A modified carbon nitride / cobalt porphyrin photocatalyst and its preparation method

Abstract

This invention discloses a modified carbon nitride / cobalt porphyrin photocatalyst and its preparation method. The photocatalyst is obtained by covalently coupling spherical cobalt porphyrin onto the surface of a thin, porous modified carbon nitride layer. It has an ultrathin layer structure with numerous pores, providing a large surface area to promote the exposure of active sites, while effectively suppressing the recombination of photogenerated carriers, thereby improving CO2 reduction efficiency. The preparation method provided by this invention is simple and the reaction is mild, making the entire synthesis process green and environmentally friendly, effectively reducing product costs, and possessing high application prospects and value.

Description

Technical Field

[0001] This invention relates to a photocatalyst, particularly to a modified carbon nitride / cobalt porphyrin photocatalyst, and also to a method for preparing the above-mentioned photocatalyst. Background Technology

[0002] Photocatalytic CO2 conversion technology has attracted much attention due to its low cost and environmental friendliness. In existing photocatalytic CO2 reduction reactions, how to rationally design catalysts to improve the separation efficiency of electrons and holes, the adsorption of CO2 molecules, and the desorption of corresponding reduction products, thereby enhancing the CO2 reduction reaction efficiency and product selectivity, is currently a research hotspot and a key issue that needs to be addressed.

[0003] Patent CN109772414A discloses a broad-spectrum-response red carbon nitride photocatalyst, which undergoes certain organic reactions during thermal polymerization to obtain broad-spectrum-response carbon nitride, thereby enhancing the light absorption capacity and electron transfer rate of carbon nitride. Based on this catalyst, it is hoped to further obtain a more efficient photocatalyst. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a modified carbon nitride / cobalt porphyrin photocatalyst and a method for preparing the above photocatalyst.

[0005] Technical solution: The present invention provides a modified carbon nitride / cobalt porphyrin photocatalyst, wherein the photocatalyst is obtained by covalently coupling spherical cobalt porphyrin onto the surface of a thin-layer porous modified carbon nitride.

[0006] Preferably, the modified carbon nitride is obtained by calcining urea and ammonium formate.

[0007] The preparation method of the above photocatalyst includes the following steps:

[0008] (1) Mix urea and ammonium formate thoroughly, grind and calcine to obtain red modified carbon nitride;

[0009] (2) The modified carbon nitride obtained in step (1) is mixed and stirred evenly with cobalt porphyrin in an organic solvent, washed and dried to obtain a composite material, wherein the mass ratio of the modified carbon nitride to cobalt porphyrin is 100:0.1~1;

[0010] (3) The composite material obtained in step (2) is calcined to obtain the modified carbon nitride / cobalt porphyrin photocatalyst.

[0011] Preferably, in step (1), the mass ratio of urea to ammonium formate is 10:0.1 to 0.5.

[0012] Preferably, in step (1), the calcination specifically involves heating to 550-600°C and then holding the temperature for calcination for 100-140 minutes.

[0013] Preferably, in step (1), the heating rate of calcination is 3 to 5 °C / min.

[0014] Preferably, in step (2), the organic solvent is ethanol, and the stirring time is 12 to 36 hours.

[0015] Preferably, in step (2), the washing is performed by centrifugation with ethanol 3 to 5 times, and the drying conditions are vacuum drying at 60 to 70°C for 10 to 12 hours.

[0016] Preferably, in step (3), the calcination specifically involves heating to 250-300°C and then holding the temperature for calcination for 50-60 minutes.

[0017] Preferably, in step (3), the heating rate of calcination is 3 to 5 °C / min.

[0018] Invention Principle: The modified carbon nitride / cobalt porphyrin photocatalyst of this invention comprises carbon nitride and cobalt porphyrin covalently coupled on the surface to form a stacked structure, making the surface of the composite more rough and providing more active sites through a porous, sponge-like structure. Simultaneously, after photoexcitation of carbon nitride and cobalt porphyrin, the holes in the cobalt porphyrin combine with the photogenerated electrons of carbon nitride to form a Z-shaped heterojunction structure. This heterojunction structure promotes the movement of excited electrons from carbon nitride towards cobalt porphyrin, thereby enhancing electron flow, improving carrier separation efficiency, and ultimately improving the photocatalytic CO2 reduction performance.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The efficiency of photocatalytic CO2 reduction is about 4 times higher than that of single carbon nitride; (2) The preparation process is simple and the cost is low, which provides a new idea for building energy-saving, low-consumption, zero-pollution and high-efficiency CO2 reduction technology. Attached Figure Description

[0020] Figure 1 Transmission electron microscopy image of 0.7Co / CN;

[0021] Figure 2 XRD patterns of CN, CoTPP, and Co / CN;

[0022] Figure 3 XPS spectrum for 0.7 Co / CN;

[0023] Figure 4 The UV-Vis spectra of CN, CoTPP, and Co / CN are shown.

[0024] Figure 5 The graph shows the photocatalytic CO2 reduction activity of CN and Co / CN.

[0025] Figure 6 BET spectra for CN and 0.7Co / CN;

[0026] Figure 7 The graph shows the photoelectric performance test results for CN and 0.7Co / CN. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0028] Example 1

[0029] (1) Weigh 10g of urea and 0.3g of ammonium formate, grind them thoroughly, heat them to 550℃ at a rate of 3℃ / min, and calcine them for 120min to obtain red modified carbon nitride.

[0030] (2) Add 5g of modified carbon nitride obtained in step (1) and 0.0025g of cobalt porphyrin to 20mL of ethanol, mix, stir in the dark for 24h, centrifuge and wash 3 times, and vacuum dry at 60℃ for 12h to obtain the composite material.

[0031] (3) The composite material obtained in step (2) is heated to 250°C at a rate of 5°C / min and calcined for 60 min to obtain modified carbon nitride / cobalt porphyrin photocatalyst 0.5Co / CN.

[0032] Example 2

[0033] Compared to Example 1, the amount of cobalt porphyrin added was changed:

[0034] (1) Weigh 10g of urea and 0.3g of ammonium formate, grind them thoroughly, heat them to 550℃ at a rate of 3℃ / min, and calcine them for 120min to obtain red modified carbon nitride.

[0035] (2) Add 5g of modified carbon nitride obtained in step (1) and 0.0035g of cobalt porphyrin to 20mL of ethanol, mix, stir in the dark for 24h, centrifuge and wash 3 times, and vacuum dry at 60℃ for 12h to obtain the composite material.

[0036] (3) The composite material obtained in step (2) is heated to 250°C at a rate of 5°C / min and calcined for 60 min to obtain modified carbon nitride / cobalt porphyrin photocatalyst 0.7Co / CN.

[0037] Example 3

[0038] Compared to Example 1, the amount of cobalt porphyrin added was changed:

[0039] (1) Weigh 10g of urea and 0.3g of ammonium formate, grind them thoroughly, heat them to 550℃ at a rate of 3℃ / min, and calcine them for 120min to obtain red modified carbon nitride.

[0040] (2) Add 5g of modified carbon nitride obtained in step (1) and 0.0045g of cobalt porphyrin to 20mL of ethanol and mix. Stir in the dark for 24h, centrifuge and wash 3 times, and vacuum dry at 60℃ for 12h to obtain the composite material.

[0041] (3) The composite material obtained in step (2) is heated to 250°C at a rate of 5°C / min and calcined for 60 min to obtain modified carbon nitride / cobalt porphyrin photocatalyst 0.9Co / CN.

[0042] Comparative Example 1

[0043] Preparation of red modified carbon nitride:

[0044] Weigh 10g of urea and 0.3g of ammonium formate, grind them thoroughly, heat them to 550℃ at a rate of 3℃ / min, and calcine them for 120min to obtain red modified carbon nitride.

[0045] Comparative Example 2

[0046] Compared to Example 1, the amount of cobalt porphyrin added was changed:

[0047] (1) Weigh 10g of urea and 0.3g of ammonium formate, grind them thoroughly, heat them to 550℃ at a rate of 3℃ / min, and calcine them for 120min to obtain red modified carbon nitride.

[0048] (2) Add 5g of modified carbon nitride obtained in step (1) and 0.0015g of cobalt porphyrin to 20mL of ethanol, mix, stir in the dark for 24h, centrifuge and wash 3 times, and vacuum dry at 60℃ for 12h to obtain the composite material.

[0049] (3) The composite material obtained in step (2) is heated to 250°C at a rate of 5°C / min and calcined for 60 min to obtain modified carbon nitride / cobalt porphyrin photocatalyst 0.3Co / CN.

[0050] Comparative Example 3

[0051] Compared to Example 1, the amount of cobalt porphyrin added was changed:

[0052] (1) Weigh 10g of urea and 0.3g of ammonium formate, grind them thoroughly, heat them to 550℃ at a rate of 3℃ / min, and calcine them for 120min to obtain red modified carbon nitride.

[0053] (2) Add 5g of modified carbon nitride obtained in step (1) and 0.005g of cobalt porphyrin to 20mL of ethanol, mix, stir in the dark for 24h, centrifuge and wash 3 times, and vacuum dry at 60℃ for 12h to obtain the composite material.

[0054] (3) The composite material obtained in step (2) is heated to 250°C at a rate of 5°C / min and calcined for 60 min to obtain the modified carbon nitride / cobalt porphyrin photocatalyst 1.0Co / CN.

[0055] like Figure 1 As shown, the morphology of the prepared photocatalyst is shown, with cobalt porphyrin supported on red carbon nitride.

[0056] Figure 2 The XRD patterns of CN, CoTPP, and Co / CN show two typical characteristic peaks at 13.19° and 27.27°, corresponding to the (100) and (002) crystal planes, representing in-plane ordered stacking and interlayer stacking, respectively. Due to the high dispersion of cobalt porphyrin, no peak corresponding to cobalt porphyrin is shown.

[0057] Figure 3 The XPS spectrum of 0.7Co / CN shows the O element modification characteristic of red carbon nitride.

[0058] Figure 4 The UV-Vis spectra of CN, CoTPP, and Co / CN show that the light absorption range of carbon nitride loaded with cobalt porphyrin is significantly broadened, thereby enhancing the performance of photocatalytic CO2 reduction by increasing light absorption.

[0059] Activity tests were conducted on the photocatalysts of the examples and comparative examples:

[0060] The photocatalytic CO2 reduction experiment was conducted in a 300 mL sealed pyrolysis top irradiation vessel (Labsolar-6A, Beijing Perfectlight). 10 mg of catalyst powder was dispersed in an aqueous solution (16 mL) containing 12 mL H2O and 4 mL TEOA as a pore sacrificial agent. After purging the reaction system of air, high-purity CO2 was introduced into the system until the pressure reached 70 kPa, and the system was circulated for 60 min to ensure uniform CO2 gas distribution.

[0061] A cooling water circulation system to promote CO2 adsorption was used to set the temperature for photocatalytic CO2 reduction to 10℃, and a 300W xenon lamp was used as the light source. The luminous intensity of the 300W xenon lamp was 650mw / cm². 2 The amount of gaseous products was determined using a gas chromatograph (GC2002, Shanghai Kechuang) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) with a capillary column.

[0062] like Figure 5 As shown in the activity test of CN and Co / CN photocatalysts, the activity improvement of 0.7Co / CN is the most significant compared with CN.

[0063] Figure 6 The BET spectra of CN and 0.7Co / CN show that both CN and 0.7Co / CN have abundant pores. Furthermore, after loading cobalt porphyrin, the specific surface area increases, which can shorten the electron transfer distance and provide abundant active sites.

[0064] Figure 7 The photoelectric performance of CN and Co / CN shows that 0.7Co / CN has higher photocurrent density and better charge separation efficiency.

Claims

1. A modified carbon nitride / cobalt porphyrin photocatalyst, characterized in that, The photocatalyst is obtained by covalently coupling spherical cobalt porphyrin onto the surface of a thin, porous modified carbon nitride; wherein, the holes of the cobalt porphyrin combine with the photogenerated electrons of the red modified carbon nitride to form a Z-shaped heterojunction structure, and the modified carbon nitride is obtained by calcining urea and ammonium formate and is modified with oxygen element; the photocatalyst is prepared by the following steps: (1) Mix urea and ammonium formate thoroughly and grind them together. Heat the mixture to 550-600°C and calcine it for 100-140 minutes to obtain red modified carbon nitride. The mass ratio of urea to ammonium formate is 10:0.1-0.

5. (2) The modified carbon nitride obtained in step (1) is mixed and stirred evenly with cobalt porphyrin in an organic solvent, washed and dried to obtain a composite material, wherein the mass ratio of the modified carbon nitride to cobalt porphyrin is 100:0.1~1; (3) The composite material obtained in step (2) is calcined and heated to 250~300°C and kept calcined for 50~60 minutes to obtain the modified carbon nitride / cobalt porphyrin photocatalyst.

2. The catalyst according to claim 1, characterized in that, In step (1), the heating rate of calcination is 3~5℃ / min.

3. The catalyst according to claim 1, characterized in that, In step (2), the organic solvent is ethanol, and the stirring time is 12~36h.

4. The catalyst according to claim 1, characterized in that, In step (2), the washing is performed by centrifugation with ethanol 3 to 5 times, and the drying conditions are vacuum drying at 60 to 70°C for 10 to 12 hours.

5. The catalyst according to claim 1, characterized in that, In step (3), the heating rate of calcination is 3~5℃ / min.

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