Conjugated polymer / modified carbon nitride heterojunction photocatalytic material as well as preparation method and application thereof

Abstract

The invention discloses a conjugated polymer / modified carbon nitride heterojunction photocatalytic material as well as a preparation method and application thereof, and belongs to the technical field of semiconductor photocatalytic materials. Compared with a pure conjugated polymer, the prepared conjugated polymer / modified carbon nitride heterojunction photocatalytic material shows obviously improved activity of photocatalytic reduction of CO2 into CH4 due to the fact that the heterojunction structure has the advantages of excellent visible light capture, delay of electron-hole recombination, rapid charge transfer and the like. The method is low in cost, convenient to operate, simple in process, green, free of pollution and wide in market application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor photocatalytic materials, and specifically relates to a conjugated polymer / modified carbon nitride heterojunction photocatalytic material and a preparation method and application thereof. Background Art

[0002] Carbon dioxide (CO2) is one of the main greenhouse gases, and its emission is one of the main causes of global climate change. Therefore, scientists seek to develop sustainable methods to convert CO2 into more valuable compounds. Photocatalytic technology provides a potential solution. By using solar light sources to drive catalysts, CO2 can be reduced to methane (CH4), an important natural gas fuel. The development of this technology is expected to achieve the recycling of CO2, reduce greenhouse gas emissions, and enable CH4 to play a role in energy supply as a clean energy source. Therefore, photocatalytic CO2 reduction to CH4 technology is regarded as a potential solution for carbon recycling and energy transformation, attracting extensive research.

[0003] The formation of a heterojunction between a conjugated polymer and modified carbon nitride can meet the urgent needs of environmental governance and energy transformation. Conjugated polymers have excellent photoelectric properties and chemical stability, while modified carbon nitride has attracted much attention due to its good photocatalytic properties. By forming a heterojunction between these two materials, their respective advantages can be fully utilized to achieve efficient conversion in photocatalytic reactions. The development of this technology is expected to provide new solutions in the field of photocatalytic CO2 reduction and promote sustainable development and the application of clean energy. In the present invention, we first proposed a conjugated polymer / modified carbon nitride heterojunction photocatalytic material, a preparation method thereof, and its application in photocatalytic CO2 reduction to CH4. Summary of the invention

[0004] The purpose of the present invention is to address the defects of current semiconductor materials in the actual photocatalytic reduction of CO2 to CH4, such as low process yield, long process, serious pollution or high cost, and to propose a conjugated polymer / modified carbon nitride heterojunction photocatalytic material with low cost, convenient operation, simple process and green and pollution-free and a preparation method thereof.

[0005] In order to achieve the above technical purpose, the technical solution adopted by the present invention is: A method for preparing a conjugated polymer / modified carbon nitride heterojunction photocatalytic material, comprising the following steps: (1) Synthesis of conjugated polymer CM: Hexachlorocyclotriphosphazene and barbituric acid were added to a hydrothermal reactor in proportion, and then acetonitrile was added. After ultrasonic treatment for 1 h, the reactor was sealed for hydrothermal reaction. The heating rate was adjusted to the reaction temperature and then kept warm for reaction. After the reaction was completed, the reactor was naturally cooled to room temperature. The brown precipitate was washed with deionized water, acetonitrile and ethanol in sequence. After washing, it was dried in a vacuum oven at 60°C for 24 h to obtain a CM sample. (2) Synthesis of modified carbon nitride: Melamine and thiourea were mixed according to the mass ratio and mechanically ground for 30 min, and then heated to a certain temperature in a nitrogen atmosphere and calcined for 4 h to obtain modified carbon nitride, which was recorded as S,G-CN. (3) Synthesis of conjugated polymer / modified carbon nitride heterojunction photocatalytic material (S,G-CN / CM): The conjugated polymer CM and modified carbon nitride S,G-CN were mixed in a certain mass ratio and mechanically ground for 30 min to obtain the final product, the conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM.

[0006] Preferably, in step (1), the dosage ratio of hexachlorocyclotriphosphazene, barbituric acid and acetonitrile is 0.3-0.5 mol: 1 mol: 8-10 L.

[0007] Preferably, during the hydrothermal reaction in step (1), the heating rate is adjusted to 10°C / min to raise the temperature to 180°C, and the reaction is kept at this temperature for 30-32 hours.

[0008] Preferably, the specific method of high temperature calcination in step (2) is: heating to 550° C. at a rate of 10° C. / min and calcining for 4 hours.

[0009] Preferably, in step (2), the mass ratio of melamine to thiourea is 1:1.

[0010] Preferably, in step (3), the mass ratio of the conjugated polymer CM to the modified carbon nitride S,G-CN is 1:1.

[0011] The present invention also provides a conjugated polymer / modified carbon nitride heterojunction photocatalytic material prepared by the above method.

[0012] The present invention also provides an application of a conjugated polymer / modified carbon nitride heterojunction photocatalytic material in preparing CH4 by photocatalytic CO2 reduction.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a simple self-assembly process, does not involve complicated synthesis steps, only uses low-cost and environmentally friendly solvents and a controllable heating process, and does not require cumbersome post-treatment processes to obtain a conjugated polymer / modified carbon nitride heterojunction photocatalytic material. The preparation process is simple and reliable; (2) The phosphazene conjugated polymer / modified carbon nitride heterojunction photocatalytic material (S,G-CN / CM) prepared by the method of the present invention has an ultra-high CO2 reduction to CH4 yield of 977.5 μmol / g compared with pure conjugated polymer CM, which is 19.5 times higher than that of the conjugated polymer under the same conditions. This is because the heterojunction structure material obtained by the present invention has a large and strong interface contact, excellent visible light absorption capacity, porous structure, spatially separated redox sites, and rapid separation of photoinduced charge carriers.

[0014] (3) The conjugated polymer / modified carbon nitride heterojunction photocatalytic material provided by the present invention has the characteristics of low cost, green and pollution-free, mild process conditions, and suitability for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the XRD test result diagram of different samples of the present invention; Figure 2 TEM image of the final product conjugated polymer / modified carbon nitride heterojunction photocatalytic material S, G-CN / CM obtained in Example 1 of the present invention; Figure 3 This is a test diagram of the photocatalytic activity of Example 1 of the present invention and the comparative example catalyst in the photocatalytic reduction of CO2 to produce methane; Figure 4 The impedance spectra of the catalyst materials of Example 1 of the present invention and the comparative example; Figure 5 Graphs showing the photocurrent of catalyst materials of Example 1 of the present invention and the comparative example. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below in conjunction with specific embodiments, but is not limited thereto.

[0017] Example 1 A conjugated polymer / modified carbon nitride heterojunction photocatalytic material is prepared by the following method: (1) Synthesis of conjugated polymer (CM): Weigh 0.43 g of hexachlorocyclotriphosphazene and 0.39 g of barbituric acid into a 50 mL hydrothermal autoclave, and add 30 mL of acetonitrile. Ultrasonicate for 1 h, seal the hydrothermal autoclave and place it in the hydrothermal autoclave, and seal the hydrothermal autoclave. Then, heat the hydrothermal autoclave to 180 °C at a heating rate of 10 °C / min and keep the reaction for 30 h. After the reaction is cooled, wash the brown precipitate with deionized water, acetonitrile, and ethanol in sequence, and dry it in a vacuum oven at 60 °C for 24 h to obtain a conjugated polymer CM sample; (2) Synthesis of modified carbon nitride: Weigh 1 g of melamine and 1 g of thiourea, mix and grind them for 30 min, then heat to 550 °C at a heating rate of 10 °C / min under nitrogen atmosphere and calcine for 4 h to obtain modified carbon nitride, denoted as S,G-CN; (3) Synthesis of conjugated polymer / modified carbon nitride heterojunction photocatalytic material (S,G-CN / CM): Weigh 0.5 mg CM and 0.5 mg S,G-CN, mix and grind them for 30 min to obtain the final product, conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM.

[0018] Example 2 A conjugated polymer / modified carbon nitride heterojunction photocatalytic material is prepared by the following method: (1) Synthesis of conjugated polymer (CM): Weigh 10.43 g of hexachlorocyclotriphosphazene and 12.8 g of barbituric acid into the inner tank of a hydrothermal autoclave, and add 1 L of acetonitrile. Ultrasonicate for 1 h, seal the inner tank of the hydrothermal autoclave and place it in the hydrothermal autoclave, and seal the hydrothermal autoclave. Then, heat the hydrothermal autoclave to 180 °C at a heating rate of 10 °C / min and keep the reaction for 30 h. After the reaction is cooled, wash the brown precipitate with deionized water, acetonitrile, and ethanol in sequence, and dry it in a vacuum oven at 60 °C for 24 h to obtain a conjugated polymer CM sample; (2) Synthesis of modified carbon nitride: Weigh 2 g of melamine and 2 g of thiourea, mix and grind them for 30 min, then heat to 550 °C at a heating rate of 10 °C / min under nitrogen atmosphere and calcine for 4 h to obtain modified carbon nitride, denoted as S,G-CN; (3) Synthesis of conjugated polymer / modified carbon nitride heterojunction photocatalytic material (S,G-CN / CM): Weigh 2 mg CM and 2 mg S,G-CN, mix and grind them for 30 min to obtain the final product, conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM.

[0019] Example 3 A conjugated polymer / modified carbon nitride heterojunction photocatalytic material is prepared by the following method: (1) Synthesis of conjugated polymer (CM): Weigh 17.38 g of hexachlorocyclotriphosphazene and 12.8 g of barbituric acid into the inner tank of a hydrothermal kettle, and add 800 mL of acetonitrile. Ultrasonicate for 1 h, seal the inner tank of the hydrothermal kettle and place it in the hydrothermal kettle, and seal the hydrothermal kettle. Then, heat the hydrothermal kettle to 180°C at a heating rate of 10°C / min and keep the reaction for 30 h. After the reaction is cooled, wash the brown precipitate with deionized water, acetonitrile, and ethanol in sequence, and dry it in a vacuum oven at 60°C for 24 h to obtain a conjugated polymer CM sample; (2) Synthesis of modified carbon nitride: Weigh 2 g of melamine and 2 g of thiourea, mix and grind them for 30 min, then heat to 550 °C at a heating rate of 10 °C / min under nitrogen atmosphere and calcine for 4 h to obtain modified carbon nitride, denoted as S,G-CN; (3) Synthesis of conjugated polymer / modified carbon nitride heterojunction photocatalytic material (S,G-CN / CM): Weigh 1 mg CM and 1 mg S,G-CN, mix and grind them for 30 min to obtain the final product, conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM.

[0020] Comparative Example 1 A conjugated polymer / modified carbon nitride heterojunction photocatalytic material is prepared by the following method: (1) Weigh 2 g of thiourea and heat it to 550 °C at a heating rate of 10 °C / min under a nitrogen atmosphere, and then calcine it for 4 h to obtain a product, which is recorded as S-CN; (2) Weigh 0.43 g of hexachlorocyclotriphosphazene and 0.39 g of barbituric acid into a 50 mL hydrothermal autoclave, and add 30 mL of acetonitrile. Ultrasonicate for 1 h, seal the hydrothermal autoclave and place it in the hydrothermal autoclave, and seal the hydrothermal autoclave. Then, heat the hydrothermal autoclave to 180 °C at a heating rate of 10 °C / min and keep the reaction for 30 h. After the reaction is cooled, wash the brown precipitate with deionized water, acetonitrile, and ethanol in sequence, and dry it in a vacuum oven at 60 °C for 24 h to obtain the product conjugated polymer CM; (3) Weigh 0.5 mg CM and 0.5 mg S-CN, mix and grind them for 30 min to obtain the final product, conjugated polymer / modified carbon nitride heterojunction photocatalytic material S-CN / CM.

[0021] Comparative Example 2 A conjugated polymer / modified carbon nitride heterojunction photocatalytic material is prepared by the following method: (1) Weigh 2 g of melamine and heat it to 550 °C at a heating rate of 10 °C / min under a nitrogen atmosphere, and then calcine it for 4 h to obtain a product, which is recorded as G-CN; (2) Weigh 0.43 g of hexachlorocyclotriphosphazene and 0.39 g of barbituric acid into a 50 mL hydrothermal autoclave, and add 30 mL of acetonitrile. Ultrasonicate for 1 h, seal the hydrothermal autoclave and place it in the hydrothermal autoclave, and seal the hydrothermal autoclave. Then, heat the hydrothermal autoclave to 180 °C at a heating rate of 10 °C / min and keep the reaction for 30 h. After the reaction is cooled, wash the brown precipitate with deionized water, acetonitrile, and ethanol in sequence, and dry it in a vacuum oven at 60 °C for 24 h to obtain the product conjugated polymer CM; (3) Weigh 0.5 mg CM and 0.5 mg G-CN, mix and grind them for 30 min to obtain the final product, conjugated polymer / modified carbon nitride heterojunction photocatalytic material G-CN / CM.

[0022] Performance Testing The conjugated polymer / modified carbon nitride heterojunction photocatalytic material S, G-CN / CM obtained in Example 1 of the present invention was used as a test example, and the products of Comparative Examples 1 and 2, as well as the conjugated polymer CM obtained in step (1) of Example 1 and the modified carbon nitride S, G-CN material obtained in step (2) were used as different comparative examples. The XRD of different catalyst materials in the test examples and comparative examples was tested. The test results are shown in FIG. Figure 1 .from Figure 1 It can be seen that the prepared S,G-CN / CM sample exhibits a weak diffraction peak, which is similar to the diffraction peaks of CM and S,G-CN samples, and no impurity peaks appear, proving that the S,G-CN / CM sample is synthesized.

[0023] The conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM sample obtained in Example 1 of the present invention was subjected to TEM test. Figure 2 As shown. Figure 2 It can be seen that the S,G-CN / CM sample shows a structure in which multiple thin layers cover each other, which can greatly reduce the recombination of carriers and thus improve the utilization rate of photogenerated electron-hole pairs.

[0024] The conjugated polymer / modified carbon nitride heterojunction photocatalytic material S, G-CN / CM obtained in Example 1 of the present invention was used as a test example, and the products of Comparative Examples 1 and 2, as well as the conjugated polymer CM obtained in step (1) of Example 1 and the modified carbon nitride S, G-CN material obtained in step (2) were used as different comparative examples. The photocatalytic activity of the different catalyst materials in the test examples and comparative examples in the photocatalytic reduction of CO2 to prepare methane was tested. The results are as follows: Figure 3 As shown. Figure 3It can be seen that the rate of catalytic reduction of CO2 to produce CH4 under visible light irradiation is 977.5 μmol / g, showing excellent photocatalytic activity, which is significantly higher than the catalytic activity of other comparative materials, and 19.5 times higher than the conjugated polymer CM under the same conditions, while the catalytic activity of the modified carbon nitride S, G-CN material alone is very low. The conjugated polymer / modified carbon nitride heterojunction photocatalytic material S, G-CN / CM composed of the two in the present invention has an obvious synergistic effect on catalytic reduction of CO2 to produce CH4 under light irradiation. This is because the material prepared by the method of the present invention has a large and strong interface contact, excellent visible light absorption capacity, a porous structure, spatially separated redox sites, and rapid separation of photoinduced charge carriers.

[0025] The conjugated polymer / modified carbon nitride heterojunction photocatalytic material S, G-CN / CM obtained in Example 1 of the present invention was used as a test example, and the products of Comparative Examples 1 and 2, as well as the conjugated polymer CM obtained in step (1) of Example 1 and the modified carbon nitride S, G-CN material obtained in step (2) were used as different comparative examples. The impedance of different catalyst materials in the test examples and comparative examples was tested. The specific results are shown in Figure 4 .from Figure 4 It can be seen that the S,G-CN / CM sample prepared in Example 1 of the present invention has the smallest Enquist radius, which indicates that the charge transfer resistance in the heterostructure is small, allowing rapid transport and separation of photoinduced charges.

[0026] The conjugated polymer / modified carbon nitride heterojunction photocatalytic material S, G-CN / CM obtained in Example 1 of the present invention was used as a test example, and the products of Comparative Examples 1 and 2, as well as the conjugated polymer CM obtained in step (1) of Example 1 and the modified carbon nitride S, G-CN material obtained in step (2) were used as different comparative examples. The photocurrent results of different catalyst materials in the test examples and comparative examples were tested. Figure 5 .like Figure 5 As shown, the conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM sample obtained by the present invention shows the strongest photocurrent value, indicating that after CN mixed with thiourea and melamine is calcined and formed with CM to form a heterojunction, the heterojunction material can greatly reduce the recombination of carriers, thereby improving the utilization rate of photogenerated electron-hole pairs.

[0027] It should be noted that the above embodiments are only partial embodiments of the preferred methods of implementing the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a conjugated polymer / modified carbon nitride heterojunction photocatalytic material, characterized in that: It includes the following steps: (1) Synthesis of conjugated polymer CM: Hexachlorocyclotriphosphazene and barbituric acid were added to a hydrothermal reactor in proportion, and then acetonitrile was added. After ultrasonic treatment for 1 h, the reactor was sealed for hydrothermal reaction. The heating rate was adjusted to the reaction temperature and then kept warm for reaction. After the reaction was completed, the reactor was naturally cooled to room temperature. The brown precipitate was washed with deionized water, acetonitrile and ethanol in sequence. After washing, it was dried in a vacuum oven at 60°C for 24 h to obtain a CM sample. (2) Synthesis of modified carbon nitride: Melamine and thiourea were mixed according to the mass ratio and mechanically ground for 30 min, and then heated to a certain temperature in a nitrogen atmosphere and calcined for 4 h to obtain modified carbon nitride, which was recorded as S,G-CN. (3) Synthesis of conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM: The conjugated polymer CM and modified carbon nitride S,G-CN were mixed according to the mass ratio and mechanically ground for 30 min to obtain the final product, the conjugated polymer / modified carbon nitride heterojunction photocatalytic material S,G-CN / CM.

2. The method for preparing the conjugated polymer / modified carbon nitride heterojunction photocatalytic material according to claim 1, characterized in that: In step (1), the dosage ratio of hexachlorocyclotriphosphazene, barbituric acid and acetonitrile is 0.3-0.5 mol:1 mol:8-10L.

3. The method for preparing the conjugated polymer / modified carbon nitride heterojunction photocatalytic material according to claim 1, characterized in that: During the hydrothermal reaction in step (1), the heating rate is adjusted to 10°C / min and the temperature is raised to 180°C, and the reaction is kept at this temperature for 30-32 hours.

4. The method for preparing the conjugated polymer / modified carbon nitride heterojunction photocatalytic material according to claim 1, characterized in that: The specific method of high temperature calcination in step (2) is: heating to 550°C at a rate of 10°C / min and calcining for 4 h.

5. The method for preparing the conjugated polymer / modified carbon nitride heterojunction photocatalytic material according to claim 1, characterized in that: The mass ratio of melamine to thiourea in step (2) is 1:

1.

6. The method for preparing the conjugated polymer / modified carbon nitride heterojunction photocatalytic material according to claim 1, characterized in that: In step (3), the mass ratio of the conjugated polymer CM to the modified carbon nitride S,G-CN is 1:

1.

7. A conjugated polymer / modified carbon nitride heterojunction photocatalytic material, characterized in that: The method is prepared by any one of claims 1 to 6.

8. Use of the conjugated polymer / modified carbon nitride heterojunction photocatalytic material according to claim 7 in the photocatalytic reduction of CO2 to produce CH4.

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