Preparation method of mixed matrix composite membrane for regulating and controlling inclined arrangement of one-dimensional materials by utilizing magnetic field

Abstract

The invention discloses a preparation method of a mixed matrix composite membrane for regulating and controlling inclined arrangement of one-dimensional materials by utilizing a magnetic field. According to the method, ferroferric oxide and a metal organic framework (ZIF-8) are loaded on a halloysite nanotube (HNT) to prepare a magnetic ZIF composite halloysite nanotube (ZMHNT), the ZMHNT is mixed with polyether block polyamide, a polyethersulfone (PES) base membrane covered by polydimethylsiloxane (PDMS) is coated with the mixture, and meanwhile, the mixture is placed in a magnetic field environment to be subjected to orientation adjustment, so that the composite membrane is obtained. And preparing the mixed matrix composite membrane with one-dimensional fillers in inclined arrangement. According to the preparation method, the ZIF-8 grows on the HNT, the continuous ZIF-8 layer is coated on the pipe orifice to screen CO2 and N2, and the ZMHNT is arranged in the membrane at a relatively large inclination angle and in a penetrating manner under the acting force of a magnetic field, so that the anisotropy is overcome, the diffusion speed of gas in the hollow pipe of the ZMHNT is enhanced, and the gas separation performance of the mixed matrix composite membrane is improved.

Description

Technical Field

[0001] The present invention belongs to the field of gas separation membrane materials, and particularly relates to a method for preparing a mixed matrix composite membrane by using a magnetic field to regulate the inclined arrangement of one-dimensional materials. Background Art

[0002] Since the Industrial Revolution, the carbon dioxide emissions of human society have increased significantly, leading to a series of natural disasters such as ocean acidification, ice sheet melting, and hurricanes intensifying. As a key means to achieve carbon neutrality, various carbon capture technologies have received extensive attention. Among them, the membrane separation method has attracted much attention due to its advantages such as low energy consumption, easy coupling, and low cost.

[0003] Carbon dioxide separation membranes mainly include polymer membranes, inorganic membranes, and mixed matrix membranes. Among them, polymer membranes have low cost and are easy to process, and have good film-forming properties, but there is a trade-off effect between permeation flux and selectivity; the flux and selectivity of inorganic membranes can reach relatively high levels, but their film-forming properties are poor and the cost is high. Mixed matrix membranes can combine the advantages of polymer membranes and inorganic membranes, and can break the trade-off limitation between the selectivity and permeability of traditional membranes. Metal-organic framework materials (MOFs), as a kind of porous materials, are composed of metal ions and organic ligands, and have the advantages of ultra-high specific surface area, high porosity, adjustable pore size, and chemical stability, etc.; among the materials in various dimensions in the mixed matrix membrane, the internal continuous hollow structure of one-dimensional tubular materials can provide a stable high-speed transmission channel for gas molecules, and the composite one-dimensional materials prepared by combining MOF and one-dimensional tubular materials can simultaneously play a screening and selection and transmission role in the membrane. However, for example, in the gas separation work such as Rijia Lin et al. in the article "Mixed-Matrix Membranes with Metal–Organic Framework-Decorated CNT Fillers for Efficient CO2 Separation", where MIL-101 is loaded on CNT and incorporated into polyimide to prepare a mixed matrix membrane, the MOF one-dimensional materials themselves cannot directly form a direct-through channel in the membrane, and the performance improvement is limited. Therefore, regulating the material orientation to form a direct-through channel in the membrane is expected to further improve the gas performance of the membrane.

[0004] The present invention prepares magnetic ZIF composite halloysite nanotubes ZMHNT. First, Fe3O4 is loaded on the wall of HNT to endow the material with magnetism, and then ZIF-8 and PDA are coated on the wall and the orifice of the tube. On the one hand, the interfacial compatibility between the inorganic material and the polymer is improved, and on the other hand, a continuous ZIF selective layer is formed at the orifice of the tube to realize the screening of CO2 / N2 by the tubular material. Then, ZMHNT is mixed with Pebax and spin-coated on the PES / PDMS composite membrane. Through the regulation of an external magnetic field, ZMHNT is arranged in the membrane with a large inclination angle and a penetrating arrangement, forming a direct channel for CO2 gas molecules, thereby improving the gas permeability and selectivity of the membrane. Summary of the Invention

[0005] Aiming at the problem that most existing one-dimensional materials cannot significantly improve the performance in the mixed matrix membrane, the purpose of the present invention is to provide a preparation method of a mixed matrix composite membrane that uses a magnetic field to regulate the inclined arrangement of one-dimensional materials.

[0006] The technical solution of the present invention:

[0007] A preparation method of a mixed matrix composite membrane that uses a magnetic field to regulate the inclined arrangement of one-dimensional materials, and the synthesis steps are as follows:

[0008] Step 1: Using halloysite nanotubes HNT as a template, magnetite is loaded on the surface of HNT by the oxidation co-precipitation method to synthesize magnetic halloysite nanotubes MHNT;

[0009] Step 2: Coating polydopamine and ZIF-8 on the surface of MHNT to obtain magnetic ZIF composite halloysite nanotubes ZMHNT;

[0010] Step 3: Coating the mixed matrix casting solution containing ZMHNT and Pebax on the PDMS / PES substrate membrane to obtain a mixed matrix composite membrane, and using an external magnetic field regulation method to prepare a mixed matrix composite membrane with an inclined arrangement of fillers.

[0011] Further, the specific process of step 1 is as follows: HNT is dispersed in water and mixed with ferrous sulfate heptahydrate FeSO4·7H2O to obtain a suspension, and the pH range of the suspension is adjusted to 8.5 - 12; the suspension system is placed in an oil bath for heating and stirring reaction. After the reaction, filtration is carried out, and the solid is placed in a blast drying oven at 40 - 80 °C for drying for 12 - 24 h to obtain magnetic halloysite nanotubes MHNT.

[0012] Furthermore, the mass ratio of HNT to ferrous sulfate heptahydrate FeSO4·7H2O is 1:8 - 1:2; the reagent for adjusting the pH of the suspension is ammonia water; the reaction temperature is 60 - 90 °C, and the reaction time is 3 - 6 h.

[0013] Further, the specific process of step 2 is as follows: Disperse the magnetic halloysite nanotubes MHNT obtained in step 1 in water, add an aqueous solution of dopamine hydrochloride and mix evenly to obtain a dispersion liquid, adjust the pH value to the range of 8 - 10 for PDA coating reaction; after the reaction, centrifuge, and put the centrifuged solid into a blast drying oven at 40 - 80 °C for drying for 12 - 24 h to obtain halloysite nanotubes PHNT coated with PDA. Ultrasonically disperse the halloysite nanotubes PHNT coated with PDA in methanol, add zinc nitrate and 2-methylimidazole, ultrasonically disperse and then mechanically stir and react, and centrifuge after the reaction. Take the centrifuged solid and put it into a blast drying oven at 40 - 80 °C for drying for 12 - 24 h to obtain magnetic ZIF composite halloysite nanotubes ZMHNT.

[0014] Furthermore, the reagent for adjusting the pH of the dispersion liquid is potassium hydroxide; the time of the PDA coating reaction is 0.5 - 1.5 h; the concentration of the aqueous solution of dopamine hydrochloride is 1 - 2 g / L, and the ratio of the volume (mL) of the aqueous solution of dopamine hydrochloride to the mass (g) of MHNT is 100 - 50:1; the centrifugation conditions after the PDA coating reaction are: the centrifugation time is 10 - 30 min, and the centrifugation speed is 7000 - 11000 rpm.

[0015] Furthermore, the molar ratio of zinc nitrate and 2-methylimidazole added is 1:2 - 8; the mass ratio of the halloysite nanotubes PHNT coated with PDA to zinc nitrate is 1:3 - 10; the reaction time is 2 - 5 h, and the mechanical stirring speed is 200 - 600 rpm; the centrifugation time is 10 - 30 min, and the centrifugation speed is 7000 - 11000 rpm.

[0016] Further, the process of the mixed matrix casting solution in step 3 is as follows: Add the magnetic ZIF composite halloysite nanotubes ZMHNT obtained in step 2 into a Pebax casting solution, the concentration of Pebax in the casting solution is 1 - 5 wt%, and the mass fraction of the magnetic ZIF composite halloysite nanotubes ZMHNT in the Pebax casting solution is 5% - 20%; after stirring, ultrasonically remove the bubbles in the casting solution and at the same time make the filler evenly disperse in the solution to obtain a mixed matrix casting solution.

[0017] Further, in step 3, the mixed matrix casting solution is coated onto a base film by a doctor blade method or a casting method, and the selected PES substrate has a cut-off molecular weight of 10000 - 50000 Da.

[0018] Further, in step 3, two magnets with a strength of 0.5 - 1 T are selected and placed on the upper and lower sides of the glass plate with the mixed matrix composite membrane attached respectively. There are gaps between the two magnets and the glass plate with the mixed matrix composite membrane, and magnetic field action is carried out for 12 - 24 h. Then, the glass plate is placed in a blast drying oven at 40 - 80 °C and dried for 12 - 24 h to obtain a mixed matrix composite membrane with fillers arranged obliquely.

[0019] Furthermore, the preparation method of the PDMS / PES base membrane: Using PDMS as the solute, n - heptane as the solvent, dibutyltin dilaurate and tetraethyl orthosilicate as the catalyst and cross - linker respectively; the mass ratio of the cross - linker, catalyst to PDMS is 5:4 - 1:4 - 1, and a 2wt% - 5wt% PDMS coating solution is prepared. The PDMS coating solution is coated on the PES substrate by the doctor - blade method or the casting method, and the membrane is put into the oven and dried for 0.5 - 1 h to obtain the PDMS / PES base membrane.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention prepares magnetic ZIF - composite halloysite nanotubes ZMHNT. The magnetic ZIF - composite halloysite nanotubes ZMHNT itself has a tubular structure and can provide a high - speed gas transmission channel in the membrane; by coating ZIF - 8 and PDA on the outside of the tube, the compatibility between the reinforcing material and the polymer matrix is enhanced. The continuous ZIF - 8 layer coated on the tube orifice can screen CO2 and N2. At the same time, under the regulation of an external magnetic field, ZMHNT can achieve a large inclination angle and a through - type arrangement in the selective layer of the membrane, thereby strengthening the diffusion rate of CO2 gas in the hollow tube of ZMHNT. The continuously coated ZIF - 8 material at the tube orifice can screen CO2 and N2, improving the gas permeability and selectivity of the mixed matrix composite membrane. Description of the Drawings

[0021] Figure 1 It is a scanning electron microscope picture of the magnetic ZIF - composite halloysite nanotubes ZMHNT in Example 1.

[0022] Figure 2 It is a transmission electron microscope picture of the magnetic ZIF - composite halloysite nanotubes ZMHNT in Example 1.

[0023] Figure 3 It is an XRD spectrum of the magnetic ZIF - composite halloysite nanotubes ZMHNT and magnetic halloysite nanotubes MHNT in Example 1.

[0024] Figure 4 It is a scanning electron microscope picture of the cross - section of the mixed matrix composite membrane under the magnetic field action in Example 1.

[0025] Figure 5 It is a scanning electron microscope picture of the cross - section of the mixed matrix composite membrane dried conventionally in Example 2.

[0026] Figure 6 Gas separation performance comparison diagrams of different membranes in Examples 1-2 and Comparative Examples. Detailed implementation mode

[0027] Example 1

[0028] Preparation of magnetic halloysite nanotubes: Add 1 g of HNT powder into a 200 mL reagent bottle, weigh 100 mL of deionized water and pour it into the bottle to mix with HNT, and mechanically stir for 30 min to make HNT evenly dispersed in water. Then add 3 g of FeSO4·7H2O powder into the HNT suspension, and ultrasonically stir for 30 min to form a uniform suspension in the bottle. During this process, the liquid in the bottle gradually changes from white to green. Then add ammonia water to the bottle drop by drop, and dip the liquid with a glass rod onto the pH test paper to observe the pH value until the pH value reaches 9. During this process, the color of the liquid in the bottle gradually changes from green to dark green. Set the temperature of the oil bath to 80 °C, place the bottle in the pot, mechanically stir and react for 4 h, and set the mechanical stirring speed to 400 rpm. After the reaction, take out the bottle, let it stand at room temperature for 15 min until the temperature drops, and then use a vacuum filtration bottle to separate the solid-liquid two phases in the bottle. This process is continuously washed 3 times with deionized water. Then place the filter paper carrying the black solid in a 70 °C blast drying oven and dry for 12 h to obtain a magnetic one-dimensional material, named MHNT.

[0029] Preparation of magnetic ZIF composite halloysite nanotubes: Take 1 g of MHNT and place it in a 200 mL reagent bottle, add 100 mL of deionized water, ultrasonically disperse for 20 min, add 0.2 g of dopamine hydrochloride and stir for 40 min. Then add 1.5 mol / L KOH solution, and while dripping, dip the liquid with a glass rod onto the pH test paper to observe the pH value until the pH value reaches 9, and stir for 40 min. After the reaction, place the liquid in a centrifuge tube and centrifuge at a speed of 10,000 r / min for 15 min in the centrifuge, wash twice with water and methanol respectively, and then put it in a 70 °C blast drying oven and dry for 12 h to obtain a magnetic one-dimensional material carrying PDA, named PHNT. Next, take 0.1 g of PHNT and place it in a 200 mL reagent bottle, add 150 mL of methanol, ultrasonically disperse for 20 min, then add 0.3 g of zinc nitrate and 0.16 g of 2-methylimidazole, ultrasonically stir for 20 min to make the particles mix evenly, and then place the reagent bottle at room temperature for mechanical stirring, with the speed set to 400 rpm, and react for 3 h. After the reaction, place the liquid in a centrifuge tube and centrifuge at a speed of 10,000 r / min for 15 min in the centrifuge, wash twice with methanol, and then put it in a 70 °C blast drying oven and dry for 12 h to obtain magnetic ZIF composite halloysite nanotubes (ZMHNT).

[0030] Preparation of a Mixed Matrix Composite Membrane with Inclined Arrangement of Filler: Weigh 0.6 g of Pebax and add it to a 100 mL flask. Measure 17.4 mL of water and 52 mL of ethanol. After mixing the three together, carry out condensation reflux at 80 °C for 4 h to obtain a Pebax polymer solution, and cool it for later use. Next, add the ZMHNT material to 5 g of the Pebax polymer solution according to a mass percentage of 10%, stir for 1 h, and then ultrasonicate for 1 h to remove bubbles. At the same time, prepare a 2 wt% PDMS coating solution. Calculate the mass of PDMS as 0.5 g, the mass of n - heptane as 22 g, the mass of the catalyst as 0.4 g, and the mass of the cross - linker as 0.4 g according to the mass ratio. First, mix PDMS and n - heptane, and after it is completely dissolved, add the cross - linker and stir to mix; after mixing evenly, add the catalyst and continue to stir until a uniform PDMS coating solution is formed. Fix the PES substrate on the glass plate with tape, and use the doctor - blade method or casting method to coat the PDMS coating solution on the PES substrate, and place the membrane in a 40 °C forced - air oven to dry for 0.5 - 1 h to obtain a PDMS / PES base membrane. Before this, scrape the PDMS solution on a PES base membrane with a molecular weight cut - off of 20000 Da to prepare a composite membrane. Then, scrape the casting solution on the PDMS / PES composite membrane, and place the glass plate with the membrane in the magnetic field provided by two square magnets with a magnetic field strength of 0.6 T, and place it at room temperature for 12 h. Then transfer the glass plate into a 40 °C oven to dry for 12 h to completely remove the solvent, that is, obtain a mixed matrix composite membrane with inclined arrangement of filler, denoted as 10 wt% ZMHNT - magnetic field.

[0031] Example 2

[0032] The main steps are the same as in Example 1. The prepared mixed matrix composite membrane is directly dried. The difference is that after taking the casting solution with a mass fraction of 10% that is completely dispersed after ultrasonication and scraping it on the PDMS / PES composite membrane, place the glass plate with the membrane in a 40 °C forced - air oven and dry it for 24 h until the solvent is completely removed to obtain a directly dried mixed matrix composite membrane.

[0033] Example 3

[0034] The main steps are the same as in Example 1. The differences are as follows: during the synthesis of MHNT, add ammonia water to adjust the pH value to 11, the reaction temperature is 90 °C, and the reaction time is 6 h; during the synthesis of ZMHNT, the reaction time for preparing PHNT is 1.5 h, the addition amount of 2 - methylimidazole is 0.66 g, and the reaction time is 5 h.

[0035] Example 4

[0036] The main steps are the same as those in Example 1. The differences are as follows: during the synthesis of MHNT, ammonia water is added dropwise to adjust the pH value to 8.5, the reaction temperature is 60 °C, and the reaction time is 3 h; during the synthesis of ZMHNT, the reaction time for preparing PHNT is 1.5 h, the addition amount of 2-methylimidazole is 0.32 g, and the reaction is carried out for 2 h.

[0037] Comparative example

[0038] The main steps are the same as those in Example 1. A pure Pebax composite membrane without magnetic ZIF composite halloysite nanotubes is prepared. The difference is that ZMHNT is not added to the casting solution. After taking the casting solution that is completely dispersed after ultrasonic treatment and scraping it on the PDMS / PES composite membrane, the glass plate with the membrane is placed in a blast drying oven at 40 °C and dried for 12 h until the solvent is completely removed to obtain a pure Pebax composite membrane.

[0039] The gas permeability of the membranes in Examples 1-2 and the comparative example was tested. The results show that for the directly dried mixed matrix composite membrane prepared, under the test conditions of a doping amount of 10 wt%, 25 °C, and 2 bar, the CO2 permeation rate is 129.92 GPU, and the CO2 / N2 selectivity is 34.95. The CO2 permeation rate of the mixed matrix composite membrane with the fillers arranged obliquely is 154.52 GPU, and the CO2 / N2 selectivity is 40.23.

Claims

1. A method for preparing a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field, characterized in that, The synthesis steps are as follows: Step 1: Using halloysite nanotubes HNT as a template, load iron oxide on the surface of HNT by oxidative coprecipitation method to synthesize magnetic halloysite nanotubes MHNT; Step 2: Coating polydopamine and ZIF-8 on the surface of MHNT to obtain magnetic ZIF composite halloysite nanotubes ZMHNT; Step 3: Coating the mixed matrix casting solution containing ZMHNT and Pebax on the PDMS / PES substrate membrane to obtain a mixed matrix composite membrane, and using an external magnetic field regulation method to prepare a mixed matrix composite membrane with the fillers arranged obliquely.

2. The preparation method of a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 1, wherein, The specific process of Step 1 is as follows: Disperse HNT in water and mix it with ferrous sulfate heptahydrate FeSO4·7H2O to obtain a suspension, and adjust the pH range of the suspension to 8.5 - 12; Place the suspension system in an oil bath for heating and stirring reaction. After the reaction, perform suction filtration, and put the solid into a blast drying oven at 40 - 80°C for drying for 12 - 24 h to obtain magnetic halloysite nanotubes MHNT.

3. The method for preparing a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 2, wherein The mass ratio of NT to ferrous sulfate heptahydrate FeSO4·7H2O is 1:8 - 1:2; The reagent for adjusting the pH of the suspension is ammonia water; The reaction temperature is 60 - 90°C, and the reaction time is 3 - 6 h.

4. The preparation method of a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 1, wherein The specific process of Step 2 is as follows: Disperse the magnetic halloysite nanotubes MHNT obtained in Step 1 in water, and add an aqueous solution of dopamine hydrochloride and mix evenly to obtain a dispersion, and adjust the pH value range to 8 - 10 for PDA coating reaction; After the reaction, centrifuge, and put the centrifuged solid into a blast drying oven at 40 - 80°C for drying for 12 - 24 h to obtain PDA-coated halloysite nanotubes PHNT; Ultrasonically disperse the PDA-coated halloysite nanotubes PHNT in methanol, add zinc nitrate and 2-methylimidazole, ultrasonically disperse and then mechanically stir and react. After the reaction, centrifuge; Take the centrifuged solid and put it into a blast drying oven at 40 - 80°C for drying for 12 - 24 h to obtain magnetic ZIF composite halloysite nanotubes ZMHNT.

5. A method for preparing a mixed matrix composite membrane with one-dimensional materials arranged obliquely by magnetic field regulation according to claim 4, characterized in that, The reagent for adjusting the pH of the dispersion is potassium hydroxide; The time for PDA coating reaction is 0.5 - 1.5 h; The concentration of the aqueous solution of dopamine hydrochloride is 1 - 2 g / L, and the volume (mL) of the aqueous solution of dopamine hydrochloride and the mass (g) of MHNT ratio is 100 - 50:1; The centrifugation conditions after PDA coating reaction are: the centrifugation time is 10 - 30 min, and the centrifugation speed is 7000 - 11000 rpm.

6. The preparation method of a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 4, wherein The molar ratio of zinc nitrate and 2-methylimidazole added is 1:2 - 8; The mass ratio of PDA-coated halloysite nanotubes PHNT to zinc nitrate is 1:3 - 10; The reaction time is 2 - 5 h, and the mechanical stirring speed is 200 - 600 rpm; The centrifugation time is 10 - 30 min, and the centrifugation speed is 7000 - 11000 rpm.

7. A method for preparing a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 1, characterized in that, The process of the mixed matrix casting solution in step 3 is as follows: The magnetic ZIF composite halloysite nanotubes ZMHNT obtained in step 2 are added to the Pebax casting solution, the concentration of Pebax in the casting solution is 1-5 wt%, and the mass fraction of the magnetic ZIF composite halloysite nanotubes ZMHNT in the Pebax casting solution is 5%-20%; after stirring, bubbles in the casting solution are removed by ultrasonic treatment, and at the same time, the fillers are uniformly dispersed in the solution to obtain a mixed matrix casting solution.

8. The preparation method of a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 1, characterized in that, In step 3, the mixed matrix casting solution is coated on the base film by a doctor blade method or a casting method, and the cut-off molecular weight of the selected PES substrate is 10,000-50,000 Da.

9. The preparation method of a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 1, wherein, In step 3, two magnets with a strength of 0.5-1 T are respectively placed on the upper and lower sides of the glass plate with the mixed matrix composite film attached, and there are gaps between the two magnets and the glass plate of the mixed matrix composite film for magnetic field action for 12-24 h, and then the glass plate is placed in a blast drying oven at 40-80 °C for drying for 12-24 h to obtain a mixed matrix composite film with the fillers arranged obliquely.

10. A method for preparing a mixed matrix composite membrane for regulating the inclined arrangement of one-dimensional materials by using a magnetic field according to claim 1, characterized in that, Preparation method of PDMS / PES base film: Using PDMS as the solute, n-heptane as the solvent, dibutyltin dilaurate and tetraethyl orthosilicate as the catalyst and crosslinking agent respectively; the mass ratio of the crosslinking agent, catalyst to PDMS is 5:4-1:4-1, and a 2 wt%-5 wt% PDMS coating solution is prepared; the PDMS coating solution is coated on the PES substrate by a doctor blade method or a casting method, and the film is placed in an oven for drying for 0.5-1 h to obtain a PDMS / PES base film.

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