A preparation method of a mixed matrix composite membrane using a magnetic field to regulate one-dimensional material inclined arrangement

Abstract

A preparation method of a mixed matrix composite membrane with one-dimensional material tilt arrangement regulated by a magnetic field. The method prepares magnetic ZIF composite halloysite nanotubes (ZMHNT) by loading ferroferric oxide and metal organic framework (ZIF-8) on halloysite nanotubes (HNT), and mixes the ZMHNT with polyether block polyamide, coats the mixture on a polyether sulfone (PES) base film covered by polydimethylsiloxane (PDMS), and places the mixture in a magnetic field environment for orientation adjustment to prepare a mixed matrix composite membrane with one-dimensional filler tilt arrangement. The application grows ZIF-8 on HNT, screens CO2 and N2 through the continuous ZIF-8 layer coated on the pipe opening, and makes ZMHNT realize a large tilt angle and a penetrating arrangement in the membrane under the action of a magnetic field force, overcomes anisotropy, strengthens the diffusion speed of the gas in the hollow pipe of ZMHNT, and improves the gas separation performance of the mixed matrix composite membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of gas separation membrane materials, and particularly relates to a preparation method of a mixed matrix composite membrane with one-dimensional material inclined arrangement regulated by a magnetic field. BACKGROUND

[0002] Since the industrial revolution, the carbon dioxide emission of human society has increased significantly, leading to a series of natural disasters including ocean acidification, ice cap melting, and hurricane intensification. As a key means to achieve carbon neutrality, various carbon capture technologies have attracted widespread attention. Among them, the membrane separation method is concerned because of its low energy consumption, easy coupling, and low cost.

[0003] Carbon dioxide separation membranes mainly include polymer membranes, inorganic membranes, and mixed matrix membranes. The polymer membrane has low cost and good film-forming performance, but there is a trade-off effect between permeation flux and selectivity; the flux and selectivity of the inorganic membrane can reach a high level, but its film-forming property is poor and the cost is high. The mixed matrix membrane can combine the advantages of polymer membranes and inorganic membranes, and can break the trade-off limit between selectivity and permeability of traditional membranes. Metal-organic framework (MOFs) is a kind of porous material combined by metal ions and organic ligands, which has the advantages of super-high specific surface area, high porosity, adjustable pore size, and chemical stability; among the materials in each dimension of the mixed matrix membrane, the internal continuous hollow structure of the one-dimensional tubular material can provide a stable high-speed transmission channel for gas molecules, and the composite one-dimensional material prepared by combining MOFs and one-dimensional tubular material can simultaneously play the roles of screening selection and transmission in the membrane. However, 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, MIL-101 is loaded on CNT and mixed into polyimide to prepare a mixed matrix membrane, the one-dimensional material of MOF itself cannot form a straight-through channel in the membrane, and the performance improvement is limited. Therefore, regulating the orientation of the material to form a straight-through channel in the membrane is expected to further improve the gas performance of the membrane.

[0004] The application prepares magnetic ZIF composite halloysite nanotubes ZMHNT. First, Fe3O4 is loaded on the HNT wall to endow the material with magnetism. Then, ZIF-8 and PDA are coated on the wall and the mouth of the tube. On the one hand, the interface compatibility between inorganic materials and polymers is improved. On the other hand, a continuous ZIF selective layer is formed at the mouth of the tube, realizing the sieving of CO2 / N2 by the tubular material. Then, ZMHNT is mixed with Pebax, and is scraped on a PES / PDMS composite membrane. Through external magnetic field regulation, ZMHNT is arranged in a large inclination and a penetrating manner in the membrane, forming a straight-through channel for CO2 gas molecules, so that the gas permeability and selectivity of the membrane are improved. SUMMARY

[0005] In view of the fact that most one-dimensional materials cannot significantly improve the performance in the mixed matrix membrane, the application aims to provide a preparation method of a mixed matrix composite membrane using a magnetic field to regulate the inclined arrangement of one-dimensional materials.

[0006] The technical scheme of the application is as follows:

[0007] The preparation method of the mixed matrix composite membrane using a magnetic field to regulate the inclined arrangement of one-dimensional materials comprises the following steps:

[0008] In step 1, halloysite nanotubes HNT are used as a template, and Fe3O4 is loaded on the surface of the HNT through an oxidation co-precipitation method to synthesize magnetic halloysite nanotubes MHNT.

[0009] In step 2, polydopamine and ZIF-8 are coated on the surface of the MHNT to obtain magnetic ZIF composite halloysite nanotubes ZMHNT.

[0010] In step 3, a mixed matrix casting solution containing ZMHNT and Pebax is coated on a PDMS / PES base membrane to obtain a mixed matrix composite membrane. A mixed matrix composite membrane with inclined arrangement of fillers is prepared by using an external magnetic field regulation method.

[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. The pH of the suspension is adjusted to a range of 8.5-12. The suspension system is placed in an oil bath for heating and stirring reaction. After the reaction is completed, the solid is dried in a 40-80℃ air oven for 12-24h to obtain magnetic halloysite nanotubes MHNT.

[0012] Further, 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℃, and the reaction time is 3-6h.

[0013] Further, the specific process of step 2 is: the magnetic halloysite nanotubes MHNT obtained in step 1 are dispersed in water, and a dopamine hydrochloride aqueous solution is added to mix uniformly to obtain a dispersion liquid, and a PDA coating reaction is carried out by adjusting the pH value in the range of 8-10; after the reaction is completed, centrifugation is carried out, and the solid after centrifugation is placed in a 40-80℃ air oven for drying for 12-24h to obtain PDA-coated halloysite nanotubes PHNT. The PDA-coated halloysite nanotubes PHNT are ultrasonically dispersed in methanol, zinc nitrate and 2-methylimidazole are added, and after ultrasonic dispersion, mechanical stirring and reaction are carried out, and after the reaction is completed, centrifugation is carried out. The solid after centrifugation is placed in a 40-80℃ air oven for drying for 12-24h to obtain magnetic ZIF composite halloysite nanotubes ZMHNT.

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

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

[0016] Further, the process of mixing the matrix casting solution in step 3 is: the magnetic ZIF composite halloysite nanotubes ZMHNT obtained in step 2 are added to a Pebax casting solution, the concentration of Pebax in the casting solution is 1-5wt%, and the mass fraction of the magnetic ZIF composite halloysite nanotubes ZMHNT in the Pebax casting solution is 5%-20%; after stirring, ultrasonic is used to remove bubbles in the casting solution, and at the same time, the filler is uniformly dispersed in the solution to obtain a mixed matrix casting solution.

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

[0018] Further, in step 3, two magnets with the strength of 0.5-1T are selected and placed on the upper and lower sides of the glass plate with the mixed matrix composite film, respectively, and gaps are left between the two magnets and the glass plate with the mixed matrix composite film, and then the magnetic field is applied for 12-24h, and then the glass plate is placed in a 40-80℃ air oven for drying for 12-24h, so that the mixed matrix composite film with the filler arranged in an inclined manner is obtained.

[0019] Further, the preparation method of the PDMS / PES-based film is as follows: taking PDMS as a solute, n-heptane as a solvent, and dibutyltin dilaurate and tetraethyl orthosilicate as a catalyst and a crosslinking agent, respectively; the mass ratio of the crosslinking agent, the catalyst and PDMS is 5:4-1:4-1, and 2wt%-5wt% of the PDMS coating solution is prepared.

[0020] Compared with the prior art, the magnetic ZIF composite halloysite nanotube ZMHNT prepared by the application has a tubular structure, can provide a high-speed gas transmission channel in the film, and can enhance the compatibility between the ZIF-8 and PDA reinforcing material coated outside the tube and the polymer matrix, so that the continuous ZIF-8 layer coated at the tube opening can screen CO2 and N2, and under the regulation of an external magnetic field, the ZMHNT can be arranged in a large inclination and a penetrating manner in the selected layer of the film, so as to strengthen the diffusion speed of CO2 gas in the hollow tube of the ZMHNT, the continuous ZIF-8 material coated at the tube opening can screen CO2 and N2, and the gas permeability and selectivity of the mixed matrix composite film are improved. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

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

[0025] Figure 5 It is a cross-sectional scanning electron microscope picture of the mixed matrix composite film under ordinary drying in Example 2.

[0026] Figure 6 A comparison chart of the gas separation performance of the different membranes of Examples 1-2 and Comparative Examples. DETAILED DESCRIPTION

[0027] Example 1

[0028] Preparation of magnetic halloysite nanotubes: 1 g of HNT powder was added to a 200 mL reagent bottle, 100 mL of deionized water was weighed into the bottle and mixed with the HNT, and mechanical stirring was performed for 30 min to uniformly disperse the HNT in the water. Then 3 g of FeSO4·7H2O powder was added to the HNT suspension, and ultrasonic treatment was performed for 30 min to form a uniform suspension in the bottle. During this process, the liquid in the bottle gradually changed from white to green. Then ammonia water was added to the bottle several times, and the PH value was observed on the PH test paper using a glass rod to dip the liquid. The process was continued until the PH value reached 9. During this process, the liquid color in the bottle gradually changed from green to dark green. The temperature of the oil bath was set to 80°C, the bottle was placed in the pot, mechanical stirring was performed, and the reaction was allowed to proceed for 4 h. The stirring speed was set to 400 rpm. After the reaction was completed, the bottle was removed, and the temperature was allowed to decrease at room temperature for 15 min. Then the solid-liquid two-phase in the bottle was separated using vacuum filtration. The process was washed with deionized water for 3 times. Then the filter paper carrying the black solid was placed in a 70°C air oven for drying for 12 h to obtain a magnetic one-dimensional material, which was named MHNT.

[0029] Preparation of magnetic ZIF composite halloysite nanotubes: 1 g of MHNT was placed in a 200 mL reagent bottle, 100 mL of deionized water was added, and ultrasonic treatment was performed for 20 min to disperse. Then 0.2 g of dopamine hydrochloride was added and stirred for 40 min. Then 1.5 mol / L of KOH solution was added, and the PH value was observed on the PH test paper using a glass rod to dip the liquid. The process was continued until the PH value reached 9, and stirring was performed for 40 min. After the reaction was completed, the liquid was placed in a centrifuge tube, and the centrifuge was set to a speed of 10000 r / min for 15 min. The liquid was washed with water and methanol for 2 times, and then placed in a 70°C air oven for drying for 12 h to obtain a magnetic one-dimensional material carrying PDA, which was named PHNT. Next, 0.1 g of PHNT was placed in a 200 mL reagent bottle, 150 mL of methanol was added, and ultrasonic treatment was performed for 20 min to disperse. Then 0.3 g of zinc nitrate and 0.16 g of 2-methyl imidazole were added, and ultrasonic treatment was performed for 20 min to uniformly mix the particles. Then the reagent bottle was placed in a room temperature mechanical stirrer, the stirring speed was set to 400 rpm, and the reaction was allowed to proceed for 3 h. After the reaction was completed, the liquid was placed in a centrifuge tube, and the centrifuge was set to a speed of 10000 r / min for 15 min. The liquid was washed with methanol for 2 times, and then placed in a 70°C air oven for drying for 12 h to obtain magnetic ZIF composite halloysite nanotubes (ZMHNT).

[0030] Preparation of a mixed matrix composite membrane with tilted filler arrangement: 0.6 g of Pebax was weighed and added to a 100 mL flask. 17.4 mL of water and 52 mL of ethanol were measured and mixed together. The mixture was then refluxed at 80 °C for 4 h to obtain a Pebax polymer solution, which was cooled for later use. Next, ZMHNT material was added to 5 g of the Pebax polymer solution at a mass percentage of 10%, stirred for 1 h, and then sonicated for 1 h to remove air bubbles. Simultaneously, a 2 wt% PDMS coating solution was prepared. The mass ratio of PDMS was calculated to be 0.5 g, n-heptane 22 g, catalyst 0.4 g, and crosslinking agent 0.4 g. First, PDMS and n-heptane were mixed until completely dissolved. Then, the crosslinking agent was added and stirred until a uniform PDMS coating solution was formed. A PES substrate was adhered to a glass plate with adhesive tape. PDMS coating solution was then applied to the PES substrate using a blade coating or casting method. The film was then dried in a 40°C oven for 0.5-1 hour to obtain a PDMS / PES base film. Prior to this, a composite film was prepared by blade coating a PDMS solution onto a PES base film with a molecular weight cutoff of 20000 Da. A casting solution was then blade coated onto the PDMS / PES composite film. The glass plate with the film attached was placed in a magnetic field provided by two square magnets with a magnetic field strength of 0.6T and left at room temperature for 12 hours. Afterward, the glass plate was transferred to a 40°C oven and dried for 12 hours to completely remove the solvent, thus obtaining a mixed matrix composite film with tilted filler arrangement, denoted as 10wt% ZMHNT-magnetic field.

[0031] Example 2

[0032] The main steps are the same as in Example 1. The prepared material is a directly dried mixed matrix composite membrane. The difference is that a casting solution with a mass fraction of 10% after ultrasonication is taken, coated onto the PDMS / PES composite membrane, and then the glass plate with the membrane is placed in a 40℃ forced-air oven to dry for 24 hours until the solvent is completely removed, thus obtaining a directly dried mixed matrix composite membrane.

[0033] Example 3

[0034] The main steps are the same as in Example 1. The difference is that in the synthesis of MHNT, ammonia water is added dropwise to adjust the pH value to 11, the reaction temperature is 90℃, and the reaction time is 6h; in the synthesis of ZMHNT, the reaction time for preparing PHNT is 1.5h, the amount of 2-methylimidazole added is 0.66g, and the reaction time is 5h.

[0035] Example 4

[0036] The main steps are the same as in Example 1. The difference is that in the synthesis of MHNT, ammonia water is added dropwise to adjust the pH value to 8.5, the reaction temperature is 60℃, and the reaction time is 3h; in the synthesis of ZMHNT, the reaction time for preparing PHNT is 1.5h, the amount of 2-methylimidazole added is 0.32g, and the reaction time is 2h.

[0037] Comparative Example

[0038] The main steps are the same as 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. The casting solution, which is completely dispersed after ultrasonication, is scraped onto the PDMS / PES composite membrane. The glass plate with the membrane is placed in a 40℃ forced-air oven and dried for 12 hours until the solvent is completely removed, thus obtaining a pure Pebax composite membrane.

[0039] Gas permeability tests were conducted on the membranes of Examples 1-2 and the comparative example. The results showed that the prepared directly dried mixed matrix composite membrane, under the test conditions of 10 wt% doping, 25°C, and 2 bar, had a CO2 permeation rate of 129.92 GPU and a CO2 / N2 selectivity of 34.95. The prepared mixed matrix composite membrane with tilted filler arrangement had a CO2 permeation rate of 154.52 GPU and a CO2 / N2 selectivity of 40.23.

Claims

1. A method for preparing a hybrid matrix composite membrane using a magnetic field to control the tilted arrangement of one-dimensional materials, characterized in that, The synthesis steps are as follows: Step 1: Using halloysite nanotubes (HNT) as templates, magnetic halloysite nanotubes (MHNT) were synthesized by loading iron oxide (Fe3O4) onto the surface of HNTs via an oxidation co-precipitation method. Step 2: Coating the surface of MHNT with polydopamine and ZIF-8 to obtain magnetic ZIF composite halloysite nanotubes ZMHNT; Step 3: Coat the PDMS / PES base membrane with a mixed matrix casting solution containing ZMHNT and Pebax to obtain a mixed matrix composite membrane. Prepare the mixed matrix composite membrane with the filler arranged at an angle by using an external magnetic field control method.

2. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 1, characterized in that, 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 is completed, it is filtered, and the solid is placed in a forced-air drying oven at 40-80℃ for 12-24h to obtain magnetic halloysite nanotubes MHNT.

3. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 2, characterized in that, The mass ratio of HNT and ferrous sulfate heptahydrate FeSO4·7H2O is 1:8-1:2; ammonia water is used to adjust the pH of the suspension; the reaction temperature is 60-90℃ and the reaction time is 3-6h.

4. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 1, characterized in that, The specific process of step 2 is as follows: the magnetic halloysite nanotubes MHNT obtained in step 1 are dispersed in water, and dopamine hydrochloride aqueous solution is added and mixed evenly to obtain a dispersion. The pH value is adjusted to 8-10 for PDA coating reaction. After the reaction, the solid is centrifuged and placed in a 40-80℃ forced-air drying oven to dry for 12-24 hours to obtain PDA-coated halloysite nanotubes PHNT. The PDA-coated halloysite nanotubes PHNT are ultrasonically dispersed in methanol, zinc nitrate and 2-methylimidazole are added, and after ultrasonic dispersion, mechanical stirring and reaction are carried out. After the reaction, the solid is centrifuged. The centrifuged solid is placed in a 40-80℃ forced-air drying oven to dry for 12-24 hours to obtain magnetic ZIF composite halloysite nanotubes ZMHNT.

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

6. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 4, characterized in that, The molar ratio of zinc nitrate to 2-methylimidazole 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, the mechanical stirring speed is 200-600 rpm; the centrifugation time is 10-30 min, and the centrifugation speed is 7000-11000 rpm.

7. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 1, characterized in that, The preparation 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 magnetic ZIF composite halloysite nanotubes (ZMHNT) in the Pebax casting solution is 5%-20%. After stirring, the bubbles in the casting solution are removed by ultrasonication, and the filler is uniformly dispersed in the solution to obtain the mixed matrix casting solution.

8. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 1, characterized in that, In step 3, the mixed matrix casting solution is coated onto the PDMS / PES base film using a scraping or casting method. The molecular weight cutoff of the PES substrate in the PDMS / PES base film is 10,000-50,000 Da.

9. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 1, characterized in that, In step 3, two magnets with a strength of 0.5-1T are placed on the upper and lower sides of the glass plate with the mixed matrix composite film attached, respectively. A gap is left between the two magnets and the glass plate with the mixed matrix composite film to perform magnetic field action for 12-24 hours. Then, the glass plate is placed in a forced-air drying oven at 40-80℃ for 12-24 hours to obtain a mixed matrix composite film with the filler arranged at an angle.

10. The method for preparing a hybrid matrix composite membrane with one-dimensional material tilted arrangement controlled by a magnetic field according to claim 1, characterized in that, Preparation method of PDMS / PES base film: PDMS is used as solute, n-heptane is used as solvent, and dibutyltin dilaurate and tetraethyl orthosilicate are used as catalyst and crosslinking agent, respectively; the mass ratio of crosslinking agent, catalyst and 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 blade coating or casting method, and the film is placed in an oven to dry for 0.5-1h to obtain PDMS / PES base film.

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