Chromium-based MOFs material Cr-bpdc-tph and preparation method and application thereof

Abstract

The invention discloses a chromium-based MOFs material Cr-bpdc-tph as well as a preparation method and application of the chromium-based MOFs material Cr-bpdc-tph. The preparation method comprises the following steps: (1) simply mixing reaction raw materials, and synthesizing a segmented ligand tph by using a high-temperature solid-phase method; (2) purifying tph through hydrochloric acid dissolution, acetone precipitation and suction filtration; (3) fully mixing a metal source, an organic ligand, an acid regulator and the pyridine-water solution, putting the mixture into a reaction kettle, and reacting at high temperature; and (4) after the reaction is finished, naturally cooling to room temperature, washing with a solvent, centrifuging and drying to obtain the MOFs material Cr-bpdc-tph. The chromium-based MOFs material Cr-bpdc-tph synthesized by the method disclosed by the invention is uniform in size and good in crystallinity, and has ultrahigh thermal stability and chemical stability. Cr-bpdc-tph shows excellent performance on water vapor adsorption and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of water adsorbent preparation, and specifically relates to a chromium-based MOFs material Cr-bpdc-tph and a preparation method and application thereof. Background Art

[0002] Water adsorbents have broad applications in indoor humidity control, water collection, gas drying, and cyclic cooling / heating. Traditional water adsorbents, such as silica gel and zeolite, face their own problems. For example, silica gel has poor water vapor adsorption capacity under dry conditions and is only suitable for water vapor adsorption in high humidity environments, while zeolite has an extremely high regeneration temperature (about 250°C) and consumes huge energy. These problems limit the practical application of traditional water adsorbents.

[0003] Metal organic framework (MOFs) materials have ultra-high specific surface area and porosity, adjustable pore size, multi-element structure, low regeneration temperature and high water vapor adsorption capacity, showing great application prospects in the field of water adsorption. Usually, MOFs materials have poor hydrolysis stability and chemical stability, which makes it difficult to meet the practical application under harsh conditions. Therefore, it is of great practical significance to develop a new water adsorbent with high water vapor adsorption capacity, low regeneration temperature and excellent stability. Summary of the invention

[0004] In view of the problems that traditional water adsorbents have a small adsorption capacity in a dry environment and that MOFs materials have insufficient stability, the purpose of the present invention is to provide a chromium-based MOFs material Cr-bpdc-tph and a preparation method and application thereof. The chromium-based MOFs material Cr-bpdc-tph has excellent stability, high stability, and a large water vapor adsorption capacity, can be widely used in water adsorption, and has good application prospects.

[0005] In order to solve the problems of the prior art, the technical solution adopted by the present invention is:

[0006] A method for preparing a chromium-based MOFs material Cr-bpdc-tph comprises the following steps:

[0007] Step 1, taking 4-pyridinecarboxamidine hydrochloride and sodium tricyanomethanide in a mass ratio of 6:1, placing in a reaction kettle lined with polytetrafluoroethylene, heating and reacting for 14-20 hours to obtain a brown solid product;

[0008] Step 2, using 5-15wt% hydrochloric acid to fully dissolve the brown solid product, and filtering to remove unreacted solids and impurities to obtain a brown clear liquid, then adding acetone to precipitate a brown precipitate, filtering to collect to obtain a brown product; repeating the dissolution and precipitation operations 2-3 times to obtain a brown product tph;

[0009] Step 3: Chromium nitrate nonahydrate, 4,4-diphenyl dicarboxylic acid, and tph are mixed in a mass ratio of 1:1.25:1.5, added to a mixed solution of pyridine and water, and then hydrofluoric acid is added. After high-temperature reaction, the obtained gray powder is washed with N, N-dimethylformamide and ethanol three times respectively, centrifuged to remove the supernatant, and dried to obtain a chromium-based MOF. s Material Cr-bpdc-tph, wherein the volume fraction of pyridine in the mixed solution of pyridine and water is not less than 20%, and the volume ratio of hydrofluoric acid to water in the mixed solution is not more than 1:15.

[0010] As an improvement, in step 1, the mass of 4-pyridinecarboximidamide hydrochloride is 4.5 g, the mass of sodium tricyanomethanide is 0.75 g, the heating time is 16 hours, and the heating temperature is 200°C.

[0011] As an improvement, the concentration of hydrochloric acid in step 2 is 10 wt %.

[0012] As an improvement, in step 3, the amount of chromium nitrate nonahydrate used is 0.2 g, the amount of 4,4-diphenyldicarboxylic acid used is 0.1513 g, the amount of TPH used is 0.14 g, the pyridine is 3 ml, the water is 2 ml, and the hydrofluoric acid is 100 μl.

[0013] As an improvement, in step 3, the amount of N,N-dimethylformamide used each time is 30-50 ml, the washing time is 20 minutes for the first and second times, and 12 hours for the third time; the amount of ethanol used each time is 30-50 ml, the washing time is 20 minutes each time, and the drying temperature is 60°C.

[0014] The chromium-based MOFs material Cr-bpdc-tph prepared by the above preparation method has the structural formula (Cr 3 O)(bpdc) 3 (tph), the specific structure is each Cr 3 The O trimer connects six carboxylic acid ligands bpdc and three nitrogen-containing ligands tph to form a regular spindle-shaped MOFs material with a particle size of 1-2μm. 3+ The extremely low hydrolysis rate ensures that Cr-bpdc-tph has excellent acid-base stability.

[0015] The application of the chromium-based MOFs material Cr-bpdc-tph prepared by the above preparation method in water adsorption.

[0016] As an improvement, the application includes pre-treating the chromium-based MOFs material Cr-bpdc-tph by ethanol activation.

[0017] Beneficial effects:

[0018] Compared with the prior art, the present invention provides a chromium-based MOFs material Cr-bpdc-tph and a preparation method and application thereof. The preparation method is simple, and the chromium-based MOFs material Cr-bpdc-tph shows ultra-high chemical stability, can remain stable in solutions with pH values ​​of 1 and 14, and has excellent thermal stability. At room temperature of 25°C, Cr-bpdc-tph has a large water vapor adsorption capacity of 1.02 grams of water per gram of adsorbent, and the adsorption heat of Cr-bpdc-tph is 44.5 kJ / mol. The lower adsorption heat reduces the energy consumption of regeneration, making it have obvious advantages in terms of recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of the segmented ligand tph of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 1 of the present invention;

[0020] Figure 2 This is a schematic structural diagram of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention;

[0021] Figure 3 This is a scanning electron microscope image of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention;

[0022] Figure 4 The three-dimensional electron rotation diffraction pattern of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention;

[0023] Figure 5 The PXRD spectrum of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention;

[0024] Figure 6 Thermogravimetric curve of Cr-bpdc-tph, a chromium-based MOFs material prepared in Example 2 of the present invention;

[0025] Figure 7 The PXRD spectrum of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention after being immersed in a 1 mol / L HCl aqueous solution and a 1 mol / L NaOH solution for two days;

[0026] Figure 8 This is a graph of nitrogen adsorption measured after the chromium-based MOF material Cr-bpdc-tph prepared in Example 2 of the present invention was immersed in a 1 mol / L HCl aqueous solution and a 1 mol / L NaOH solution for two days respectively.

[0027] Fig. 9This is a water adsorption diagram of the chromium-based MOF material Cr-bpdc-tph prepared in Example 2 of the present invention;

[0028] Fig.10 This is the water adsorption cycle diagram of the chromium-based MOF material Cr-bpdc-tph prepared in Example 2 of the present invention.

[0029] Fig.11 This is the adsorption heat curve of the chromium-based MOF material Cr-bpdc-tph prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The following examples will enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0031] Example 1 Preparation of the splitting ligand tph

[0032] Weigh 4.5g of 4-pyridine carboxamidine hydrochloride and 0.75g of sodium tricyanomethanide, stir and mix, put into a metal reactor, heat to 200°C in a blast oven, and keep warm for 16 hours. Take out after natural cooling, fully dissolve and filter with 120ml of 10%wt hydrochloric acid solution to remove reaction impurities. Add 50-100ml of acetone to the supernatant until the brown precipitate no longer precipitates, and filter to obtain a crude product of brown precipitate TPH. Dissolve the crude product of TPH with 10%wt hydrochloric acid solution, filter to remove impurities, add 120ml of acetone to the supernatant until the brown precipitate no longer precipitates, filter again to obtain a higher purity TPH, and place it in an oven at 60°C to dry for 12 hours.

[0033] Figure 1 This is a schematic diagram of the structure of the split ligand tph in the chromium-based MOF material Cr-bpdc-tph. The gray balls in this structure are carbon atoms, and the blue balls are nitrogen atoms. It is a tridentate nitrogen-containing organic ligand.

[0034] Example 2 Preparation of stable chromium-based MOF material Cr-bpdc-tph

[0035] 0.2 g of chromium nitrate nonahydrate, 0.1513 g of 4,4-biphenyldicarboxylic acid, 0.14 g of tph prepared in Example 1, 3 ml of pyridine, 2 ml of water, and 100 μl of hydrofluoric acid were added to the reactor, stirred with a magnetic stirrer for 1 hour to fully mix, and then placed in a 220°C blast oven for heating reaction for 16 hours. After natural cooling, the product was washed and filtered three times with DMF and ethanol respectively, and then dried in an oven at 60°C for 12 hours to obtain a chromium-based MOFs material Cr-bpdc-tph, wherein the amount of N,N-dimethylformamide used each time was 30 ml, and the washing time was 20 minutes for the first and second times and 12 hours for the third time; the amount of ethanol used each time was 30 ml, and the washing time was 20 minutes each time.

[0036] Figure 2 This is a schematic structural diagram of the chromium-based MOF material Cr-bpdc-tph prepared in Example 2 of the present invention.

[0037] Figure 3 This is a scanning electron microscope image of the chromium-based MOFs material Cr-bpdc-tph. From the image, it can be seen that the chromium-based MOFs material Cr-bpdc-tph presents a regular spindle shape with a size of about 1-2μm.

[0038] Figure 4 This is the three-dimensional electron rotation diffraction pattern of the chromium-based MOFs material Cr-bpdc-tph.

[0039] Figure 5 This is the PXRD spectrum of chromium-based MOFs material Cr-bpdc-tph.

[0040] Example 3 Stability test of chromium-based MOFs material Cr-bpdc-tph

[0041] Thermal stability test: 4 mg of chromium-based MOFs material Cr-bpdc-tph was taken for thermal stability test in a nitrogen atmosphere on a thermogravimeter at a test temperature of 50-800°C.

[0042] Chemical stability test: 120 mg of chromium-based MOFs material Cr-bpdc-tph was taken and soaked in 1 mol / L HCl aqueous solution and 1 mol / L NaOH aqueous solution for 2 days. After centrifugal filtration, it was exchanged with 30 ml ethanol for 3 days. The ethanol solvent was changed every day, filtered and dried, and then X-ray powder diffraction test and 77K nitrogen adsorption test were performed.

[0043] Figure 6 This is the thermogravimetric curve of the chromium-based MOFs material Cr-bpdc-tph. The sample hardly decomposes before 400°C, showing excellent thermal stability.

[0044] Figure 7 This is the PXRD spectrum of the chromium-based MOFs material Cr-bpdc-tph after being immersed in 1 mol / L HCl aqueous solution and 1 mol / L NaOH solution for two days. The peak shape remains unchanged, proving that Cr-bpdc-tph has good stability.

[0045] Figure 8 The nitrogen adsorption curves of the chromium-based MOFs material Cr-bpdc-tph measured after being immersed in 1 mol / L HCl aqueous solution and 1 mol / L NaOH solution for two days respectively indicate that Cr-bpdc-tph has ultra-high chemical stability.

[0046] Example 4 Water adsorption test of chromium-based MOFs material Cr-bpdc-tph

[0047] Take 100 mg of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2, soak it in ethanol for 3 days for pretreatment, change the ethanol every day, and then heat and degas at 120°C for 10 hours. Then, the sample is subjected to a water vapor adsorption test on a fully automatic four-station vapor adsorption instrument connected to an external constant temperature circulating water bath.

[0048] Water adsorption cycle test: The tested Cr-bpdc-tph was reheated and degassed at 120℃ for 3 hours to remove the water that was not completely desorbed, and then the water adsorption test was performed again. The pressure range taken was P / P 0 =0.2-0.9, repeat 10 times.

[0049] Fig. 9 This is the water adsorption diagram of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention, and its adsorption amount is as high as 1.02 g / g.

[0050] Fig.10 This is the water adsorption cycle diagram of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention. After 10 cycles, the chromium-based MOF material Cr-bpdc-tph shows excellent cycle stability.

[0051] Fig.11 This is the adsorption heat curve of the chromium-based MOFs material Cr-bpdc-tph prepared in Example 2 of the present invention, which is about 44.5 kJ mol -1 .

[0052] In summary, the present invention firstly adopts a high-temperature solid-phase method to prepare the segmented ligand tph, and then uses a hydrothermal synthesis method to prepare the chromium-based MOFs material Cr-bpdc-tph. The successful preparation of the material was proved by scanning electron microscopy, three-dimensional electron rotation diffraction, and x-ray powder diffraction. Thermogravimetric analysis and nitrogen adsorption test after acid and alkali solution treatment further showed that the chromium-based MOFs material Cr-bpdc-tph has excellent thermal stability and chemical stability. Finally, through the water vapor adsorption test, Cr-bpdc-tph showed 1.02g at 25°C. -1 The adsorption heat of Cr-bpdc-tph is 44.5 kJ / mol, which shows obvious advantages in recycling and has good application prospects.

Claims

1. A method for preparing a chromium-based MOFs material Cr-bpdc-tph, characterized in that: The following steps are involved: Step 1, taking 4-pyridinecarboxamidine hydrochloride and sodium tricyanomethanide in a mass ratio of 6:1, placing in a reaction kettle lined with polytetrafluoroethylene, heating and reacting for 14-20 hours to obtain a brown solid product; Step 2, using 5-15 wt % hydrochloric acid to fully dissolve the brown solid product, and filtering to remove unreacted solids and impurities to obtain a brown clear liquid, then adding acetone to precipitate a brown precipitate, filtering to collect and obtain a brown product; Repeat the dissolution and precipitation operations 2-3 times to obtain a brown product tph; Step 3, mixing chromium nitrate nonahydrate, 4,4-biphenyldicarboxylic acid, and tph in a mass ratio of 1:1.25:1.5, adding to a mixed solution of pyridine and water, and then adding hydrofluoric acid, after high-temperature reaction, washing the obtained gray powder with N, N-dimethylformamide and ethanol three times respectively, centrifuging to remove the supernatant, and drying to obtain a chromium-based MOFs material Cr-bpdc-tph, wherein the volume fraction of pyridine in the mixed solution of pyridine and water is not less than 20%, and the volume ratio of hydrofluoric acid to water in the mixed solution is not more than 1:

15.

2. The method for preparing a chromium-based MOFs material Cr-bpdc-tph according to claim 1, characterized in that: In step 1, the mass of 4-pyridinecarboxamidine hydrochloride is 4.5 g, the mass of sodium tricyanomethanide is 0.75 g, the heating time is 16 hours, and the heating temperature is 200°C.

3. The method for preparing a chromium-based MOFs material Cr-bpdc-tph according to claim 1, characterized in that: The concentration of hydrochloric acid in step 2 is 10wt%.

4. The method for preparing a chromium-based MOFs material Cr-bpdc-tph according to claim 1, characterized in that: In step 3, the amount of chromium nitrate nonahydrate used is 0.2 g, the amount of 4,4-diphenyldicarboxylic acid used is 0.1513 g, the amount of TPH used is 0.14 g, the amount of pyridine is 3 ml, the amount of water is 2 ml, and the amount of hydrofluoric acid is 100 μl.

5. The method for preparing a chromium-based MOFs material Cr-bpdc-tph according to claim 1, characterized in that: In step 3, the amount of N,N-dimethylformamide used each time is 30-50 ml, the washing time is 20 minutes for the first and second times, and 12 hours for the third time; the amount of ethanol used each time is 30-50 ml, the washing time is 20 minutes each time, and the drying temperature is 60°C.

6. The chromium-based MOFs material Cr-bpdc-tph prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The structural formula of the chromium-based MOFs material Cr-bpdc-tph is (Cr3O)(bpdc)3(tph), and the specific structure is that each Cr3O trimer connects six carboxylic acid ligands bpdc and three nitrogen-containing ligands tph to finally form a regular spindle-shaped MOFs material with a particle size of 1-2 μm.

7. Application of the chromium-based MOFs material Cr-bpdc-tph prepared by the preparation method according to claim 1 in water adsorption.

8. The use according to claim 7, characterized in that: The chromium-based MOFs material Cr-bpdc-tph was immersed in ethanol for activation pretreatment.

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