CN108976433B - Method for preparing metal organic framework nanosheet by liquid phase stripping method - Google Patents
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Abstract
The invention discloses a method for preparing Metal Organic Framework (MOF) nanosheets by a liquid phase stripping method, which comprises the following steps: (1) zeolitic imidazolate frameworks ZIF-7 via hydrothermal conversionLayered MOF precursor Zn2(bim)4(ii) a (2) Dispersing the layered precursor into a mixed solvent of ionic liquid and deionized water, carrying out ultrasonic treatment for a period of time, and centrifuging the obtained dispersion liquid at low speed to remove the non-stripped Zn after the ultrasonic treatment is finished2(bim)4The upper layer solution is MOF nanosheet dispersion; (3) and centrifuging the obtained nanosheet dispersion at a high speed, washing with ethanol for several times, and finally drying in vacuum to obtain the MOF nanosheet. The method is simple, short in time consumption and high in stripping efficiency, and the prepared MOF nanosheet has a large transverse area, high crystallinity and a relatively complete structure.
Description
Technical Field
The invention relates to a method for preparing metal organic framework Zn by a liquid phase stripping method2(bim)4A method of a nano-sheet belongs to the technical field of preparation of a two-dimensional Metal Organic Framework (MOF) nano-sheet.
Background
Metal Organic Framework (MOF) materials are crystalline porous coordination polymers formed by the ordered assembly of metal ion or ion cluster nodes with organic ligands. Two-dimensional (2D) nanomaterials with atomic or molecular thickness have unique dimension-related properties that make them of great interest. The 2D MOF nano material not only keeps the crystalline porous framework structure of the MOF material, but also keeps the thickness of the MOF material at the atomic level, and is a novel graphene-like material. Compared with the traditional layered MOF crystal, the 2D MOF nanosheet has the advantages of larger specific surface area, more active sites, smaller mass transfer resistance, higher diffusion rate and the like, and has wide application prospects in the fields of catalysis, photoelectric conversion devices, sensing, membrane separation and the like. Compared with graphene and other graphene-like materials, the 2D MOF nanosheet has a variable metal center and organic ligands, has a designable structure, and is easy to functionalize. However, the preparation method is limited, because the connection mode of the metal-ligand in the MOF assembly process is a coordination bond, compared with a covalent bond, the coordination bond has lower energy, the coordination reaction is extremely sensitive to the preparation conditions and is easily influenced by various experimental parameters of a reaction system, so that the preparation method of the graphene is not suitable for the preparation of the 2D MOF material.
The 2D MOF nano-sheet is mainly prepared by two ways of a top-down peeling method and a bottom-up assembling method. Most of the currently reported 2D MOF nanosheets are prepared by a peeling method, such as Top-down fabrication of crystalline Metal-organic framework nanosheets (Chemical Communications,47(29),8436-8438) and Metal-organic framework nanosheets as building blocks for molecular sizing membranes (Science,346(6215),1356-1359), but the above methods generally have the problems of irregular 2D MOF nanosheet structure, irregular framework structure, collapsed crystal structure damage, low yield (generally < 15%), unstable dispersion and the like.
Disclosure of Invention
The invention aims to provide a method for preparing Metal Organic Framework (MOF) nanosheets by a liquid phase stripping method, which can greatly shorten the ultrasonic time and improve the stripping efficiency, and can obtain nanosheets with large transverse area, high crystallinity and relatively complete structures.
In order to solve the technical problems, the invention adopts the following technical scheme: a method for preparing MOF nanosheets by a liquid phase stripping method comprises the following steps:
(1) synthesis of layered MOF precursor Zn by hydrothermal conversion of known zeolitic imidazolate frameworks (ZIF-7)2(bim)4(bim ═ benzimidazole);
(2) the precursor Zn obtained in the step (1) is2(bim)4Dispersing in aqueous solution containing ionic liquid, ultrasonic treating, and centrifuging at low speed to remove non-peeled precursor Zn2(bim)4The upper layer solution is MOF nanosheet dispersion;
(3) and (3) centrifuging the MOF nanosheet dispersion liquid obtained in the step (2) at a high speed, washing with ethanol for a plurality of times, and drying in vacuum to obtain the MOF nanosheet.
In the step (1) of the preparation method, the zeolite imidazolate framework (ZIF-7) and Zn2(bim)4Can be obtained commercially or synthesized according to known literature. For example, an inorganic salt containing zinc ions is mixed with benzeneDissolving imidazole in DMF according to a certain molar ratio, magnetically stirring for 1-24h, standing at room temperature for 24-72h, centrifugally separating the product, washing with methanol and deionized water for three times respectively, and drying the product in a vacuum drying oven at 60 ℃ for 48h to obtain a zeolitic imidazolate framework ZIF-7; dispersing the obtained ZIF-7 in deionized water, refluxing at 80-100 ℃ for 24-72h, performing centrifugal separation, washing the deionized water and methanol for three times respectively, and performing vacuum drying overnight to obtain layered MOF precursor Zn2(bim)4(ii) a The inorganic salt containing zinc ions is one of zinc chloride, zinc nitrate, zinc acetate and the like; the molar ratio of the inorganic salt containing zinc ions to the benzimidazole is 1: 1-1: 20.
in the above-mentioned production method, in step (2), precursor Zn is added2(bim)4Dispersing into the aqueous solution of the ionic liquid, and dispersing the precursor Zn in the aqueous solution2(bim)4The concentration of the ionic liquid is 1-10mg/m L, the suspension is subjected to ultrasonic treatment, the ultrasonic power is 100-400W, the ultrasonic time is 10-360min, then the suspension is centrifuged for 2-10min under the condition of 2000-5000rpm, and the obtained upper turbid dispersion liquid is MOF nanosheet dispersion liquid, the ionic liquid is one of 1-butyl-3-methylimidazole tetrafluoroborate, 1-octyl-3-methylimidazole chloride, 1-ethyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide, 1-butyl-3-methylimidazole hexafluorophosphate and the like, the water is water commonly used in the field, preferably deionized water, and the mass ratio of the ionic liquid to the water is 1: 9-9: 1.
In the step (3) of the preparation method, the nanosheet dispersion obtained in the step (2) is subjected to high-speed centrifugation at 10000-15000rpm for 5-20min, then the centrifugate is washed with ethanol for several times to remove ionic liquid, and vacuum drying is carried out at 60-100 ℃ to obtain the MOF nanosheet.
The method for preparing the metal organic framework nanosheet by adopting the liquid phase stripping method has the following beneficial effects:
1. the method does not use a volatile organic solvent, and is a green method for preparing the MOF nanosheet.
2. The method has high stripping efficiency, and can obtain nanosheets with large transverse area, high crystallinity and relatively complete structures.
3. The method shortens the ultrasonic time in the dispersion process.
Drawings
FIG. 1 is a layered MOF precursor Zn2(bim)4Scanning electron micrograph (c).
FIG. 2 shows Zn after exfoliation2(bim)4Transmission electron microscopy of nanoplatelets.
FIG. 3Zn2(bim)4XRD patterns before and after peeling.
FIG. 4Zn2(bim)4Graph of thermal weight loss before and after peeling.
FIG. 5 Zn in comparative example2(bim)4Transmission electron micrograph after stripping.
FIG. 6 Zn in comparative example2(bim)4Graph of thermal weight loss before and after peeling.
Detailed Description
The invention is further described with reference to the following figures and specific examples, which are not intended to be limiting.
Example 1:
0.01mol of Zn (NO)3)2·6H2Dissolving O and 0.1mol of benzimidazole in 1000m L DMF, magnetically stirring for 1h, standing the solution at room temperature for 24h, centrifuging, washing with methanol and deionized water for three times respectively, drying in a vacuum drying oven at 80 ℃ for 24h to obtain ZIF-7, dispersing the obtained ZIF-7 solid into 500ml of deionized water, refluxing at 80 ℃ for 48h, centrifuging, washing with deionized water and methanol for three times respectively, and drying at 50 ℃ overnight to obtain a layered MOF precursor Zn2(bim)4The scanning electron micrograph is shown in FIG. 1; precursor Zn2(bim)4(mass m)0) The mass ratio of the 1-octyl-3-methylimidazole chloride salt dispersed in the ionic liquid to the deionized water is 1: 1, precursor Zn in dispersion2(bim)4The concentration of the nano-film is 1mg/m L, ultrasonic treatment is carried out by an ultrasonic cell crusher, the ultrasonic power is 150W, the ultrasonic time is 120min, the centrifugal separation is carried out at the rotating speed of 3000rpm for 20min, the obtained liquid is the dispersion liquid of the MOF nano-film, the nano-film dispersion liquid is centrifuged at the high speed of 15000rpm, and then the washing is carried out for 3 times by 95 percent ethanol, 6 timesVacuum drying at 0 ℃ to obtain MOF nanosheets, and weighing the obtained MOF nanosheets to obtain m1Stripping efficiency is m1/m0The transmission electron micrograph thereof is shown in fig. 2, which is 60%. As can be seen from FIG. 2, the MOF nanosheets obtained by the method of the present invention are successfully exfoliated, and have a large lateral area. XRD before and after exfoliation is shown in figure 3, indicating that the method of the invention is able to maintain the crystalline structure of MOFs. The thermogravimetric curves before and after stripping are shown in fig. 4, which shows that the method of the invention can maintain the relative integrity of the MOF structure and has little influence on the stability of the material.
Comparative example 1 was 0.025gZn2(bim)4Dispersing into 100ml of mixed solvent of methanol and n-propanol (volume ratio is 1: 1), placing in a ball mill, mechanically grinding at the speed of 60rpm for 1h, diluting the mixture by 2.5 times, and performing water bath ultrasound for 30 min. Standing the obtained suspension for one week, wherein the material dispersed in the solvent is Zn2(bim)4The stripping efficiency of the nano-sheet is 15%, an electron micrograph after stripping is shown in figure 5, and the transverse area is obviously smaller than that obtained by the method. Fig. 6 is a graph of the thermal weight loss before and after peeling of the comparative example, showing that the structural integrity of the peeled material is destroyed and the stability is significantly reduced.
Example 2:
0.01mol of Zn (NO)3)2·6H2Dissolving O and 0.15mol of benzimidazole in 1000m L DMF, magnetically stirring for 1h, standing the solution at room temperature for 48h, washing and drying the solution in the same way as in example 1 to obtain ZIF-7, dispersing the obtained ZIF-7 solid in 500ml of deionized water, refluxing at 100 ℃ for 24h, and centrifugally washing and drying the solution to obtain a layered MOF precursor Zn2(bim)4(ii) a By reacting a layered precursor Zn2(bim)4Dispersing the obtained product into a solution with the mass ratio of ionic liquid 1-octyl-3-methylimidazole chloride salt to deionized water being 3: 2, wherein the concentration of the layered MOF in the dispersion liquid is 2mg/m L, the 400w ultrasonic time is 60min, and the rest of the experimental processes are the same as those in example 1, so that an MOF nanosheet is obtained, and the stripping efficiency is 55%.
Example 3:
0.01mol of Zn (NO)3)2·6H2Dissolving O and 0.2mol benzimidazole in 1000m L DMF, magnetically stirring for 1h, and mixing the solutionThe solution was allowed to stand at room temperature for 72 hours, and washed and dried as in example 1 to obtain ZIF-7. Dispersing the obtained ZIF-7 solid into 500ml of deionized water, refluxing for 48h at 100 ℃, and centrifugally washing and drying to obtain layered MOF precursor Zn2(bim)4(ii) a By reacting a layered precursor Zn2(bim)4Dispersing the obtained product into a solution of ionic liquid 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt and deionized water in a mass ratio of 7: 3, wherein the concentration of the layered MOF in the dispersion liquid is 3mg/m L, carrying out ultrasonic treatment by using an ultrasonic cell crusher, the ultrasonic power is 300W, the ultrasonic time is 180min, and the rest of the experimental processes are the same as those in example 1, so that an MOF nanosheet is obtained, and the stripping efficiency is 70%.
Claims (1)
1. A method for preparing a metal organic framework nanosheet by a liquid phase stripping method is characterized by comprising the following steps:
(1) synthesis of layered MOF precursor Zn by hydrothermal conversion of known zeolitic imidazolate frameworks (ZIF-7)2(bim)4；
(2) The precursor Zn obtained in the step (1) is2(bim)4Dispersing in aqueous solution containing ionic liquid, ultrasonic treating, and centrifuging at low speed to remove non-peeled precursor Zn2(bim)4The upper layer solution is MOF nanosheet dispersion;
(3) centrifuging the MOF nanosheet dispersion liquid obtained in the step (2) at a high speed, washing with ethanol for several times, and drying in vacuum to obtain MOF nanosheets;
in step (2), precursor Zn2(bim)4The concentration of the ionic liquid is 1-10mg/m L, the suspension is subjected to ultrasonic treatment, the ultrasonic power is 100-400W, the ultrasonic time is 10-360min, the suspension is centrifuged for 2-10min under the condition of 5000rpm of 2000-4, the ionic liquid is one of 1-butyl-3-methylimidazole tetrafluoroborate, 1-octyl-3-methylimidazole chloride salt, 1-ethyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt and 1-butyl-3-methylimidazole hexafluorophosphate, the water is deionized water, and the mass ratio of the ionic liquid to the water is 1: 9-9: 1;
in the step (3), the nanosheet dispersion obtained in the step (2) is subjected to high-speed centrifugation at 10000-15000rpm for 5-20min, then the centrifugate is washed with ethanol, and vacuum drying is carried out at 60-100 ℃ to obtain the MOF nanosheet.
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| CN110527105A (en) * | 2019-08-26 | 2019-12-03 | 南京航空航天大学 | A kind of ultra-thin two-dimension porous metals organic frame nanometer sheet and preparation method thereof |
| CN111718492A (en) * | 2019-11-13 | 2020-09-29 | 中南大学 | Preparation and application of large-size single-layer two-dimensional MOF nanosheet |
| CN111718493B (en) * | 2020-06-10 | 2021-11-02 | 江南大学 | Method for preparing MAMS-1 nanosheet by liquid-phase stripping method and application thereof |
| CN114504071A (en) * | 2022-01-24 | 2022-05-17 | 华南理工大学 | Metal organic framework sterilization material based on ultrasonic assistance and preparation method and application thereof |
| CN114534517B (en) * | 2022-03-08 | 2023-04-28 | 国家纳米科学中心 | Nanofiltration membrane constructed based on two-dimensional MOF and graphene oxide sheets, and preparation method and application thereof |
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| CN105709610B (en) * | 2014-11-30 | 2017-12-22 | 中国科学院大连化学物理研究所 | Support type ultra-thin two-dimension stratiform MOF films and preparation method thereof |
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