Preparation Method and Application of a ZrO2 / UiO-66-NH2 Composite Catalyst

Abstract

The invention discloses a preparation method and application of a ZrO2 / UiO-66-NH2 composite catalyst, belonging to the technical field of photocatalytic materials. Using UiO-66-NH2 as a precursor, a ZrO2 / UiO-66-NH2 composite material is obtained through solvothermal treatment. The uniformly dispersed ZrO2 and UiO-66-NH2 in the composite material form a tight heterojunction, and the large interfacial area provides an efficient channel for photogenerated carriers. In the reaction of photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde, using molecular oxygen as an oxidant, the efficient conversion of benzyl alcohol is realized, and benzaldehyde is the only product. The preparation process of the invention is simple, and it has good economic benefits in the direction of photocatalytic green organic synthesis.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to a preparation method of a ZrO2 / UiO-66-NH2 photocatalyst and its photocatalytic oxidation application. Background Art

[0002] Aromatic aldehydes are important industrial raw materials or intermediates, and are widely used in the production of medicines, spices, dyes, resins, etc. Among them, benzaldehyde is widely used in the synthesis of various organic compounds, including seasonings, food additives, perfumes, aniline dyes, and drugs. Benzaldehyde is usually produced by hydrolysis of benzyl chloride or oxidation of toluene, but harmful oxidants are easily used in the process and toxic by-products are easily generated. Compared with the traditional industrial method for producing benzaldehyde, using solar energy to drive the photocatalytic oxidation reaction of benzyl alcohol with molecular oxygen as the oxidant is an environmentally friendly method. Because solar energy is naturally abundant, environmentally friendly, renewable, and easy to operate. To date, many photocatalysts for synthesizing aromatic aldehydes have been developed, such as semiconductor materials. However, due to the common disadvantages of single semiconductor materials, such as poor light absorption ability and low electron-hole separation efficiency, the combination of semiconductors is an effective solution, which reduces the recombination of electron-hole pairs through the mutual transfer of electrons between semiconductors. Taking CdS as an example, CdS particles are prone to aggregation during the preparation process, resulting in a decrease in specific surface area and poor separation efficiency. In an article titled CdS-decorated UiO-66(NH2) nanocomposites fabricated by a facile photodeposition process: an efficient and stable visible-light-driven photocatalyst for selective oxidation of alcohols published by Shen in Journal of Materials Chemistry A, based on CdS, CdS-UiO-66(NH2) was designed. Due to the ultra-high specific surface area and micropore distribution of UiO-66(NH2), it can anchor and disperse CdS to achieve efficient charge separation. However, due to the different specific properties of each semiconductor, designing an efficient photocatalyst with suitable physical and chemical properties and practical application value is still a challenging task.

[0003] Metal-organic frameworks (MOFs) have attracted extensive attention from researchers in photocatalysis due to their semiconductor properties and tunable structures. The metal clusters in MOFs can be regarded as inorganic semiconductor quantum entities, while the organic ligands are active antennas, so MOFs exhibit semiconductor properties. At the same time, because MOFs have a large specific surface area and the characteristics of uniform but tunable MOF cavities, they have become promising photocatalysts. Aiming at the problem of high recombination rate of photo-generated carriers in single-phase MOF photocatalysts, combined with the positive effect of heterojunctions on electron-hole separation, in recent years, researchers have prepared supported semiconductor oxides by pyrolyzing MOFs to form a tighter heterojunction to improve the photocatalytic reaction activity. In an article published by He in Angewandte titled Engineering a Self-Grown TiO2 / Ti-MOF Heterojunction with Selectively Anchored High-Density Pt Single-Atomic Cocatalysts for Efficient Visible-Light-Driven Hydrogen Evolution, TiO2 / Ti-BPDC-Pt photocatalyst was constructed by surface pyrolysis reconstruction method using Pt-anchored Ti-BPDC-Pt as the precursor for visible-light hydrogen evolution performance research. Compared with single-phase and heterojunction catalysts formed by other methods, the method of in-situ growing defective TiO2 on Ti-BPDC-Pt is more conducive to the formation of a tight heterojunction interface and has higher photocatalytic hydrogen evolution activity. Summary of the Invention

[0004] Aiming at the above problems existing in current photocatalysts, the present invention for the first time uses a solvothermal treatment method to in-situ grow ZrO2 on the metal-organic framework material UiO-66-NH2. The uniformly dispersed ZrO2 and UiO-66-NH2 form a tight heterojunction, and the large interfacial area provides an efficient channel for photo-generated carriers, significantly improving the activity of UiO-66-NH2 in the photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A preparation method of a ZrO2 / UiO-66-NH2 photocatalyst, the steps are as follows:

[0007] Step 1: Prepare the metal-organic framework material UiO-66-NH2 by solvothermal method;

[0008] Step 2: Disperse the metal-organic framework material UiO-66-NH2 prepared in Step 1 in an alcohol organic solvent, fully stir, and then place it in a high-pressure reaction kettle for solvothermal treatment;

[0009] Step 3: Centrifuge the reacted suspension, collect the solid product, wash it with ethanol, and obtain the composite photocatalyst ZrO2 / UiO-66-NH2 derived from UiO-66-NH2 after vacuum drying.

[0010] In Step 2, the molar ratio of the metal-organic framework material UiO-66-NH2 to the alcohol organic solvent is 1:5000 - 1:8000; the alcohol organic solvent is a high-boiling-point alcohol such as n-pentanol or n-octanol, or a mixed solvent of ethylene glycol, ethanol, methanol and the aforementioned high-boiling-point alcohol. The solvothermal treatment temperature is 180 - 240 °C, and the solvothermal treatment time is 1.5 - 3 h.

[0011] Application of a ZrO2 / UiO-66-NH2 photocatalyst in the photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde. The application is as follows: Add the ZrO2 / UiO-66-NH2 photocatalyst into an acetonitrile solution containing 0.04 mol / L benzyl alcohol. In an oxygen atmosphere, first adsorb in the dark for 0.5 h, then turn on a 30 W LED light source with a wavelength range of 420 - 800 nm, and carry out the photocatalytic reaction at room temperature for 5 h. After the reaction is completed, centrifuge and dry the reaction solution, and take the supernatant for gas chromatography analysis of the product composition.

[0012] Compared with other technologies, the beneficial effects of the present invention are mainly reflected in that a heterojunction composite material formed by the metal-organic framework material UiO-66-NH2 and ZrO2 prepared by the solvothermal method is used in the reaction of photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde with molecular oxygen as the oxidant, and a relatively high benzyl alcohol conversion rate (86.2%) and a relatively high benzaldehyde selectivity (99.9%) can be obtained simultaneously, with the characteristics of simple operation and environmental friendliness. Description of the Drawings

[0013] Figure 1 High-resolution transmission electron microscope photos of UiO-66-NH2-2h with a solvothermal treatment time of 2 h in Example 1 (A is the photo of UiO-66-NH2-2h with a scale of 100 nm, B is the photo of UiO-66-NH2-2h with a scale of 10 nm, and C is the local lattice fringe photo of UiO-66-NH2-2h in Figure B).

[0014] Figure 2 XRD patterns of the catalysts with different solvothermal treatment times in Example 2. Detailed Embodiments

[0015] The following further illustrates the specific embodiments of the present invention through the drawings and examples.

[0016] Example 1

[0017] (1) Preparation of UiO-66-NH2

[0018] Weigh 2.1 g of ZrCl4 and 1.7 g of 2-aminoterephthalic acid, measure 180 mL of N,N-dimethylformamide, add them to a flask, stir at room temperature for 0.5 h, transfer to a high-pressure reactor, and react at 120 °C for 48 h; cool and centrifuge the reaction suspension, wash successively with N,N-dimethylformamide and ethanol, and obtain the metal-organic framework material UiO-66-NH2 after vacuum drying.

[0019] (2) Preparation of ZrO2 / UiO-66-NH2

[0020] Weigh 0.5 g of the metal-organic framework material UiO-66-NH2, disperse it in 120 mL of an alcohol organic solvent, stir well, place it in a high-pressure reactor, and perform solvothermal treatment at 220 °C for 2 h. After the solvothermal reaction ends and cools to room temperature, centrifuge the suspension, collect the solid product, wash with ethanol, and obtain the UiO-66-NH2-derived composite photocatalyst ZrO2 / UiO-66-NH2 after vacuum drying, named UiO-66-NH2-2h.

[0021] Figure 1 Figure 14 is the high-resolution transmission electron microscopy image of UiO-66-NH2-2h with a solvothermal preparation time of 2 h in Example 1. The scale bars of Figures A and B are 100 nm and 10 nm respectively, and Figure C is the local lattice fringe image of UiO-66-NH2-2h in Figure B. Lattice fringes belonging to the (011) crystal plane of ZrO2 can be found in Figures B and C, and the lattice spacing is 0.295 nm. It is proved that uniformly dispersed ZrO2 can be obtained on the surface of UiO-66-NH2 through 2 h of solvothermal treatment.

[0022] Example 2

[0023] Effect of different solvothermal treatment times on the photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde

[0024] Prepare UiO-66-NH2 according to the method in (1) of Example 1, and obtain different catalysts by changing the solvothermal treatment time in (2) of Example 1, named UiO-66-NH2-xh (x represents the solvothermal treatment time).

[0025] The catalysts obtained by heat-treating 50 mg for different solvent treatment times were added to a reaction flask containing a solution of benzyl alcohol / acetonitrile (concentration 0.04 mol / L). First, they were adsorbed in the dark for 0.5 h, then the light source was turned on, and the photocatalytic reaction was carried out at room temperature for 5 h. After the reaction, the reaction solution was centrifuged and dried, and the supernatant was taken for gas chromatography analysis of the product composition. The analysis results are shown in Table 1. It can be seen that with the extension of the solvent heat treatment time, no by-products were generated during the reaction process, and the selectivity of benzaldehyde remained unchanged at 99%; however, the conversion rate showed a trend of first increasing and then decreasing. When the solvent thermal preparation time was 1 h, the conversion rate of benzyl alcohol was 34.5%; when the time was extended to 2 h, the conversion rate of benzyl alcohol was 86.2%; when the solvent thermal preparation time was further extended to 3 h, 4 h, and 24 h, the conversion rates of benzyl alcohol were 56.7%, 43.6%, and 36.1% respectively. This indicates that there is an optimal ratio between the two in the UiO-66-NH2 and ZrO2 composite material.

[0026] Figure 2 XRD patterns of the catalysts with different solvent thermal preparation times. It can be seen from the figure that with the extension of the solvent heat treatment time, the diffraction peak intensity of UiO-66-NH2 gradually decreased. After 3 hours of solvent heat treatment, the diffraction peak of UiO-66-NH2 disappeared, and the diffraction peak of ZrO2 appeared. As the solvent heat time was further extended to 24 h, the diffraction peak of UiO-66-NH2 completely disappeared, and the diffraction peak of ZrO2 was enhanced. This indicates that with the extension of the solvent heat time, UiO-66-NH2 on the catalyst surface gradually collapsed and gradually derived ZrO2.

[0027] Table 1 Results of the photocatalytic oxidation of benzyl alcohol to benzaldehyde with different solvent heat treatment times of UiO-66-NH2

[0028] Solvothermal treatment time (h) Conversion rate of benzyl alcohol (%) Selectivity of benzaldehyde (%) 1.0 34.5 99.9 2.0 86.2 99.9 3.0 56.7 99.9 4.0 43.6 99.9 24.0 36.1 99.9

[0029] Example 3

[0030] Effect of different solvent heat treatment temperatures on the photocatalytic oxidation of benzyl alcohol to benzaldehyde

[0031] UiO-66-NH2 was prepared according to the method in (1) of Example 1. On the premise that the solvent heat treatment time was kept at 2 h unchanged, different catalysts were obtained by changing the solvent heat treatment temperature in (2) of Example 1.

[0032] 50 mg of the catalyst obtained by heat-treating in different solvents at different temperatures was added to a reaction flask containing a benzyl alcohol / acetonitrile solution (concentration: 0.04 mol / L). First, it was adsorbed in the dark for 0.5 h, then the light source was turned on, and the photocatalytic reaction was carried out at room temperature for 5 h. After the reaction, the reaction solution was centrifuged and dried, and the supernatant was taken for gas chromatography analysis of the product composition. The analysis results are shown in Table 2. As the temperature increased, the conversion rate of benzyl alcohol showed a trend of first increasing and then decreasing, because the amount of ZrO2 generated during the preparation process with the same treatment time but different treatment temperatures was different. The conversion rate of benzyl alcohol was the highest when the solvent heat-treatment temperature was 220 °C.

[0033] Table 2 Results of photocatalytic oxidation of benzyl alcohol to benzaldehyde over UiO-66-NH2 with different solvent heat-treatment temperatures

[0034]

[0035] Comparative Example 1

[0036] Photocatalytic oxidation of benzyl alcohol to benzaldehyde without light

[0037] The photocatalyst UiO-66-NH2-2h was prepared according to the method of Example 1. 50 mg of it was added to a reaction flask containing a benzyl alcohol / acetonitrile solution (concentration: 0.04 mol / L). The light source was not turned on, and the reaction was carried out at room temperature in the dark for 5 h. After the reaction, the reaction solution was centrifuged and dried, and the supernatant was taken for chromatographic analysis. The reaction results are shown in Table 3. It can be seen that under the condition of no light, benzyl alcohol hardly underwent conversion, and benzaldehyde could not be detected by chromatography. Thus, it was concluded that the oxidation of benzyl alcohol to benzaldehyde catalyzed by UiO-66-NH2-2h was a light-driven reaction process.

[0038] Comparative Example 2

[0039] Photocatalytic oxidation of benzyl alcohol to benzaldehyde without a catalyst

[0040] The benzyl alcohol / acetonitrile solution (concentration: 0.04 mol / L) was added to a reaction flask, ensuring an oxygen atmosphere, but no photocatalyst was added. The light source was turned on, and the photocatalytic reaction was carried out at room temperature for 5 h. After the reaction, the reaction solution was centrifuged and dried, and the supernatant was taken for chromatographic analysis. The reaction results are shown in Table 3. It can be seen that under the condition of no catalyst, benzyl alcohol also hardly underwent conversion, and benzaldehyde could not be detected by chromatography. Thus, it was concluded that the photocatalyst UiO-66-NH2-2h could accelerate the rapid conversion of benzyl alcohol to benzaldehyde.

[0041] Comparative Example 3

[0042] The photocatalyst UiO-66-NH2 was prepared according to the method in (1) of Example 1. 50 mg of it was added to a reaction flask containing a benzyl alcohol / acetonitrile (concentration 0.04 mol / L) solution. First, it was adsorbed in the dark for 0.5 h, then the light source was turned on, and the photocatalytic reaction was carried out at room temperature for 5 h. After the reaction, the reaction solution was centrifuged and dried, and the supernatant was taken for gas chromatography analysis of the product composition. The reaction results are shown in Table 3. Using UiO-66-NH2 as the photocatalyst, the reaction activity was low, and only a very small amount of benzaldehyde was generated. Moreover, due to the Brønsted acid sites present in UiO-66-NH2, disproportionation of benzyl alcohol occurred to form the by-product toluene.

[0043] Comparative Example 4

[0044] 50 mg of commercial ZrO2 was added to a reaction flask containing a benzyl alcohol / acetonitrile (concentration 0.04 mol / L) solution. First, it was adsorbed in the dark for 0.5 h, then the light source was turned on, and the reaction time was 5 h. After the reaction, the reaction solution was centrifuged and dried, and the supernatant was taken for chromatographic analysis. The reaction results are shown in Table 3. Using commercial ZrO2 as the catalyst, benzyl alcohol hardly underwent conversion, and benzaldehyde was not detected by chromatography.

[0045] Comparative Example 5

[0046] The photocatalyst UiO-66-NH2 was prepared according to the method in (1) of Example 1. 25 mg was taken and mechanically mixed with commercial ZrO2 at a mass ratio of 1:1, and then added to a reaction flask containing a benzyl alcohol / acetonitrile (concentration 0.04 mol / L) solution. It was adsorbed in the dark for 0.5 h, the light source was turned on, and the photocatalytic reaction was carried out at room temperature for 5 h. After the reaction, the reaction solution was centrifuged and dried, and the supernatant was taken for gas chromatography analysis of the product composition. The reaction results are shown in Table 3. The effect was worse than that using UiO-66-NH2-2h as the catalyst, indicating that there was a certain interaction between the derived ZrO2 and UiO-66-NH2 rather than a simple mechanical mixing effect, and there was an optimal ratio between the two.

[0047] Table 3 Reaction results of different catalyst systems for the photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde

[0048]

[0049] In summary, the above results show that in-situ growth of ZrO2 on the metal-organic framework material UiO-66-NH2 by the solvothermal treatment method promoted the coupling between UiO-66-NH2 and ZrO2 and formed a heterojunction structure, and significantly improved the activity of single-phase UiO-66-NH2 in the photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde by utilizing the synergistic effect between the two.

Claims

1. A preparation method of a ZrO2 / UiO-66-NH2 photocatalyst, characterized in that, Here are the steps: Step 1: Prepare the metal organic framework material UiO-66-NH2 by solvothermal method; Step 2: Disperse the metal organic framework material UiO-66-NH2 prepared in step 1 in an alcohol organic solvent, stir it thoroughly, and place it in a high pressure reactor for solvent thermal treatment; Step 3: The suspension after the reaction is centrifuged, and the solid product is collected, washed with ethanol, and vacuum dried to obtain the UiO-66-NH2-derived composite photocatalyst ZrO2 / UiO-66-NH2.

2. The preparation method according to claim 1, wherein, In step 2, the molar ratio of the metal organic framework material UiO-66-NH2 to the alcohol organic solvent is 1:5000~1:8000.

3. The preparation method according to claim 1, characterized in that, In step 2, the alcohol organic solvent is a high-boiling point alcohol, or a mixed solvent of a high-boiling point alcohol and one or more of ethylene glycol, ethanol, and methanol; wherein the high-boiling point alcohol is n-pentanol and / or n-octanol.

4. The preparation method according to claim 1, wherein In step 2, the solvent thermal treatment temperature is 180~240°C, and the solvent thermal treatment time is 1.5~3 h.

5. Use of a ZrO2 / UiO-66-NH2 photocatalyst prepared by the preparation method described in any one of claims 1-4 in the photocatalytic oxidation of benzyl alcohol to prepare benzaldehyde, characterized in that, The ZrO2 / UiO-66-NH2 photocatalyst was added to an acetonitrile solution containing 0.04 mol / L benzyl alcohol. In an oxygen atmosphere, it was first adsorbed in the dark for 0.5 h, and then a 30 W LED light source with a wavelength range of 420-800 nm was turned on to carry out a photocatalytic reaction at room temperature for 5 h.

Images