A photocatalyst for catalyzing carbon dioxide reduction and its preparation method and application

Abstract

The present invention discloses a photocatalyst for catalyzing carbon dioxide reduction, a preparation method and an application thereof, and relates to the field of photocatalytic technology. The present invention molecularly dopes carbon nitride nanosheets and introduces porphyrin molecules to improve the shortcomings of the original carbon nitride nanosheets, such as serious carrier recombination, small visible light absorption range, and low catalytic site activity. At the same time, by anchoring different metals as different active sites, the photocatalyst for catalyzing carbon dioxide reduction of the present invention can photocatalytically and efficiently reduce low-concentration carbon dioxide to carbon monoxide, has the characteristics of high catalytic reduction efficiency and high selectivity, and has good application prospects in photocatalytic carbon dioxide reduction.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and in particular to a photocatalyst for catalyzing carbon dioxide reduction, a preparation method and an application thereof. Background Art

[0002] The widespread use of fossil fuels and anthropogenic CO2 emissions have led to climate and energy crises that urgently need to be addressed. Photocatalytic CO2 conversion, which uses solar energy as the sole power source to produce fuels and chemicals, is one of the promising methods for CO2 elimination and energy conservation. However, most research on photocatalysts focuses on the reduction of high-concentration CO2, while the reduction of low-concentration CO2 often leads to reduced photocatalytic activity. From a practical perspective, it is crucial to develop powerful photocatalysts that can effectively convert low-concentration CO2 into high-value-added products. Summary of the invention

[0003] The purpose of the present invention is to provide a photocatalyst for catalyzing the reduction of carbon dioxide and a preparation method and application thereof, so as to solve the problems existing in the above-mentioned prior art. The present invention grafts porphyrin molecules onto carbon nitride nanosheets for modification, and finally anchors different metals as reaction active sites, so as to achieve photocatalytic reduction of carbon dioxide to produce carbon monoxide under low concentration of carbon dioxide and without sacrificial agents, thereby ensuring high catalytic efficiency and selectivity.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is to provide a method for preparing a photocatalyst for catalyzing carbon dioxide reduction, comprising the following steps:

[0006] The carbon nitride nanosheets are grafted with porphyrin molecules and then anchored with metal ions to obtain the photocatalyst for catalyzing carbon dioxide reduction.

[0007] Furthermore, the preparation method comprises the following steps:

[0008] (1) reacting carbon nitride nanosheets with tetrakis(4-carboxyphenyl)porphine (TCPP) at 60-100°C, washing and drying to obtain a carbon nitride nanosheet grafted porphyrin product, namely UCN-TCPP;

[0009] (2) reacting the carbon nitride nanosheet (UCN) grafted porphyrin product and metal salt in a solvent at 100° C., collecting and drying the precipitate, and then pyrolyzing it at 300-350° C. in a protective atmosphere. After washing and drying, UCN-TCPP-M is obtained, which is the photocatalyst for catalyzing carbon dioxide reduction.

[0010] The structure of meso-tetrakis(4-carboxyphenyl)porphine is as follows:

[0011]

[0012] Furthermore, the metal salt includes zinc salt, nickel salt, copper salt, cobalt salt, iron salt or tin salt.

[0013] Furthermore, the molar ratio of the carbon nitride nanosheets to meso-tetrakis(4-carboxyphenyl)porphine is 2:1-4:1; and the molar ratio of the carbon nitride nanosheet grafted porphyrin product to the metal salt is 1:2-1:4.

[0014] Furthermore, the carbon nitride nanosheets are prepared by the following steps:

[0015] Urea is pyrolyzed at 400° C. to obtain a prepolymer, and then the prepolymer is pyrolyzed at 650-690° C. in a protective atmosphere to obtain carbon nitride nanosheets.

[0016] Furthermore, the UCN-TCPP preparation process is as follows:

[0017] The meso-tetrakis(4-carboxyphenyl)porphine is mixed with benzotriazole-1-yl-oxytripyrrolidinophosphine hexafluorophosphate PyBOP and N,N-diisopropylethylamine (DIEA) in a molar ratio of 1:2:4, the obtained mixture is mixed with the carbon nitride nanosheets and reacted at 60-100°C, and the carbon nitride nanosheets are washed and dried to obtain a porphyrin grafted product, namely UCN-TCPP.

[0018] The second technical solution of the present invention is to provide a photocatalyst for catalyzing the reduction of carbon dioxide prepared by the above preparation method.

[0019] The third technical solution of the present invention is to provide the use of the above-mentioned photocatalyst for catalyzing the reduction of carbon dioxide in the preparation of carbon monoxide by photocatalytic reduction of carbon dioxide.

[0020] Furthermore, the concentration of the carbon dioxide is 10-15%.

[0021] Technical solution 4 of the present invention: Provide a method for preparing carbon monoxide by catalytic reduction of carbon dioxide by the above-mentioned photocatalyst, comprising the following steps:

[0022] The photocatalyst is placed in a carbon dioxide gas environment and photocatalytically reacted at a light source power of 150-300W to obtain carbon monoxide. The present invention can simultaneously improve the shortcomings of the original UCN, such as severe carrier recombination, small visible light absorption range, and low catalytic site activity, by molecular doping the original UCN and introducing porphyrin molecules; at the same time, different active sites can be used by anchoring different metals. This method of molecular doping and anchoring metals on the original UCN provides a strategy for synthesizing photocatalysts with high catalytic activity under mild conditions.

[0023] The present invention discloses the following technical effects:

[0024] The photocatalyst for catalyzing carbon dioxide reduction of the present invention can photocatalytically reduce low-concentration carbon dioxide to carbon monoxide with high efficiency, and has the characteristics of high catalytic reduction efficiency and high selectivity.

[0025] The photocatalyst of the present invention has cheap raw materials for preparation, is non-toxic itself, does not require sacrificial agents and toxic photosensitizers, and does not require precious metals, and has good application prospects in photocatalytic carbon dioxide reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 Electron micrographs of the UCN prepared in Example 1 of the present invention, and the photocatalysts prepared in Examples 1-5 and Comparative Example 1;

[0028] Figure 2 XRD spectra of the UCN prepared in Example 1 of the present invention, Examples 1-5 and the photocatalyst prepared in Comparative Example 1;

[0029] Figure 3 The UV-visible diffuse reflectance spectra of the UCN prepared in Example 1 of the present invention, the UCN-TCPP-Zn prepared in Example 1, the UCN-TCPP-Ni prepared in Example 4, and the UCN-TCPP-Cu prepared in Example 5;

[0030] Figure 4 Fourier transform infrared reflectance spectra of UCN prepared in Example 1 of the present invention, UCN-TCPP-Zn prepared in Example 1, UCN-TCPP-Ni prepared in Example 4, and UCN-TCPP-Cu prepared in Example 5;

[0031] Figure 5 This is a graph showing the reduction performance of the UCN prepared in Example 1 of the present invention, Examples 1-5 and the photocatalyst prepared in Comparative Example 1 under low concentration of carbon dioxide;

[0032] Figure 6 These are the charge separation test characterization and verification results of the UCN prepared in Example 1 of the present invention, the UCN-TCPP-Zn prepared in Example 1, the UCN-TCPP-Ni prepared in Example 4, and the UCN-TCPP-Cu prepared in Example 5. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0035] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0036] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0037] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0038] In an embodiment of the present invention, a urea precursor is first calcined at high temperature to obtain a raw UCN, which is then modified by grafting porphyrin molecules, and finally different metals are anchored as reaction active sites, thereby efficiently reducing low-concentration carbon dioxide to produce carbon monoxide by photocatalysis in the absence of a sacrificial agent.

[0039] Example 1

[0040] (1) Place 10 g of urea in a muffle furnace at 5 °C min -1 The temperature was raised to 400 °C at a heating rate of 1.5 °C and pyrolyzed at 400 °C for 3 h to obtain a prepolymer. The prepolymer was heated in a tubular furnace at 5 °C min -1 The temperature was raised to 670 °C at a heating rate of 1.5 °C and pyrolyzed at 670 °C in an argon atmosphere for 2 h to obtain UCN.

[0041] (2) 0.6 mmol UCN was dispersed in DMF and ultrasonically treated for 2 h. 0.3 mmol TCPP, 0.6 mmol PyBOP and 1.2 mmol DIEA (molar ratio 1:2:4) were dissolved in 40 mL DMF and ultrasonically treated for 2 h. The two solutions were mixed and reacted at 100 °C for 24 h. The reactants were washed with DMF, ultrapure water and ethanol in sequence and dried in an oven at 80 °C overnight to obtain UCN-TCPP.

[0042] (3) Disperse 0.1 mmol UCN-TCPP in DMF and ultrasonicate for 2 h to make the sample uniformly dispersed. Dissolve 0.2 mmol anhydrous zinc acetate in 20 mL DMF and add the above dispersed solution. Ultrasonicate for 3 h. Stir and heat the mixed solution at 100 °C for 12 h, collect it by centrifugation and dry it in an oven at 80 °C overnight. -1 The mixture was pyrolyzed at 350 °C in a nitrogen atmosphere for 5 h at a heating rate of 100 ℃. The collected powders were washed with 2% HCl, ultrapure water and ethanol in sequence and dried in an oven at 80 °C overnight to obtain UCN-TCPP-Zn.

[0043] Example 2

[0044] The only difference from Example 1 is that the reaction temperature in step (2) is 60°C, which is marked as UCN-TCPP-Zn-60°C.

[0045] Example 3

[0046] The only difference from Example 1 is that the reaction temperature in step (2) is 80°C, which is marked as UCN-TCPP-Zn-80°C.

[0047] Example 4

[0048] The only difference from Example 1 is that anhydrous zinc acetate in step (3) is replaced by an equimolar amount of nickel nitrate. The product is labeled UCN-TCPP-Ni.

[0049] Example 5

[0050] The only difference from Example 1 is that anhydrous zinc acetate in step (3) is replaced by an equimolar amount of copper nitrate. The product is labeled UCN-TCPP-Cu.

[0051] Comparative Example 1

[0052] Physically mix UCN and ZnTCPP (zinc tetrakis(4-carboxyphenyl)porphine) to prepare UCN-ZnTCPP photocatalyst:

[0053] 50 mg of UCN (prepared in Example 1) was dispersed in anhydrous ethanol and ultrasonically dispersed for 2 h to make the sample uniformly dispersed. 2 mg of ZnTCPP was dispersed in 20 mL of anhydrous ethanol and ultrasonically dispersed for 2 h. The two solutions were mixed and stirred at room temperature for 24 h. The solutions were washed with ultrapure water and ethanol for multiple times, and dried in an oven at 80°C overnight to obtain UCN-ZnTCPP.

[0054] Figure 1 Electron micrographs of the UCN prepared in Example 1 of the present invention, and the photocatalysts prepared in Examples 1-5 and Comparative Example 1; Figure 2 XRD spectra of the UCN prepared in Example 1 of the present invention, Examples 1-5 and the photocatalyst prepared in Comparative Example 1.

[0055] Figure 3 The UV-visible diffuse reflectance spectra of the UCN prepared in Example 1 of the present invention, the UCN-TCPP-Zn prepared in Example 1, the UCN-TCPP-Ni prepared in Example 4, and the UCN-TCPP-Cu prepared in Example 5; Figure 4 Fourier transform infrared reflectance spectra of UCN prepared in Example 1 of the present invention, UCN-TCPP-Zn prepared in Example 1, UCN-TCPP-Ni prepared in Example 4, and UCN-TCPP-Cu prepared in Example 5.

[0056] Performance Test:

[0057] The performance of the above materials was tested by gas chromatography using Beijing SolarLab-6A photocatalytic system under 300W xenon lamp irradiation:

[0058] The performance of UCN-TCPP-Zn prepared in Test Example 1:

[0059] The products prepared in Examples 1-5 and Comparative Example 1 and the UCN prepared in step (1) of Example 1 were dispersed in a photocatalytic reaction tank, and ultrapure water was added to obtain a 2 g / L photocatalyst aqueous dispersion, which was then added to a reactor of a photocatalytic system. The reactor was connected to the photocatalytic system, and carbon dioxide gas with a concentration of 15% was introduced. The condensation water was turned on, the temperature was controlled at 5°C, and the xenon lamp was turned on for illumination.

[0060] The performance of the products prepared in Examples 1-5, Comparative Example 1 and the UCN prepared in step (1) of Example 1 for catalytic reduction of carbon dioxide to produce carbon monoxide is shown in Tables 1 and Figure 5 .

[0061] Table 1

[0062] CO production efficiency (μmol / g / h) <![CDATA[CH4 production efficiency (μmol / g / h)]]> Selectivity (%) UCN 15.11 0.42 97.3 Example 1 155.56 3.01 98.1 Example 2 120.05 2.48 98.0 Example 3 135.12 2.63 98.1 Example 4 110.23 2.45 97.8 Example 5 131.28 2.32 98.3 Comparative Example 1 114.32 2.18 98.1

[0063] Among them, selectivity (%) = CO production efficiency / (CO production efficiency + CH4 production efficiency)*100%.

[0064] Charge separation testing of photocatalysts:

[0065] 2 mg of photocatalyst was dispersed in 1 mL of 1% Nafion ethanol solution, the glassy carbon electrode coated with photocatalyst was used as the working electrode, the platinum electrode and the Ag / AgCl electrode were used as the counter electrode and reference electrode respectively. The photocurrent test was carried out under the conditions of 0.2 M Na2SO4 solution as the electrolyte and 300 W xenon lamp as the visible light source.

[0066] Figure 6 The charge separation test characterization verification results of the UCN prepared in Example 1 of the present invention, the UCN-TCPP-Zn prepared in Example 1, the UCN-TCPP-Ni prepared in Example 4, and the UCN-TCPP-Cu prepared in Example 5 are shown. Figure 6 It can be seen that the present invention effectively improves the problems of severe carrier recombination, small visible light absorption range and low catalytic site activity of the original UCN.

[0067] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a photocatalyst for catalyzing carbon dioxide reduction, characterized in that: The following steps are involved: (1) reacting carbon nitride nanosheets and meso-tetrakis(4-carboxyphenyl)porphine at 60-100°C, washing and drying to obtain a carbon nitride nanosheet grafted porphyrin product, namely UCN-TCPP; (2) reacting the carbon nitride nanosheet grafted porphyrin product and the metal salt in a solvent at 100° C., collecting and drying the precipitate, and then pyrolyzing it at 300-350° C. in a protective atmosphere, washing and drying, to obtain UCN-TCPP-M, which is the photocatalyst for catalyzing carbon dioxide reduction; The metal salt includes zinc salt, nickel salt, copper salt, cobalt salt, iron salt or tin salt; The molar ratio of the carbon nitride nanosheets to meso-tetrakis(4-carboxyphenyl)porphine is 2:1-4:1; The molar ratio of the carbon nitride nanosheet grafted porphyrin product to the metal salt is 1:2-1:4; The carbon nitride nanosheets are prepared by the following steps: Urea is pyrolyzed at 400° C. to obtain a prepolymer, and then the prepolymer is pyrolyzed at 650-690° C. in a protective atmosphere to obtain carbon nitride nanosheets.

2. The preparation method according to claim 1, characterized in that: The preparation process of step (1) is as follows: the meso-tetrakis (4-carboxyphenyl) porphine is mixed with benzotriazole-1-yl-oxytripyrrolidinophosphine hexafluorophosphate and N,N-diisopropylethylamine in a molar ratio of 1:2:4, the obtained mixture is mixed with the carbon nitride nanosheets and reacted at 60-100° C., and the carbon nitride nanosheets are washed and dried to obtain a carbon nitride nanosheet grafted porphyrin product, namely UCN-TCPP.

3. A photocatalyst for catalyzing the reduction of carbon dioxide obtained by the preparation method according to any one of claims 1 to 2.

4. Use of the photocatalyst for catalytic reduction of carbon dioxide as claimed in claim 3 in preparing carbon monoxide by photocatalytic reduction of carbon dioxide.

5. A method for preparing carbon monoxide by catalytic reduction of carbon dioxide using the photocatalyst according to claim 3, characterized in that: The method comprises the following steps: placing the photocatalyst in a carbon dioxide gas environment, and performing a photocatalytic reaction under a light source power of 150-300W to obtain carbon monoxide.

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