CN112191111B - An ionic liquid/metal organic framework ZIF-8 composite membrane and its preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of membrane separation, and provides a preparation method and application of an ionic liquid/ZIF-8 composite membrane. The invention adopts a one-pot method to obtain a dense and defect-free ionic liquid/ZIF-8 composite membrane with a thickness of 1 μm; the obtained composite membrane can be applied to gas separation. _The preparation process of the invention is simple, and the developed composite membrane has good ^{gas permeation separation performance} and _{stability .} The gas separation factor was 55, which exceeded the Robeson upper limit (2008).

Description

An ionic liquid/metal organic framework ZIF-8 composite membrane and its preparation method and application

technical field

The invention belongs to the technical field of membrane separation, and in particular relates to an ionic liquid/metal organic framework ZIF-8 composite membrane and a preparation method and application thereof

Background technique

H ₂ , CO ₂ and CH 4 gases often exist in the form of mixed gas in the water gas shift hydrogen production (H ₂ /CO ₂ ), natural gas (CO ₂ /CH ₄ ) and biogas (CO ₂ /CH ₄ ) and other energy gases and industrial Therefore, high-efficiency gas separation is of great significance to the environment, energy, chemical industry and other fields. Membrane separation technology has the advantages of small footprint, easy linear amplification, energy saving and consumption reduction, and simple operation, and has attracted great attention in the field of gas separation. The key to membrane separation technology lies in the development of membrane materials with high selectivity, high permeability and high stability.

Metal-organic frameworks (MOFs) are porous crystalline materials with periodic network structures formed by self-assembly of metal ions and organic ligands. Its rich framework structure, tunable pore structure and surface functionalization make it a new generation of membrane materials. ZIF-8 is a typical material in MOFs, which is self-assembled from metal ions Zn ²⁺ and 2-methylimidazolate, and is widely used in the study of membrane materials. At present, the growth methods of ZIF-8 films are mainly: in-situ growth method, secondary growth method, layer-by-layer self-assembly method, pair diffusion method, electrochemical growth method (a preparation method of metal-organic framework ZIF-8 film [P ]. Chinese invention patent, CN201210269544, 2012-8-1; a metal-organic framework film and its preparation method and application [P]. Chinese invention patent, CN201310373159, 2013-8-23), etc., but ZIF-8 films are ubiquitous The problem of large film thickness (16-60μm) and poor osmotic separation performance. _At present, there are few reports _on MOF/ionic liquid related composite membranes. Chem.C, 2013, 117, 18434), which uses a seed crystal secondary growth method to prepare a ZIF-69 film with a thickness of 60 μm, and then uses a dip coating method to support the ionic liquid in the ZIF-69 film layer and the film layer The surface (the thickness of the surface ionic liquid is as high as 240 μm, because the film thickness of the composite membrane is as high as 300 μm, the CO ₂ permeability is only 5.6×10 ^-11 mol m ^-2 s ^-1 Pa ^-1 . At present, the metal organic framework membrane and ionic Liquid/metal-organic framework composite membranes generally have the problems of large membrane thickness and osmotic separation performance to be improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an ionic liquid/ZIF-8 composite membrane and its preparation method and application.

To achieve the above object, the technical scheme adopted in the present invention is:

A method for preparing an ionic liquid/metal organic framework ZIF-8 composite membrane, comprising mixing ionic liquid, ZIF-8 sol and ZIF-8 metal precursor with organic ligands, wherein the ratio of ionic liquid to ZIF-8 sol is 0.2g-0.7g ionic liquid/10mL ZIF-8 sol, the mass ratio of ionic liquid and ZIF-8 is 1:1-2:1, and the mass ratio of metal precursor and organic ligand of ZIF-8 is 1:5 -2:1, inject the above mixed solution into a reactor equipped with a carrier, and perform thermal crystallization at least twice through a solvent to obtain a composite membrane.

The above method further promotes the interactive growth of ZIF-8 particles to form continuous nanocomposite films on APTES-modified sheet-like porous alumina substrates.

The ionic liquid is 1-butyl-3-methylimidazole bis-trifluoromethanesulfonimide salt [Bmim][Tf ₂ N];

The mixed solution of the metal precursor of ZIF-8 and the organic ligand is a solution containing zinc ions and a solution containing 2-methylimidazole ligand; wherein, the mass ratio of the inorganic zinc salt and 2-methylimidazole For: 1:4-1:1.

Going further:

(1) Preparation of ZIF-8 sol:

1) Dissolve the inorganic zinc salt and the organic ligand 2-methylimidazole in the solvent respectively, then obtain two solutions dissolved in the solvent and stir at room temperature for reaction, and stir vigorously for 10min-24h for use;

2) the above-mentioned reactant is centrifuged to collect the precipitate, and after washing, the precipitate is dispersed in the solvent; the supernatant is further collected by centrifugation to obtain a ZIF-8 sol with a concentration of 0.5-3 mg/mL;

(2) Solvent thermal crystallization:

1) Preparation of the reaction mixture: adding the imidazole ligand solution to the zinc ion solution, stirring vigorously to form a uniform mixture; then adding the ionic liquid and the above-mentioned ZIF-8 sol to the above-mentioned mixture, and stirring uniformly;

2) Crystallization: the above-mentioned reaction mixture is transferred to the reaction kettle fixed with the pretreatment substrate for crystallization, and after being lowered to room temperature, it is a crystallization, and at least two crystallization reactions are carried out, and then taken out, rinsed with a solvent and dried, That is, a composite film is formed on the surface of the substrate.

The pretreatment substrate is to polish the surface of the substrate until the surface is smooth, wash and then dry; after drying, it is activated by HCl solution, and then treated with 3-aminopropyltriethoxysilane (APTES) toluene solution under the action of inert gas for 1- 5h, vacuum-dried for 2-5h, set aside.

In the step (1), 1) the inorganic zinc salt is one or more of zinc nitrate hexahydrate, zinc nitrate tetrahydrate, and zinc acetate; the mass ratio of the inorganic zinc salt and 2-methylimidazole is: 1:4-1:1; the mass ratio of the solvent and 2-methylimidazole is 20:1-60:1.

In the step (2), 1) the imidazole ligand solution is that 2-methylimidazole is dissolved in the solvent, and the zinc ion solution is that the inorganic zinc salt is dissolved in the solvent; the mass ratio of the inorganic zinc salt and 2-methylimidazole is It is 1:4-1:1; the mass ratio of solvent and 2-methylimidazole is 20:1-60:1; wherein, the inorganic zinc salt is a kind of zinc nitrate hexahydrate, zinc nitrate tetrahydrate and zinc acetate or several; the solvent is one or more of water, ethanol and methanol.

In the step (1), the solvent in 1) and 2) is one or a mixture of water, ethanol and methanol.

The crystallization temperature is 100-180° C., and the crystallization time is 4-10 h.

The drying temperature is 50-150° C., and the drying time is 1-10 h.

The ionic liquid/metal organic framework ZIF-8 composite membrane prepared according to the described preparation method.

An application of a nano-ionic liquid/ZIF-8 composite membrane, the application of the composite membrane in gas separation.

The present invention has the following advantages:

The invention adopts a one-pot method to obtain an ionic liquid/ZIF-8 composite membrane with a thickness of 1 μm; the obtained composite membrane can be applied to gas separation. The preparation method of the present invention has a simple process, and the developed composite membrane has good gas permeation separation performance and stability; specifically:

(1) The present invention prepares a dense continuous ionic liquid/ZIF-8 composite membrane by a one-pot method. Specifically, the ionic liquid, ZIF-8 sol and ZIF-8 metal precursor are mixed with organic ligands and then solvothermally crystallized. The one-pot method adopted by the method is simple and easy to operate. The addition of ionic liquid is beneficial to the interactive growth between ZIF-8 particles.

(2) The thickness of the composite membrane obtained by the present invention is only 1 μm, and the ultra-thin membrane thickness enables it to have high gas permeability and separation factor, and its H ₂ permeability reaches 1.5×10 ^-6 mol m ^-2 s ^{- 1} Pa ^-1 , the separation factor of H ₂ /CO ₂ mixture is 55, which exceeds the Robeson upper limit (2008). At the same time, the composite membrane has good operating stability, and its H ₂ /CO ₂ selective separation performance remains unchanged after the composite membrane runs for 120 h.

Description of drawings

Fig. 1 is the TEM picture of the nano ZIF-8 sol of the specific embodiment 1 of the present invention;

Fig. 2 is the SEM image of the ionic liquid/ZIF-8 composite film crystallized once in the specific embodiment 1 of the present invention;

FIG. 3 is a SEM image of the ionic liquid/ZIF-8 composite film crystallized twice in the specific example 2 of the present invention.

Fig. 4 is the XRD spectrum of the ionic liquid/ZIF-8 composite film crystallized twice of the specific embodiment 2 of the present invention;

5 is the permeation rate and selectivity of the ionic liquid/ZIF-8 composite membrane crystallized twice to a single gas (H ₂ , CO ₂ , N ₂ and CH ₄ ) according to the specific embodiment 2 of the present invention;

FIG. 6 is the stability of the ZIF-8/ionic liquid composite membrane crystallized twice to H ₂ /CO ₂ permeation separation (V _H2 : V _CO2 =1:1) according to the specific embodiment 2 of the present invention;

Detailed ways

The preparation method of the composite material of the present invention includes the following steps: preparation of ZIF-8 sol, pretreatment of sheet-like porous alumina substrate, and solvothermal crystallization. The composite membrane of the invention has good gas permeation separation performance and stability.

Example 1

(1) Preparation of ZIF-8 sol:

1) Dissolve zinc nitrate hexahydrate (1.47g) and 2-methylimidazole (3.25g) in 100ml of anhydrous methanol, respectively, to obtain a methanol solution of zinc nitrate and a methanol solution of 2-methylimidazole, respectively. The methanol solution of zinc was poured into methanol solution of 2-methylimidazole, and the solution was stirred at room temperature for 1 h.

2) The above-mentioned reactant is centrifuged at least once to completely remove the unreacted precursor, and each centrifugation condition is centrifugation at 8000-10000rpm for 10min, and the collected precipitate is washed with methanol and dispersed in methanol after washing; further, the centrifugation condition is: The supernatant was collected by centrifugation at 8000-10000 rpm for 10 min to obtain a ZIF-8 sol (see Figure 1 ) with a concentration of 1.5 mg/mL.

As shown in Figure 1, the ZIF-8 particles in the colloidal solution basically presented a single crystal dispersion state, and the size of the ZIF-8 particles was about 45 nm.

(2) Pretreatment of flaky porous alumina substrate:

1) Sand the substrate surface with 1000-mesh, 2000-mesh and 3000-mesh sandpaper in turn until the substrate surface is smooth. Wash with ethanol and deionized water, and dry at 105 °C for 10 h.

2) The substrate was activated with 1 mol L ^-1 of HCl solution, then treated with 2 mmol L ^-1 of 3-aminopropyltriethoxysilane (APTES) toluene solution at 110 °C for 2 h under argon protection, and vacuum dried for 2 h .

(3) Solvent thermal crystallization:

1) preparation of reaction mixture: 0.3g zinc nitrate hexahydrate is dissolved in 11.2g methanol solution, 0.66g 2-methylimidazole is added in 11.2g methanol solution, gained imidazole ligand solution is added in above-mentioned zinc ion solution, Stir for 5 min, and after mixing, a mixed solution containing ligands and metal ions was obtained; then 10 mL of ZIF-8 sol containing ionic liquid [Bmim][Tf ₂ N] (0.5 g) was added to the mixed solution containing ligands and metal ions , stir well.

2) Crystallization: The above reaction mixture was transferred to a reaction kettle with a fixed substrate, crystallized at 150°C for 5 hours, lowered to room temperature, taken out for crystallization once, rinsed with methanol, and dried at 100°C for 2 hours, that is, a composite was formed on the surface of the substrate. membrane.

As shown in Figure 2, after one crystallization, a non-dense ZIF-8 film layer was formed on the surface of the substrate, and there were macroporous defects.

Example 2

(1) Preparation of ZIF-8 sol:

1) Dissolve zinc nitrate hexahydrate (1.47g) and 2-methylimidazole (3.25g) in 100ml of anhydrous methanol, respectively, to obtain a methanol solution of zinc nitrate and a methanol solution of 2-methylimidazole, respectively. The methanol solution of zinc was poured into the methanol solution of 2-methylimidazole, and the solution was stirred at room temperature for 1 h.

2) The above-mentioned reactants are centrifuged at least once so that the unreacted precursors are completely removed, and each centrifugation condition is 8000-10000rpm for 10min, and the collected precipitate is washed with methanol, and dispersed in methanol after washing; further, the centrifugation condition is 8000 rpm. The supernatant was collected by centrifugation at -10000 rpm for 10 min to obtain a ZIF-8 sol (see Figure 1 ) with a concentration of 1.5 mg/mL.

It is shown from Figure 1 that the ZIF-8 particles in the colloidal solution are basically in a single crystal dispersion state, and the size of the ZIF-8 particles is about 45 nm.

(2) Pretreatment of flaky porous alumina substrate:

1) Sand the substrate surface with 1000-mesh, 2000-mesh and 3000-mesh sandpaper in turn until the substrate surface is smooth. Wash with ethanol and deionized water, and dry at 105 °C for 10 h.

2) The substrate was activated with 1 mol L ^-1 of HCl solution, then treated with 2 mmol L ^-1 of 3-aminopropyltriethoxysilane (APTES) toluene solution at 110 °C for 2 h under argon protection, and vacuum dried for 2 h .

(3) Solvent thermal crystallization:

1) preparation of reaction mixture: 0.3g zinc nitrate hexahydrate is dissolved in 11.2g methanol solution, 0.66g 2-methylimidazole is added in 11.2g methanol solution, gained imidazole ligand solution is added in above-mentioned zinc ion solution, Stir for 5 min, and after mixing, a mixed solution containing ligands and metal ions was obtained; then 10 mL of ZIF-8 sol containing ionic liquid [Bmim][Tf ₂ N] (0.5 g) was added to the mixed solution containing ligands and metal ions , stir well.

2) Crystallization: transfer the reaction mixture into a reaction kettle with a fixed substrate, crystallize at 150° C. for 5 hours, then drop to room temperature for one crystallization, and then perform crystallization again according to this process, and take out two crystallizations after crystallization The final product was rinsed with methanol and dried at 100 °C for 2 h, that is, a composite film was formed on the surface of the substrate.

Figure 3 shows that the ionic liquid/metal organic framework ZIF-8 composite film layer is continuous and dense, the thickness of the composite film is about 1 μm, and there is no obvious delamination interface between the film layer and the substrate.

Figure 4 shows that the ZIF-8 in the composite membrane has very high purity and crystallinity, and the addition of a small amount of ionic liquid has no effect on the crystal structure of ZIF-8.

The permeation separation performance test of single gas (H ₂ , CO ₂ , N ₂ or CH ₄ ) was carried out on the ionic liquid/metal organic framework ZIF-8 composite membrane.

Figure 5 shows that the composite membrane has good H ₂ /CO ₂ separation performance, the composite membrane has a high permeability to H ₂ 1.43×10 ^-6 mol m ^-2 s ^-1 Pa ^-1 , H ₂ /CO ₂ The ideal separation factors of , H ₂ /N ₂ and H ₂ /CH ₄ are 68.6, 25 and 25.5, respectively.

The ionic liquid/metal organic framework ZIF-8 composite membrane was tested for the operation stability of H ₂ /CO ₂ mixed gas separation. Test conditions: H ₂ /CO ₂ mixed gas volume ratio of 1:1, temperature 25 ℃, inlet air The side pressure is 1 bar.

It is shown in Figure 6 that the selective separation performance of H ₂ /CO ₂ remains unchanged after the composite membrane runs for 120 h, with good stability.

Claims (8)

1. a preparation method of ionic liquid/metal organic framework ZIF-8 composite membrane, is characterized in that: (1) Preparation of ZIF-8 sol: 1) Dissolve the inorganic zinc salt and the organic ligand 2-methylimidazole in a solvent respectively, and then obtain two kinds of solutions dissolved in the solvent, stir and react at room temperature, and wait for use; 2) The reactant was centrifuged to collect the precipitate, and after washing, the precipitate was dispersed in the solvent; the supernatant was collected by centrifugation to obtain a ZIF-8 sol with a concentration of 0.5-3 mg/mL; (2) Solvent thermal crystallization: 1) Preparation of the reaction mixture: add the imidazole ligand solution to the zinc ion solution, stir vigorously to form a uniform mixture; then add the ionic liquid and the above ZIF-8 sol to the above mixture, and stir evenly; 2) Crystallization: The reaction mixture is transferred to the reaction kettle with the pretreatment substrate fixed for crystallization, and after it is lowered to room temperature, it is crystallization once, and the crystallization reaction is performed at least twice, and then taken out, rinsed with solvent and dried, that is, A composite film is formed on the surface of the substrate; In step (1), the mass ratio of 1) inorganic zinc salt and 2-methylimidazole is 1:4-1:1; In step (2), 1) the ionic liquid is 1-butyl-3-methylimidazole bis-trifluoromethanesulfonimide salt; In step (2), 1) the ratio of ionic liquid and ZIF-8 sol is 0.2 g-0.7 g ionic liquid/10 mL ZIF-8 sol, and the mass ratio of ionic liquid and ZIF-8 is 1:1-2:1; In step (2), 1) the imidazole ligand solution is to dissolve 2-methylimidazole into the solvent, and the zinc ion solution is to dissolve the inorganic zinc salt into the solvent; the mass ratio of the inorganic zinc salt and 2-methylimidazole is 1 :4-1:1. 2. by the preparation method of the described ionic liquid/metal organic framework ZIF-8 composite membrane of claim 1, it is characterized in that: described pretreatment substrate is that the substrate surface is ground to smooth surface, and dry after washing; The solution was activated, and then treated with a toluene solution of 3-aminopropyltriethoxysilane for 1-5h under the action of an inert gas, dried under vacuum for 2-5h, and used. 3. The preparation method of ionic liquid/metal organic framework ZIF-8 composite membrane according to claim 1, characterized in that: in step (1) 1) the inorganic zinc salt is zinc nitrate hexahydrate, zinc nitrate tetrahydrate , one or more of zinc acetate; the mass ratio of the solvent and 2-methylimidazole is 20:1-60:1. 4. The preparation method of ionic liquid/metal-organic framework ZIF-8 composite membrane according to claim 1, characterized in that: in step (2), the mass ratio of 1) solvent and 2-methylimidazole is 20:1- 60:1; wherein, the inorganic zinc salt is one or more of zinc nitrate hexahydrate, zinc nitrate tetrahydrate, and zinc acetate; the solvent is one or more of water, ethanol and methanol. 5. The preparation method of the ionic liquid/metal organic framework ZIF-8 composite membrane according to claim 1, characterized in that: in step (1), 1) and 2) the solvent is one of water, ethanol, methanol or A mix of several. 6 . The method for preparing an ionic liquid/metal organic framework ZIF-8 composite film according to claim 1 , wherein the crystallization temperature is 100-180° C. and the crystallization time is 4-10 h. 7 . 7. An ionic liquid/metal organic framework ZIF-8 composite membrane prepared by the method for preparing an ionic liquid/metal organic framework ZIF-8 composite membrane according to claim 1. 8. An application of the ionic liquid/metal organic framework ZIF-8 composite membrane according to claim 7, characterized in that: the application of the composite membrane in gas separation.

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