Alkali metal modified ZnO-Au composite aerogel as well as method and application thereof

Abstract

The invention discloses an alkali metal modified ZnO-Au composite aerogel as well as a method and application thereof, and belongs to the technical field of aerogel material preparation. The method comprises the following steps: 1) dispersing zinc acetate dihydrate, alkali carbonate and chloroauric acid in a mixed solvent of water and ethylene glycol, and stirring and mixing to form a suspension; 2) adding a small amount of nitric acid into the mixed solution to obtain a clear solution; 3) adding citric acid into the clarified solution, and standing at a certain temperature to form gel; the preparation method is simple and convenient to operate, the raw materials are easy to obtain, the preparation period is short, and the prepared aerogel can be widely applied to various catalytic reactions.

Description

Technical Field

[0001] This invention belongs to the field of aerogel material preparation technology, specifically relating to an alkali metal-modified ZnO-Au composite aerogel, its method, and its application. Background Technology

[0002] Metal oxide aerogels not only possess the typical characteristics of aerogels, such as low density, high specific surface area, and abundant porous structure, but also exhibit advantages such as compositional diversity and structural stability, providing ample space for the construction of novel functional aerogel materials. For this reason, metal oxides have long been widely used as catalyst supports for dispersing noble metal nanoparticles or directly as catalysts in various chemical reactions.

[0003] ZnO, as a mature photocatalytic material, has attracted widespread attention due to its low cost, high catalytic activity, diverse preparation methods, simple processing, and ease of doping modification. As a direct wide-bandgap semiconductor, ZnO exhibits high exciton binding energy and electron mobility at room temperature, demonstrating excellent photosensitivity. However, its photogenerated electron-hole pairs readily recombine rapidly within the particle and on its surface, and its narrow light absorption range significantly limits further enhancement of ZnO's photocatalytic activity.

[0004] To address the aforementioned issues, current research primarily employs strategies such as noble metal deposition, transition metal ion doping, and semiconductor composites to suppress electron-hole recombination, thereby improving photocatalytic efficiency. Among these, the introduction of noble metal nanoparticles, especially gold (Au) nanoparticles, has been proven to significantly enhance the photocatalytic performance of ZnO. Au nanoparticles, through localized surface plasmon resonance (LSPR), not only expand the light absorption range but also effectively promote interfacial electron transfer, thus improving photocatalytic efficiency. However, directly loading noble metals onto semiconductor surfaces presents challenges such as easy leaching, poor stability and reproducibility, and susceptibility to photocorrosion. Furthermore, excessively high noble metal loadings may actually become electron-hole recombination centers, reducing photocatalytic activity.

[0005] On the other hand, alkali metal modification has been shown to effectively enhance catalyst performance in various catalytic reactions, such as water-gas shift, ammonia synthesis, Fischer-Tropsch synthesis, and volatile organic compound oxidation. By combining the porous structure of aerogels, the photocatalytic properties of ZnO, the plasma effect of Au nanoparticles, and the promoting effect of alkali metal modification, it is hoped that a highly efficient composite aerogel material can be developed as a high-performance catalyst for various gas-phase and liquid-phase photocatalytic reactions. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects in the prior art and to provide an alkali metal modified ZnO-Au composite aerogel, its method and application.

[0007] The specific technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a method for preparing alkali metal-modified ZnO-Au composite aerogel, as detailed below: S1: Disperse zinc acetate dihydrate, alkali metal carbonate and chloroauric acid in a mixed solvent of water and ethylene glycol, and stir to form a suspension; S2: Add nitric acid to the suspension to obtain a clear solution; S3: Add citric acid to the clarified solution, heat and let stand to form a gel; S4: Freeze-dry the gel to obtain the precursor aerogel; S5: The precursor aerogel is calcined at high temperature to obtain alkali metal modified ZnO-Au composite aerogel.

[0008] Preferably, the alkali metal carbonate is one of lithium carbonate, sodium carbonate, or potassium carbonate.

[0009] Preferably, the molar ratio of zinc acetate dihydrate, chloroauric acid and alkali metal carbonate in the suspension is (1~5): (0.001~0.05): 0.1.

[0010] Preferably, the molar ratio of water to ethylene glycol in the mixed solvent is (4~8):1.

[0011] Preferably, in step S2, the volume ratio of nitric acid to the mixed solvent is (0.01~0.05):1.

[0012] Preferably, in step S3, the molar ratio of citric acid to zinc acetate dihydrate is (0.5~2):1; and the heating and settling temperature is 40℃-60℃.

[0013] Preferably, in step S4, the freezing temperature is -40°C and the freeze-drying pressure is less than 100 Pa.

[0014] Preferably, in step S5, the high-temperature calcination is carried out in an air atmosphere, the calcination temperature is 300-800℃, the heating rate is 1-20℃ / min, and the holding time is 1-24 hours.

[0015] In a second aspect, the present invention provides an alkali metal-modified ZnO-Au composite aerogel obtained by the preparation method described in any one of the first aspects.

[0016] Thirdly, the present invention provides an application of the alkali metal-modified ZnO-Au composite aerogel described in the second aspect in photocatalytic reactions.

[0017] Compared with the prior art, the present invention has the following advantages: The alkali metal-modified ZnO-Au composite aerogel material obtained by this invention has a large specific surface area and porosity. Alkali metal ions modify ZnO nanoparticles, and gold nanoparticles are in-situ supported and uniformly dispersed within the three-dimensional network structure of the ZnO aerogel. The preparation method provided by this invention is simple to operate, uses readily available raw materials, and has a short preparation cycle. The resulting aerogel can be widely used in various catalytic reactions. Attached Figure Description

[0018] Figure 1 The image shows a scanning electron microscope (SEM) image of the lithium-ion modified ZnO-Au composite aerogel prepared in Example 1. Figure 2 Scanning electron microscope image of the sodium ion modified ZnO-Au composite aerogel prepared in Example 2; Figure 3 This is a scanning electron microscope image of the potassium ion-modified ZnO-Au composite aerogel prepared in Example 3; Figure 4 Images showing the photocatalytic oxygen-free coupling performance of the potassium ion-modified ZnO-Au composite aerogel prepared in Example 3; Figure 5 The XRD patterns are of the lithium-ion modified ZnO-Au composite aerogel (i.e., Li-ZnO-Au) prepared in Example 1, the sodium-ion modified ZnO-Au composite aerogel (i.e., Na-ZnO-Au) prepared in Example 2, the potassium-ion modified ZnO-Au composite aerogel (i.e., K-ZnO-Au) prepared in Example 3, and the ZnO-Au composite aerogel (i.e., ZnO-Au) obtained in Comparative Example 1. Detailed Implementation

[0019] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0020] This invention provides a method for preparing alkali metal-modified ZnO-Au composite aerogel, the specific preparation method of which is as follows: S1: Disperse zinc acetate dihydrate, alkali metal carbonate and chloroauric acid in a mixed solvent of water (such as deionized water) and ethylene glycol, and stir to form a suspension.

[0021] In a preferred embodiment of the present invention, the alkali metal carbonate is preferably one of lithium carbonate, sodium carbonate or potassium carbonate.

[0022] In a preferred embodiment of the present invention, the molar ratio of zinc acetate dihydrate, chloroauric acid and alkali metal carbonate in the suspension is (1~5): (0.001~0.05): 0.1.

[0023] In a preferred embodiment of the present invention, the molar ratio of water to ethylene glycol in the mixed solvent is (4~8):1.

[0024] S2: Add nitric acid to the obtained suspension to obtain a clear solution.

[0025] In a preferred embodiment of the present invention, the volume ratio of nitric acid to the mixed solvent is (0.01~0.05):1.

[0026] S3: Add citric acid to the resulting clear solution, heat and let stand to form a gel.

[0027] In a preferred embodiment of the present invention, the molar ratio of citric acid to zinc acetate dihydrate is (0.5~2):1.

[0028] In a preferred embodiment of the present invention, the temperature for heating and settling is 40°C-60°C.

[0029] S4: The obtained gel is freeze-dried to obtain the precursor aerogel.

[0030] In a preferred embodiment of the present invention, the freezing temperature is -40°C and the freeze-drying pressure is less than 100 Pa.

[0031] S5: The obtained precursor aerogel was calcined at high temperature to obtain alkali metal modified ZnO-Au composite aerogel.

[0032] In a preferred embodiment of the present invention, the high-temperature calcination is carried out in an air atmosphere, the calcination temperature is 300-800℃, the heating rate is 1-20℃ / min, and the holding time is 1-24 hours.

[0033] The alkali metal ions prepared in this invention modify ZnO nanoparticles, and gold nanoparticles are in situ loaded and uniformly dispersed in the three-dimensional network structure of ZnO aerogel. This material can be applied to photocatalytic reactions.

[0034] The following examples will illustrate the preparation method of the present invention and the performance of the obtained materials.

[0035] Example 1 In this embodiment, a lithium-ion modified ZnO-Au composite aerogel was prepared. The specific preparation method is as follows: 1) Dissolve 0.1 mol zinc acetate dihydrate, 0.005 mol chloroauric acid and 0.01 mol lithium carbonate in a mixed solvent of 60 mL deionized water and 40 mL ethylene glycol, and stir until homogeneous to obtain a suspension; 2) Add 3 mL of nitric acid to the suspension obtained in step 1) and stir until homogeneous to obtain a clear solution; 3) Add 0.1 mol of citric acid to the clear solution obtained in step 2), stir until homogeneous, and let stand in a 40°C oven to form a gel; 4) Freeze-dry the gel obtained in step 3) at a temperature of -40℃ and a freeze-drying pressure of less than 100Pa to obtain the precursor aerogel; 5) The precursor aerogel obtained in step 4) is placed in a muffle furnace for calcination at a heating rate of 5℃ / min, a temperature of 500℃, and a holding time of 8 hours. After the calcination is completed and the product is allowed to cool naturally, lithium ion modified ZnO-Au composite aerogel is obtained.

[0036] The scanning electron microscope (SEM) image of the lithium-ion modified ZnO-Au composite aerogel prepared in this embodiment is shown below. Figure 1 As shown in the figure, gold nanoparticles are uniformly dispersed in the three-dimensional network structure of ZnO aerogel. The diameter of the gold nanoparticles is 15 nm, the diameter of the zinc oxide nanoparticles is 30 nm, and the specific surface area is 145 m². 2 / g.

[0037] Example 2 In this embodiment, a sodium ion-modified ZnO-Au composite aerogel was prepared. The specific preparation method is as follows: 1) Dissolve 0.1 mol zinc acetate dihydrate, 0.005 mol chloroauric acid and 0.1 mol sodium carbonate in a mixed solvent of 80 mL deionized water and 40 mL ethylene glycol, and stir until homogeneous to obtain a suspension; 2) Add 3 mL of nitric acid to the suspension obtained in step 1) and stir until homogeneous to obtain a clear solution; 3) Add 0.1 mol of citric acid to the clear solution obtained in step 2), stir until homogeneous, and let stand in a 60°C oven to form a gel; 4) Freeze-dry the gel obtained in step 3) at a temperature of -40℃ and a freeze-drying pressure of less than 100Pa to obtain the precursor aerogel; 5) The precursor aerogel obtained in step 4) is placed in a muffle furnace for calcination at a heating rate of 5℃ / min, a temperature of 400℃, and a holding time of 3 hours. After the calcination is completed and the product is allowed to cool naturally, sodium ion modified ZnO-Au composite aerogel is obtained.

[0038] The scanning electron microscope (SEM) image of the sodium ion-modified ZnO-Au composite aerogel prepared in this embodiment is shown below. Figure 2 As shown in the figure, gold nanoparticles are uniformly dispersed in the three-dimensional network structure of ZnO aerogel. The diameter of the gold nanoparticles is 10 nm, the diameter of the zinc oxide nanoparticles is 20 nm, and the specific surface area is 197 m². 2 / g.

[0039] Example 3 In this embodiment, a potassium ion-modified ZnO-Au composite aerogel was prepared. The specific preparation method is as follows: 1) Dissolve 0.1 mol zinc acetate dihydrate, 0.005 mol chloroauric acid and 0.05 mol potassium carbonate in a mixed solvent of 50 mL deionized water and 30 mL ethylene glycol, and stir until homogeneous to obtain a suspension; 2) Add 3 mL of nitric acid to the suspension obtained in step 1) and stir until homogeneous to obtain a clear solution; 3) Add 0.1 mol of citric acid to the clear solution obtained in step 2), stir until homogeneous, and let stand in a 40°C oven to form a gel; 4) Freeze-dry the gel obtained in step 3) at a temperature of -40℃ and a freeze-drying pressure of less than 100Pa to obtain the precursor aerogel; 5) The precursor aerogel obtained in step 4) is placed in a muffle furnace for calcination at a heating rate of 5℃ / min, a temperature of 600℃, and a holding time of 3 hours. After the calcination is completed and the product is allowed to cool naturally, potassium ion modified ZnO-Au composite aerogel is obtained.

[0040] The scanning electron microscope (SEM) image of the potassium ion-modified ZnO-Au composite aerogel prepared in this embodiment is shown below. Figure 3 As shown in the figure, gold nanoparticles are uniformly dispersed in the three-dimensional network structure of ZnO aerogel, with a diameter of 14 nm for the gold nanoparticles and a diameter of 31 nm for the zinc oxide nanoparticles, resulting in a specific surface area of ​​78 m². 2 / g.

[0041] Comparative Example 1 In this comparative example, a ZnO-Au composite aerogel was prepared. The specific preparation method is as follows: 1) Dissolve 0.1 mol zinc acetate dihydrate and 0.005 mol chloroauric acid in a mixed solvent of 50 mL deionized water and 30 mL ethylene glycol, and stir until homogeneous to obtain a suspension; 2) Add 3 mL of nitric acid to the suspension obtained in step 1) and stir until homogeneous to obtain a clear solution; 3) Add 0.1 mol of citric acid to the clear solution obtained in step 2), stir until homogeneous, and let stand in a 40°C oven to form a gel; 4) Freeze-dry the gel obtained in step 3) at a temperature of -40℃ and a freeze-drying pressure of less than 100Pa to obtain the precursor aerogel; 5) The precursor aerogel obtained in step 4) is placed in a muffle furnace for calcination at a heating rate of 5℃ / min, a temperature of 600℃, and a holding time of 3 hours. After the calcination is completed and the product is allowed to cool naturally, ZnO-Au composite aerogel is obtained.

[0042] The photocatalytic performance of the potassium-modified ZnO-Au composite aerogel catalyst prepared in Example 3 for the oxygen-free coupling reaction of methane was tested and compared with the photocatalytic performance of the ZnO-Au composite aerogel catalyst prepared in Comparative Example 1. The results are as follows: Figure 4 As shown in the figure, the potassium ion-modified ZnO-Au composite aerogel catalyst prepared in Example 3 and the ZnO-Au composite aerogel catalyst prepared in Comparative Example 1 achieved photocatalytic coupling of methane to ethane yields of 38.75 μmol / g and 5.83 μmol / g, respectively, within 8 hours, representing a 6.65-fold increase.

[0043] XRD tests were performed on the samples from the above embodiments and comparative examples, and the results are as follows: Figure 5 As shown in the figure, the diffraction peaks of ZnO in the sample modified with alkali metal ions are shifted to some extent compared to ZnO without alkali metal ion modification, indicating successful modification with alkali metal ions. Furthermore, from... Figure 5 Obvious Au diffraction peaks can be observed, indicating the successful composite of Au nanoparticles.

[0044] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing an alkali metal-modified ZnO-Au composite aerogel, characterized in that, Specifically as follows: S1: Disperse zinc acetate dihydrate, alkali metal carbonate and chloroauric acid in a mixed solvent of water and ethylene glycol, and stir to form a suspension; S2: Add nitric acid to the suspension to obtain a clear solution; S3: Add citric acid to the clarified solution, heat and let stand to form a gel; S4: Freeze-dry the gel to obtain the precursor aerogel; S5: The precursor aerogel is calcined at high temperature to obtain alkali metal modified ZnO-Au composite aerogel.

2. The method for preparing an alkali metal-modified ZnO-Au composite aerogel according to claim 1, characterized in that, The alkali metal carbonate is one of lithium carbonate, sodium carbonate, or potassium carbonate.

3. The method for preparing an alkali metal-modified ZnO-Au composite aerogel according to claim 1, characterized in that, In the suspension, the molar ratio of zinc acetate dihydrate, chloroauric acid and alkali metal carbonate is (1~5): (0.001~0.05): 0.

1.

4. The method for preparing an alkali metal-modified ZnO-Au composite aerogel according to claim 1, characterized in that, In the mixed solvent, the molar ratio of water to ethylene glycol is (4~8):

1.

5. The method for preparing an alkali metal-modified ZnO-Au composite aerogel according to claim 1, characterized in that, In S2, the volume ratio of nitric acid to the mixed solvent is (0.01~0.05):

1.

6. The method for preparing an alkali metal-modified ZnO-Au composite aerogel according to claim 1, characterized in that, In S3, the molar ratio of citric acid to zinc acetate dihydrate is (0.5~2):1; the heating and settling temperature is 40℃-60℃.

7. The method for preparing an alkali metal-modified ZnO-Au composite aerogel according to claim 1, characterized in that, In step S4, the freezing temperature is -40°C and the freeze-drying pressure is less than 100 Pa.

8. The method for preparing an alkali metal-modified ZnO-Au composite aerogel according to claim 1, characterized in that, In step S5, the high-temperature calcination is carried out in an air atmosphere, with a calcination temperature of 300-800℃, a heating rate of 1-20℃ / min, and a holding time of 1-24 hours.

9. An alkali metal-modified ZnO-Au composite aerogel obtained by the preparation method according to any one of claims 1 to 8.

10. An application of the alkali metal-modified ZnO-Au composite aerogel according to claim 9 in photocatalytic reactions.

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