Modified nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses a modified nanofiltration membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, contacting a polyethersulfone-based membrane with a polycation solution and then with a polyanion solution, and circulating for at least one time; a nanofiltration membrane is obtained; s2, firstly combining the nanofiltration membrane with an amine substance, and then adsorbing a bacteriostatic agent to obtain the modified nanofiltration membrane, the bacteriostatic agent is an inorganic bacteriostatic agent containing metal ions. The modified nanofiltration membrane prepared by the preparation method disclosed by the invention has a good antibacterial effect, effectively avoids the defects that antibacterial components are dissolved and bacterial colonies exceed the standard in a use process, and also has a relatively long service life.

Description

Technical Field

[0001] The present invention specifically relates to a modified nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] Nanofiltration membranes used in household water purification are mainly based on the cross-flow filtration principle. As the nanofiltration membrane is used, a large number of bacteria will grow on the membrane surface, affecting the membrane flow and effluent water quality, which will shorten the life of the membrane and increase the cost of use. In extreme cases, anaerobic bacteria may grow in large numbers on the membrane, producing nitrogen- and sulfur-containing bacterial metabolites, causing the membrane assembly to stink, greatly affecting the user experience.

[0003] At present, most of the nanofiltration membranes used in household water purification equipment are polyamide formulas, which do not inhibit the growth of microorganisms and bacteria. During use, bacterial metabolites will affect the water quality and even cause odor. The existing technology will inject silver-containing components into the nanofiltration membrane element, but this method may cause the antibacterial components to dissolve into the water, causing excessive heavy metals in drinking water, affecting the safety of drinking water, and also reducing the service life and antibacterial effect of the nanofiltration membrane. Summary of the invention

[0004] The present invention provides a modified nanofiltration membrane and its preparation method and application to overcome the defects of the prior art that the antibacterial components of the nanofiltration membrane are easily dissolved, resulting in poor antibacterial effect and excessive heavy metals in the effluent. The modified nanofiltration membrane of the present invention has good antibacterial effect, effectively avoids the defects of antibacterial component dissolution and excessive bacterial colonies during use, and also has a long service life.

[0005] The present invention provides a method for preparing a modified nanofiltration membrane, which comprises the following steps:

[0006] S1. contacting the polyethersulfone-based membrane with a polycation solution and then with a polyanion solution, the number of cycles being at least 1, to obtain a nanofiltration membrane;

[0007] S2. The nanofiltration membrane is first combined with an amine substance, and then an antibacterial agent is adsorbed to obtain the modified nanofiltration membrane; the antibacterial agent is an inorganic antibacterial agent including metal ions.

[0008] In the present invention, the pore size of the polyethersulfone-based membrane may be 0.1-0.5 μm, for example 0.45 μm.

[0009] In the present invention, the porosity of the polyethersulfone-based membrane may be 70%-90%, for example 85%.

[0010] In the present invention, the polyethersulfone (PES) base membrane can be commercially available or prepared by a preparation method in the art. The preparation method is preferably to prepare a membrane from a casting liquid; the casting liquid includes a membrane-forming polymer, a porogen and a solvent; and the membrane-forming polymer is polyethersulfone.

[0011] Wherein, the number average molecular weight of the PES is preferably 500,000.

[0012] The porogen may be a substance conventionally used in the art, preferably polyethylene glycol (PEG) and / or polyvinyl pyrrolidone (PVP), and the number average molecular weight of the polyethylene glycol is more preferably 800. Its function is to precipitate and dissolve in the coagulation bath of the casting solution during the phase transformation process of the casting solution into a film after the film is scraped, thereby forming pores.

[0013] The solvent may be an organic solvent commonly used in the art that can dissolve polyethersulfone, and preferably at least one of N-methylpyrrolidone (NMP), dimethylacetamide (DMAC) and dimethyl sulfoxide (DMSO).

[0014] Wherein, based on the mass of the casting solution, the mass proportion of the polyethersulfone may be 18%-25%, for example, 20%.

[0015] Wherein, based on the mass of the casting solution, the mass proportion of the porogen may be 10%-20%, for example, 15%.

[0016] Wherein, based on the mass of the casting solution, the mass proportion of the solvent may be 50%-71%, for example, 65%.

[0017] The method for preparing the casting solution into a film can be a doctor blade method or an electrostatic spinning method, and the doctor blade method is preferred.

[0018] In some specific embodiments, the method for preparing the casting liquid into a membrane is to sequentially subject the casting liquid to stirring, degassing, film scraping and coagulation bath film formation to obtain the polyethersulfone-based membrane.

[0019] Wherein, the coagulation bath may be water.

[0020] In the present invention, the surface of the polyethersulfone-based membrane has oxygen-containing functional groups, which can make it negatively charged in water and positively charged with polyethyleneimine. Polyethyleneimine can be introduced into the surface of the polyethersulfone-based membrane by electrostatic attraction to construct a separation layer.

[0021] In the present invention, the solute in the polycation solution can be a conventional positively charged substance in the art, preferably a polyamine, such as polyethyleneimine and / or tetraethylenepentamine.

[0022] The number average molecular weight of the polyethyleneimine (PEI) is preferably 600-10000, more preferably 1800-7000, such as 1800.

[0023] In the present invention, the solute in the polyanion solution may be a conventional positively charged substance in the art, preferably graphene oxide and / or sodium dodecylbenzene sulfonate.

[0024] In the present invention, the concentration of the solute in the polycation solution may be 0.1 g / L-0.8 g / L, for example 0.4 g / L.

[0025] In the present invention, the concentration of the solute in the polyanion solution may be 0.1 g / L-1 g / L, for example 0.1 g / L.

[0026] In the present invention, the relative amounts of the polyethersulfone-based membrane and the polycation solution may be (0.1-1) g polyethersulfone-based membrane / mL polycation solution, such as 0.5 g polyethersulfone-based membrane / mL polycation solution.

[0027] In the present invention, the relative amounts of the polyethersulfone-based membrane and the polyanion solution may be (0.1-1) g polyethersulfone-based membrane / mL polyanion solution, for example, 0.5 g polyethersulfone-based membrane / mL polyanion solution.

[0028] In step S1, the solvent in the polycation solution may be water.

[0029] In step S1, the solvent in the polyanion solution may be water.

[0030] In step S1, the contact operation can be to immerse the polyethersulfone base membrane in the polycation solution or the polyanion solution; or, to coat the polycation solution or the polyanion solution on the polyethersulfone base membrane; during the contact process, the solute of the polycation solution or the solute of the polyanion solution self-assembles on the surface of the polyethersulfone base membrane to construct a separation layer structure, wherein one full contact is to form a single layer; each time a polycation monolayer and a polyanion monolayer are formed in sequence, it is called one cycle. The number of cycles is preferably 1-5 times, more preferably 1-3 times. If the number of cycles is too many, the membrane flux may decrease.

[0031] In step S1, the contact time may be 10-60 min, for example, 30 min.

[0032] In step S1, the temperature of the contact system may be 20-30°C, for example, 25°C.

[0033] In some specific embodiments, in step S1, the weight average molecular weight of polyethyleneimine is 1800, the concentration of polyethyleneimine is 0.4 g / L, the concentration of graphene oxide is 0.1 g / L, the immersion time is 30 min each time, 3 cycles are performed in total, and 6 monolayers are assembled.

[0034] Step S1 utilizes the principle of layer-by-layer self-assembly to construct a selective separation layer on the surface of the polyethersulfone base membrane, so that the prepared nanofiltration membrane is negatively charged, and then combines with positively charged amine substances through electrostatic action. The amine substances can combine with antibacterial ions through chelation coordination, so that the modified nanofiltration membrane has good antibacterial properties.

[0035] In the present invention, the amine substance can be a polyamine, and the polyamine is preferably at least one of tetraethylenepentamine, chitosan, polyvinyl imidazole, polyethyleneimine, triethylenetetramine, N-carboxymethyl chitosan, ethylenediamine, polyallylamine, diethylenetriamine, pentaethylenehexamine, piperazine, p-aminobenzene and m-aminobenzene.

[0036] In step S2, the combining is preferably performed in a solution, and the solvent in the solution is more preferably at least one of water, methanol aqueous solution, ethanol aqueous solution and propanol aqueous solution.

[0037] Wherein, in the combined raw material system, the concentration of the amine substance may be 1%-5%, for example, 2%.

[0038] In step S2, the combining time may be 10-60 min, such as 20 min, 30 min or 40 min.

[0039] In step S2, the temperature of the combination may be 20-30°C, for example 25°C.

[0040] In the present invention, the metal ions may be zinc ions and / or silver ions. Metal ions can be introduced into nanofiltration membranes through chemical adsorption and coordination with amine substances, making them highly stable and not easy to lose. When metal ions (zinc ions, copper ions, etc.) contact the cell membrane of microorganisms, the cell membrane is negatively charged and Coulomb attraction occurs with the metal ions, and the two are firmly combined, causing the metal ions to penetrate the cell membrane, enter the microorganism, and react with the sulfhydryl groups on the proteins in the microorganisms to coagulate the proteins, destroy the activity of the microorganism synthase, and interfere with the synthesis of the microorganism DNA, causing the microorganism to lose the ability to divide and reproduce and die, thereby achieving the antibacterial effect.

[0041] In the present invention, the antibacterial agent may be at least one of zinc sulfate, zinc nitrate, zinc chloride and silver nitrate.

[0042] In the present invention, the mass ratio of the amine substance to the antibacterial agent can be (100-200):1, for example, 1:100.

[0043] In the present invention, the mass ratio of the amine substance to the polyethersulfone-based membrane may be (1-5):100, for example, 1:100.

[0044] In the present invention, the mass ratio of the antibacterial agent to the polyethersulfone-based membrane may be (1-5): (10000-20000), for example, 1:10000.

[0045] In step S2, the adsorption is preferably performed in a solution.

[0046] Wherein, the solvent in the solution is preferably water.

[0047] Wherein, in the adsorbed raw material system, the concentration of the antibacterial agent is preferably 1wt%-4wt%, such as 1wt%, 1.5wt% or 2wt%.

[0048] In step S2, the adsorption time may be 10-60 min, for example, 10 min, 30 min or 60 min.

[0049] In step S2, the temperature of the adsorption system may be 20-30°C, such as 20°C, 25°C or 30°C.

[0050] The present invention also provides a modified nanofiltration membrane prepared by the above-mentioned preparation method.

[0051] The present invention also provides a modified nanofiltration membrane, which includes a polyethersulfone base membrane and a selective separation layer; the selective separation layer is composed of polycations and polyanions bonded by electrostatic action; the polyethersulfone base membrane and the polycations in the selective separation layer are bonded by electrostatic action; the selective separation layer is bonded to amine substances by electrostatic action, and the amine substances then adsorb inorganic antibacterial agents including metal ions by chelation.

[0052] The present invention also provides an application of the modified nanofiltration membrane as described above in the field of water treatment.

[0053] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0054] The reagents and raw materials used in the present invention are commercially available.

[0055] The positive and progressive effects of the present invention are:

[0056] The present invention prepares a nanofiltration membrane through layer-by-layer self-assembly of polyethyleneimine and graphene oxide, and introduces amine groups and antibacterial agents into the surface of the nanofiltration membrane to give the nanofiltration membrane an antibacterial function. The obtained modified nanofiltration membrane has good antibacterial performance, and the antibacterial rate is as high as more than 99.9%. When it is applied to water treatment, it can effectively avoid the defects of excessive bacterial colonies and odor of membrane components, and at the same time, it can also make the membrane have a longer service life, which can reach more than 6000L. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The present invention is a process flow chart for preparing a polyethersulfone-based membrane. DETAILED DESCRIPTION

[0058] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0059] Example 1

[0060] (1) Preparation of PES-based membrane: The casting solution is stirred, degassed, and scraped, and then separated into a membrane in a coagulation bath to obtain a PES-based membrane; the casting solution is composed of 20% PES (number average molecular weight of 500,000), 15% PEG-800 and 65% nitrogen methyl pyrrolidone; the pore size of the prepared PES-based membrane is 0.45 μm; the porosity is 85%; Figure 1 Schematic diagram of the preparation process of PES-based membrane

[0061] (2) Self-assembly: The PES-based membrane obtained in step (1) was soaked in polyethyleneimine for 30 min, taken out, and then soaked in a graphene oxide solution for 30 min; this cycle was repeated three times to obtain a nanofiltration membrane; wherein the number average molecular weight of polyethyleneimine was 1800;

[0062] (3) Antibacterial modification: The nanofiltration membrane prepared in step (2) is combined with an amine solution and then placed in a zinc nitrate solution to adsorb zinc ions, thereby obtaining a modified nanofiltration membrane.

[0063] The amounts of the substances used in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1, and the process parameters are shown in Table 2, wherein step (2) of Comparative Examples 1 and 2 is to soak in the same solution for 6 times, and the other preparation steps are the same as those in Example 1.

[0064] Comparative Example 3

[0065] The only difference from Example 1 is that in step (2), the order of immersing in the polyethyleneimine solution and the graphene oxide solution is reversed.

[0066] Comparative Example 4

[0067] The only difference from Example 1 is that no amine substance is added in step (3).

[0068] Table 1

[0069]

[0070]

[0071]

[0072] Table 2

[0073]

[0074]

[0075] Effect Example

[0076] 1. Antibacterial rate

[0077] With reference to GB 21551.2-2010 Special requirements for antibacterial materials with antibacterial, sterilizing and purification functions for household and similar electrical appliances, the antibacterial rates of the modified nanofiltration membranes prepared in Examples 1-5 and Comparative Examples 1-4 of the present application against Escherichia coli were tested.

[0078] 2. Membrane life

[0079] Test method: The modified nanofiltration membranes prepared in Examples 1-5 and Comparative Examples 1-4 were assembled into membrane modules and tested according to GB34914-2021 standard.

[0080] 3. Heavy metal content in the soaking solution

[0081] Test method: According to the Ministry of Health's Weifajianfa

[2001] No. 161 document, Appendix 2, "Sanitary Safety Evaluation Standards for Drinking Water Transmission and Distribution Equipment and Protective Materials", the immersion method is used to test the amount of heavy metal precipitation in the immersion liquid.

[0082] Table 3

[0083]

[0084] The modified nanofiltration membranes prepared in Examples 1-5 of the present invention have good antibacterial rates, with an antibacterial rate against Escherichia coli as high as 99.99%, and a service life of more than 6000 L. The service life of Examples 2 and 3 can be as high as 8000 L.

[0085] Compared with Example 1, Comparative Example 1 differs in that no polycation is added, and its antibacterial rate against Escherichia coli is 89.34%, which is 10.65% lower than that in Example 1, while its service life is greatly reduced, only 2000 L, which is 33% of the service life of the modified nanofiltration membrane obtained in Example 1.

[0086] Compared with Example 1, Comparative Example 2 differs in that no polyanion is added, and its antibacterial rate against Escherichia coli is 84.32%, which is 15.67% lower than that in Example 1, while the service life is greatly reduced, only 2000 L, which is 33% of the service life of the modified nanofiltration membrane obtained in Example 1.

[0087] Compared with Example 1, Comparative Example 3 is different in that it is first immersed in a polyanion solution and then immersed in a polycation solution, which is the opposite order of Example 1. Its antibacterial rate against Escherichia coli is greatly reduced to only 78.45%; its service life is also only 2000L, which is 33% of the service life of the modified nanofiltration membrane obtained in Example 1.

[0088] Compared with Example 1, Comparative Example 4 differs in that the nanofiltration membrane is not modified with amine substances, and its antibacterial rate against Escherichia coli is extremely poor, only 66.43%, and its service life is only 2000L.

[0089] It can be seen from the heavy metal content of the soaking liquid in Table 3 that the solution of the present invention can effectively bind antibacterial ions and has a good antibacterial effect during use; while the nanofiltration membrane prepared in the comparative example failed to introduce a large amount of zinc ions or the binding was not strong, and they were washed away in the pretreatment stage of the soaking experiment, so the antibacterial effect was poor.

[0090] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified nanofiltration membrane, It is characterized in that It includes the following steps: S1. contacting the polyethersulfone-based membrane with a polycation solution first, and then with a polyanion solution, the number of cycles being at least 1; obtaining a nanofiltration membrane; S2. The nanofiltration membrane is first combined with an amine substance, and then an antibacterial agent is adsorbed to obtain the modified nanofiltration membrane; the antibacterial agent is an inorganic antibacterial agent including metal ions.

2. The method for preparing the modified nanofiltration membrane according to claim 1, It is characterized in that In step S1, the solute in the polycation solution is a polyamine, preferably polyethyleneimine and / or tetraethylenepentamine; more preferably, the number average molecular weight of the polyethyleneimine is 600-10000, further preferably 1800-7000, for example 1800; and / or, in step S1, the concentration of the solute in the polycation solution is 0.1 g / L-0.8 g / L, for example 0.4 g / L; And / or, in step S1, the solute in the polyanion solution is graphene oxide and / or sodium dodecylbenzene sulfonate; and / or, in step S1, the concentration of the solute in the polyanion solution is 0.1 g / L-1 g / L, for example 0.1 g / L; and / or, in step S1, the relative amount of the polyethersulfone-based membrane and the polycation solution is (0.1-1) g polyethersulfone-based membrane / mL polycation solution, for example 0.5 g polyethersulfone-based membrane / mL polycation solution; And / or, in step S1, the relative amount of the polyethersulfone-based membrane and the polyanion solution is (0.1-1) g polyethersulfone-based membrane / mL polyanion solution, for example, 0.5 g polyethersulfone-based membrane / mL polyanion solution.

3. The method for preparing the modified nanofiltration membrane according to claim 1, It is characterized in that In step S1, the contact time is 10-60 minutes, for example, 30 minutes; And / or, in step S1, the temperature of the contacting system is 20-30°C, for example, 25°C; and / or, in step S1, the solvent in the polycation solution is water; and / or, in step S1, the solvent in the polyanion solution is water; And / or, in step S1, the number of cycles is 1-5 times, preferably 1-3 times.

4. The method for preparing the modified nanofiltration membrane according to claim 1, It is characterized in that In step S2, the amine substance is a polyamine, and the polyamine is preferably at least one of tetraethylenepentamine, chitosan, polyvinyl imidazole, polyethyleneimine, triethylenetetramine, N-carboxymethyl chitosan, ethylenediamine, polyallylamine, diethylenetriamine, pentaethylenehexamine, piperazine, p-aminobenzene and m-aminobenzene; And / or, in step S2, the metal ions are zinc ions and / or silver ions; And / or, in step S2, the mass ratio of the amine substance to the antibacterial agent is (100-200):1, for example, 100:1; And / or, in step S2, the mass ratio of the amine substance to the polyethersulfone-based membrane is (1-5):100, for example, 1:100; And / or, in step S2, the mass ratio of the antibacterial agent to the polyethersulfone-based membrane is (1-5): (10000-20000), for example, 1:10000.

5. The method for preparing the modified nanofiltration membrane according to claim 1, It is characterized in that In step S2, the combination is carried out in a solution, and the solvent in the solution is preferably at least one of water, methanol aqueous solution, ethanol aqueous solution and propanol aqueous solution; in the combined raw material system, the concentration of the amine substance is more preferably 1%-5%, for example 2%; And / or, in step S2, the combining time is 10-60 min, such as 20 min, 30 min or 40 min; and / or, in step S2, the temperature of the combination is 20-30°C, for example 25°C; And / or, in step S2, the antibacterial agent is at least one of zinc sulfate, zinc nitrate, zinc chloride and silver nitrate; And / or, in step S2, the adsorption is carried out in a solution; wherein the solvent in the solution is preferably water; wherein, in the adsorbed raw material system, the concentration of the antibacterial agent is preferably 1wt%-4wt%, for example, 1wt%, 1.5wt% or 2wt%; And / or, in step S2, the adsorption time is 10-60 min, for example, 10 min, 30 min or 60 min; And / or, in step S2, the temperature of the adsorption system is 20-30°C; for example, 20°C, 25°C or 30°C.

6. The method for preparing the modified nanofiltration membrane according to claim 1, It is characterized in that The pore size of the polyethersulfone-based membrane is 0.1-0.5 μm, for example 0.45 μm; and / or, the porosity of the polyethersulfone-based membrane is 70%-90%, for example 85%; And / or, the method for preparing the polyethersulfone-based membrane is to prepare a membrane from a casting solution; the casting solution comprises a membrane-forming polymer, a porogen and a solvent; the membrane-forming polymer is polyethersulfone; The number average molecular weight of the polyethersulfone is preferably 500,000; the porogen is preferably polyethylene glycol and / or polyvinyl pyrrolidone, and the number average molecular weight of the polyethylene glycol is more preferably 800; and the solvent is preferably at least one of N-methylpyrrolidone, dimethylacetamide and dimethyl sulfoxide.

7. The method for preparing the modified nanofiltration membrane according to claim 6, It is characterized in that Based on the mass of the casting solution, the mass proportion of the film-forming polymer is 18%-25%, for example, 20%; And / or, based on the mass of the casting solution, the mass proportion of the porogen is 10%-20%, for example, 15%; And / or, based on the mass of the casting solution, the mass proportion of the solvent is 50%-71%, for example 65%; And / or, the method of preparing the casting solution into a film is a doctor blade method or an electrostatic spinning method; preferably, the doctor blade method.

8. A modified nanofiltration membrane, It is characterized in that The modified nanofiltration membrane is prepared by the preparation method of the modified nanofiltration membrane described in any one of claims 1 to 7.

9. A modified nanofiltration membrane, It is characterized in that The modified nanofiltration membrane includes a polyethersulfone base membrane and a selective separation layer; the selective separation layer is composed of polycations and polyanions bonded by electrostatic action; the polyethersulfone base membrane and the polycations in the selective separation layer are bonded by electrostatic action; the selective separation layer is bonded to amine substances by electrostatic action, and the amine substances then adsorb inorganic antibacterial agents including metal ions by chelation.

10. Use of the modified nanofiltration membrane according to claim 8 or 9 in the field of water treatment.

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