as catalysts, added to 30 mL of pure water, and O2 was continuously introduced into the water. Samples were taken every 20 min and tested in an ultraviolet spectrophotometer. The test results are shown in FIG. Figure 8 shown.

[0091] Figure 8 It can be seen that different ratios of DEB to CN lead to differences in the photocatalytic performance of the synthesized composites. Under irradiation conditions of λ ≥ 420nm, pDEB produced a hydrogen peroxide concentration of 149μM after 100 minutes, while the concentrations of hydrogen peroxide produced at DEB to CN mass ratios of 3:1, 4:1, and 5:1 were 176μM, 205μM, and 154μM, respectively. The performance was optimal when the DEB to CN mass ratio was 4:1, while the performance of samples synthesized under other ratios was lower than that of samples synthesized under this condition.

[0092] (2)Catalytic activity test of different proportions of DEP monomers

[0093] Under the condition of xenon lamp irradiation (λ≥420nm, 60mW cm -2 ), 15mg of the material synthesized in Example 4, Example 5, Example 6 and Comparative Example 3 was taken as a catalyst in 30mL pure water, O2 was continuously introduced into the water, and the sample liquid was taken every 20min for detection in the ultraviolet spectrophotometer, and the test results are shown in Table 2. Figure 9

[0094] Figure 9 It can be seen that different proportions of DEP and CN will cause differences in the photocatalytic performance of the synthesized composite material. Under the condition of λ≥420nm irradiation, the concentration of hydrogen peroxide produced by pDEP at 100min was 41μM, while the concentration of hydrogen peroxide produced at 100min under the conditions of DEP and CN mass ratio of 3:1, 4:1 and 5:1 was 70μM, 117μM and 58μM respectively. The performance is best when the mass ratio of DEP and CN is 4:1, and the performance of other proportions is less than that of the sample synthesized under this condition.

[0095] (3)Catalytic activity test of different proportions of DED monomers

[0096] Under the condition of xenon lamp irradiation (λ≥420nm, 60mW cm -2 ), 15mg of the material synthesized in Example 7, Example 8, Example 9 and Comparative Example 4 was taken as a catalyst in 30mL pure water, O2 was continuously introduced into the water, and the sample liquid was taken every 20min for detection in the ultraviolet spectrophotometer, and the test results are shown in Table 3. Figure 10

[0097] Figure 10 It can be seen that different proportions of DED and CN will cause differences in the photocatalytic performance of the synthesized composite material. Under the condition of λ≥420nm irradiation, the concentration of hydrogen peroxide produced by pDED at 100min was 18μM, while the concentration of hydrogen peroxide produced at 100min under the conditions of DED and CN mass ratio of 3:1, 4:1 and 5:1 was 37μM, 41μM and 32μM respectively. The performance is best when the mass ratio of DED and CN is 4:1, and the performance of other proportions is less than that of the sample synthesized under this condition.

[0098] (4)Effect of different organic monomers on catalytic performance

[0099] In order to explore the influence of different organic monomers on the construction of full-organic polymer S-type heterojunction photocatalytic material, three organic monomers with different molecular structures were used to form composite materials with carbon nitride. Under the condition of xenon lamp irradiation (λ≥420nm, 60mW cm​​-2 ) condition, 15 mg of the material synthesized in Example 2, Example 5 and Example 8 was taken as catalyst in 30 mL of pure water, O2 was continuously introduced into the water, and sample liquid was taken every 20 min for detection in a UV spectrophotometer. The test results are shown in Figure 11 .

[0100] As shown in Figure 11 , under the condition of xenon lamp irradiation (λ≥420 nm, 60 mW cm -2 ), the pDEB-CN-4 of Example 2, the pDEP-CN-4 of Example 5 and the pDED-CN-4 of Example 8 produced hydrogen peroxide concentrations of 205 μM, 117 μM and 41 μM respectively at 100 min. The performance of the synthesized pDEB-CN-4 all-organic polymer S-type heterojunction photocatalytic material is much higher than that of pDEP-CN-4 and pDED-CN-4. It is proved that the selected monomer structure of the application has superiority for constructing S-type heterojunction composite material.

[0101] (5) Effect of constructing S-type heterojunction on catalytic performance

[0102] In order to explore the effect of constructing all-organic polymer S-type heterojunction on the catalytic performance of the catalyst, the photocurrent response and electrochemical impedance test were carried out on the electrochemical workstation by using a three-electrode system, Ag / AgCl was used as the reference electrode, Pt wire was used as the working electrode, FTO uniformly coated with catalyst was used as the working electrode, and the test results are shown in Figure 12 .

[0103] As shown in Figure 12 , under the condition of xenon lamp irradiation (λ≥420 nm, 60 mW cm -2 ), compared with CN of Comparative Example 1 and pDEB of Comparative Example 2, pDEB-CN-4 of Example 2 showed the largest photocurrent density. In addition, Figure 12 , in the electrochemical impedance test, pDEB-CN-4 of Example 2 showed the smallest electrochemical impedance. This shows that the S-type heterojunction constructed by the application can effectively improve the separation efficiency of photo-generated carriers, and thus is conducive to the improvement of the performance of photocatalytic production of hydrogen peroxide.

Claims

1. An all-organic polymer S-type heterojunction photocatalytic material, characterized in that: The material includes a carrier and an organic polymer grown on the surface of the carrier. The organic monomer is polymerized on the carbon nitride surface to form an all-organic polymer S-type heterojunction. The organic monomer is 1,4-diethynylbenzene, 2,5-diethynylpyridine or 3,6-diethynylpyridazine.

2. The all-organic polymer S-type heterojunction photocatalytic material according to claim 1, characterized in that: The mass ratio of the organic monomer to the carrier carbon nitride is 3:1 to 5:

1.

3. The all-organic polymer S-type heterojunction photocatalytic material according to claim 1, characterized in that: The carbon nitride is porous carbon nitride.

4. A method for preparing the all-organic polymer S-type heterojunction photocatalytic material according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Add carbon nitride and catalyst to polar alkaline solution and mix well; (2) placing the organic monomer in the mixed solution prepared in step (1) to cause a polymerization reaction, thereby in situ generating an all-organic polymer S-type heterojunction photocatalytic material.

5. The method for preparing the all-organic polymer S-type heterojunction photocatalytic material according to claim 4, characterized in that: The catalyst is cuprous chloride. 6 . The method for preparing an all-organic polymer S-type heterojunction photocatalytic material according to claim 4 , wherein the polymerization reaction temperature is 40 to 80° C. 7 . The method for preparing an all-organic polymer S-type heterojunction photocatalytic material according to claim 4 , wherein the polymerization reaction time is 4 to 8 hours. 8 . The method for preparing an all-organic polymer S-type heterojunction photocatalytic material according to claim 4 , wherein the polar solvent in the polar alkaline solution is pyridine. 9 . The method for preparing an all-organic polymer S-type heterojunction photocatalytic material according to claim 4 , wherein the polar base in the polar base solution is piperidine.

10. Use of the all-organic polymer S-type heterojunction photocatalytic material according to any one of claims 1 to 3 in photocatalytic production of hydrogen peroxide.

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