An antibacterial polyimide microfiltration membrane, its preparation method and application

Abstract

The present invention discloses a preparation method of an antibacterial polyimide microfiltration membrane, which specifically comprises the following steps: dissolving soluble polyimide powder in a solvent to obtain a polymer solution, and then dissolving bovine serum albumin in deionized water to obtain an aqueous solution of bovine serum albumin; adding the aqueous solution of bovine serum albumin to the polymer solution, adding a surfactant, and then emulsifying and ultrasonicating to obtain a polymer inverse emulsion; pouring the polymer inverse emulsion onto a substrate, and obtaining a polymer porous film after film formation; soaking the polymer porous film in an alkali solution, taking it out after soaking and transferring it to a solution containing metal ions to introduce metal ions to obtain a metal ion-loaded polyimide porous membrane; performing heat treatment to obtain an antibacterial polyimide microfiltration membrane; the method for preparing the porous polyimide film of the present invention is simple and efficient, and realizes the antibacterial performance of the film by inducing the reduction of metal ions through heat treatment without adding an external reducing agent, and has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of antibacterial microfiltration membranes, and particularly relates to an antibacterial polyimide microfiltration membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Water pollution is a global environmental protection issue. Polluted water is the cause of serious waterborne diseases. For example, bacterial pathogens in drinking water supplies pose a threat to public health. Currently, disinfectants used to inactivate pathogens in water include chlorine dioxide, ozone, and chlorine. However, these traditional water disinfection methods have some known drawbacks. For example, they require high concentrations of disinfectants and a long reaction time to inactivate pathogens. They react with various components in water and may form disinfection by-products that are carcinogenic. A membrane is a barrier between two phases that allows specific components to selectively transfer from one side to the other. In recent years, membrane filtration methods have received extensive attention due to their advantages such as simple operation, low cost, and high efficiency. Microfiltration is a pressure-driven filtration process with a membrane pore size range of 0.1 - 10 μm, which can effectively remove bacteria, particles, and pollutants in liquid solutions, and this is an important step in wastewater pretreatment and water purification. In addition, the widespread use of chemical disinfectants has led to an increasing resistance of bacteria to various disinfectants. Therefore, there is an urgent need for a new method to remove bacteria from water to meet the requirements of effective antibacterial activity and acceptable filtration flux.

[0003] The main mechanism for microfiltration membranes to remove bacteria is size exclusion. The diameter of bacteria is usually greater than 0.2 μm. For example, the size of Escherichia coli is 0.5 - 2.0 μm. The water droplet templating method can effectively design structures and pore sizes suitable for microfiltration applications by simply changing experimental parameters. In addition, based on the size exclusion effect, the intercepted bacteria will induce membrane biofouling during the filtration process. Therefore, it is usually necessary to combine antibacterial agents to inhibit bacterial growth and the formation of biofouling to improve the filtration efficiency of the membrane. Generally, bactericide molecules are incorporated into the membrane. Over time, the release of the bactericide will lead to a decrease in the antibacterial performance of the membrane and may cause secondary pollution. Copper or silver nanoparticles are effective functional nanoparticles in biological applications and have been widely used in water disinfection. Silver nanoparticles can pierce the cell wall of microorganisms, damage the cell membrane, and ultimately inhibit their growth. Copper nanoparticles can bind to proteins inside the cell membrane and have high antibacterial activity. During the water purification process, they are mainly used to prevent the formation of bacterial growth on the membrane surface or in the pores. However, under high concentration conditions, these functional nanoparticles will settle on the membrane, resulting in pore blockage and subsequently reducing the water flux. Summary of the Invention

[0004] The object of the present invention is to provide an antibacterial polyimide microfiltration membrane. Based on the water droplet templating method, the present invention can prepare a dense and controllable porous structure in one step by simply changing experimental parameters, and there is no need to pre-mix some antibacterial agents or introduce external reducing agents to prepare an antibacterial active microfiltration membrane.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a preparation method of an antibacterial polyimide microfiltration membrane, and the preparation method specifically includes the following steps:

[0006] S1. Dissolve soluble polyimide powder in a solvent to obtain a polymer solution, and then dissolve bovine serum albumin in deionized water to obtain an aqueous bovine serum albumin solution;

[0007] S2. Add the aqueous bovine serum albumin solution to the polymer solution, then add a surfactant, and then perform emulsification ultrasound to obtain a polymer inverse emulsion;

[0008] S3. Pour the polymer inverse emulsion obtained in step S2 onto a substrate, and obtain a polymer porous film after film formation;

[0009] S4. Immerse the polymer porous film obtained in step S3 in an alkali solution, take it out after immersion and transfer it to a solution containing metal ions to introduce metal ions through an ion exchange reaction to obtain a metal ion-loaded polyimide porous membrane;

[0010] S5. Perform heat treatment on the metal ion-loaded polyimide porous membrane obtained in step S4 to obtain an antibacterial polyimide microfiltration membrane.

[0011] The process of the present invention for preparing an antibacterial polyimide film based on the water droplet templating method can prepare an ordered porous membrane with dynamically controllable structure through the water droplet templating method. The prepared polyimide porous membrane is first chemically modified by immersing it in an alkali solution to form carboxylic acid groups, and then metal ions are introduced through an ion exchange reaction. Subsequent heat treatment of the metal ion-loaded polyimide porous membrane triggers the reduction of metal ions. Through this process, porous polyimide / copper or polyimide / silver and other materials can be prepared, thereby enhancing the antibacterial property of the film.

[0012] Preferably, in step S1, the solvent is chloroform, and the concentration of the polymer solution is 20 - 40 mg / ml. Chloroform is used as the film-forming solvent, and this solvent has the best film-forming texture and pore-forming effect during film formation.

[0013] Preferably, in the step S1, the concentration of the bovine serum albumin aqueous solution is 40-80 mg / ml, and the water-oil ratio is 1-8%. Bovine serum albumin acts as an emulsifier in this system to stabilize the emulsion water droplets. It is dissolved in deionized water to prepare bovine serum albumin aqueous solutions with different concentrations, and then the aqueous solution is added to the polyimide solution at a certain water-oil ratio to prepare a reverse emulsion. A bovine serum albumin aqueous solution with a lower concentration is insufficient to stabilize the emulsion water droplets in the reverse emulsion, and it is easy to form a random macroporous structure after film formation, which damages the film properties. Under higher concentration conditions, in this polyimide system, the connectivity between the pores in the bulk layer after film formation becomes poor. Therefore, after repeated experiments, the concentration of the bovine serum albumin aqueous solution is selected to be 40-80 mg / ml, and within the regulation range of this water-oil ratio, the film-forming effect of the film is good, and a film with an extremely high porosity and fewer defects can be obtained.

[0014] Preferably, in the step S1, the surfactant is poloxamer F127. The addition of poloxamer F127 can improve the hydrophilicity of the film.

[0015] Preferably, in the step S3, the film-forming temperature is 5-35 °C, and the relative humidity for film formation is 55-95%. When the environmental temperature is low, the solvent volatilizes slowly, and the condensed water droplets have a longer growth time, resulting in larger pore diameters on the film surface; when the humidity is low, it is difficult for the condensed water droplets to replenish water during the film-forming process, and it is difficult to form a regular and ordered porous structure in the polyimide film.

[0016] Preferably, in the step S4, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is 0.5-1 mol / L, and the soaking time is 5-10 h. During the alkali treatment of the polyimide film, a higher alkaline solution concentration will cause damage to the film in a short time, while a lower alkaline solution concentration will lead to insufficient hydrolysis. In this system, after repeated experiments, the appropriate concentration of the alkaline solution is determined to be 0.5-1 mol / L, and it will not cause excessive hydrolysis of the film within the selected alkali treatment duration range, thus damaging its mechanical strength and other properties. And by controlling the alkali treatment duration, the regulation of different hydrolysis depths in the bulk layer of the film can be achieved, thereby realizing the introduction of different contents of metal ions. Preferably, in the step S4, the solution containing metal ions is a copper sulfate solution or a silver nitrate solution.

[0017] Preferably, in the step S5, the heat treatment temperature is 250 - 325 °C. Under the heat treatment condition of 250 °C, it is sufficient to meet the reduction of metal ions. At the same time, by changing the heat treatment temperature, the regulation of the particle size of metal nanoparticles can be achieved. After multiple repeated experiments, under the heat treatment temperature condition of 325 °C and below, the reduction of metal ions can be triggered without damaging the morphological structure of the PI porous membrane, thus affecting the film performance.

[0018] The second object of the present invention is to provide an antibacterial polyimide microfiltration membrane prepared according to the above preparation method.

[0019] The third object of the present invention is to provide an application of the antibacterial polyimide microfiltration membrane in the field of water disinfection. Through alkali treatment and subsequent heat treatment processes, the metal ion-loaded polyimide porous membrane triggers the reduction of metal ions, endowing the film with antibacterial properties and simultaneously improving the solvent resistance of the film.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The method for preparing the porous polyimide film of the present invention is simple and efficient, and realizes the antibacterial performance of the film by triggering the reduction of metal ions through heat treatment without adding an external reducing agent, having good application prospects;

[0022] 2. The present invention uses soluble polyimide as the film-forming material with good processing performance. By using the water droplet template method, a polyimide porous membrane with dynamically controllable structure can be prepared in one step. Through alkali treatment and subsequent heat treatment processes, the metal ion-loaded polyimide porous membrane triggers the reduction of metal ions, endowing the film with antibacterial properties and simultaneously improving the solvent resistance of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the contact angle diagram of the antibacterial polyimide microfiltration membrane prepared in Comparative Example 1 of the present invention.

[0024] Figure 2 It is the contact angle diagram of the antibacterial polyimide microfiltration membrane prepared in Example 3 of the present invention.

[0025] Figure 3 It is the scanning electron microscope image of the antibacterial polyimide microfiltration membrane prepared in Example 1 of the present invention.

[0026] Figure 4 It is the scanning electron microscope image of the antibacterial polyimide microfiltration membrane prepared in Example 2 of the present invention.

[0027] Figure 5 It is the scanning electron microscope image of the antibacterial polyimide microfiltration membrane prepared in Example 3 of the present invention.

[0028] Figure 6SEM image of the antibacterial polyimide microfiltration membrane prepared in Example 4 of the present invention.

[0029] Figure 7 SEM image of the antibacterial polyimide microfiltration membrane prepared in Example 5 of the present invention.

[0030] Figure 8 SEM image of the antibacterial polyimide microfiltration membrane prepared in Example 6 of the present invention. Detailed implementation manners

[0031] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the specific embodiments of the present invention in detail with reference to the accompanying drawings.

[0032] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0033] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention's specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and embodiments of this application are only exemplary.

[0034] The technical solution adopted by the present invention is: a preparation method of an antibacterial polyimide microfiltration membrane, and the preparation method specifically includes the following steps:

[0035] S1. Dissolve the soluble polyimide powder in a solvent to obtain a polymer solution, and then dissolve bovine serum albumin in deionized water to obtain an aqueous bovine serum albumin solution;

[0036] S2. Add the aqueous bovine serum albumin solution to the polymer solution, then add a surfactant, and then perform emulsification and ultrasonic treatment to obtain a polymer inverse emulsion;

[0037] S3. Pour the polymer inverse emulsion obtained in step S2 onto a substrate, and obtain a polymer porous film after film formation;

[0038] S4. Immerse the polymer porous film obtained in step S3 in an alkali solution, take it out after immersion and transfer it to a solution containing metal ions to introduce metal ions through an ion exchange reaction to obtain a metal ion-loaded polyimide porous membrane;

[0039] S5. Heat-treat the metal ion-loaded polyimide porous membrane obtained in step S4 to obtain an antibacterial polyimide microfiltration membrane.

[0040] The process of the present invention for preparing an antibacterial polyimide film based on the water droplet templating method can prepare an ordered porous membrane with dynamically controllable structure through the water droplet templating method. The prepared polyimide porous membrane is first chemically modified by soaking in an alkali solution to form carboxylic acid groups, and then metal ions are introduced through an ion exchange reaction. Subsequent heat treatment of the metal ion-loaded polyimide porous membrane triggers the reduction of metal ions. Through this process, materials such as porous polyimide / copper or polyimide / silver can be prepared, thereby enhancing the antibacterial property of the film.

[0041] The present invention uses soluble polyimide as the film-forming material, which has good processing performance. By using the water droplet templating method, a polyimide porous membrane with dynamically controllable structure can be prepared in one step. Through alkali treatment and subsequent heat treatment processes, the metal ion-loaded polyimide porous membrane triggers the reduction of metal ions, endowing the film with antibacterial property and simultaneously improving the solvent resistance of the film.

[0042] In a specific embodiment, in step S1, the solvent is chloroform, and the concentration of the polymer solution is 20 - 40 mg / ml. Chloroform is used as the film-forming solvent, and this solvent has the best film-forming texture and pore-forming effect during film formation.

[0043] In a specific embodiment, in step S1, the concentration of the bovine serum albumin aqueous solution is 40 - 80 mg / ml, and the water-oil ratio is 1 - 8%.

[0044] In a specific embodiment, in step S1, the surfactant is poloxamer F127. The addition of poloxamer F127 can improve the hydrophilicity of the film.

[0045] In a specific embodiment, in step S3, the film-forming temperature is 5 - 35 °C, and the relative humidity for film formation is 55 - 95%. When the ambient temperature is low, the solvent volatilizes slowly, and the condensed water droplets obtain a longer growth time, resulting in larger pore diameters on the film surface; when the humidity is low, it is difficult for the condensed water droplets to replenish water during the film-forming process, and it is difficult to form a regular and ordered porous structure in the polyimide film.

[0046] In a specific embodiment, in step S4, the alkali solution is sodium hydroxide solution or potassium hydroxide solution, and the concentration of the alkali solution is 0.5 - 1 mol / L, and the soaking time is 5 - 10 h.

[0047] In a specific embodiment, in step S4, the solution containing metal ions is copper sulfate solution or silver nitrate solution.

[0048] In a specific embodiment, in step S5, the heat treatment temperature is 250 - 325 °C.

[0049] The technical effects of the present invention will be described below in conjunction with specific embodiments.

[0050] Example 1

[0051] This example provides an antibacterial polyimide microfiltration membrane, which is prepared by the following method:

[0052] S1. Dissolve the soluble polyimide powder in chloroform to prepare a polymer solution with a concentration of 30 mg / mL. Dissolve bovine serum albumin as an emulsifier in deionized water to obtain an aqueous solution of bovine serum albumin. Add the aqueous solution of bovine serum albumin to the polymer solution, add the surfactant poloxamer F127, and perform emulsifying ultrasound for 15 min at room temperature to obtain a polymer inverse emulsion with a water-oil ratio of 2%.

[0053] S2. Pour the polymer inverse emulsion onto a clean substrate to obtain a polymer porous film, with a film-forming temperature of 25 °C and a relative humidity of 45%.

[0054] S3. Immerse the polymer porous film in an alkaline solution at room temperature for 5 h, and then transfer the film to a solution of copper sulfate to introduce metal ions through an ion exchange reaction.

[0055] S4. Obtain the antibacterial polyimide microfiltration membrane by inducing the reduction of metal ions through heat treatment without adding an external reducing agent, with a heat treatment temperature of 250 °C.

[0056] Example 2

[0057] The difference from Example 1 is only that the relative humidity in step S2 of this example is 75%, and the others are the same as in Example 1, which will not be elaborated here.

[0058] Example 3

[0059] The difference from Example 1 is only that the relative humidity in step S2 of this example is 85%, and the others are the same as in Example 1, which will not be elaborated here.

[0060] Example 4

[0061] The difference from Example 1 is only that the relative humidity in step S2 of this example is 95%, and the others are the same as in Example 1, which will not be elaborated here.

[0062] Example 5

[0063] The difference from Example 1 is only that the relative humidity in step S2 of this example is 75% and the temperature is 15 °C, and the others are the same as in Example 1, which will not be elaborated here.

[0064] Example 6

[0065] The difference from Example 1 is only that the relative humidity in step S2 of this example is 75% and the temperature is 35°C, and the others are the same as those in Example 1, which will not be elaborated here.

[0066] Comparative Example 1

[0067] The difference from Example 3 is only that no surfactant was added during the preparation process of this comparative example, and the others are the same as those in Example 3, which will not be elaborated here.

[0068] The performance of the antibacterial polyimide microfiltration membranes prepared in Examples 1-6 and Comparative Example 1 was detected, and the detection results are as Figures 1 - 8 shown.

[0069] Figure 1 is the contact angle of the antibacterial polyimide microfiltration membrane prepared in Comparative Example 1, Figure 2 and

[0070] is the contact angle of the antibacterial polyimide microfiltration membrane prepared in Example 3. The contact angle test results were measured by a static water contact angle measuring instrument of the German DSA100 model, and the volume of the measuring water droplet used was 4 μL. Figure 1 and Figure 2 It can be seen that for the polyimide porous membrane prepared without adding surfactant F127, the surface of the film shows hydrophobic properties, and its contact angle value is 126°. For the polyimide porous membrane prepared by adding poloxamer F127 in the inverse emulsion, the surface of the film changes from hydrophobic to hydrophilic, and its contact angle value is 76°.

[0071] All samples were characterized by scanning electron microscopy. The surface and cross-section of the samples were gold-plated to ensure their conductivity. The cross-sectional morphology test results of the porous thin films are as Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 shown. Figure 3 is the scanning electron micrograph of the antibacterial polyimide microfiltration membrane prepared in Example 1 of the present invention. It can be seen from Figure 3 that for the antibacterial polyimide microfiltration membrane prepared under the low humidity condition of 45%, a porous structure with chaotic and disordered surface and extremely uneven pore sizes is formed on its surface, and the number of holes in the film body layer is scarce and the porosity is low. Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 are the scanning electron micrographs of the antibacterial polyimide microfiltration membranes prepared in Example 2, Example 3, Example 4, Example 5 and Example 6 respectively. It can be seen from Figures 4 - 6It can be seen that the porous morphologies obtained under three humidity conditions above 75% are quite similar. Regardless of the humidity level, a multi-layer porous structure is formed throughout the cross-section, showing a very high porosity. From Figure 4 、 Figure 7 and Figure 8 it can be seen that a multi-layer pore structure covering the entire body layer is formed in the body layer of the film under three temperature conditions, and its dependence on external experimental conditions is relatively low.

[0072] In summary, in this method, by preparing a porous polyimide film under high humidity conditions, a rich porous structure can be found in its scanning electron micrograph. After adding the surfactant F127, the hydrophilicity of the film is improved, which is beneficial to increasing the flux of the porous film. This method has a relatively low dependence on external experimental conditions, and a multi-layer porous structure is formed throughout the body layer, showing a very high porosity. The size and size distribution of the surface pores can be regulated by changing the experimental parameters, so as to be applicable to microfiltration applications.

[0073] The inventor found through in-depth research that by controlling experimental conditions such as the environmental humidity, temperature, and solution concentration of the water droplet template method, effective regulation of the pore morphology formed on the surface and in the body layer can be achieved. By controlling the processes of alkali treatment and subsequent heat treatment of the polyimide film, including the alkali treatment and subsequent ion exchange conditions (time, concentration, and temperature), the preparation of an antibacterial polyimide film can be realized.

[0074] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A preparation method of an antibacterial polyimide microfiltration membrane, characterized in that, The preparation method specifically includes the following steps: S1. Dissolve soluble polyimide powder in a solvent to obtain a polymer solution, and then dissolve bovine serum albumin in deionized water to obtain an aqueous bovine serum albumin solution; in step S1, the solvent is chloroform, the concentration of the polymer solution is 20 - 40 mg / ml; the concentration of the aqueous bovine serum albumin solution is 40 - 80 mg / ml, and the water-oil ratio is 1 - 8%; S2. Add the aqueous bovine serum albumin solution to the polymer solution, then add a surfactant, and then perform emulsification and ultrasonic treatment to obtain a polymer inverse emulsion; S3. Pour the polymer inverse emulsion obtained in step S2 onto a substrate, and obtain a polymer porous film after film formation; S4. Immerse the polymer porous film obtained in step S3 in an alkali solution, take it out after immersion and transfer it to a solution containing metal ions to introduce metal ions through an ion exchange reaction to obtain a metal ion-loaded polyimide porous membrane; S5. Perform heat treatment on the metal ion-loaded polyimide porous membrane obtained in step S4 to obtain an antibacterial polyimide microfiltration membrane.

2. The preparation method of the antibacterial polyimide microfiltration membrane according to claim 1, characterized in that, In step S1, the surfactant is poloxamer F127.

3. The preparation method of the antibacterial polyimide microfiltration membrane according to claim 1, characterized in that, In step S3, the film formation temperature is 5 - 35 °C, and the relative humidity for film formation is 55 - 95%.

4. The preparation method of the antibacterial polyimide microfiltration membrane according to claim 1, wherein, In step S4, the alkali solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkali solution is 0.5 - 1 mol / L, and the immersion time is 5 - 10 h.

5. The preparation method of the antibacterial polyimide microfiltration membrane according to claim 4, characterized in that, In step S4, the solution containing metal ions is a copper sulfate solution or a silver nitrate solution.

6. The preparation method of the antibacterial polyimide microfiltration membrane according to claim 1, characterized in that, In step S5, the heat treatment temperature is 250 - 325 °C.

7. An antibacterial polyimide microfiltration membrane, characterized in that, Prepared according to the preparation method described in any one of claims 1 - 6.

8. An application of the antibacterial polyimide microfiltration membrane as described in claim 7 in the field of water disinfection.

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