A tannin surface-modified polydimethylsiloxane / polyether sulfone ultrathin composite membrane, preparation method and application

Abstract

The present application belongs to the technical field of gas-liquid two-phase gas separation membrane, such as separating gas from liquid, and discloses a tannin surface modified polydimethylsiloxane / polyether sulfone ultra-thin composite membrane, a preparation method and application, which is a composite membrane using tannin surface modification, taking polyether sulfone as a porous support layer as a base film and polydimethylsiloxane as a dense membrane separation layer, and can act on the gas-liquid phase interface to realize the exchange of gas and liquid O2 and CO2. The present application is applied to the preparation of a composite membrane material with high CO2 / O2 selectivity, high gas permeability and good anti-pollution performance. The overall film preparation process of the present application is simple, the raw material price is low, the film can resist high temperature and high pressure, and has great application potential. The tannin surface modification method is simple, can improve the hydrophilicity of the PDMS / PES composite membrane, improve the anti-pollution performance, and is more conducive to gas separation in a gas-liquid two-phase environment.

Description

Technical Field

[0001] This invention belongs to the technical field of gas-liquid two-phase gas separation membranes, such as separating gases from liquids. It relates to a tannic acid-modified polydimethylsiloxane / polyethersulfone ultrathin composite membrane, its preparation method, and its application. It is a composite membrane that uses tannic acid surface modification, with polyethersulfone as a porous support layer as the base membrane and a polydimethylsiloxane dense membrane as the separation layer. It can act at the gas-liquid interface to realize the exchange of O2 and CO2 between gas and liquid. Background Technology

[0002] Gas-liquid two-phase gas separation membrane materials must possess good gas permeability, suitable gas selectivity, and antifouling properties, while also preventing leakage during use. Currently, the main membrane used for gas-liquid interfaces that meets these requirements is poly-4-methyl-1-pentene (PMP) membrane. However, the production chain of PMP (propylene dimer - PMP resin - PMP hollow fiber membrane) is expensive, and there are problems such as difficulty in preparing gradient micropores and liquid leakage.

[0003] Polydimethylsiloxane (PDMS) has a Si-O-Si inorganic backbone and organic side chains. It is a non-toxic, highly hydrophobic, transparent polymer with the molecular formula (C2H6OSi)n. The structure of PDMS is shown in the figure.

[0004]

[0005] Its glass transition temperature is very low, approximately -127℃, and it possesses a flexible framework structure. Numerous studies have shown that PDMS materials exhibit high gas permeability and superior material stability, meeting the requirements of special membrane materials with high CO2 and O2 permeability. This material stability also allows it to exist long-term in gas-liquid two-phase contact environments without releasing harmful substances or posing a threat to the liquid phase solution. Furthermore, PDMS materials are domestically produced in my country and are relatively inexpensive. In their article "Highly permeable innovative PDMS coated polyethersulfone membranes embedded with activated carbon for gas separation," Bilal Haider et al. used spin-coating to coat a layer of PDMS onto an asymmetric PES membrane embedded with activated carbon for gas separation. In their article "Hemocompatible polydimethylsiloxane / polysulfone ultrathin composite membrane for extracorporeal membrane oxygenation," Du et al. prepared a PDMS / PSF composite membrane using PDMS as the coating solution and polysulfone PSF as the base membrane, demonstrating superior gas separation performance compared to PMP membranes. Although PDMS coated composite membranes have outstanding gas separation performance, when applied to gas-liquid two-phase gas separation, the hydrophobicity of PDMS in contact with the liquid medium can cause irreversible protein adsorption, resulting in membrane fouling. Therefore, improving the hydrophilicity and antifouling properties of PDMS coated composite membranes is of great significance.

[0006] Using tannic acid as a polyphenol ligand, iron ions Fe 3+ As an inorganic crosslinking agent, it can rapidly assemble high-strength coordination compound films on the surface of composite membranes in a one-step process. This method is simple, fast, versatile, and has secondary reaction activity. It can improve the hydrophilicity of composite membranes, alleviate membrane fouling problems, and is more conducive to gas separation in gas-liquid two-phase environments. Summary of the Invention

[0007] This invention addresses the limitations of PDMS materials by providing a simple and inexpensive method to prepare a PDMS / PES composite membrane using polyethersulfone (PES) as a base membrane and carrying PDMS material. The membrane is then modified with a one-step tannic acid (TA) self-assembly modification method. The PES material, used as the base membrane, is safe, non-toxic, and can directly contact various solutions or mixtures, and it does not easily decompose under conventional high-temperature and high-pressure sterilization. The density of the PDMS material prevents liquid leakage and gas embolism, while also achieving good gas separation performance. The tannic acid surface modification method is simple and can improve the hydrophilicity and antifouling properties of the PDMS / PES composite membrane.

[0008] The technical solution of this invention:

[0009] A tannic acid-modified polydimethylsiloxane / polyethersulfone ultrathin composite membrane includes a composite membrane base and a coating layer. The composite membrane base is made of polyethersulfone, and the coating layer is a densely separated PDMS layer self-assembled from tannic acid. The thickness of the polydimethylsiloxane / polyethersulfone ultrathin composite membrane is adjustable from 70 to 150 μm, and the thickness of the coating layer is adjustable from 0.07 to 5 μm as needed. The composite membrane base exhibits a loose, finger-like porous structure with large internal cavities and numerous micropores on its surface. The coating layer thickness increases with increasing coating solution concentration. Tannic acid and Fe... 3+ Layer-by-layer self-assembly is repeatedly used to modify the composite membrane.

[0010] A method for preparing a tannic acid-modified polydimethylsiloxane / polyethersulfone ultrathin composite film, comprising the following steps:

[0011] (1) Pretreatment of PES base membrane: The PES base membrane was immersed in a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 1:1 and kept at 80°C for 24 hours to remove impurities in the pores of the PES base membrane and improve the permeation flux.

[0012] (2) PDMS selective layer coating: Polydimethylsiloxane / polyethersulfone ultrathin composite membranes were prepared using a wet film coating method; firstly, a coating solution was prepared, with PDMS as the solute and isooctane as the solvent, and the concentration of the PDMS coating solution was 1%wt-2%wt; poly(methylhydrosiloxane) and platinum catalyst were used as crosslinking agent and catalyst, respectively; the mass ratio of crosslinking agent, catalyst and PDMS was 1:1:100; the PES base membrane pretreated in step (1) was taken out from the washing solution, the surface moisture was absorbed, and it was cut into squares. Fold the four sides backward to prevent the coating from contacting the reverse side of the PES base film; after the coating solution has been allowed to stand to remove bubbles, pour it into the tank, immerse the smooth side of the PES base film into the coating solution, tilt it during immersion so that the entire surface of the PES base film is submerged in the coating solution, the contact time between the PES base film and the coating solution is 2-3 seconds, then quickly lift the PES base film and tilt it to stand still for 30 minutes; press the coated PES base film flat on a glass plate and dry it at 85℃ for 2 hours to obtain a polydimethylsiloxane / polyethersulfone ultrathin composite film;

[0013] (3) TA surface modification: Prepare 0.8 mg / ml FeCl3·6H2O aqueous solution and 3.2 mg / ml TA aqueous solution, immerse the polydimethylsiloxane / polyethersulfone ultrathin composite film in FeCl3·6H2O aqueous solution; sonicate for 1 hour to completely wet the polydimethylsiloxane / polyethersulfone ultrathin composite film; at the same time, place equal volumes of FeCl3·6H2O aqueous solution and TA aqueous solution in a 30℃ constant temperature device for 1 hour; place the sonicated polydimethylsiloxane / polyethersulfone ultrathin composite film in equal volumes of FeCl3·6H2O aqueous solution and TA aqueous solution at a constant temperature, shake and keep at this temperature for 2 hours, and then rinse the modified polydimethylsiloxane / polyethersulfone ultrathin composite film with deionized water;

[0014] Repeat step (3) multiple times for layer-by-layer assembly modification. After the modification is completed, dry at room temperature to obtain a tannic acid-modified polydimethylsiloxane / polyethersulfone ultrathin composite film.

[0015] A tannic acid-modified polydimethylsiloxane / polyethersulfone ultrathin composite membrane enables gas separation in a gas-liquid two-phase environment.

[0016] The beneficial effects of this application are as follows: This invention is applied to the preparation of composite membrane materials with high CO2 / O2 selectivity, stable chemical properties, and antifouling performance. The overall membrane fabrication process of this invention is simple. By selecting polyethersulfone (PES) with high mechanical strength as the base membrane, the limitations of the coating material's low mechanical strength are overcome, resulting in a composite membrane with an ultra-thin selective layer, which significantly improves gas flux. Simultaneously, the presence of a dense skin layer prevents gas embolism and feed leakage. Both PES and PDMS are non-toxic and do not affect the liquid phase during contact. The presence of tannic acid improves the hydrophilicity of the composite membrane, mitigating membrane fouling and facilitating gas separation in a gas-liquid two-phase environment. Furthermore, this invention uses relatively inexpensive materials, greatly reducing the preparation cost of such special membrane materials. Attached Figure Description

[0017] Figure 1 These are scanning electron microscope images of the polyethersulfone-based membrane and the PDMS / PES composite membrane. (a) The top surface of the polyethersulfone-based membrane; (b) The cross-section of the polyethersulfone-based membrane; (c) The top surface of the PDMS / PES composite membrane; (d) The cross-section of the prepared PDMS / PES composite membrane; (e) The top surface of the PDMS / PES composite membrane after TA modification once; (f) The top surface of the PDMS / PES composite membrane after TA modification twice; (g) The top surface of the PDMS / PES composite membrane after TA modification three times.

[0018] Figure 2 The figures show the energy dispersive spectroscopy (EDS) spectra of the PDMS / PES composite membranes before and after tannic acid modification. (a) Energy dispersive spectroscopy (EDS) spectra of the PDMS / PES composite membranes; (b) Energy dispersive spectroscopy (EDS) spectra of the PDMS / PES composite membranes after three TA modifications.

[0019] Figure 3 The figures show the contact angle measurements of PDMS / PES composite membranes prepared before and after tannic acid modification. (a) The figure shows the contact angle measurement results of the PDMS / PES composite membrane; (b) The figure shows the contact angle measurement results of the PDMS / PES composite membrane after TA modification once; (c) The figure shows the contact angle measurement results of the PDMS / PES composite membrane after TA modification twice; (d) The figure shows the contact angle measurement results of the PDMS / PES composite membrane after TA modification three times.

[0020] Figure 4Figure 1 shows the CO2 gas permeability and CO2 / O2 selectivity of the PDMS / PES composite membrane and the PDMS / PES composite membrane after tannic acid surface modification as a function of coating solution concentration. (a) Figure 2 shows the CO2 gas permeability and CO2 / O2 selectivity of the 1% wt PDMS / PES composite membrane as a function of operating pressure; (b) Figure 3 shows the CO2 gas permeability and CO2 / O2 selectivity of the 2% wt PDMS / PES composite membrane as a function of operating pressure.

[0021] Figure 5 This is a schematic diagram showing the changes in CO2 gas permeability and CO2 / O2 selectivity of the PDMS / PES composite membrane after tannic acid surface modification.

[0022] Figure 6 The images show scanning electron microscope (SEM) images of platelet adhesion in the PDMS / PES composite membrane before and after tannic acid modification. (a) SEM image of platelet adhesion in the PDMS / PES composite membrane; (b) SEM image of platelet adhesion after one TA modification. Detailed Implementation

[0023] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0024] Example 1:

[0025] The PES-based membrane was immersed in a mixed solution of anhydrous ethanol and deionized water in a 1:1 volume ratio and kept at 80°C for 24 hours to remove impurities such as glycerol from the membrane pores and improve the permeation flux.

[0026] Table 1. Pretreatment results of the base film

[0027]

[0028] Preparation of PDMS composite membrane: Poly(methylhydrosiloxane) and platinum catalyst were selected as crosslinking agent and catalyst, respectively. A wet coating method was used to prepare the PDMS composite membrane. First, a coating solution was prepared using PDMS as the solute and isooctane as the solvent. The masses of both were calculated based on the expected PDMS concentration and total mass of the coating solution and added to the reagent bottle. The mass ratio of crosslinking agent to PDMS was 1:10, and the mass ratio of catalyst to PDMS was 1:100. A 1% coating solution concentration composite membrane was prepared, with calculated amounts of 0.6 g PDMS, 0.06 g crosslinking agent, 0.006 g catalyst, and 59.334 g isooctane. After the PDMS was completely dissolved in isooctane, the crosslinking agent was added dropwise using a differential method. It was important to wait a moment after each addition to ensure uniform mixing and prevent localized excessive concentrations that could lead to explosive polymerization. The catalyst addition procedure was the same as that for the crosslinking agent. The base film is cut into a square shape with all four sides folded back to prevent the coating from contacting the reverse side of the PES base film. After the coating solution is allowed to stand and degas, it is poured into a tank. The smooth side of the PES porous support base film is immersed in the coating solution, tilting slowly while maintaining the speed to ensure that the entire surface of the PES base film is submerged in the coating solution. The contact time between the film and the coating solution is 2-3 seconds. Then, the film is quickly lifted out and tilted and left to stand still for 30 minutes. The coated film is then flattened on a glass plate and dried in a normal oven at 85°C for 2 hours to obtain a polydimethylsiloxane / polyethersulfone ultrathin composite film.

[0029] TA surface modification: Prepare a 0.8 mg / ml FeCl3·6H2O aqueous solution and a 3.2 mg / ml TA aqueous solution. Immerse the PDMS / PES composite membrane in the FeCl3·6H2O aqueous solution. Sonicate for 1 hour to ensure complete wetting of the composite membrane. Simultaneously, keep equal volumes of FeCl3·6H2O and TA aqueous solutions in a constant temperature device for 1 hour. Place the sonicated PDMS / PES composite membrane in a FeCl3·6H2O aqueous solution maintained at 30℃, add an equal volume of TA aqueous solution at the same temperature, shake, and maintain at this temperature for 2 hours. Then rinse the modified composite membrane with deionized water. Repeat the above steps for multiple layer-by-layer self-assembly modification. After modification, dry at room temperature.

[0030] To explore the microstructure of the prepared materials, scanning electron microscopy was used to observe the microstructure of the PDMS / PES composite films prepared in Example 1 before and after TA modification (e.g., Figure 1 (As shown). The PDMS / PES composite membranes prepared in Example 1 before and after TA modification were analyzed using EDS spectroscopy (e.g., as shown). Figure 2 The characterization results are shown in Table 2. The water contact angles (e.g., before and after TA modification) of the PDMS / PES composite membranes prepared in Example 1 were measured using a contact angle meter equipped with a camera. Figure 3 (b)(c)(d) are shown).

[0031] Example 2:

[0032] To measure the pure gas permeation performance of the prepared composite membrane, PDMS / PES composite membranes with coating solution concentrations of 1% and 2% were prepared using the method in Example 1 as experimental materials. The pure gas permeation rate was measured using a self-made stainless steel membrane permeation device. The membrane bath was pressurized from the coating side, with the transmembrane pressure of the composite membrane ranging from 0.1 to 0.5 MPa. The water bath temperature was kept constant, and the humidity was controlled at 35-40% using a dehumidifier. The prepared composite membrane was embedded in a stainless steel module, maintaining a constant membrane area. Pure gas was introduced to purge the upper and lower gas paths for approximately 10 minutes to ensure complete removal of any remaining gas. The permeation rates of carbon dioxide and oxygen were measured separately. After the prepared membrane was placed in a position where the gas flow rate stabilized, the gas permeation volumetric flow rate was measured using a soap bubble flow meter. (1 GPU = 10...) -6 cm 3 / cm 2 The permeation rate, expressed as s cmHg, is determined by the following equation:

[0033]

[0034] Where J is the gas permeability (GPU); ΔV is the volume of gas passing through the flow meter; T is the room temperature (25℃); and A is the membrane area, calculated to be 12.56 cm². 2 t represents the time it takes for the gas to pass through the flow meter, in seconds; Δp represents the test pressure difference, in MPa. Each data point was measured in triplicate, and the average value was taken.

[0035] Figure 4 To study the gas permeability and CO2 / O2 selectivity of PDMS / PES composite membranes with 1% and 2% coating solution concentrations prepared according to the method of Example 1.

[0036] Example 3:

[0037] To measure the changes in hydrophilicity and hydrophobicity of membrane materials, four types of TA layer-by-layer self-assembly surface-modified PDMS / PES composite membranes were prepared using the method in Example 1 (0-3 times). A 0.8 mg / ml FeCl3·6H2O aqueous solution and a 3.2 mg / ml TA aqueous solution were prepared, and the PDMS / PES composite membranes were immersed in the FeCl3·6H2O aqueous solution. The membranes were ultrasonically treated for 1 hour to ensure complete wetting. Simultaneously, equal volumes of FeCl3·6H2O and TA aqueous solutions were pre-placed in a constant temperature device for 1 hour. The ultrasonically treated PDMS / PES composite membranes were then placed in a FeCl3·6H2O aqueous solution maintained at 30°C, and an equal volume of TA aqueous solution at the same temperature was added. After shaking, the membranes were maintained at this temperature for 2 hours. The modified composite membranes were then rinsed with deionized water. This process was repeated multiple times for layer-by-layer self-assembly modification. After modification, the membranes were dried at room temperature.

[0038] The surface changes of the PDMS / PES composite film prepared in Example 3 after repeated TA surface modification were observed using scanning electron microscopy (e.g., ...). Figure 1 As shown). The PDMS / PES composite film prepared in Example 3 after TA repeated surface modification was analyzed using EDS spectroscopy (e.g., as shown). Figure 2 (As shown). The water contact angle change of the PDMS / PES composite membrane prepared in Example 3 after repeated surface modification was measured using a contact angle meter equipped with a camera (e.g., Figure 3 (As shown). Changes in the antifouling performance of the composite membrane were observed through protein adsorption experiments on the membrane surface. The gas permeability and selectivity of the composite membrane after multiple modifications with tannic acid were tested (e.g., ...). Figure 5 (As shown).

[0039] The microstructure of the PDMS / PES composite film prepared in Example 1 before and after coating and after TA modification was observed using scanning electron microscopy. The thickness of the dense PDMS layer can reach 70 nm (e.g., Figure 1 As shown in the figure, the surface of the composite membrane after PDMS coating is smooth and flat, without defects and rough structure. Its surface roughness is significantly different from that of the polyethersulfone material. Tannic acid also has obvious adhesion on the membrane surface. After repeated modification, the amount of adhesion increases.

[0040] The EDS characterization results show that silicon accounts for 6.21% of the composite film by mass. In terms of atomic percentage, carbon atoms form the organic framework, accounting for 56.47%. Since polyethersulfone does not contain silicon, the silicon in the composite film can be considered to originate from the PDMS coating layer. The EDS characterization results indicate that PDMS has been successfully coated on the PES base film surface, while the tannic acid-modified composite film shows a decrease in silicon content and an increase in the C / O ratio, indicating successful tannic acid modification.

[0041] Table 2 Elemental analysis results of the composite membrane

[0042]

[0043] The water contact angles of the TA-modified PDMS / PES composite membranes prepared in Example 1 before and after modification were measured using a contact angle meter equipped with a camera (e.g., ...). Figure 3 As shown, the contact angle of the PDMS coated film is 120°. The contact angle of the composite film surface after tannic acid modification is significantly reduced. With the increase of modification times, the water contact angle can be reduced to 60°, and the hydrophilicity is significantly improved.

[0044] Figure 4The graphs show the gas permeability and CO2 / O2 selectivity of PDMS / PES composite membranes with 1% and 2% coating solution concentrations prepared according to the method of Example 1. As can be seen from the graphs, PES membranes with different pore sizes have different gas performance as base membranes. The O2 gas permeability of the PDMS / PES composite membrane reaches 1175 GPU, the CO2 gas permeability reaches 6542 GPU, and the CO2 / O2 selectivity can reach 5.56.

[0045] After modification with tannic acid, the gas permeability and selectivity of the composite membrane decrease, but the overall level remains relatively high. With each subsequent modification, the gas permeability decreases continuously. Figure 5 As shown.

[0046] like Figure 6 As shown, the platelet adhesion on the surface of the composite membrane is reduced after tannic acid modification, thus improving its anti-fouling performance.

[0047] This invention provides a method for preparing tannic acid-modified polydimethylsiloxane / polyethersulfone ultrathin composite membranes. It develops a simple, standardized, and universal composite membrane coating method to prepare PDMS composite membranes with superior performance. By adopting a composite membrane approach, the base membrane and selective layer are separately controlled, and a high-strength tannic acid coordination compound film is rapidly assembled on the composite membrane surface in a one-step process. The presence of the base membrane provides mechanical support for coating the ultrathin PDMS layer, while the PDMS layer provides excellent gas exchange performance and leak-proof properties. The tannic acid surface modification improves the hydrophilicity of the composite membrane, reduces protein adsorption, and enhances antifouling performance. Simultaneously, tests show that the prepared composite membrane meets all required standards for gas permeability, hydrophilicity / hydrophobicity, and antifouling performance. Furthermore, the base membrane and coating materials used are relatively inexpensive and can be produced domestically, demonstrating good practicality and economic efficiency. This provides technical support for my country to break through technological blockades imposed by other countries, prepare special membrane materials, and develop downstream related application equipment.

Claims

1. A tannic acid surface-modified polydimethylsiloxane / polyether sulfone ultrathin composite membrane, characterized in that, The tannic acid surface modified polydimethylsiloxane / polyether sulfone ultra-thin composite membrane comprises a composite membrane base film and a coating layer; wherein the composite membrane base film is a polyether sulfone material, and the coating layer is a PDMS dense separation layer self-assembled by tannic acid; the thickness of the polydimethylsiloxane / polyether sulfone ultra-thin composite membrane can be adjusted in the range of 70-150 μm, and the thickness of the coating layer can be adjusted in the range of 0.07-5 μm according to requirements; wherein the composite membrane base film presents a loose finger-like pore state, the internal cavity is large, and the surface is covered with micropores, and the thickness of the coating layer increases with the increase of the concentration of the coating solution.

2. A process for the preparation of tannic acid surface-modified polydimethylsiloxane / polyether sulfone ultrathin composite membrane, characterized by, The steps are as follows: (1) PES base film pretreatment: immerse the PES base film in a mixed solution of anhydrous ethanol and deionized water with a volume ratio of 1:1, and keep it at 80°C for 24 h to remove impurities in the pores of the PES base film and improve the permeation flux; (2) PDMS selective layer coating: polydimethylsiloxane / polyether sulfone ultra-thin composite membrane is prepared by using wet film dip coating method; first, prepare the coating solution, take PDMS as solute, isooctane as solvent, and the concentration of PDMS coating solution is 1%wt-2%wt; take polymethylhydrogen siloxane and platinum gold catalyst as crosslinking agent and catalyst respectively; the mass ratio of crosslinking agent, catalyst and PDMS is 1:1:100; take out the PES base film pretreated in step (1) from the washing solution, absorb the surface moisture, cut into square, fold the four edges backward to prevent the coating from contacting the reverse side of the PES base film; pour the coating solution into the tank after standing and degassing, immerse the smooth side of the PES base film in the coating solution, tilt to immerse the surface of the PES base film in the coating solution, the contact time of the PES base film with the coating solution is 2-3 s, then quickly lift the PES base film, and tilt to stand for 30 min; press the coated PES base film flat on the glass plate, and dry at 85°C for 2 h to obtain the polydimethylsiloxane / polyether sulfone ultra-thin composite membrane; (3) TA surface modification: configure 0.8 mg / ml FeCl3·6H2O aqueous solution and 3.2 mg / ml TA aqueous solution, immerse the polydimethylsiloxane / polyether sulfone ultra-thin composite membrane in the FeCl3·6H2O aqueous solution, and ultrasonic treat for 1 hour to make the polydimethylsiloxane / polyether sulfone ultra-thin composite membrane fully infiltrate; at the same time, pre-place equal volume of FeCl3·6H2O aqueous solution and TA aqueous solution in a 30°C constant temperature device for 1 h; place the ultrasonic treated polydimethylsiloxane / polyether sulfone ultra-thin composite membrane in equal volume of FeCl3·6H2O aqueous solution and TA aqueous solution kept at constant temperature, shake and keep at this temperature for 2 h, then rinse the modified polydimethylsiloxane / polyether sulfone ultra-thin composite membrane with deionized water; Repeat step (3) for multiple layer-by-layer assembly modification, and dry at room temperature after modification to obtain the tannic acid surface modified polydimethylsiloxane / polyether sulfone ultra-thin composite membrane.

3. The tannic acid surface modified polydimethylsiloxane / polyether sulfone ultra-thin composite membrane of claim 1 is used to realize the separation of gas in a gas-liquid two-phase environment.

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