Chitosan composite nanofiltration membrane and preparation method thereof

Abstract

The application provides a preparation method of a new MOFs particle doped chitosan nanofiltration membrane, which concentrates the crystallization of MOFs particles in a subsequent membrane preparation process, and uses the MOFs particles doped on a support as nucleation centers to attract the "nutrients" in a casting solution to the surface of the support to grow into MOFs particles, so that the content of MOFs particles on the surface of the membrane is reduced, the probability of MOFs loss is reduced, and the movement process of the "nutrients" is also beneficial to the formation of loose pore structures, and is beneficial to the application of the chitosan membrane in nanofiltration.

Description

TECHNICAL FIELD

[0001] The present application relates to a nanofiltration membrane and a preparation method thereof, in particular to a chitosan composite nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] Nanofiltration is a common membrane separation technology, with a rejection range of 200-2000, and its operating pressure is lower than that of reverse osmosis. The rejection rate of monovalent ions is much lower than that of divalent ions, and it has good separation effect on organic pollutants.

[0003] Chitosan is obtained by deacetylation of chitin widely existing in nature, and has good biological functionality and compatibility, blood compatibility, safety, and microbial degradation, so it is widely concerned by various industries, and significant progress has been made in application research in many fields. Its above-mentioned advantages also make it an ideal separation membrane material. Because chitosan has a large number of hydrophilic groups, chitosan and other components have been blended to prepare nanofiltration membranes for application in the prior art.

[0004] For nanofiltration membranes, the higher the water flux, the better. In order to continue to improve the water flux and the pollution resistance, other materials are often added to the nanofiltration membrane. MOFs material is a common hydrophilic additive due to its regular molecular sieve structure. However, during the MOFs addition process, the membrane performance is easily lost due to particle agglomeration. To improve this situation, CN117018888A patent selects in-situ preparation of MOFs particles to be doped in the chitosan pervaporation separation membrane layer. According to its description, it actually realizes in-situ polymerization of MOFs particles during the aging process of the casting solution. Moreover, some MOFs particles are also embedded on the surface of the membrane, so it is easy to suck out the inorganic particles on the surface of the membrane during the pervaporation vacuum suction process, thereby causing pollution in the separation process. Moreover, the doping of moFs and chitosan generally results in a dense membrane layer, so that the membrane is generally used for more precise pervaporation, and less for nanofiltration process.

[0005] Therefore, it is necessary to optimize the doping method of the prior art so as to be used in the nanofiltration process. SUMMARY

[0006] The present application optimizes the existing doping method to make the MOFs doped chitosan membrane applied to the nanofiltration process and solves the problem of easy falling off of the particles on the surface of the membrane.

[0007] The present application provides a preparation method of a chitosan composite nanofiltration membrane, comprising the following steps:

[0008] (1) preparing an ultrafiltration membrane support doped with MOFs nanoparticles;

[0009] (2) Pouring a casting solution containing fumaric acid, ZrOCl2·8H2O, chitosan, and acetic acid on the surface of the support to form a chitosan film containing MOFs particles;

[0010] (3) Continuing to place the chitosan film in a trimesoyl chloride organic solution for crosslinking, thereby obtaining a nanofiltration membrane.

[0011] Preferably, the ultrafiltration membrane is prepared by the following steps:

[0012] (1-1) Mixing, defoaming, and uniformly mixing a film-forming polymer, an additive, MOFs nanoparticles, and a solvent to form an ultrafiltration membrane casting solution;

[0013] (1-2) Uniformly coating the ultrafiltration membrane casting solution on a glass plate and placing it in a coagulation bath for phase inversion;

[0014] (1-3) Drying to form a film.

[0015] Preferably, the mass content of the film-forming polymer, the additive, and the MOFs nanoparticles in the ultrafiltration membrane casting solution is 15-35 wt%, 0.5-3 wt%, and 0.5-10 wt%, respectively.

[0016] Preferably, the MOFs particles are MOF-81, the film-forming polymer is one or more of polysulfone, polyethersulfone, polyacrylonitrile, polyethylene, polytetrafluoroethylene, and polyvinylidene fluoride, and the additive is one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, and lithium chloride.

[0017] Preferably, the casting solution in step (2) is prepared by the following steps:

[0018] (2-1) Dissolving chitosan in an acetic acid solution, and sequentially adding fumaric acid and ZrOCl2·8H2O, and reacting at 60-80°C for 1-2 h, and standing to defoam to form a casting solution;

[0019] (2-2) Laying the support on the bottom of a container, pouring the casting solution on the surface of the support, and placing it at 40-60°C for continued reaction for 2-5 h to form a film.

[0020] Preferably, the concentration of chitosan in the casting solution is 2-5 wt%, the concentration of acetic acid is 2-5 wt%, the concentration of fumaric acid is 0.05-0.5 wt%, and the concentration of ZrOCl2·8H2O is 0.1-1.5 wt%.

[0021] Preferably, the concentration of trimesoyl chloride in step (3) is 0.05-0.5 wt%, and the crosslinking time is 5-20 min.

[0022] The application further provides the chitosan composite nanofiltration membrane prepared according to the method, which comprises an ultrafiltration membrane support and a chitosan nanofiltration layer, and MOF particles are doped in the ultrafiltration membrane support and the chitosan nanofiltration layer.

[0023] The application further provides application of the chitosan composite nanofiltration membrane prepared in the field of water treatment.

[0024] Beneficial effects:

[0025] The application concentrates the crystallization of the MOF particles in the subsequent membrane preparation process, and uses the MOF particles doped on the support as nucleation centers to attract the ''nutrients'' in the casting solution to the surface of the support to grow into MOF particles, so that the content of the MOF particles on the surface of the membrane is reduced, the probability of MOF loss is reduced, and the movement process of the ''nutrients'' is also conducive to the formation of loose pore structures, which is conducive to the application of the chitosan membrane in nanofiltration. Moreover, the MOF particles in the support can improve the overall water flux of the membrane. DETAILED DESCRIPTION

[0026] The application will be further described below in combination with examples, but the protection scope of the application is not limited thereto.

[0027] Example 1

[0028] (1-1) After polyether sulfone 20wt%, polyvinylpyrrolidone 0.5wt%, MOF nanoparticles (average particle size 87nm) and N-N dimethylacetamide are uniformly mixed, the ultrafiltration membrane casting solution is formed by standing and defoaming;

[0029] (1-2) The above ultrafiltration membrane casting solution is uniformly scraped on a glass plate, and is immersed in a coagulation bath of pure water for phase inversion;

[0030] (1-3) Drying at 60 DEG C to form a support;

[0031] (2-1) Chitosan is dissolved in acetic acid solution, and fumaric acid and ZrOCl2.8H2O are added in sequence, and the reaction is carried out at 70 DEG C for 2h, and the casting solution is formed by standing and defoaming, the concentration of chitosan in the casting solution is 3wt%, the concentration of acetic acid is 2.5wt%, the concentration of fumaric acid is 0.2wt%, and the concentration of ZrOCl2 is 0.55wt%;

[0032] (2-2) The support is laid on the bottom of the container, and the casting solution is poured on the surface of the support, and the chitosan membrane is formed by continuing to seal the reaction at 50 DEG C for 4h;

[0033] (3) The above chitosan membrane is further placed in a 0.2wt% concentration of trimesoyl chloride organic solution for crosslinking for 10min to obtain a nanofiltration membrane.

[0034] Comparative Example 1

[0035] (1-1) Polyethersulfone 20wt%, polyvinylpyrrolidone 0.5wt% and N-N dimethylacetamide were mixed uniformly, and then left to stand to form an ultrafiltration membrane casting solution;

[0036] (1-2) The ultrafiltration membrane casting solution was uniformly coated on a glass plate, and then immersed in a coagulation bath of pure water for phase inversion;

[0037] (1-3) Dried at 60°C to form a support;

[0038] (2-1) Chitosan was dissolved in an acetic acid solution, and then fumaric acid and ZrOCl2·8H2O were added in sequence, and reacted at 70°C for 2h, and then left to stand to form a casting solution, wherein the concentration of chitosan was 3wt%, the concentration of acetic acid was 2.5wt%, the concentration of fumaric acid was 0.2wt%, and the concentration of ZrOCl2 was 0.55wt%;

[0039] (2-2) The casting solution was poured on the surface of the support and dried at room temperature to form a chitosan membrane;

[0040] (3) The chitosan membrane was further placed in a 0.2wt% concentration of trimesoyl chloride organic solution for crosslinking for 10min to obtain a nanofiltration membrane.

[0041] Comparative Example 2

[0042] (1-1) Polyethersulfone 20wt%, polyvinylpyrrolidone 0.5wt%, MOFs nanoparticles (average particle size 87nm) and N-N dimethylacetamide were mixed uniformly, and then left to stand to form an ultrafiltration membrane casting solution;

[0043] (1-2) The ultrafiltration membrane casting solution was uniformly coated on a glass plate, and then immersed in a coagulation bath of pure water for phase inversion;

[0044] (1-3) Dried at 60°C to form a support;

[0045] (2-1) Chitosan was dissolved in an acetic acid solution, and then fumaric acid and ZrOCl2·8H2O were added in sequence, and reacted at 70°C for 6h, and then left to stand to form a casting solution, wherein the concentration of chitosan was 3wt%, the concentration of acetic acid was 2.5wt%, the concentration of fumaric acid was 0.2wt%, and the concentration of ZrOCl2 was 0.55wt%;

[0046] (2-2) The casting solution was poured on the surface of the support and dried at room temperature to form a chitosan membrane;

[0047] (3) The above chitosan membrane is continuously placed in a 0.2 wt% concentration of trimesoyl chloride organic solution for crosslinking for 10 min to obtain a nanofiltration membrane.

[0048] Comparative Example 3

[0049] (1-1) Polyethersulfone 20 wt%, polyvinylpyrrolidone 0.5 wt%, MOFs nanoparticles (average particle size 87 nm) and N-N dimethylacetamide are uniformly mixed, and then left to stand to form an ultrafiltration membrane casting solution;

[0050] (1-2) The above ultrafiltration membrane casting solution is uniformly coated on a glass plate, and then immersed in a coagulation bath of pure water for phase inversion;

[0051] (1-3) Drying at 60°C to form a support;

[0052] (2-1) Chitosan is dissolved in an acetic acid solution, and fumaric acid and ZrOCl2·8H2O are sequentially added, and then reacted at 70°C for 4 h, left to stand to form a casting solution, the concentration of chitosan in the casting solution is 3 wt%, the concentration of acetic acid is 2.5 wt%, the concentration of fumaric acid is 0.2 wt%, and the concentration of ZrOCl2 is 0.55 wt%;

[0053] (2-2) The support is laid flat at the bottom of a container, and the casting solution is poured onto the surface of the support, and then placed at 50°C for further closed reaction for 2 h to form a chitosan membrane;

[0054] (3) The above chitosan membrane is continuously placed in a 0.2 wt% concentration of trimesoyl chloride organic solution for crosslinking for 10 min to obtain a nanofiltration membrane.

[0055] The nanofiltration membranes prepared in the above examples and comparative examples are subjected to separation experiments at 25°C, 0.6 MPa, and 1 g / L of magnesium chloride, (1) the separation data of the nanofiltration membranes are tested for 1 h; (2) the nanofiltration membranes are flushed at a water flow pressure of 10 MPa for 12 h, and then the separation performance of the nanofiltration membranes is further tested. The characterization results are shown in the following table:

[0056] Table 1 Characterization results of different examples and comparative examples

[0057] The above description is only a preferred embodiment of the present application, and therefore cannot limit the scope of the present application, i.e. equivalent changes and modifications made according to the scope and content of the present patent should still be within the scope of the present application.

Claims

1. A method for preparing a chitosan composite nanofiltration membrane, characterized by It comprises the following steps: (1) preparing an ultrafiltration membrane support body doped with MOFs nanoparticles; (2) pouring a casting solution containing fumaric acid, ZrOCl2·8H2O, chitosan and acetic acid on the surface of the above ultrafiltration membrane support body to form a chitosan membrane containing MOFs nanoparticles, wherein the MOFs nanoparticles doped on the ultrafiltration membrane support body serve as nucleation centers; (3) continuing to place the above chitosan membrane in a trimesoyl chloride organic solution for crosslinking, thereby obtaining a nanofiltration membrane; wherein the ultrafiltration membrane support body in step (1) is prepared by the following steps: (1-1) uniformly mixing a film-forming polymer, an additive, MOFs nanoparticles and a solvent, and defoaming to form an ultrafiltration membrane casting solution; (1-2) uniformly coating the above ultrafiltration membrane casting solution on a glass plate, and immersing it in a coagulation bath for phase inversion; (1-3) drying to form a film; The chitosan membrane in step (2) is prepared by the following steps: (2-1) dissolving chitosan in an acetic acid solution, and sequentially adding fumaric acid and ZrOCl2·8H2O, and reacting at 60-80℃ for 1-2h, and standing to defoam to form a casting solution; (2-2) placing the ultrafiltration membrane support body on the bottom of a container, uniformly pouring the casting solution on the surface of the ultrafiltration membrane support body, and continuing to react at 40-60℃ for 2-5h to form a film.

2. The method of claim 1, wherein, The mass content of the film-forming polymer, the additive and the MOFs nanoparticles in the ultrafiltration membrane casting solution is 15-35wt%, 0.5-3wt% and 0.5-10wt%, respectively.

3. The method of claim 2, wherein, The MOFs nanoparticles are MOF-81, and the film-forming polymer is one or more of polysulfone, polyethersulfone, polyacrylonitrile, polyethylene, polytetrafluoroethylene and polyvinylidene fluoride; the additive is one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol and lithium chloride.

4. The method of claim 1, wherein, The concentration of chitosan in the casting solution is 2-5wt%, the concentration of acetic acid is 2-5wt%, the concentration of fumaric acid is 0.05-0.5wt%, and the concentration of ZrOCl2·8H2O is 0.1-1.5wt%.

5. The method of claim 1, wherein, The concentration of trimesoyl chloride in step (3) is 0.05-0.5wt%, and the crosslinking time is 5-20min.

6. The chitosan composite nanofiltration membrane prepared according to the preparation method of claim 1, characterized in that It comprises an ultrafiltration membrane support body and a chitosan nanofiltration layer, and the inside of the ultrafiltration membrane support body and the inside of the chitosan nanofiltration layer are respectively blended with MOFs nanoparticles.

7. Application of the chitosan composite nanofiltration membrane according to claim 6 in the field of water treatment.

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