Preparation method of functionalized UiO-66 for ammonia adsorption

Abstract

The invention discloses a preparation method of functionalized UiO-66 for ammonia adsorption, belonging to the field of adsorption and purification of toxic and harmful gases. By introducing a small amount of lower alcohols and monocarboxylic acid ligands into the precursor for ultra-fine regulation, the synergistic effect of the two can effectively stabilize the precursor, regulate the balance between the nucleation and growth of MOFs, and make the material have higher crystallinity and more stable products. On this basis, after eluting the unstable ligands with acid, while increasing the porosity and specific surface area of the material, the original ultra-microporous structure (0.6 nm) is maintained, which hinders the adsorption of larger gases such as N2 and CO2, and exhibits excellent adsorption selectivity for NH3. The functionalized UiO-66 material prepared by this invention not only has a large specific surface area and high ammonia adsorption performance, but also has a simple preparation process, stable products, good crystallinity, and is easy to industrialize.

Description

Technical Field

[0001] The present invention specifically relates to a preparation method of functionalized UiO-66 for ammonia adsorption, belonging to the field of adsorption and purification of toxic and harmful gases. Background Art

[0002] Ammonia is a typical alkaline gas with pollution and strong corrosiveness, which is extremely harmful to humans and the environment. At the same time, as a carbon-free hydrogen energy carrier, developing efficient ammonia storage technology to carry hydrogen is an effective means to reduce carbon dioxide emissions and is of great significance for achieving the "dual carbon" goal. In recent years, metal-organic framework materials (MOFs) have received extensive attention as a potential material for adsorption and purification of toxic and harmful gases. Among them, zirconium-based MOFs are widely used in the separation of various small molecule gases due to the stability of the Zr-O bond. Especially in ammonia adsorption, it can effectively reduce the attack of ammonia with lone pair electrons on the coordination bond between metal and ligand and maintain the stability of the structure.

[0003] In the synthesis of MOFs, selecting organic ligands with functional groups can in-situ synthesize MOFs with unique functions. Functionalized MOFs materials can be applied to different aspects by utilizing the properties of different functional groups, but there are problems such as poor crystallinity and unstable products in the preparation process. In addition, the research of the article with DOI 10.1016 / j.ces.2014.08.050 shows that when large functional groups are introduced into UiO-66 for functionalization, the large surface groups will block the small voids in the framework, resulting in a decrease in the porosity and specific surface area of the material. To address these problems, many researchers use defect engineering to improve the porosity and adsorption sites of the material. For example, the article with DOI 10.1039 / D2EN01035F prepares a series of hierarchically porous MOF materials through competitive coordination, but the mesoporous and macroporous structures will lead to a decrease in selectivity in some gas adsorption and separation processes. Therefore, while improving the specific surface area and porosity of functionalized zirconium-based MOFs, enhancing the crystallinity, preparation stability and maintaining appropriate pore cages of the material are the keys to improving gas adsorption and separation. Summary of the Invention

[0004] The purpose of the present invention is to improve the porosity, specific surface area and synthesis stability of functionalized UiO-66 while maintaining the ultra-microporous structure to solve the above problems, thereby improving the application of functionalized UiO-66 in ammonia adsorption and separation.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A UiO-66-(OH) with high yield, high crystallinity, large specific surface area and ultra-microporous structure 2Preparation method of metal-organic framework material. The material uses zirconium chloride and 2,5-dihydroxyterephthalic acid as raw materials, acetic acid and DMF as solvents, and different contents of benzyl alcohol and formic acid are added. The two act synergistically to regulate the crystallization rate and coordination environment, and then the target product is obtained after removing unstable ligands with hydrochloric acid.

[0007] The specific preparation method includes the following steps:

[0008] Step 1, Disperse zirconium chloride, 2,5-dihydroxyterephthalic acid and acetic acid in DMF, and stir magnetically for 30 min until the solid is completely dissolved;

[0009] Step 2, Add a small amount of benzyl alcohol and formic acid to the above solution, ultrasonically treat for 10 - 30 min to make the solvent disperse evenly, and then carry out solvothermal reaction on the mixed solution at 100 - 150 °C;

[0010] Step 3, Wait for the reaction to cool to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of hydrochloric acid and DMF for 1 - 6 h, wash 3 - 6 times with DMF and methanol respectively, and obtain UiO-66-(OH) after centrifugation and vacuum drying 2 ;

[0011] Preferably, in step 1, the molar ratio of zirconium chloride, 2,5-dihydroxyterephthalic acid and acetic acid is 1:1:40; the molar ratio of zirconium chloride and DMF is 1:250;

[0012] Preferably, in step 2, the molar ratio of zirconium chloride and benzyl alcohol is 1:20; the molar ratio of zirconium chloride and formic acid is 1:10;

[0013] Preferably, the ultrasonic treatment time in step 2 is 20 min;

[0014] Preferably, the solvothermal reaction temperature in step 2 is 120 °C; the holding time is 24 h;

[0015] Preferably, in step 3, the volume of the mixed solution is 50 mL; the volume percentage of hydrochloric acid is 10%; the soaking time is 2 h;

[0016] Preferably, in step 3, wash 3 times with DMF and methanol respectively; vacuum dry at 60 °C for 12 h;

[0017] Finally, UiO-66-(OH) can be obtained with a yield of more than 78 wt% 2 Metal-organic framework material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Through the synergistic effect of lower alcohols and monocarboxylic acid ligands, the present invention prepares functionalized UiO-66 with high crystallinity, stable products, which is conducive to large-scale production and preparation;

[0020] (2) The present invention can improve the problem of blocking small voids in the framework due to the introduction of large functional groups for functionalization, and maintain the ultra-microporous structure while increasing the specific surface area and porosity of the material;

[0021] (3) The preparation method of the present invention is simple, energy-saving and environmentally friendly, can effectively improve the ammonia adsorption performance and has excellent adsorption selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 X-ray powder diffraction (XRD) patterns of the samples obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2.

[0023] Figure 2 Polarizing microscope images of the samples obtained in Example 1, Example 2 and Example 3.

[0024] Figure 3 Thermogravimetric analysis curves (TGA) of the samples obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2.

[0025] Figure 4 Adsorption-desorption curves and pore size distribution diagrams of the samples obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2.

[0026] Figure 5 Performance evaluation diagrams of Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 in ammonia adsorption.

[0027] Figure 6 Adsorption selectivity evaluation diagram of the sample obtained in Example 1 for carbon dioxide and nitrogen. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The present invention will be further described below in conjunction with the drawings, examples and comparative examples. The specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Example 1

[0030] Step 1, Disperse 668 mg of zirconium chloride, 500 mg of 2,5-dihydroxyterephthalic acid and 6.6 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solid is completely dissolved;

[0031] Step 2: Then, add 3 mL of benzyl alcohol and 1 mL of formic acid, and ultrasonicate for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0032] Step 3: After the reaction is completed, cool it naturally to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of hydrochloric acid and DMF for 2 h. The volume of the mixed solution is 50 mL, and the volume percentage of hydrochloric acid is 10%. After centrifugation and washing with DMF and methanol three times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-(OH). 2 。

[0033] Example 2

[0034] Step 1: Disperse 668 mg of zirconium chloride, 500 mg of 2,5-dihydroxyterephthalic acid and 6.6 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solid is completely dissolved.

[0035] Step 2: Then, add 3 mL of benzyl alcohol and 0.5 mL of formic acid, and ultrasonicate for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0036] Step 3: After the reaction is completed, cool it naturally to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of hydrochloric acid and DMF for 2 h. The volume of the mixed solution is 50 mL, and the volume percentage of hydrochloric acid is 10%. After centrifugation and washing with DMF and methanol three times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-(OH). 2 。

[0037] Example 3

[0038] Step 1: Disperse 668 mg of zirconium chloride, 500 mg of 2,5-dihydroxyterephthalic acid and 6.6 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solid is completely dissolved.

[0039] Step 2: Then, add 3 mL of benzyl alcohol and 2 mL of formic acid, and ultrasonicate for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0040] Step 3: After the reaction is completed, naturally cool to room temperature, pour off the supernatant, soak the obtained solid material in a mixed solution of hydrochloric acid and DMF for 2 h. The volume of the mixed solution is 50 mL, and the volume percentage of hydrochloric acid is 10%. After centrifugation and washing with DMF and methanol three times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-(OH). 2 。

[0041] Example 4

[0042] Step 1: Disperse 600 mg of zirconium oxychloride, 458.4 mg of 2-sulfonic acid terephthalic acid and 4.3 mL of acetic acid in 60 mL of DMF, and magnetically stir for 30 min until the solid is completely dissolved;

[0043] Step 2: Then add 2 mL of absolute ethanol and 1.8 mL of benzoic acid, ultrasonically treat for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and keep it at 130 °C for 24 hours.

[0044] Step 3: After the reaction is completed, naturally cool to room temperature, pour off the supernatant, soak the obtained solid material in a mixed solution of nitric acid and DMF for 3 h. The volume of the mixed solution is 50 mL, and the volume percentage of nitric acid is 10%. After centrifugation and washing with DMF and methanol four times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-SO 3 H.

[0045] Example 5

[0046] Step 1: Disperse 600 mg of zirconium nitrate, 435.4 mg of 2-sulfonic acid terephthalic acid and 4 mL of acetic acid in 60 mL of DMF, and magnetically stir for 30 min until the solid is completely dissolved;

[0047] Step 2: Then add 2.1 mL of methanol and 4 mL of lactic acid, ultrasonically treat for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and keep it at 150 °C for 12 hours.

[0048] Step 3: After the reaction is completed, naturally cool to room temperature, pour off the supernatant, soak the obtained solid material in a mixed solution of hydrochloric acid and DMF for 6 h. The volume of the mixed solution is 60 mL, and the volume percentage of hydrochloric acid is 5%. After centrifugation and washing with DMF and methanol three times respectively, vacuum dry at 80 °C for 12 hours to obtain the target product UiO-66-SO 3 H.

[0049] Example 6

[0050] Step 1: Disperse 500 mg of zirconium oxychloride, 282.6 mg of 2-hydroxyterephthalic acid, and 3.5 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solids are completely dissolved;

[0051] Step 2: Then add 2.3 mL of propanol and 3.5 mL of citric acid, sonicate for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless-steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0052] Step 3: After the reaction is completed, cool it naturally to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of sulfuric acid and DMF for 4 h. The volume of the mixed solution is 60 mL, and the volume percentage of sulfuric acid is 5%. After centrifugation and washing with DMF and methanol three times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-OH.

[0053] Example 7

[0054] Step 1: Disperse 500 mg of zirconium chloride, 390.8 mg of 2-hydroxyterephthalic acid, and 5 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solids are completely dissolved;

[0055] Step 2: Then add 1.2 mL of ethylene glycol and 1.6 mL of trifluoroacetic acid, sonicate for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless-steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0056] Step 3: After the reaction is completed, cool it naturally to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of sulfuric acid and DMF for 4 h. The volume of the mixed solution is 60 mL, and the volume percentage of sulfuric acid is 10%. After centrifugation and washing with DMF and methanol three times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-OH.

[0057] Example 8

[0058] Step 1: Disperse 500 mg of zirconium chloride, 545.3 mg of 1,2,4,5-benzenetetracarboxylic acid, and 5 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solids are completely dissolved;

[0059] Step 2: Then add 3.2 mL of propylene glycol and 6.5 mL of salicylic acid, sonicate for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless-steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0060] Step 3: After the reaction is completed, naturally cool to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of oxalic acid and DMF for 4 h. The volume of the mixed solution is 60 mL, and the volume percentage of oxalic acid is 15%. After centrifugation and washing with DMF and methanol 4 times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-COOH.

[0061] Example 9

[0062] Step 1: Disperse 650 mg of zirconium oxychloride, 365.4 mg of 2-aminoterephthalic acid and 5.8 mL of acetic acid in 60 mL of DMF, and magnetically stir for 30 min until the solid is completely dissolved;

[0063] Step 2: Then add 2.4 mL of absolute ethanol and 3 mL of succinic acid, ultrasonically treat for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless steel autoclave with a PTFE liner, and keep it at 120 °C for 24 hours.

[0064] Step 3: After the reaction is completed, naturally cool to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of nitric acid and DMF for 4 h. The volume of the mixed solution is 60 mL, and the volume percentage of nitric acid is 20%. After centrifugation and washing with DMF and methanol 6 times respectively, vacuum dry at 80 °C for 6 hours to obtain the target product UiO-66-NH 2 。

[0065] Example 10

[0066] Step 1: Disperse 560 mg of zirconium nitrate, 348.5 mg of 2-nitroterephthalic acid and 3.8 mL of acetic acid in 50 mL of DMF, and magnetically stir for 30 min until the solid is completely dissolved;

[0067] Step 2: Then add 2 mL of methanol and 1.6 mL of benzoic acid, ultrasonically treat for 20 min to obtain a mixed solution. Transfer the obtained mixed solution to a 100 mL stainless steel autoclave with a PTFE liner, and keep it at 150 °C for 24 hours.

[0068] Step 3: After the reaction is completed, naturally cool to room temperature, pour out the supernatant, soak the obtained solid material in a mixed solution of hydrochloric acid and DMF for 1 h. The volume of the mixed solution is 60 mL, and the volume percentage of hydrochloric acid is 15%. After centrifugation and washing with DMF and methanol 3 times respectively, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-NO 2 。

[0069] Comparative Example 1

[0070] Step 1: Disperse 668 mg of zirconium chloride, 500 mg of 2,5-dihydroxyterephthalic acid, and 6.6 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solids are completely dissolved to obtain a mixed solution.

[0071] Step 2: Transfer the above mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0072] Step 3: After the reaction is completed, naturally cool to room temperature, pour off the supernatant, wash the obtained solid material with DMF and methanol three times each, and obtain the target product UiO-66-(OH) after centrifugation and vacuum drying at 60 °C for 12 hours. 2 。

[0073] Comparative Example 2

[0074] Step 1: Disperse 668 mg of zirconium chloride, 500 mg of 2,5-dihydroxyterephthalic acid, and 6.6 mL of acetic acid in 50 mL of DMF, and stir magnetically for 30 min until the solids are completely dissolved to obtain a mixed solution.

[0075] Step 2: Transfer the above mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and keep it at 120 °C for 24 hours.

[0076] Step 3: After the reaction is completed, naturally cool to room temperature, pour off the supernatant, soak the obtained solid material in a mixed solution of hydrochloric acid and DMF for 2 h. The volume of the mixed solution is 50 mL, and the volume percentage of hydrochloric acid is 10%. After centrifugation and washing with DMF and methanol three times each, vacuum dry at 60 °C for 12 hours to obtain the target product UiO-66-(OH). 2 。

[0077] Figure 1 XRD patterns of the samples obtained in Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2. As Figure 1 can be seen, the characteristic diffraction peaks of all samples are consistent with those of the standard sample UiO-66, indicating that hydroxylated UiO-66 has been successfully prepared and the material has good crystallinity. With the introduction of benzyl alcohol and formic acid, the peak width of the material characteristic peaks gradually becomes narrower and the peak intensity increases, indicating that the crystallinity of the material is further improved.

[0078] Figure 2 Polarizing microscope images of the samples obtained in Example 1, Example 2, and Example 3, with the scale bars all being 10 μm. As Figure 2 can be seen, the UiO-66-(OH) 2 samples prepared under the synergistic action of benzyl alcohol and formic acid have good crystallinity, uniform size, and high dispersion, which is consistent with the XRD results.

[0079] Figure 3 Thermogravimetric analysis curves (TGA) of the samples obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2. As can be seen from Figure 3 it, all samples have approximately the same two-stage weight loss plateau temperatures, indicating that the samples have the same thermal stability. Comparative Example 1 and Comparative Example 2 have fewer self-defects because no monocarboxylic acid ligand was added additionally. While Example 1, Example 2 and Example 3 with added benzyl alcohol and different proportions of formic acid have more ligand defect sites, which plays an important role in improving the ammonia adsorption performance.

[0080] Figure 4 Adsorption-desorption curves and pore size distribution diagrams of the samples obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2. As can be seen from the figure, the N 2 adsorption-desorption curves of all samples show obvious type I isotherm characteristics, indicating that the pore structure of the material is mainly microporous structure, which is consistent with the pore size distribution curve results.

[0081] Analyzing the results, as shown in Table 1, compared with the comparative examples, the synergistic effect of benzyl alcohol and formic acid can effectively stabilize the precursor, making the material have higher crystallinity, uniform pore size distribution. After removing the unstable ligands with acid, more defect sites are generated, increasing the specific surface area and pore volume of the material, up to 1180.5 m 2 / g and 0.57 cm 3 / g. In addition, while increasing the specific surface area and pore volume, the ultra-microporous structure is maintained, which plays an important role in improving the ammonia adsorption selectivity.

[0082]

[0083] Table 1

[0084] Figure 5 Ammonia adsorption test results of Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 at normal temperature and pressure, with a concentration of 1,000,000 ppm and a flow rate of 20 mL / min. It can be seen that Example 1 with a larger specific surface area and pore volume has the best ammonia adsorption effect, and the saturated adsorption capacity is 200 mg / g.

[0085] Figure 6 Evaluation diagram of the adsorption selectivity of the sample obtained in Example 1 for carbon dioxide and nitrogen. Under the same reaction conditions, Example 1 with an ultra-microporous structure hardly adsorbs CO 2 and N 2 , indicating that it has excellent adsorption selectivity for ammonia.

[0086] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing functionalized UiO-66 for ammonia adsorption, characterized in that: The preparation method comprises the following steps: Step 1, dispersing the zirconium source, functionalized terephthalic acid and acetic acid in DMF, stirring evenly until the solid is completely dissolved to obtain a mixed solution; Step 2, adding benzyl alcohol and formic acid to the mixed solution, further mixing by ultrasonic treatment, and then performing a solvothermal reaction; Step 3, after the solvothermal reaction is completed, the layers are allowed to stand and the supernatant is discarded, and the obtained solid material is soaked with a solution including an acid and DMF, and then washed with DMF and methanol respectively, and then centrifuged and vacuum dried to obtain the functionalized UiO-66; The zirconium source includes one or more of zirconium chloride, zirconium oxychloride and zirconium nitrate; The functionalized terephthalic acid includes one of 2,5-dihydroxyterephthalic acid, 2-hydroxyterephthalic acid, 2-sulfonic terephthalic acid, 1,2,4,5-benzenetetracarboxylic acid, 2-nitroterephthalic acid and 2-aminoterephthalic acid; The acid includes one or more of hydrochloric acid, sulfuric acid, nitric acid and oxalic acid; The molar ratio of the zirconium source, functionalized terephthalic acid and acetic acid is (1-1.5): (1-1.5): (30-50); The molar ratio of the zirconium source to DMF is 1: (240-280), the molar ratio of the zirconium source to benzyl alcohol is 1: (10-30), and the molar ratio of the zirconium source to formic acid is 1: (5-30); The volume of the solution including the acid and DMF is 40-100 mL, wherein the volume percentage of the acid is 5%-20%.

2. The preparation method according to claim 1, characterized in that: In the step 2, the ultrasonic treatment time is 10-30 min.

3. The preparation method according to claim 1, characterized in that: In the step 2, the temperature of the solvent thermal reaction is 100-150° C., and the insulation time is 12-36 hours.

4. The preparation method according to claim 1, characterized in that: In the step 3, the solid material is soaked in the solution including acid and DMF for 1-6 hours.

5. The preparation method according to claim 1, characterized in that: In the step 3, the DMF and methanol washing times are 3-6 times.

6. The preparation method according to claim 1, characterized in that: In step 3, the vacuum drying temperature is 50-80° C., and the drying time is 8-24 hours.

7. Functionalized UiO-66 prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the functionalized UiO-66 according to claim 7 for adsorption and separation of ammonia with a concentration of 1000ppm-1000000ppm at normal temperature and pressure.

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