Preparation method of qtz-[Zn (mIm) 2] crystal

Abstract

The invention relates to a preparation method of a qtz-[Zn (mIm) 2] crystal, which comprises the following steps: mixing a zinc salt and 2-methylimidazole in deionized water, stirring to react, centrifugally washing, drying in vacuum to obtain a white powdery ZIF-8 crystal, and sintering the white powdery ZIF-8 crystal by spark plasma to obtain the qtz-[Zn (mIm) 2] crystal. Compared with the prior art, the method has the advantages that the qtz-[Zn (mIm) 2] crystal can be directly prepared from the ZIF-8 crystal, the qtz-[Zn (mIm) 2] crystal does not need to be prepared from a derivative of the ZIF-8, the preparation steps can be effectively simplified, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the preparation of ZIF materials, and in particular to a controllable synthesis method of qtz-[Zn(mIm)2] crystals. Background Art

[0002] In recent years, metal organic frameworks (MOFs) have been regarded as one of the most important material categories due to their controllable design structure, good metal skeleton, ultrahigh adsorption capacity, specific surface area, high selectivity, and permanently functionalized pore structure. The MOF family has been continuously expanded through various combinations of metal clusters and ligands and various geometric arrangements, and new MOF structures are discovered every year. Zeolitic imidazolate framework (ZIF) is a subclass of MOF, containing metal cations (usually Zn) connected by imidazolate anions. 2+ ), due to its extremely high thermal and chemical stability, it has potential applications in gas separation, chemical sensing, drug delivery and catalysis. ZIF-8, [Zn(mIm)2], mIm = 2-methylimidazole (C4N2H5) - , with a sodalite (SOD) topological structure, is a typical ZIF that has been widely studied. ZIF-8 has high porosity, especially excellent thermal stability and chemical resistance. It can maintain its good crystallinity and porosity even after being placed in various solutions such as water, methanol, ethanol and DMF for a period of time. Therefore, it is used in gas adsorption and storage, catalysis, separation, sensing, drug delivery, wastewater treatment and other fields. However, these applications require specific chemical and physical properties, which depend on the crystal structure, microstructure and chemical composition of the material, so ZIF-8 needs to be finely regulated to achieve higher utilization. The main method at present is to control the properties of ZIF-8 by controlling the synthesis conditions of ZIF-8, such as using different zinc salts (zinc nitrate, zinc hydrochloride, etc.) and reaction solvents (dimethylformamide, methanol, ethanol, etc.), changing the ratio of zinc salt to mIm and solvent, and regulating the pH value of the precursor solution. Due to the excellent stability of ZIF-8, strict conditions are required to regulate the ZIF-8 structure after synthesizing the ZIF-8 crystal. For example, when a pressure greater than 1GPa is applied to ZIF-8, a high-pressure phase or an amorphous phase will be produced; when the heat treatment temperature of ZIF-8 is higher than 550°C or the thermal decomposition temperature, zinc oxide or metallic zinc crystal phase will be produced.

[0003] The structure of the new ZIF-8 polymorph with quartz topology (qtz), qtz-[Zn(mIm)2], has attracted wide attention in the fields of gas adsorption and storage. At present, this material can only be prepared by low-temperature heat treatment (about 282°C) of amorphous ZIF-8 in argon atmosphere, or by low-temperature heat treatment (about 300°C) of layered ZIF-L with the same structural units as ZIF-8 in air atmosphere. Both preparation methods are relatively cumbersome and cannot be prepared in one step through ZIF-8 crystals, which will involve ZIF-8 derivative materials. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for preparing a new ZIF-8 polymorphic structure qtz-[Zn(mIm)2] with a quartz topological structure (qtz), which can be directly prepared using ZIF-8, thereby simplifying the preparation process.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a qtz-[Zn(mIm)2] crystal, comprising the following steps:

[0007] Step 1: mixing zinc salt with deionized water to obtain a zinc salt aqueous solution;

[0008] Step 2: Mix 2-methylimidazole with deionized water to obtain a 2-methylimidazole aqueous solution;

[0009] Step 3: stirring and mixing the zinc salt aqueous solution obtained in step 1 and the 2-methylimidazole aqueous solution obtained in step 2 to form a mixed solution; then standing at room temperature and centrifuging and washing, collecting the product, and drying it in a vacuum drying oven to obtain a white powder, namely, ZIF-8 crystals;

[0010] Step 4: spark plasma sintering the white powder obtained in step 3 to obtain qtz-[Zn(mIm)2];

[0011] Furthermore, the zinc salt in step 1 is preferably zinc nitrate or a hydrate thereof;

[0012] Furthermore, the concentration of the zinc salt aqueous solution in step 1 is preferably 0.25 to 0.35 mmol / ml;

[0013] Furthermore, the concentration of the 2-methylimidazole aqueous solution in step 2 is preferably 1.11 to 3.89 mmol / ml;

[0014] Furthermore, the volume ratio of the zinc salt aqueous solution to the 2-methylimidazole aqueous solution in step 3 is 1:9;

[0015] Furthermore, the stirring speed in step 3 is preferably 300-500 rpm;

[0016] Furthermore, the stirring time in step 3 is preferably 30 to 60 minutes;

[0017] Furthermore, the standing time in step 3 is preferably 12 to 36 hours.

[0018] Furthermore, the centrifugal speed in step 3 is 5000-10000 rpm;

[0019] Furthermore, the centrifugation time in step 3 is 3 to 10 minutes;

[0020] Furthermore, the washing solution in step 3 is preferably a methanol solution with a purity of ≥ 99.5%;

[0021] Furthermore, the drying temperature in step 3 is preferably 40-60°C;

[0022] Furthermore, the drying time in step 3 is preferably 12 to 24 hours;

[0023] Furthermore, the heating rate of the spark plasma sintering in step 4 is preferably 40-80° C. / min.

[0024] Furthermore, the sintering temperature of the spark plasma sintering in step 4 is preferably 260-300° C.;

[0025] Furthermore, the sintering pressure of the spark plasma sintering in step 4 is preferably 50-100 MPa;

[0026] Furthermore, the sintering temperature holding time of the spark plasma sintering in step 4 is preferably 1 to 10 minutes.

[0027] The beneficial effects of the present invention are at least:

[0028] Compared with the prior art, the present invention successfully realizes the preparation of qtz-[Zn(mIm)2] crystal material through an extremely simple method. The method uses ZIF-8 crystal to directly prepare qtz-[Zn(mIm)2] without the need for amorphization treatment, and the process is simple and controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a process flow chart for preparing a qtz-[Zn(mIm)2] crystal;

[0030] Figure 2 The X-ray diffraction pattern of the product qtz-[Zn(mIm)2] crystalline phase prepared in Example 1;

[0031] Figure 3 The X-ray diffraction pattern of the product qtz-[Zn(mIm)2] crystalline phase prepared in Example 2;

[0032] Figure 4 The X-ray diffraction pattern of the product qtz-[Zn(mIm)2] crystalline phase prepared in Example 3;

[0033] Figure 5 The X-ray diffraction pattern of the product qtz-[Zn(mIm)2] crystalline phase prepared in Example 4; DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further illustrated by the following embodiments.

[0035] Example 1

[0036] Dissolve 0.744g (2.5mmol) of zinc nitrate hexahydrate in 10ml of deionized water and stir until clear to obtain solution A. Dissolve 16.4g (0.2mol) of mL in 90ml of deionized water and stir until clear to obtain solution B. Slowly pour solution A into solution B and stir at 450rmp for 30 minutes to obtain a suspension, which is then allowed to stand at room temperature for 24 hours to promote crystal growth and precipitation. Centrifuge the synthesized suspension at 10,000rpm for 5 minutes and wash with methanol. Repeat the centrifugal washing operation twice. Place the washed precipitate in a vacuum drying oven at 40°C and dry for 24 hours to obtain white powdery ZIF-8 crystals.

[0037] Weigh 0.2g ZIF-8 powder, put it into a graphite mold, and then place it in a spark plasma sintering furnace, set the initial pressure to 100MPa, and keep the pressure for 5 minutes. Raise the temperature to 280℃ at a rate of 80℃ / min, keep the temperature and pressure for 5 minutes, then reduce the pressure to 50MPa, and then cool it to room temperature with water at a rate of 10℃ / min, take out the sample, and obtain qtz-[Zn(mIm)2].

[0038] Figure 2 This is the XRD diagram of the product, and the product is qtz-[Zn(mIm)2] crystal phase.

[0039] Example 2

[0040] Dissolve 0.744g (2.5mmol) of zinc nitrate hexahydrate in 10ml of deionized water and stir until clear to obtain solution A. Dissolve 8.2g (0.1mol) of mL in 90ml of deionized water and stir until clear to obtain solution B. Slowly pour solution A into solution B, stir at 300rmp for 60 minutes to obtain a suspension, and then stand at room temperature for 12 hours to promote crystal growth and precipitation. Centrifuge the synthesized suspension at 5000rpm for 10 minutes, wash with methanol, repeat the centrifugal washing operation 2 times, and dry the washed precipitate in a vacuum drying oven at 60°C for 12 hours to obtain white powdery ZIF-8 crystals.

[0041] Weigh 0.2g ZIF-8 powder and put it into a graphite mold, then place it in a spark plasma sintering furnace, set the initial pressure to 100MPa, maintain the pressure for 5min, increase the temperature to 300℃ at a rate of 80℃ / min and maintain the pressure for 2min, then reduce the pressure to 50MPa, and then cool it to room temperature with water at a rate of 10℃ / min, take out the sample, and obtain qtz-[Zn(mIm)2].

[0042] Figure 3 This is the XRD diagram of the product, and the product is qtz-[Zn(mIm)2] crystal phase.

[0043] Example 3

[0044] Dissolve 0.892g (3mmol) of zinc nitrate hexahydrate in 10ml of deionized water and stir until clear to obtain solution A. Dissolve 14.76g (0.18mol) of mLm in 90ml of deionized water and stir until clear to obtain solution B. Slowly pour solution A into solution B, stir at 500rmp for 50 minutes to obtain a suspension, and then stand at room temperature for 18 hours to promote crystal growth and precipitation. Centrifuge the synthesized suspension at 8000rpm for 8 minutes, wash with methanol, repeat the centrifugal washing operation 2 times, and dry the washed precipitate in a vacuum drying oven at 50°C for 18 hours to obtain white powdery ZIF-8 crystals.

[0045] Weigh 0.2g ZIF-8 powder and put it into a graphite mold, then place it in a spark plasma sintering furnace, set the initial pressure to 100MPa, maintain the pressure for 5min, increase the temperature to 260℃ at a rate of 60℃ / min and maintain the pressure for 10min, then reduce the pressure to 50MPa, and then cool it to room temperature with water cooling at a rate of 10℃ / min, take out the sample, and obtain the product qtz-[Zn(mIm)2].

[0046] Figure 4 This is the XRD diagram of the product, and the product is qtz-[Zn(mIm)2] crystal phase.

[0047] Example 4

[0048] Dissolve 1.041g (3.5mmol) of zinc nitrate hexahydrate in 10ml of deionized water and stir until clear to obtain solution A. Dissolve 28.7g (0.35mol) of mLm in 90ml of deionized water and stir until clear to obtain solution B. Slowly pour solution A into solution B, stir at 400rmp for 40 minutes to obtain a suspension, and then stand at room temperature for 36 hours to promote crystal growth and precipitation. Centrifuge the synthesized suspension at 1000rpm for 10 minutes, wash with methanol, repeat the centrifugal washing operation 2 times, and dry the washed precipitate in a vacuum drying oven at 40°C for 24 hours to obtain white powdery ZIF-8 crystals.

[0049] Weigh 0.2g ZIF-8 powder and put it into a graphite mold, then place it in a spark plasma sintering furnace, set the initial pressure to 100MPa, maintain the pressure for 5min, increase the temperature to 300℃ at a rate of 40℃ / min and maintain the pressure for 1min, then reduce the pressure to 50MPa, and then cool it to room temperature with water at a rate of 10℃ / min, take out the sample, and obtain the product qtz-[Zn(mIm)2].

[0050] Figure 5 This is the XRD diagram of the product, and the product is qtz-[Zn(mIm)2] crystal phase.

[0051] The above-described embodiments are only some of the preferred solutions of the present invention, but they are not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing qtz-[Zn(mIm)2] crystal, characterized in that: The following steps are involved: Step 1: mixing zinc salt with deionized water to obtain a zinc salt aqueous solution; Step 2: Mix 2-methylimidazole with deionized water to obtain a 2-methylimidazole aqueous solution; Step 3: stirring and mixing the zinc salt aqueous solution obtained in step 1 and the 2-methylimidazole aqueous solution obtained in step 2 to form a mixed solution; then standing at room temperature and centrifuging and washing, collecting the product, and drying it in a vacuum drying oven to obtain a white powder, namely, ZIF-8 crystals; Step 4: The white powder obtained in step 3 is subjected to spark plasma sintering to obtain a blocky brown product, namely qtz-[Zn(mIm)2] crystals.

2. The method for preparing the qtz-[Zn(mIm)2] crystal according to claim 1, characterized in that: The zinc salt in step 1 is zinc nitrate; the concentration of the zinc salt aqueous solution is 0.25-0.35 mmol / ml.

3. The method for preparing the qtz-[Zn(mIm)2] crystal according to claim 1, characterized in that: The concentration of the 2-methylimidazole aqueous solution in step 2 is 1.11-3.89 mmol / ml.

4. The method for preparing the qtz-[Zn(mIm)2] crystal according to claim 1, characterized in that: In step 3, the ratio of the zinc salt aqueous solution to the 2-methylimidazole aqueous solution is 1:9, the stirring speed is 300-500 rpm, the stirring time is 30-60 minutes, and the standing time is 12-36 hours.

5. The method for preparing the qtz-[Zn(mIm)2] crystal according to claim 1, characterized in that: During the centrifugation process in step 3, the centrifugal speed is 5000-10000 rpm, and the centrifugal time is 3-10 minutes.

6. The method for preparing a novel qtz-[Zn(mIm)2] crystal according to claim 1, characterized in that: In the washing process described in step 3, the washing solution is a methanol solution with a purity of ≥99.5%.

7. The method for preparing the novel qtz-[Zn(mIm)2] crystal according to claim 1, characterized in that: In the drying process described in step 3, the drying temperature is 40 to 60° C. and the drying time is 12 to 24 hours.

8. The method for preparing the novel qtz-[Zn(mIm)2] crystal according to claim 1, characterized in that: In the spark plasma sintering process in step 4, the heating rate is 40-80°C / min, the applied pressure is 50-100 MPa, the sintering temperature is 260-300°C, and the sintering temperature holding time is 1-5 minutes.

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