A layered porous organic composite membrane for organic solvent systems, method of preparation and use

Abstract

The present application relates to the technical field of porous nanomaterials, and particularly relates to a layered porous organic composite membrane for nanofiltration in an organic solvent system, a preparation method and application. The polymer material in the present application has strong adhesion and self-polymerization characteristics. The preparation method comprises the following steps: preparing a nanosheet hard template; dispersing the nanosheet into a reaction solution; adding a polymer monomer into the solution in which the nanosheet is dispersed, and depositing on the surface of the nanosheet through a self-polymerization reaction; removing the hard template by using acid etching to obtain a polymer nanosheet; and preparing a composite membrane by using a vacuum filtration method. The layered porous organic composite membrane prepared by the present application is made of polymer nanosheets by a top-down vacuum filtration method, and combines the advantages of polymer and inorganic nanosheets, and thus exhibits more excellent solvent permeability and dye retention performance than traditional polymer membranes and inorganic layered membranes.

Description

Technical Field

[0001] This invention relates to the field of porous organic materials and organic solvent nanofiltration technology, and in particular to a layered porous organic composite membrane for organic solvent systems, its preparation method, and its application in organic solvent systems. Background Technology

[0002] Compared to traditional separation technologies such as distillation, absorption, and adsorption, membrane separation technology offers advantages such as low energy consumption, high efficiency, and high economic benefits. Organic solvent nanofiltration, as an emerging membrane separation technology, is widely used in pharmaceutical and chemical industries. This technology enables solute extraction, solvent purification, and the separation and recycling of organic solvents, serving as an important means of energy conservation and environmental protection, and possessing significant scientific and research value. In the precise separation process of organic solvent systems, the separation membrane typically consists of a substrate support layer and a precision selection layer. The selective membrane material is the core of membrane technology. Although organic solvent system separation membranes were proposed in the early 1970s, large-scale application has been almost nonexistent to date, primarily due to the difficulty in developing membrane materials that combine stability and high selectivity. Membrane materials are mainly categorized into inorganic and polymeric membrane materials. Membranes prepared from inorganic materials exhibit superior separation performance, especially layered membranes made from inorganic nanosheets, which possess high separation performance, high temperature resistance, and good chemical stability. However, they suffer from poor elasticity, brittleness, and poor shear resistance. Besides inorganic materials, the rapid development of polymer materials has provided excellent material choices for the preparation of solvent-resistant separation membranes. Polymer materials offer advantages such as strong structural designability, solvent resistance, and high operability. However, most polymer materials suffer from poor stability and low permeability due to solvent dissolution and swelling. Fabricating porous organic polymer materials can effectively improve the low permeability of polymer membranes, but the preparation of porous polymers is challenging, as maintaining their toughness and film-forming properties is difficult. Therefore, the preparation of two-dimensional layered porous organic composite membranes, with their interlocking layered structure formed by stacked porous organic nanosheets, combines the unique advantages of porous polymer membrane materials and inorganic two-dimensional membrane materials, providing a new approach for the development and application of membranes in organic solvent systems.

[0003] Faced with global challenges such as energy resource constraints and environmental risks, there is an urgent need to transform traditional energy-intensive separation technologies and develop sustainable, low-energy-consumption separation methods to promote the green transformation and upgrading of industries. Membrane separation technology has been applied on a large scale in wastewater treatment, and the development of membrane separation technology applicable to organic solvent systems has become a research hotspot. Summary of the Invention

[0004] The purpose of this invention is to provide a layered porous organic composite membrane for organic solvent systems, its preparation method, and its application. The polymer nanosheets are organic porous nanomaterials. The prepared composite membrane exhibits excellent solvent permeation performance compared to conventional nanofiltration membranes, while also possessing high retention capacity. The preparation process is reproducible.

[0005] This invention provides a layered porous organic composite membrane for use in organic solvent systems. The layered porous organic composite membrane has a typical layered stacked structure and a porous structure, with a membrane thickness of 0.5–1.5 μm and a specific surface area of ​​35–45 m². 2 / g, with a minimum pore size of 1.2nm.

[0006] This invention also provides a method for preparing a layered porous organic composite membrane for organic solvent systems, the specific steps of which are as follows:

[0007] S1. Prepare a two-dimensional nanosheet hard template dispersion and adjust the pH of the dispersion. Add a certain amount of nickel nitrate hexahydrate and urea to water at a molar ratio of 1:4, stir until completely dissolved, then add ethylene glycol. Mix the solution until the components are homogeneous. Place the prepared solution in a microwave reactor. After the reaction is complete, centrifuge, wash, and collect the precipitate. After vacuum drying, grind it into a solid powder using a mortar and pestle. Disperse the powder ultrasonically in an aqueous solution, allow it to stand, collect the supernatant, and adjust the pH to 8.5 using Tris and hydrochloric acid solutions.

[0008] Preferably, the nickel hydroxide nanosheets prepared by the above method are referenced at: DOI:10.1038 / srep05787

[0009] Preferably, in the above method, the volume ratio of water to ethylene glycol is 7:1, the power of the microwave reactor is 700W, the reaction time is 3-5min, and the centrifuge speed is 4000-5000r / min.

[0010] Preferably, the concentration of the Tris solution used to adjust the pH value in the above method is 0.01 mol / L.

[0011] S2, the polymer monomer is added to the hard template dispersion to ensure that it fully adheres to the surface of the hard template;

[0012] A certain amount of Dopa or Dopa & PPD is added to the above nanosheet dispersion. After stirring and reacting for a period of time, the reaction is stopped. The mixture is then centrifuged, washed, and the precipitate is collected to remove excess and residual polymer monomers or oligomers. The precipitate at this point is Dopa@Ni(OH)2 or Dopa & PPD@Ni(OH)2 hybrid nanosheets.

[0013] Preferably, the Dopa concentration is 0.1–0.2 g / L, the ratio of Dopa to PPD during co-deposition is 1:1–1:3, the reaction time is 60–120 min, and the centrifuge speed is 4000–5000 r / min.

[0014] S3, A polymer nanosheet dispersion was obtained by acid etching, and then dispersed into an aqueous solution by centrifugation and washing;

[0015] After ultrasonically dispersing the hybrid nanosheets uniformly into deionized water, an acid solution was added for etching. After reacting for a period of time, the acid solution was removed by centrifugation multiple times to obtain polymer nanosheets.

[0016] Preferably, the acid solution is 0.1 mol / L hydrochloric acid or saturated ethylenediaminetetraacetic acid (EDTA) solution.

[0017] Preferably, the etching time is 4 to 5 hours and the centrifuge speed is 7000 to 8000 r / min.

[0018] S4. After diluting the nanosheet solution, a layered porous organic composite membrane was prepared by vacuum filtration.

[0019] Specifically, when using vacuum filtration to form a membrane, the nanosheet dispersion is first allowed to settle by gravity, then 0.1 bar pressure is applied for membrane forming, and finally 1 bar pressure is applied when the solution is 100 mL to form a membrane.

[0020] S5, the membrane prepared by vacuum filtration, is stored at 15°C for 24 hours and then left to stand at room temperature for 24 hours before use.

[0021] The layered porous organic composite membrane of the present invention is used for organic solvent nanofiltration.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] 1) This invention utilizes a two-dimensional hard template strategy to prepare polymer nanosheets. First, Ni(OH)₂ nanosheets are prepared. Taking advantage of the self-polymerization properties of Dopa, these nanosheets are uniformly attached to a hard template and then etched to obtain porous, flexible polymer nanosheets that combine the properties of both polymers and inorganic nanosheets. A two-dimensional polymer composite membrane is then prepared using a vacuum filtration method. Simultaneously, Dopa can undergo Michael addition reactions, and the addition of PPD for co-deposition can act as a pore-forming agent, improving the membrane's permeability and selectivity.

[0024] 2) The preparation method of the layered porous organic composite membrane of the present invention is simple, the raw materials are inexpensive, the operating conditions are simple and mild, and it has good solvent permeation performance and solvent retention performance. Attached Figure Description

[0025] Figure 1The image shows a scanning electron microscope (SEM) image of the surface of the Dopa nanosheets obtained in Example 1.

[0026] Figure 2 An atomic force microscope image of the surface of the Dopa two-dimensional composite film obtained in Example 1;

[0027] Figure 3 Here is a cross-sectional scanning electron microscope image of the Dopa two-dimensional composite membrane obtained in Example 1;

[0028] Figure 4 This is a pore size distribution diagram of the Dopa two-dimensional selective layer obtained in Example 1.

[0029] Figure 5 An atomic force microscope image of the Dopa@PPD nanosheets obtained in Example 2;

[0030] Figure 6 An atomic force microscope image of the surface of the Dopa@PPD two-dimensional composite film obtained in Example 2;

[0031] Figure 7 This is a cross-sectional scanning electron microscope image of the Dopa@PPD two-dimensional composite film obtained in Example 2;

[0032] Figure 8 This is a pore size distribution diagram of the Dopa@PPD two-dimensional selective layer obtained in Example 2.

[0033] Figure 9 The images show nitrogen adsorption isotherms of the two-dimensional composite membranes obtained in Examples 1 and 2.

[0034] Figure 10 The nitrogen adsorption isotherms of the composite membranes obtained in Comparative Examples 1 and 2 are shown.

[0035] Figure 11 The solvent permeation performance and dye rejection performance of the membranes were obtained for Examples 1, 2 and Comparative Examples 1, 2 and 3. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0037] All raw materials used in this invention are not particularly restricted in their source and can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0038] The devices involved in this invention are not particularly limited to those commonly used in the field, and their operation and usage are well known to those skilled in the art.

[0039] Example 1

[0040] Preparation of Ni(OH)₂ template: Add 30 ml of deionized water to a 250 ml beaker. Add a certain amount of nickel nitrate hexahydrate and urea in a molar ratio of 1:4 to the water and stir until completely dissolved. Then add 210 ml of ethylene glycol and wait for the solution to mix until the components are homogeneous. Place the prepared solution in a microwave reactor and microwave at 100% power for 4 min. Remove and allow to cool naturally to room temperature. Centrifuge at 3500 rpm to collect the precipitate. Then wash twice each with anhydrous ethanol and deionized water by centrifugation. Dry under vacuum at 90℃ for 24 h. Grind the precipitate into a solid powder using a mortar and pestle for later use.

[0041] Preparation of Dopa two-dimensional nanosheets: 1000 ml of deionized water was added to a beaker. 1.21 g of Tris was added to the water and stirred until completely dissolved. The pH of the solution was adjusted to 8.5. 0.2 g of Ni(OH)₂ nanosheets were added to the prepared Tris solution and sonicated for 40 min to disperse evenly. After standing for 3–4 h, 500 ml of the supernatant was collected and heated and stirred in a 25°C water bath. 0.5 g of Dopa was added to the above nanosheet dispersion. The reaction was stopped after 1 h. The precipitate was collected by centrifugation and washed with Tris solution to remove excess and residual Dopa. The precipitate was then Dopa@Ni(OH)₂ hybrid nanosheets. These were etched with 0.1 mol hydrochloric acid solution and then washed three times with deionized water at 8000 rpm to obtain Dopa two-dimensional porous nanosheets.

[0042] Preparation of Dopa composite membrane: The above-obtained nanosheets were dispersed in a certain amount of deionized water and gently sonicated to make them evenly dispersed. Then, a certain amount of Dopa nanosheet dispersion was added to a vacuum filtration device. The Dopa thin film composite membrane was prepared from bottom to top by vacuum filtration. After the dispersion was evacuated, the membrane was removed after 5 minutes and placed in a refrigerator at 15°C for 24 hours. Then, it was dried at room temperature for 24 hours for later use.

[0043] The nanofiltration performance test procedure for solvents is as follows:

[0044] The sample membrane was installed in the dead-end testing device, and 50 mL of the solvent to be tested was added. The driving force was controlled by adjusting the N2 pressure reducing valve. After the permeate flowed out steadily, a certain amount of solvent was collected, the volume of the collected solvent was read, and the absorbance of the solution before and after passing through the membrane was measured using a UV-Vis spectrophotometer. Throughout this process, to avoid errors caused by solvent evaporation, the solvent was always kept under liquid nitrogen protection.

[0045] The solvent permeation coefficient refers to the volume of solvent that permeates through the membrane per unit area, unit time, and unit pressure. Its calculation formula is as follows:

[0046]

[0047] In the formula:

[0048] Permeance – the solvent's permeability coefficient, in liters (Lm) -2 h -1 bar -1 ;

[0049] V—The volume of solvent permeating through the membrane, in L;

[0050] A – Effective test area of ​​the membrane, m 2 ;

[0051] t — Test time, h;

[0052] p – applied pressure, bar;

[0053] Dye Retention Rate Test: The dye retention rate is the percentage of dye molecules retained in the raw material relative to the total amount of raw material. After the flux reaches stability, a 10 mL sample is taken, and the concentrations of the original solution and the permeate are measured using a UV spectrophotometer. The dye retention rate of the membrane is then calculated using the following formula:

[0054]

[0055] In the formula: R is the rejection rate; C P C is the concentration of the permeate. F This represents the original solution concentration.

[0056] The results showed that the methanol flux of the Dopa two-dimensional layered membrane was 79.1 Lm. -2 h -1 bar -1 The retention rate of reactive black (RB) was 95.2%.

[0057] Example 2

[0058] Preparation of Ni(OH)₂ template: Add 15 ml of deionized water to a 125 ml beaker. Add a certain amount of nickel nitrate hexahydrate and urea in a molar ratio of 1:4 to the water and stir until completely dissolved. Then add 105 ml of ethylene glycol and mix until the components are homogeneous. Place the prepared solution in a microwave reactor and microwave at 80% power for 5 min. Remove and allow to cool naturally to room temperature. Centrifuge at 4000 rpm to collect the precipitate. Then wash twice each with anhydrous ethanol and deionized water by centrifugation. Dry under vacuum at 120℃ for 24 h. Grind the precipitate into a solid powder using a mortar and pestle for later use.

[0059] Preparation of Dopa & PPD two-dimensional nanosheets: 1000 ml of deionized water was added to a beaker, and 1.21 g of Tris was added to the water and stirred until completely dissolved. The pH of the solution was adjusted to 8.5. 0.3 g of Ni(OH)₂ nanosheets were added to the prepared Tris solution and sonicated for 50 min to disperse evenly. After standing for 12 h, 800 ml of the supernatant was collected and heated and stirred in a 25°C water bath. 0.8 g of Dopa and 0.4 g of PPD were added to the above nanosheet dispersion. The reaction was stopped after 2 h, and the precipitate was collected by centrifugation. The precipitate was washed with Tris solution by centrifugation to remove excess and residual Dopa and PPD. The precipitate was Dopa & PPD@α-Ni(OH)₂ hybrid nanosheets. The precipitate was etched with saturated EDTA solution and then washed three times with deionized water at 8000 rpm to obtain Dopa & PPD two-dimensional porous nanosheets.

[0060] Preparation of Dopa & PPD composite membrane: The above-obtained nanosheets were dispersed in a certain amount of deionized water and gently sonicated to make them evenly dispersed. Then, a certain amount of Dopa & PPD nanosheet dispersion was added to a vacuum filtration device. The Dopa & PPD thin film composite membrane was prepared from bottom to top using vacuum filtration. After the dispersion was evacuated, the membrane was removed after 5 minutes and placed in a refrigerator at 15°C for 24 hours. Then, it was dried at room temperature for 24 hours for later use.

[0061] Nanofiltration performance was tested using the same testing apparatus and method as in Example 1.

[0062] The results showed that the methanol flux of the Dopa & PPD two-dimensional layered membrane was 128.2 Lm. -2 h -1 bar -1 The retention rate of reactive black (RB) was 91.5%.

[0063] Comparative Example 1

[0064] Preparation of Dopa@PES composite membrane: A commercial polyethersulfone membrane (UE050) with a molecular weight cutoff of 50,000 was immersed in deionized water for 12 hours. A 1L solution of 0.01mol / L Tris was prepared in a beaker and adjusted to pH 8.5. The treated PES membrane was placed in the beaker, and 1g of Dopa was added. The mixture was then reacted in a shaker at 25℃ for 24 hours to allow Dopa to deposit uniformly on the PES membrane surface, forming a selective layer. The membrane was then removed, rinsed thoroughly with deionized water, and dried in a 35℃ oven for later use.

[0065] The results showed that the methanol flux of the Dopa@PES composite membrane was 6.2 Lm. -2 h -1 bar -1The retention rate of Reactive Black (RB) was 59.6%.

[0066] Comparative Example 2

[0067] Preparation of Dopa & PPD@PES composite membrane: A commercial polyethersulfone membrane (UE050) with a molecular weight cutoff of 50,000 was immersed in deionized water for 12 hours. A 1L solution of 0.01mol / L Tris was prepared in a beaker and adjusted to pH 8.5. The treated PES membrane was placed in the beaker, and 1g of Dopa and 0.5g of PPD were added. The mixture was then reacted in a shaker at 25℃ for 24 hours to allow Dopa and PPD to be uniformly deposited on the PES membrane surface, forming a selective layer. The membrane was then removed, rinsed with deionized water, and dried in a 35℃ oven for later use.

[0068] The results showed that the methanol flux of the Dopa&PPD@PES composite membrane was 12.9 Lm. -2 h -1 bar -1 The retention rate of Reactive Black (RB) was 55.4%.

[0069] Comparative Example 3

[0070] Preparation of GO layered membrane: The exfoliated GO nanosheets were diluted in deionized water and the concentration was tested to be 0.5 g / L. 300 μL of GO solution was dispersed in 200 mL of deionized water and sonicated for 40 min to make the nanosheets uniformly dispersed in the aqueous solution. The GO layered membrane was prepared by vacuum filtration and dried in a 60℃ forced-air drying oven for later use.

[0071] The results showed that the methanol flux of the GO layered membrane was 18.5 L / m³. -2 h -1 bar -1 The retention rate of Reactive Black (RB) was 65.8%.

[0072] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A layered porous organic composite membrane for use in organic solvent systems, characterized in that, The layered porous organic composite membrane has a typical layered stacked structure and porous structure, with a membrane thickness of 0.5~1.5 μm and a specific surface area of ​​35~45 m². 2 / g, with a minimum pore size of 1.2 nm; The method for preparing the layered porous organic composite membrane includes the following steps: S1, a two-dimensional nanosheet hard template dispersion was prepared, and the pH of the dispersion was adjusted; the two-dimensional nanosheet hard template was nickel hydroxide; the pH of the hard template dispersion was adjusted by tris(hydroxymethyl)aminomethane and hydrochloric acid. S2, the polymer monomer is added to the hard template dispersion to allow the polymer monomer to fully adhere to the surface of the hard template. The polymer monomer is uniformly polymerized and deposited on the hard template to obtain hybrid nanosheets; the polymer monomer is levodopa or levodopa and p-phenylenediamine. S3, using acid etching of hybrid nanosheets to obtain polymer nanosheet dispersion; S4. After diluting the polymer nanosheet dispersion, a layered porous organic composite membrane was prepared by vacuum filtration. S5, the membrane prepared by vacuum filtration, is stored at 15°C for 24 hours and then left to stand at room temperature for 24 hours before use.

2. The layered porous organic composite membrane for organic solvent systems according to claim 1, characterized in that: In step S2, the concentration of the polymer monomer is 0.1~0.2 mg / mL, and the reaction temperature is 25 ℃.

3. The layered porous organic composite membrane for organic solvent systems according to claim 1, characterized in that: In step S3, the pH value of the etching solution is between 1 and 2, and the temperature is between 25°C and 30°C.

4. The use of the layered porous organic composite membrane according to claim 1, characterized in that: Used for nanofiltration of organic solvents.

Images