Swelling-resistant two-dimensional layered gel thin-layer composite membrane as well as preparation method and application thereof

Abstract

The invention discloses a swelling-resistant two-dimensional layered gel thin-layer composite membrane and a preparation method thereof, and the preparation method comprises the following steps: (1) loading nanosheets onto a porous support membrane to form a two-dimensional layered membrane; (2) filling a precursor solution containing an oxidizing agent, a cross-linking agent and a functional monomer into the two-dimensional layered membrane; and (3) triggering limited polymerization and gelation of the cross-linking agent and the functional monomer in the nano channel of the two-dimensional layered film through a photothermal effect, and forming a layer of swelling-resistant two-dimensional layered gel thin-layer composite film on the porous support film. The swelling-resistant two-dimensional layered gel thin-layer composite membrane disclosed by the invention has excellent separation performance and structural stability, and can be applied to nanofiltration of a water phase solution or an organic phase solution.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a swelling-resistant two-dimensional layered gel thin-film composite membrane, its preparation method, and its application. Background Technology

[0002] In recent years, two-dimensional layered membranes, composed of atomically thin nanosheets (such as MXene, graphene oxide, and molybdenum disulfide), have gradually emerged as key applications involving fine molecular separation, such as environmental applications (water purification and carbon dioxide capture), resource applications (seawater desalination and ethanol dehydration), energy applications (lithium extraction and uranium enrichment), and pharmaceutical applications (enantiomer analysis and antibiotic recovery). Two-dimensional layered membranes possess sub-nanometer-scale interlayer channels and tunable channel chemistry, which can overcome the limitations of conventional polymer membranes and achieve efficient sieving of molecules of similar size, making them a research hotspot in novel separation membrane materials.

[0003] For example, Chinese patent CN113083036A discloses a method for preparing a two-dimensional layered composite membrane. This method utilizes electrostatic interactions to assemble nanosphere / nanosheet composite membranes, achieving efficient retention of small organic molecules and salt ions. Chinese patent CN114288875A discloses a method for preparing a PU / GO / AAO heterojunction membrane using a superassembly strategy. Utilizing Egyptian-sized nanochannels and negative channel surface charges, it can preferentially transport monovalent cations, achieving efficient sieving of monovalent / divalent cations.

[0004] However, current two-dimensional layered composite membranes have limited types and insufficient density of nanochannel surface groups that determine their interlayer chemical environment, which restricts the separation performance and application scenarios of the composite membranes. In addition, there are only weak intermolecular van der Waals interactions within the nanochannels of the composite membrane. In complex environments, especially in solvent environments, the solvent gradually enters the nanochannels, which will increase the size of the nanochannels, causing the composite membrane to swell and lose its sieving performance.

[0005] Therefore, constructing a swelling-resistant two-dimensional layered membrane with abundant functional sites, an interlayer chemical environment, and excellent layered structural stability is of great significance and practical value. Summary of the Invention

[0006] This invention provides a swelling-resistant two-dimensional layered gel thin film composite membrane and its preparation method. The swelling-resistant two-dimensional layered gel thin film composite membrane has both excellent separation performance and structural stability.

[0007] The technical solution of the present invention is as follows: A method for preparing a swelling-resistant two-dimensional layered gel thin-film composite membrane includes the following steps: (1) Nanosheets are loaded onto a porous support membrane to form a two-dimensional layered membrane; (2) Infuse a precursor solution containing an oxidant, a crosslinking agent and a functional monomer into a two-dimensional layered membrane; (3) By triggering the restricted polymerization and gelation of crosslinking agents and functional monomers in the nanochannels of the two-dimensional layered membrane through photothermal effect, a swelling-resistant two-dimensional layered gel thin film composite membrane is formed on the porous support membrane.

[0008] In the swelling-resistant two-dimensional layered gel thin-film composite membrane of the present invention, the two-dimensional layered confined channels and the gel functional groups within them work synergistically. The former plays a size sieving effect, while the latter interacts specifically with the target separation object, jointly constructing an efficient separation channel and improving the separation performance of the composite membrane. At the same time, the gel network can form topological chain entanglements and multiple interactions with the nanosheets, thereby ensuring that the layered composite membrane will not swell or deform in various complex environmental applications, and improving the long-term service stability of the layered composite membrane in various environments.

[0009] The porous support membrane is selected from one of the following: polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, cellulose acetate ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polypropylene microfiltration membrane, polyvinylidene fluoride microfiltration membrane, polytetrafluoroethylene microfiltration membrane, polyethersulfone microfiltration membrane, and nylon microfiltration membrane.

[0010] More preferably, the porous support membrane is a nylon microfiltration membrane.

[0011] Preferably, the nanosheets are nanosheets with photothermal effect; more preferably, at least one of MXene nanosheets, graphene oxide (GO) nanosheets, and molybdenum disulfide (MoS2) nanosheets.

[0012] Step (1) includes: filtering the suspension of nanosheets onto a porous support membrane, wherein the concentration of nanosheets in the suspension is 0.01~10 g / L.

[0013] Preferably, the loading of the two-dimensional layered membrane on the porous support membrane is 0.1~1 mg / cm³. 2 Further preferably, it is 0.2~0.6 mg / cm³. 2 .

[0014] The restricted polymerization and gelation of functional monomers in the nanochannels of a two-dimensional layered membrane triggered by photothermal effect is achieved by the generation of free radicals by an oxidant under the photothermal effect of the nanosheet, which induces the in-situ polymerization of crosslinking agents and functional monomers in the nanochannels of the two-dimensional layered membrane to form a gel.

[0015] Preferably, the oxidant is at least one of azobisisobutyronitrile, ammonium persulfate, sodium persulfate, and potassium persulfate; and the concentration of the oxidant in the precursor solution is 1-30 mg / mL.

[0016] Preferably, the crosslinking agent is at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate; in the precursor solution, the concentration of the crosslinking agent is 1~30 mg / mL.

[0017] Preferably, the functional monomer is at least one selected from acrylamide, acrylic acid, N-isopropylacrylamide, 2-(acryloyloxy)ethyltrimethylammonium chloride, polyethylene glycol methacrylate, and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide; and the concentration of the functional monomer in the precursor solution is 50~500 mg / mL.

[0018] Preferably, step (2) includes: coating a precursor solution containing an oxidant, a crosslinking agent and a functional monomer onto a two-dimensional layered membrane, immersing it for 1 to 10 minutes, and then draining the excess precursor solution from its surface by vacuum filtration.

[0019] More preferably, in the precursor solution, the oxidant is ammonium persulfate with a concentration of 1-5 mg / mL; the crosslinking agent is N,N'-methylenebisacrylamide with a concentration of 1-10 mg / mL; and the functional monomer is acrylamide with a concentration of 200-300 mg / mL.

[0020] Preferably, in step (3), the radiation source that triggers the gelation of the crosslinking agent and functional monomer through the photothermal effect is a xenon lamp source, with an irradiance of 500~1500 W / m². 2 .

[0021] Step (3) includes: placing the two-dimensional layered membrane filled with precursor solution under radiation source irradiation and reacting for 0.5~20 min to obtain a two-dimensional layered gel thin film composite membrane.

[0022] Step (3) utilizes the photothermal effect of nanosheets to achieve rapid local heating around the stacked nanosheets, triggering the restricted polymerization and gelation of crosslinking agents and functional monomers in the two-dimensional layered membrane nanochannels, to obtain a two-dimensional layered gel thin-film composite membrane.

[0023] The present invention also provides a swelling-resistant two-dimensional layered gel thin film composite prepared by the above preparation method.

[0024] The present invention also provides the application of the swelling-resistant two-dimensional layered gel thin film composite membrane in nanofiltration of aqueous or organic phase solutions.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the two-dimensional layered gel thin film composite membrane prepared by the present invention, the layered confined channel and the gel functional group inside it work together. The former plays a size sieving effect, while the latter interacts specifically with the target separation object to jointly construct an efficient separation channel and improve the separation performance of the composite membrane. In contrast, the traditional two-dimensional layered membrane can only rely on a few hydroxyl, fluorine and other groups carried on the surface of the nanosheet to construct the chemical environment of the nanochannel. (2) The gel network of the two-dimensional layered gel thin film composite membrane of the present invention can form topological chain entanglement and multiple interactions with the nanosheets, thereby ensuring that the layered composite membrane will not swell or deform in various complex environments and improving the long-term service stability of the layered composite membrane in various environments; while in the traditional two-dimensional layered membrane, there are only weak intermolecular van der Waals interactions in the nanochannels. In complex environments, especially in solvent environments, the solvent gradually enters the nanochannels, which will increase the size of the nanochannels, and the composite membrane will swell and lose its sieving performance. Attached Figure Description

[0026] Figure 1 Scanning electron microscope images of the MXene layered gel thin film composite membrane (a) prepared in Example 1 and the MXene layered membrane (b) prepared in Comparative Example 1; Figure 2 Scanning electron microscope (SEM) images of the cross-sections of the MXene layered gel thin-film composite membrane (a) prepared in Example 1 and the MXene layered membrane (b) prepared in Comparative Example 1. Figure 3 The changes in nanochannel size and membrane morphology of the MXene layered gel thin-film composite membrane prepared in Example 1 and the MXene layered membrane prepared in Comparative Example 1 after immersion in 0.5 mol / L sodium chloride solution for different times; Figure 4 The morphological changes of the MXene layered gel thin-film composite membrane prepared in Example 1 and the MXene layered membrane prepared in Comparative Example 1 after immersion in acetone for different times; Figure 5 Scanning electron microscope images of cross sections of the temperature-responsive MXene layered gel thin film (a) and the polycationic MXene layered gel thin film (b) prepared for Examples 2 and 3, and characterization of their characteristic properties; Figure 6 Scanning electron microscope (SEM) images of cross-sections of the GO layered gel thin film composite membrane (a) and the MoS2 layered gel thin film composite membrane (b) prepared in Examples 4 and 5, respectively. Detailed Implementation

[0027] The two-dimensional layered gel thin-film composite membrane prepared in this invention can be applied to aqueous phase and organic solvent nanofiltration. Nanofiltration tests were conducted at room temperature (298 K) using a dead-end separation device at a test pressure of 2 bar. Aqueous phase nanofiltration was exemplified by the separation of Brilliant Blue / water solution, and organic solvent nanofiltration was exemplified by the separation of Acid Fuchs Red / acetone. Solvent permeation flux and dye rejection rate are two important parameters for evaluating the performance of the separation membrane. Solvent permeation flux (P) is defined as the volume of solvent (water or acetone) permeating through a unit membrane area per unit time under a certain operating pressure, and its unit is L∙m⁻². -2 ∙h -1 ∙bar -1 The formula is: in, V This indicates the volume of solvent that has permeated, expressed in liters (L). A This represents the effective membrane area, in m². 2 ; t Indicates time, in hours (h). p This indicates the test pressure, measured in bars.

[0028] The dye rejection rate is defined as: in, C f Indicates the concentration of dye in the feed solution before treatment; C p This indicates the concentration of dye in the filtrate after treatment.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0030] Example 1 (1) A nylon microfiltration membrane was laid in a sand core funnel, and the MXene nanosheet suspension was poured in. The nylon microfiltration membrane was then filtered to a bulk density of 0.4 mg / cm³. 2 MXene layered membrane.

[0031] (2) Preparation of gel precursor solution: 2 g acrylamide, 0.04 g N,N'-methylenebisacrylamide, 0.02 g ammonium persulfate and 8 g water are stirred at room temperature to form a homogeneous solution.

[0032] (3) Coat the prepared MXene layered membrane with a gel precursor and remove excess precursor solution from the membrane surface using vacuum filtration. Finally, place the liquid membrane under a xenon lamp (light intensity: 1000 W / m²). 2 After reacting for 3 minutes, an MXene gel layered composite membrane was obtained.

[0033] Comparative Example 1 A nylon microfiltration membrane was laid in a sand core funnel, and an MXene nanosheet suspension was poured in. The mixture was then filtered through the nylon microfiltration membrane until the bulk density reached 0.4 mg / cm³. 2 MXene layered membrane.

[0034] Scanning electron microscope (SEM) images of the MXene layered gel thin-film composite membrane prepared in Example 1 and the MXene layered membrane prepared in Comparative Example 1 are shown below. Figure 1 and Figure 2 As shown, the MXene layered membrane has a rough surface morphology and a clear nanosheet layered structure in its cross-section. In contrast, the MXene layered gel thin-layer composite membrane has a high surface smoothness, and the nanosheet layered structure in its cross-section is completely filled by the polymer cross-linking network, exhibiting a dense cross-sectional morphology.

[0035] Test Example 1 The MXene layered gel thin-film composite membrane prepared in Example 1 and the MXene layered membrane prepared in Comparative Example 1 were subjected to swelling resistance tests. The membranes were placed in a 0.5 mol / L sodium chloride solution, and the nanochannel size and swelling of the membranes were tested periodically.

[0036] like Figure 3 As shown, the MXene layered gel composite membrane prepared in Example 1 maintained stable nanochannel sizes even after immersion in a high-concentration sodium chloride solution for 150 days, without swelling or rupture. In contrast, the MXene layered membrane prepared in Comparative Example 1, after immersion in a high-concentration sodium chloride solution, showed swelling and rupture after only 14 days due to ion entry into the MXene sheet channels, and the nanochannel sizes also increased significantly.

[0037] like Figure 4 As shown, the MXene layered gel thin-film composite membrane prepared in Example 1 maintained its original surface morphology and showed no defects after being immersed in the organic solvent acetone for 7 days. In contrast, the MXene layered membrane prepared in Comparative Example 1 showed obvious structural rupture after only 3 hours of immersion in acetone, and after 7 days of immersion, the MXene layered membrane was almost completely broken.

[0038] The swelling resistance of MXene layered gel composite membranes stems from the topological chain entanglement and multiple interactions that form between its gel network and nanosheets. This ensures that the layered composite membrane does not swell or deform in various complex environments, thus improving its long-term service stability under diverse conditions. In contrast, traditional two-dimensional layered membranes contain only weak intermolecular van der Waals interactions within the nanochannels. In complex environments, especially solvent environments, the gradual entry of solvents or solutes into the nanochannels leads to an increase in nanochannel size, causing the composite membrane to swell and resulting in a loss of sieving properties.

[0039] Test Example 2 The separation membranes prepared in Example 1 and Comparative Example 1 were subjected to aqueous nanofiltration performance testing, specifically the separation performance of the membranes for Brilliant Blue aqueous solution. The initial concentration of Brilliant Blue in the test solution was 100 ppm. The initial water flux of the MXene layered gel thin-film composite membrane prepared in Example 1 was 110.5 L∙m⁻¹. -2 ∙h -1 ∙bar -1 The water flux of the MXene layered gel composite membrane was 2884% higher than that of the MXene layered membrane. Simultaneously, both the MXene layered gel composite membrane and the MXene layered membrane exhibited an initial brilliant blue rejection rate of 99.9% (Table 1). The ultra-high flux gain of the MXene layered gel composite membrane originates from the introduction of a polyacrylamide gel network within its nanochannels. On one hand, the introduction of the gel increases the size of the nanochannels. On the other hand, the high-density polar amide groups on the gel network can generate stronger interactions with solvent molecules, facilitating solvent molecule transport. Simultaneously, the high-density gel network within the nanochannels can effectively repel dye molecules, ensuring the rejection performance of the separation membrane. However, because the MXene layered membrane prepared in Comparative Example 1 is highly prone to swelling, after twelve days of continuous separation, the MXene layered membrane prepared in Comparative Example 1 gradually experienced feed leakage, causing its brilliant blue rejection rate to decrease to 29.8%. In contrast, the MXene layered gel composite membrane prepared in Example 1 consistently maintained a dye rejection rate of 99.9%, fully demonstrating its excellent swelling resistance and long-term service stability.

[0040] Table 1. Separation performance of the separation membranes prepared in Example 1 and Comparative Example 1 for Brilliant Blue / aqueous solution. Test Example 3 The separation membranes prepared in Example 1 and Comparative Example 1 were subjected to organic solvent nanofiltration performance tests, specifically testing their separation performance of acid fuchsin in an acetone solution. The concentration of acid fuchsin was 50 ppm during the test. As shown in Table 2, on the first day of testing, the MXene layered gel thin-film composite membrane prepared in Example 1 exhibited superior performance, with an acetone permeation flux of 138.3 L∙m⁻¹.-2 ∙h -1 ∙bar -1 The acid fuchsin rejection rate was as high as 99.8%. The acetone permeation flux of the MXene layered gel thin-layer composite membrane was 5.5 times that of the MXene layered membrane prepared in Example 1. This is because the highly polar polyacrylamide gel network in the MXene layered gel thin-layer composite membrane prepared in Example 1 can interact strongly with acetone molecules through abundant amide groups, acting as sites to promote rapid acetone transport and significantly improving the acetone permeation flux of the separation membrane.

[0041] The separation membranes prepared in Example 1 and Comparative Example 1 were continuously tested in acetone for seven days. As shown in Table 2, the MXene layered gel thin-layer composite membrane prepared in Example 1 still exhibited stable separation performance, with its acid fuchsin rejection rate remaining at 99.5%. In contrast, the MXene layered membrane prepared in Comparative Example 1 underwent structural breakage in acetone, almost losing its sieving performance, and thus its acid fuchsin rejection rate decreased to only 6.7%.

[0042] The test results above indicate that the MXene layered gel thin-film composite membrane has highly polar nanochannel chemistry and excellent solvent resistance, enabling it to achieve long-term stable service in harsh organic solvent environments.

[0043] Table 2. Separation performance of the separation membranes prepared in Example 1 and Comparative Example 1 for acidic fuchsin / acetone solution. Examples 2-3 Based on Example 1, Examples 2 and 3 respectively replaced the functional monomers with N-isopropylacrylamide and 2-(acryloyloxy)ethyltrimethylammonium chloride, with the other conditions being the same as in Example 1, to obtain temperature-responsive MXene layered gel thin film and polycationic MXene layered gel thin film, respectively.

[0044] Figure 5 Scanning electron microscopy (SEM) images of the cross-sections of the temperature-responsive MXene layered gel thin-film composite membranes and the polycationic MXene layered gel thin-film composite membranes prepared in Examples 2 and 3, along with their characteristic properties, are shown. The introduction of gels with different properties endows the MXene layered gel thin-film composite membranes with different characteristic properties: for example, the temperature-responsive MXene layered gel thin-film composite membrane prepared from N-isopropylacrylamide exhibits temperature responsiveness similar to poly(N-isopropylacrylamide), showing hydrophilicity (26°) on the surface of the composite membrane at room temperature, while the water contact angle on the membrane surface rapidly increases to 87° at high temperatures. Figure 5In (b), the surface of the polycationic MXene layered gel thin film is covered with a high-density positively charged gel network, with a surface potential of 38.8 mV, compared to -40.0 mV for the MXene layered film.

[0045] Examples 4-5 Based on Example 1, Examples 4 and 5 respectively replaced the nanosheets with GO nanosheets and MoS2 nanosheets, while keeping the other conditions the same as in Example 1, and obtained GO layered gel thin film and MoS2 layered gel thin film respectively.

[0046] Figure 6 Scanning electron microscope (SEM) images of the cross-sections of the GO layered gel thin-film composite membrane and the MoS2 layered gel thin-film composite membrane prepared in Examples 4 and 5.

[0047] The experiments in Examples 1-5 show that the two-dimensional layered gel thin-film composite membrane and its preparation method proposed in this invention have excellent versatility. They can be applied to various nanosheets and gel functional monomers with various acrylate structures, and can construct two-dimensional layered gel thin-film composite membranes with specific nanochannel chemical environments that meet the requirements of specific separation tasks.

[0048] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a swelling-resistant two-dimensional layered gel thin-film composite membrane, characterized in that, Includes the following steps: (1) Nanosheets are loaded onto a porous support membrane to form a two-dimensional layered membrane; (2) Infuse a precursor solution containing an oxidant, a crosslinking agent and a functional monomer into a two-dimensional layered membrane; (3) By triggering the restricted polymerization and gelation of crosslinking agents and functional monomers in the nanochannels of the two-dimensional layered membrane through photothermal effect, a swelling-resistant two-dimensional layered gel thin film composite membrane is formed on the porous support membrane.

2. The method for preparing the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 1, characterized in that, The porous support membrane is selected from one of the following: polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, cellulose acetate ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polypropylene microfiltration membrane, polyvinylidene fluoride microfiltration membrane, polytetrafluoroethylene microfiltration membrane, polyethersulfone microfiltration membrane, and nylon microfiltration membrane.

3. The method for preparing the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 1, characterized in that, The nanosheets mentioned are nanosheets with photothermal effects.

4. The method for preparing the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 3, characterized in that, The nanosheets are at least one of MXene nanosheets, graphene oxide nanosheets, and molybdenum disulfide nanosheets.

5. The method for preparing the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 1, characterized in that, The loading capacity of the two-dimensional layered membrane on the porous support membrane is 0.1~1 mg / cm³. 2 .

6. The method for preparing the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 1, characterized in that, The oxidant is at least one of azobisisobutyronitrile, ammonium persulfate, sodium persulfate, and potassium persulfate; in the precursor solution, the concentration of the oxidant is 1~30 mg / mL.

7. The method for preparing the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 1, characterized in that, The crosslinking agent is at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate; in the precursor solution, the concentration of the crosslinking agent is 1~30 mg / mL.

8. The method for preparing the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 1, characterized in that, The functional monomer is at least one of acrylamide, acrylic acid, N-isopropylacrylamide, 2-(acryloyloxy)ethyltrimethylammonium chloride, polyethylene glycol methacrylate, and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide; the concentration of the functional monomer in the precursor solution is 50~500 mg / mL.

9. A swelling-resistant two-dimensional layered gel thin-film composite membrane prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the swelling-resistant two-dimensional layered gel thin-film composite membrane according to claim 9 in nanofiltration of aqueous or organic phase solutions.

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