Composite membrane with polyfunctional group organic mesoporous nano particles as middle layer and preparation method of composite membrane

Abstract

The invention belongs to the technical field of membranes, and particularly relates to a composite membrane with polyfunctional group organic mesoporous nanoparticles as a middle layer and a preparation method of the composite membrane. The composite membrane is of a three-layer structure and comprises a porous supporting layer, a middle layer and a selective separation surface layer, the middle layer is polyfunctional group organic mesoporous nanoparticles with good water dispersibility and excellent stability, and the selective separation surface layer is polyamide; the preparation method comprises the following steps: loading organic mesoporous nanoparticles on the surface of the porous support layer to form the middle layer; and polymerizing on the surface interface of the middle layer to form a selective separation surface layer. The middle layer contains polyfunctional groups, can interact with a water-phase polyamine monomer and controls the diffusion of the monomer in an interfacial polymerization process, so that the structure of the selective polymer separation layer is regulated and controlled, and the surface appearance and thickness of the separation layer are optimized; due to the mesopore hydrophilic property of the middle layer, a rapid water transmission channel can be constructed, and the membrane flux is effectively improved. The composite membrane provided by the invention has excellent water flux, salt rejection rate and monovalent and divalent anion selectivity.

Description

Technical Field

[0001] The invention belongs to the technical field of membranes, and in particular relates to a composite membrane with multi-functional organic mesoporous nanoparticles as an intermediate layer and a preparation method thereof. Background Art

[0002] Thin film composite membranes based on polyamide materials are widely used in fields such as water purification and seawater desalination due to their simple preparation method, good separation performance and excellent stability. However, traditional thin film composite membranes (TFC membranes) usually have a trade-off problem (trade-off effect) between permeability and selectivity. Therefore, the membrane needs to be modified to improve its permeability while maintaining good retention performance as much as possible. According to the properties of the membrane modification material, it can be divided into organic materials and inorganic materials. Inorganic materials usually have problems such as poor water dispersibility, easy agglomeration and poor compatibility with the selective polymer layer. They are prone to form non-selective defects during the membrane formation process, thereby affecting the separation performance of the final membrane. Organic materials are widely used in membrane modification research due to their advantages such as easy functionalization, good compatibility with the polymer matrix and low price. Using organic materials as an intermediate layer can control the diffusion of aqueous polyamine monomers, thereby regulating the structure of the selective separation layer.

[0003] The journal Environmental Science and Technology (Environ. Sci. Technol., 2018, 52, 9341-9349) reported the use of tannic acid (TA) and Fe 3+ Coordination cross-linking forms a complex intermediate layer on the bottom membrane, and further polymerization is carried out on the surface interface of the intermediate layer to prepare a composite nanofiltration membrane. 3+ The cross-linked intermediate layer is too dense and has poor water permeability, and the water flux of the prepared composite nanofiltration membrane has not been greatly improved. "Desalination" (Desalination, 2021, 516, 115230) reported the use of amino-modified metal organic framework UiO-66-NH2 nanoparticles as the intermediate layer of the thin film composite membrane to modify the membrane. However, the preparation process of UiO-66-NH2 is cumbersome and the reaction conditions are harsh, which increases the cost of membrane preparation and makes it difficult to apply on a large scale. "Surface Applied Science" (Appl. Surf. Sci., 2024, 660, 159975) used the metal organic framework ZIF-8 as the intermediate layer of the thin film composite membrane and found that the ZIF-8 modification process would have problems such as poor water dispersibility and water stability, and poor compatibility with the polyamide selective layer. The dispersibility of ZIF-8 and the interfacial bonding performance with the polyamide layer can be improved by surface etching with tannic acid, but this process step increases the complexity of membrane preparation. More importantly, the hollow structure of ZIF-8 formed during the etching process reduces the mechanical stability of the membrane, which may limit its performance in long-term operation. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite membrane with excellent stability and good separation performance, which uses multifunctional organic mesoporous nanoparticles as an intermediate layer and a preparation method thereof, so as to effectively overcome the "trade-off" effect between permeability and selectivity and improve the separation performance of the membrane.

[0005] The composite membrane provided by the present invention, which uses multifunctional organic mesoporous nanoparticles as an intermediate layer, has a three-layer structure, including a porous support layer, an intermediate layer, and a selective separation surface layer. The intermediate layer is composed of multifunctional organic mesoporous nanoparticles with good water dispersibility and excellent stability, and the selective separation surface layer is composed of polyamide. By regulating the morphology and structure of the polyamide layer, a rapid water transmission channel is constructed, ultimately obtaining a composite membrane with high flux, good hydrophilicity, and high divalent anion retention rate. The specific preparation steps are:

[0006] (1) Multifunctional organic mesoporous nanoparticles were prepared at a concentration of 0.5 to 10 μg / cm 2 The mass is loaded on the porous support layer to form an intermediate layer;

[0007] (2) Immersing the base membrane loaded with an intermediate layer of multifunctional organic mesoporous nanoparticles in an aqueous solution containing polyamines, taking it out and drying it, and then contacting it with an organic solution containing polyacyl chlorides to form a selective separation surface layer on the intermediate layer through interfacial polymerization reaction. After taking it out and washing it, a thin film composite membrane is obtained.

[0008] in:

[0009] The multifunctional organic mesoporous nanoparticles are at least one of mesoporous tannic acid (TA) nanoparticles or mesoporous polydopamine (PDA) nanoparticles, and are prepared in an aqueous phase by a micelle self-assembly process of an amphiphilic block copolymer;

[0010] The porous support layer is a hollow fiber membrane or a flat membrane of polyethersulfone, polysulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, polyphenylene ether, etc.;

[0011] The concentration of the aqueous phase containing the polyamine is 0.5-5 g / L;

[0012] The polyamine is an aliphatic or aromatic polyamine monomer;

[0013] The concentration of the organic phase containing polyacyl chloride is 0.05-3 g / L;

[0014] The polyacyl chloride is one of trimesoyl chloride (TMC), adipoyl chloride and sebacoyl chloride;

[0015] The organic solvent of the organic phase is one of n-hexane, cyclohexane and heptane;

[0016] The thin film composite membrane with multifunctional organic mesoporous nanoparticles as the intermediate layer is obtained according to the above preparation method.

[0017] The present invention discloses a thin film composite membrane with multifunctional organic mesoporous nanoparticles as an intermediate layer, wherein the intermediate layer has both multifunctional group and mesoporous structural characteristics. The hydrophilic multifunctional groups give the particles good water dispersibility, allowing them to be evenly dispersed on the membrane surface. At the same time, the charge of the functional groups can enhance the membrane's selectivity for ions of different valence states. In addition, the multifunctional groups interact with aqueous phase monomers, slowing down the migration rate of aqueous phase monomers to the organic phase, effectively regulating the interfacial polymerization reaction and the morphology of the polyamide layer, forming a separation surface layer with a Turing structure, and increasing the effective separation area of ​​the membrane. The multifunctional groups also improve the compatibility of the nanoparticles with the membrane and their stability in the membrane.

[0018] The nanoparticles' mesoporous structure and hydrophilicity allow them to act as a drainage layer for the dense polyamide layer, promoting rapid water passage and reducing mass transfer resistance, thereby increasing membrane flux. The high surface area and pores of the mesoporous structure further optimize the water transport path and enhance separation efficiency.

[0019] The present invention provides a thin-film composite membrane with multifunctional organic mesoporous nanoparticles as the intermediate layer. The preparation method is simple, the reaction conditions are mild, and it is easy to scale up. Furthermore, the nanoparticles significantly improve the membrane's water flux at relatively low loadings while maintaining essentially unchanged salt rejection, demonstrating excellent cost-effectiveness and potential for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a transmission electron microscopy (TEM) image of the mesoporous tannic acid (TA) nanoparticles used in Examples 1-9.

[0021] Figure 2 TEM image of mesoporous polydopamine (PDA) nanoparticles used in Examples 10-11.

[0022] Figure 3 This is the Turing morphology of the surface of the thin film composite membrane with mesoporous tannic acid as the intermediate layer prepared in Example 3. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described in detail below through examples. However, these examples are only provided for illustration and are not intended to limit the present invention.

[0024] Examples 1-5

[0025] Preparation method of composite membrane:

[0026] (1) Mesoporous TA nanoparticles were prepared at a concentration of x μg / cm 2The mass of (x = 1.59, 2.39, 3.18, 3.98, 4.77) was loaded on the polyethersulfone (PES) base membrane to form the middle layer;

[0027] (2) The base membrane loaded with the mesoporous TA nanoparticle intermediate layer was immersed in a 1.5 g / L piperazine aqueous solution, removed and dried, and then contacted with a 1 g / L trimesoyl chloride n-hexane solution to form a selective separation surface layer on the intermediate layer through interfacial polymerization reaction. The composite membrane was removed and washed to obtain a composite membrane;

[0028] The pure water flux and the rejection rate of 2 g / L Na2SO4 and 2 g / L NaCl of the prepared composite membrane are shown in Table 1.

[0029] Table 1. Performance of composite membranes with different loading weights of mesoporous TA nanoparticles as the intermediate layer*

[0030]

[0031] *Note: Operating pressure 0.4MPa

[0032] As can be seen from Table 1, the pure water flux of the composite membrane can be effectively improved at a lower loading mass of mesoporous TA nanoparticles, the salt rejection rate remains basically unchanged, and good monovalent and divalent anion selectivity is exhibited.

[0033] Examples 6-9

[0034] Preparation method of composite membrane:

[0035] (1) Multifunctional TA mesoporous nanoparticles were prepared at a temperature of 3.18 μg / cm 2 The mass is loaded on the PES bottom film to form the middle layer;

[0036] (2) The base membrane loaded with the mesoporous TA nanoparticle intermediate layer was immersed in an xg / L (x=1, 2, 2.5, 3) piperazine aqueous solution, taken out and dried, and then contacted with a 1g / L trimesoyl chloride n-hexane solution to form a selective separation surface layer on the intermediate layer through interfacial polymerization reaction. The base membrane was taken out and washed to obtain a composite membrane;

[0037] The pure water flux and the rejection rate of 2 g / L Na2SO4 and 2 g / L NaCl of the prepared composite membrane are shown in Table 2.

[0038] Table 2. Performance of composite membranes with mesoporous TA nanoparticles as the intermediate layer at different piperazine concentrations*

[0039]

[0040] *Note: Operating pressure 0.4MPa

[0041] As can be seen from Table 2, under the action of mesoporous TA nanoparticles, the effect of piperazine concentration on membrane performance is weakened; as the piperazine concentration increases, the pure water flux of the membrane decreases and the salt retention rate increases, while it has excellent selectivity for monovalent and divalent anions.

[0042] Examples 10-11

[0043] Preparation method of composite membrane:

[0044] (1) Mesoporous polydopamine nanoparticles were prepared at a concentration of x μg / cm 2 The mass of (x = 1.59, 4.77) is loaded on the PES bottom film to form the middle layer;

[0045] (2) The bottom membrane of the mesoporous polydopamine nanoparticle intermediate layer was immersed in a 1.5 g / L piperazine aqueous solution, removed and dried, and then contacted with a 1 g / L trimesoyl chloride n-hexane solution to form a selective separation surface layer on the intermediate layer through interfacial polymerization reaction. The bottom membrane was removed and washed to obtain a composite membrane;

[0046] The pure water flux and the rejection rate of 2 g / L Na2SO4 and 2 g / L NaCl of the prepared composite membrane are shown in Table 3.

[0047] Table 3. Properties of thin film composite membranes with different loading weights of mesoporous polydopamine nanoparticles as the intermediate layer*

[0048]

[0049] *Note: Operating pressure 0.4MPa

[0050] As can be seen from Table 3, mesoporous polydopamine nanoparticles also have a good modification effect on the thin film composite membrane, and have good selectivity for monovalent and divalent anions.

Claims

1. A method for preparing a composite membrane with multifunctional organic mesoporous nanoparticles as an intermediate layer, characterized in that: The composite membrane has a three-layer structure, including a porous support layer, an intermediate layer and a selective separation surface layer; The middle layer is composed of multifunctional organic mesoporous nanoparticles with good water dispersibility and excellent stability, and the selective separation surface layer is polyamide. By regulating the morphology and structure of the polyamide layer, a fast water transmission channel is constructed, ultimately obtaining a composite membrane with high flux, good hydrophilicity, and high divalent anion retention rate. The specific preparation steps are as follows: (1) Multifunctional organic mesoporous nanoparticles were prepared at a concentration of 0.5-10 μg / cm 2 The mass is loaded on the porous support layer to form an intermediate layer; (2) The base membrane loaded with the middle layer of multifunctional organic mesoporous nanoparticles is immersed in an aqueous solution containing polyamines, taken out and dried, and then brought into contact with an organic solution containing polyacyl chlorides. A selective separation surface layer is formed on the middle layer through interfacial polymerization reaction, and then taken out and washed to obtain a composite membrane.

2. The preparation method according to claim 1, characterized in that The multifunctional organic mesoporous nanoparticles are at least one of mesoporous tannic acid (TA) nanoparticles and mesoporous polydopamine (PDA) nanoparticles.

3. The preparation method according to claim 1, characterized in that The porous support layer is one of polyethersulfone, polysulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyphenylene ether, and is in the form of a hollow fiber membrane or a flat membrane.

4. The preparation method according to claim 1, characterized in that The concentration of the aqueous phase containing the polyamine is 0.5-5 g / L; the polyamine is an aliphatic or aromatic polyamine monomer.

5. The preparation method according to claim 1, characterized in that The concentration of the organic phase containing polyacyl chloride is 0.05-3 g / L; the polyacyl chloride is one of trimesoyl chloride, adipoyl chloride, and sebacoyl chloride; and the organic solvent of the organic phase is one of n-hexane, cyclohexane, and heptane.

6. A thin film composite membrane with multifunctional organic mesoporous nanoparticles as an intermediate layer obtained by the preparation method according to any one of claims 1 to 5.

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