Palladium-doped Co3O4 nanosheets and their application in photocatalytic reduction of CO2 to produce acetic acid

Abstract

The application discloses a kind of palladium-doped Co3O4 Nanosheet and its preparation method, and specifically discloses its application in photocatalytic reduction CO2 production acetic acid.The application is synthesized by using hydrothermal method first four cobalt oxide, then adding palladium source to the alkaline dispersion liquid of four cobalt oxide, and stirring to make it react, and successfully prepares palladium-doped four cobalt oxide nanosheet.The palladium-doped four cobalt oxide nanosheet prepared by the application is applied to the reaction of photocatalytic reduction carbon dioxide, which can greatly improve the catalytic reduction efficiency of CO2, and the product of photocatalytic reduction carbon dioxide is acetic acid.The application uses palladium-doped four cobalt oxide nanosheet to photocatalytic reduction carbon dioxide, and the yield of product acetic acid can be as high as 14 μmol / g / h, which is much higher than that of undoped four cobalt oxide nanosheet (3 μmol / g / h).

Description

Technical Field

[0001] This invention relates to palladium-doped cobalt tetroxide nanosheets and their application in the photocatalytic reduction of carbon dioxide to produce acetic acid, belonging to the field of nanomaterials and photocatalysis technology. Background Technology

[0002] Over the past two decades, scientific research has shown that converting carbon atoms in CO2 into usable fuels is a realistic possibility. This could not only alleviate the greenhouse effect caused by excessive CO2 in the atmosphere but also create new value, thus attracting considerable attention from researchers. Among the numerous studies on carbon dioxide reduction, photocatalytic reduction of CO2 has been extensively studied due to its environmental friendliness and low cost. Utilizing the combined energy of solar energy, a renewable energy source, and the photocatalyst to convert CO2 and water molecules into valuable compounds shows great promise.

[0003] However, in practical applications, due to the high C=O bond dissociation energy of carbon dioxide (~750 kJ mol⁻¹), it is difficult to activate and convert the extremely stable CO₂ molecules into carbon-based fuels. Currently, CO₂ photoreduction products are still limited to C1 products, such as carbon monoxide (CO), methane (CH₄), and methanol (CH₃OH), which greatly limits their application. In fact, C2 products generated by CO₂ photocatalytic reduction have a larger application market due to their higher density; for example, acetic acid has wide applications in textiles, automobiles, construction, and food additives. However, to date, industrial acetic acid is usually produced through hydroxylation or oxidation of methanol, alkanes, and ethylene, which is both energy-intensive and highly polluting. Therefore, the rational design of efficient photocatalysts and the exploration of their selective conversion of CO₂ into acetic acid are urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing palladium-doped cobalt tetroxide nanosheets. The method involves first synthesizing cobalt tetroxide using a hydrothermal method, then adding a palladium source to an alkaline dispersion of cobalt tetroxide and stirring to allow the reaction to proceed. The resulting dry powder is the palladium-doped cobalt tetroxide nanosheet. Applying the palladium-doped cobalt tetroxide nanosheets prepared by this invention to the photocatalytic reduction of carbon dioxide significantly improves the catalytic reduction efficiency of CO2 and greatly increases the yield of acetic acid from CO2.

[0005] To achieve the above objectives, the present invention first provides a method for preparing palladium-doped cobalt tetroxide nanosheets, comprising the following steps:

[0006] (1) Hydrothermal synthesis of Co3O4 nanosheets: Cobalt source and CTAB are added to a mixed solution of ethylene glycol and distilled water. After stirring evenly, the mixture is transferred to a high-pressure reactor with a polytetrafluoroethylene liner for reaction. After the reaction is complete, the mixture is cooled to room temperature, centrifuged to separate the product, washed and dried, and the dried powder is placed in a muffle furnace for calcination to obtain the powder, which is Co3O4 nanosheets.

[0007] (2) Disperse the Co3O4 nanosheets obtained in step (1) in deionized water and ultrasonically disperse for 30 min to obtain a uniform dispersion. Adjust the pH of the dispersion to 9-11 using a pH adjuster. Add palladium source solution under oil bath conditions, stir to allow it to react, separate the obtained solid and wash and dry it to obtain palladium-doped Co3O4 nanosheet powder.

[0008] In one embodiment of the present invention, the mass ratio of the cobalt source to CTAB is 0.2 to 0.3.

[0009] In one embodiment of the present invention, the cobalt source includes any one of cobalt acetylacetonate (Co(acac)3), cobalt acetate, cobalt chloride, cobalt nitrate, and cobalt sulfate.

[0010] In one embodiment of the present invention, in step (1), the volume ratio of ethylene glycol to distilled water is 5 to 6.

[0011] In one embodiment of the present invention, in step (1), after adding the cobalt source and CTAB to the mixed solution of ethylene glycol and distilled water, the mixture is stirred at a speed of 600~800 r / min for 20~40 min.

[0012] In one embodiment of the present invention, in step (1), the temperature during the reaction in the autoclave is 180~200℃ and the time is 24~48h.

[0013] In one embodiment of the present invention, in step (1), the atmosphere in which the dried powder is calcined in a muffle furnace is an air atmosphere, the calcination temperature is 320~350℃, and the calcination time is 5~60min.

[0014] In one embodiment of the present invention, in step (2), the concentration of Co3O4 nanosheets in the dispersion is 4~4.5 mg / mL.

[0015] In one embodiment of the present invention, in step (2), the pH adjuster is an alkaline pH adjuster, which includes any one of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0016] In one embodiment of the present invention, in step (2), the temperature of the oil bath is 90~100℃, and the stirring reaction time is 1~2h.

[0017] In one embodiment of the present invention, in step (2), the palladium source includes any one of H2PdCl4, PdCl2, and Na2PdCl4.

[0018] In one embodiment of the present invention, in steps (1) and (2), the drying is vacuum drying at a temperature of 60°C.

[0019] The present invention also provides palladium-doped cobalt tetroxide nanosheets prepared according to the above method.

[0020] This invention also provides the application of the above-mentioned palladium-doped cobalt tetroxide nanosheets in the field of photocatalysis.

[0021] In one embodiment of the invention, the application includes use as a catalyst in the photocatalytic reduction of carbon dioxide.

[0022] In one embodiment of the present invention, the photocatalytic reduction of carbon dioxide includes the following steps: placing palladium-doped Co3O4 nanosheet powder in a sealed container, injecting water into the container, filling it with CO2, and then evacuating the container. A 300 W xenon lamp is used to simulate sunlight as the light source for the reaction, and the reaction is carried out for 2 to 10 hours to obtain acetic acid.

[0023] Beneficial effects of the present invention

[0024] (1) In this invention, palladium-doped cobalt tetroxide nanosheets were successfully prepared by first synthesizing cobalt tetroxide by hydrothermal method, then adding palladium source to alkaline dispersion of cobalt tetroxide and stirring to make it react.

[0025] (2) Applying the palladium-doped cobalt tetroxide nanosheets prepared in this invention to the photocatalytic reduction of carbon dioxide can greatly improve the catalytic reduction efficiency of CO2, and the product of photocatalytic reduction of carbon dioxide is acetic acid.

[0026] (3) The present invention uses palladium-doped cobalt tetroxide nanosheets to photocatalytically reduce carbon dioxide, and the yield of the product acetic acid can be as high as 14 μmol / g / h, which is much greater than that of undoped cobalt tetroxide nanosheets (3 μmol / g / h).

[0027] (4) The preparation method is simple to operate, and the Pd-doped Co3O4 ultrathin nanosheets prepared have strong catalytic ability; the established practical method for photocatalytic reduction of CO2 is highly efficient, stable, environmentally friendly and sustainable. Attached Figure Description

[0028] Figure 1The images show the XRD diffraction patterns of palladium-doped Co3O4 nanosheets and Co3O4 nanosheets prepared in Example 2 and Comparative Example 4, where (a) is the XRD pattern of Co3O4 nanosheets and (b) is the XRD pattern of palladium-doped Co3O4 nanosheets.

[0029] Figure 2 The images show the transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images of palladium-doped Co3O4 nanosheets prepared in Example 2 and Comparative Example 4, where (AB) are the TEM and HRTEM images of Co3O4 nanosheets, and (CD) are the TEM and HRTEM images of palladium-doped Co3O4 nanosheets.

[0030] Figure 3 X-ray photoelectron spectroscopy (XPS) of palladium-doped Co3O4 nanosheets prepared in Example 2 and commercial PdO.

[0031] Figure 4 The graph shows the yield of acetic acid obtained by photocatalytic reduction of carbon dioxide from palladium-doped Co3O4 nanosheets (black) and Co3O4 nanosheets (gray) prepared in Example 3 and Comparative Example 5.

[0032] Figure 5 X-ray photoelectron spectroscopy (XPS) spectra of Co3O4 nanosheets prepared for Comparative Example 1 and commercial PdO.

[0033] Figure 6 X-ray photoelectron spectroscopy (XPS) spectra of Co3O4 nanosheets prepared for Comparative Example 2 and commercial PdO.

[0034] Figure 7 X-ray photoelectron spectroscopy (XPS) spectra of Co3O4 nanosheets prepared for Comparative Example 3 and commercial PdO. Detailed Implementation

[0035] Example 1

[0036] A method for preparing palladium-doped cobalt tetroxide nanosheets includes the following steps:

[0037] (1) 600 mg Co(acac)3 and 2.2 g CTAB were added to a mixed solution of 60 mL ethylene glycol and 11 mL distilled water. After stirring vigorously at 600~800 r / min for 20 min, the mixture was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, sealed, and heated at 180 °C for 24 h. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged to separate the product, washed several times with ethanol and water, and then placed in a vacuum drying oven and dried at 60 °C. The dried powder was placed in a muffle furnace and calcined at 320 °C in air atmosphere for 30 min to obtain cobalt tetroxide nanosheet powder.

[0038] (2) Disperse 200 mg of the product obtained in step (1) in 45 mL of deionized water and sonicate for 30 min to obtain a uniform dispersion. Then add 60 µL of Na2CO3 solution (0.25 M) to the round-bottom flask containing the dispersion to adjust the pH of the Co3O4 dispersion to 10. Immerse the round-bottom flask in an oil bath at 100 °C, and then add 5 mL of 2 mM H2PdCl4 solution dropwise to the stirred Co3O4 suspension. Stir continuously at 100 °C for 1 h. Finally, wash the prepared sample twice with deionized water and vacuum dry at 60 °C to obtain the powder, which is palladium-doped Co3O4 nanosheets. Store it in a desiccator for later use.

[0039] Example 2

[0040] The structure of the prepared palladium-doped Co3O4 nanosheets was identified, and the results are shown in the figure. Figures 1-3 The preparation method of palladium-doped Co3O4 nanosheets is the same as that in Example 1.

[0041] Figure 1 (b) is the XRD diffraction pattern of palladium-doped Co3O4 nanosheets; Figure 2 (CD) are transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of palladium-doped Co3O4 nanosheets; Figure 3 X-ray photoelectron spectroscopy (XPS) of palladium-doped Co3O4 nanosheets. Figure 1 (b) Figure 2 (D) and Figure 3 As can be seen, palladium was successfully doped into Co3O4. HRTEM analysis and lattice spacing testing further confirm that the prepared product is Pd-Co3O4.

[0042] Example 3: Photocatalytic reduction of CO2 to CH3COOH by palladium-doped Co3O4

[0043] 3 mg of palladium-doped Co3O4 powder was uniformly dispersed on a glass slide and placed in a sealed glass apparatus. 2 mL of water was added to the container, followed by the introduction of high-purity CO2 (99.999% purity), and then a vacuum was applied. This process was repeated three times. A 300 W xenon lamp was used to simulate sunlight as the light source for the reaction. After 10 hours of reaction, CH3COOH was obtained. The preparation method of the palladium-doped Co3O4 powder was the same as in Example 1.

[0044] The yield of CH3COOH was determined by nuclear magnetic resonance spectroscopy, with DMSO as an internal standard. The yield of acetic acid was defined as the amount of acetic acid / amount of catalyst / catalytic time. Figure 4 The yield of acetic acid obtained from the photocatalytic reduction of carbon dioxide by palladium-doped Co3O4 nanosheets (black) is shown. Figure 4 It can be seen that palladium-doped Co3O4 nanosheets have a high acetic acid yield, which can reach 14 μmol / g / h.

[0045] Comparative Example 1

[0046] 600 mg Co(acac)3, 2.2 g CTAB, and 5 mL of 2 mM H2PdCl4 were added to a mixed solution of 60 mL ethylene glycol and 11 mL distilled water. The mixture was stirred at 600–800 rpm for 20 minutes. The mixture was then transferred to a 100 mL PTFE-lined autoclave, sealed, and heated at 180 °C for 24 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The resulting product was centrifuged, washed several times with ethanol and water, and then dried in a vacuum drying oven. The dried powder was calcined in a muffle furnace at 320 °C in air for 30 min to obtain Co3O4 nanosheet powder.

[0047] Figure 5 The X-ray photoelectron spectroscopy (XPS) spectra of Co3O4 nanosheets prepared in Comparative Example 1 and commercial PdO are shown in the figure. It can be seen from the figure that no characteristic peaks of Pd appear in Comparative Example 1, indicating that the product obtained is not palladium-doped Co3O4 nanosheets.

[0048] Comparative Example 2

[0049] 600 mg Co(acac)3 and 2.2 g CTAB were added to a mixture of 60 mL ethylene glycol and 11 mL distilled water. The mixture was stirred at 600–800 rpm for 20 minutes. The mixture was then transferred to a 100 mL PTFE-lined autoclave, sealed, and heated at 180 °C for 24 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was centrifuged, washed several times with ethanol and water, and then dried in a vacuum drying oven. The dried powder was calcined in a muffle furnace at 320 °C in air for 30 min. 200 mg of the product was first dispersed in 45 mL of deionized water in a 100 mL round-bottom flask, and then sonicated for 30 minutes to obtain a uniform dispersion. Then, 60 µL of Na2CO3 solution (0.25 M) was added to adjust the pH of the Co3O4 dispersion to 10. The round-bottom flask was then immersed in a 100°C oil bath. Subsequently, 5 mL of 2 mM H2PdCl4 solution was added dropwise to the stirred Co3O4 dispersion. The mixture was stirred continuously at 100°C for 30 min. Finally, the prepared sample was washed twice with deionized water and then vacuum dried at 60°C to obtain Co3O4 nanosheet powder.

[0050] Figure 6 The X-ray photoelectron spectroscopy (XPS) spectra of Co3O4 nanosheets prepared in Comparative Example 2 and commercial PdO are shown in the figure. It can be seen from the figure that no characteristic peaks of Pd appear in Comparative Example 2, indicating that the product obtained is not palladium-doped Co3O4 nanosheets.

[0051] Comparative Example 3

[0052] 600 mg Co(acac)3 and 2.2 g CTAB were added to a mixture of 60 mL ethylene glycol and 11 mL distilled water. After vigorous stirring for 20 minutes, the mixture was transferred to a 100 mL PTFE-lined autoclave, sealed, and heated at 180 °C for 24 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was centrifuged, washed several times with ethanol and water, and then dried in a vacuum drying oven. The dried powder was calcined in a muffle furnace at 320 °C in air for 30 min. 200 mg of the product was first dispersed in 45 mL of deionized water in a 100 mL round-bottom flask, and then sonicated for 30 minutes to obtain a uniform dispersion. Then, 60 µL of Na2CO3 solution (0.25 M) was added to adjust the pH of the Co3O4 dispersion to approximately 10. The round-bottom flask was then immersed in a 60°C oil bath. Subsequently, 5 mL of 2 mM H2PdCl4 solution was added dropwise to the stirred Co3O4 dispersion. The mixture was stirred continuously at 60°C for 1 h. Finally, the prepared sample was washed twice with deionized water and then vacuum dried at 60°C to obtain Co3O4 nanosheet powder.

[0053] Figure 7 The X-ray photoelectron spectroscopy (XPS) spectra of Co3O4 nanosheets prepared in Comparative Example 3 and commercial PdO are shown in the figure. It can be seen from the figure that no characteristic peaks of Pd appear in Comparative Example 3, indicating that the product obtained is not palladium-doped Co3O4 nanosheets.

[0054] Comparative Example 4: Preparation of Co3O4 Nanosheets

[0055] 600 mg Co(acac)3 and 2.2 g CTAB were added to a mixture of 60 mL ethylene glycol and 11 mL distilled water. After vigorous stirring for 20 minutes, the mixture was transferred to a 100 mL PTFE-lined autoclave, sealed, and heated at 180 °C for 24 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was centrifuged, washed several times with ethanol and water, and then dried in a vacuum drying oven. The dried powder was calcined in a muffle furnace at 320 °C in air for 30 min to obtain the original Co3O4 nanosheets, which were stored in a desiccator for later use.

[0056] Figure 1 (a) is the XRD diffraction pattern of Co3O4 nanosheets; Figure 2 (AB) show transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of Co3O4 nanosheets. Figure 1 (a) and Figure 2 (A~B) It can be seen that the product obtained in Comparative Example 4 is Co3O4 nanosheets.

[0057] Comparative Example 5

[0058] 3 mg of Co3O4 powder was uniformly dispersed on a glass slide and placed in a sealed glass apparatus. 2 mL of water was added to the container, followed by the introduction of high-purity CO2 (99.999% purity), and then a vacuum was applied. This process was repeated three times. A 300 W xenon lamp was used to simulate sunlight as the light source for the reaction. After 10 hours of reaction, CH3COOH was obtained. The preparation method of the Co3O4 powder was the same as in Comparative Example 4.

[0059] Figure 4 The yield of acetic acid obtained from the photocatalytic reduction of carbon dioxide by Co3O4 nanosheets was shown. Figure 4 It can be seen that the undoped Co3O4 nanosheets have poor catalytic performance, with an acetic acid yield of only 3 μmol / g / h.

[0060] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined in the claims of this invention.

Claims

1. The application of palladium-doped cobalt tetroxide nanosheets in improving the yield of photocatalytic CO2 reduction to acetic acid, characterized in that, The application method involves placing palladium-doped Co3O4 nanosheet powder in a sealed container, injecting water into the container, filling it with CO2, and then evacuating it. A 300 W xenon lamp is used to simulate sunlight as the light source for the reaction, and the reaction is carried out for 2-10 hours to obtain acetic acid. The preparation method of palladium-doped Co3O4 nanosheets includes the following steps: (1) Hydrothermal synthesis of Co3O4 nanosheets: Cobalt source and CTAB are added to a mixed solution of ethylene glycol and distilled water. After stirring evenly, the mixture is transferred to a high-pressure reactor with a polytetrafluoroethylene liner for reaction. After the reaction is complete, the mixture is cooled to room temperature, centrifuged to separate the product, washed and dried, and the dried powder is placed in a muffle furnace for calcination to obtain the powder, which is Co3O4 nanosheets. (2) Disperse the Co3O4 nanosheets obtained in step (1) in deionized water and ultrasonically disperse for 30 min to obtain a uniform dispersion. Adjust the pH of the dispersion to 9~11 using a pH adjuster. Add palladium source solution under oil bath conditions of 90~100℃ and stir to react for 1~2 h. Separate the obtained solid and wash and dry it to obtain palladium-doped Co3O4 nanosheet powder.

2. The application according to claim 1, characterized in that, The mass ratio of the cobalt source to CTAB is 0.2 to 0.3, and the cobalt source includes any one of cobalt acetylacetonate, cobalt acetate, cobalt chloride, cobalt nitrate, and cobalt sulfate.

3. The application according to claim 1, characterized in that, In step (1), after adding the cobalt source and CTAB to the mixed solution of ethylene glycol and distilled water, the mixture is stirred at a speed of 600~800 r / min for 20~40 min, and the volume ratio of ethylene glycol to distilled water is 5~6.

4. The application according to claim 1, characterized in that, In step (1), the reaction temperature in the autoclave is 180~200℃ and the time is 24~48h.

5. The application according to claim 1, characterized in that, In step (1), the atmosphere during calcination of the dried powder in the muffle furnace is an air atmosphere, the calcination temperature is 320~350℃, and the calcination time is 5~60min.

6. The application according to claim 1, characterized in that, In step (2), the concentration of Co3O4 nanosheets in the dispersion is 4~4.5 mg / mL, and the pH adjuster is an alkaline pH adjuster, which includes any one of sodium carbonate, sodium bicarbonate and sodium hydroxide.

7. The application according to claim 1, characterized in that, In step (2), the palladium source includes any one of H2PdCl4, PdCl2, and Na2PdCl4.

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