Amino quantum dot doped cellulose acetate-based phase conversion film as well as preparation method and application thereof

Abstract

The invention discloses an amino quantum dot doped cellulose acetate-based phase conversion film and a preparation method and application thereof, and relates to the technical field of high polymer material separation membranes, the preparation method comprises the following steps: mixing cellulose acetate and a solvent, and sequentially carrying out stirring, ultrasonic treatment, filtration and standing defoaming treatment to obtain a cellulose acetate casting solution; scraping the cellulose acetate membrane casting solution on a support plate to form a liquid membrane, carrying out air retention treatment, and carrying out non-solvent induced phase inversion treatment on the liquid membrane in a coagulating bath to obtain a cellulose acetate membrane; mixing the cellulose acetate membrane with an alkaline aqueous solution, and carrying out hydrolysis treatment to obtain a cellulose acetate membrane subjected to hydrolysis treatment; and mixing the hydrolyzed cellulose acetate membrane with an amino quantum dot solution, carrying out an adsorption reaction, washing, and freeze-drying to obtain the amino quantum dot doped cellulose acetate-based phase conversion membrane. The phase conversion membrane prepared by the invention has higher retention rate and flux, and can be used as a high-performance separation membrane material.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material separation membranes, and in particular to an amino quantum dot-doped cellulose acetate-based phase conversion membrane, a preparation method thereof, and applications thereof. Background Art

[0002] Separation membranes are semipermeable membranes with selective permeability, capable of selectively transmitting different components in a mixture based on differences in their physical and chemical properties (such as size, shape, and charge). Separation membranes are widely used in water treatment, pharmaceuticals, and energy.

[0003] Methods for preparing separation membranes include phase inversion, interfacial polymerization, thermally induced phase separation, or electrospinning.

[0004] However, the separation performance of the separation membranes obtained by existing separation membrane preparation technologies is limited, and they have the following main defects: (1) Trade-off effect between selectivity and permeability: increasing the selectivity of the membrane often leads to a decrease in permeability, and vice versa; (2) Under harsh conditions such as high temperature, high pressure or strong acid and alkali, many traditional polymer membranes are prone to degradation, swelling or pore structure destruction, resulting in a decrease in separation performance; (3) The membrane surface is easily contaminated by organic matter, colloids or microorganisms, forming a fouling layer, which significantly reduces the flux and separation efficiency and increases operating costs; (4) Existing preparation methods (such as phase inversion method) are difficult to achieve a highly uniform pore size distribution, which affects the selectivity and mass transfer efficiency of the membrane. Summary of the Invention

[0005] The main purpose of the present invention is to propose an amino quantum dot-doped cellulose acetate-based phase conversion membrane and its preparation method and application, aiming to solve the problems of low retention and flux of separation membranes in the prior art.

[0006] To achieve the above object, the present invention provides a method for preparing an amino quantum dot-doped cellulose acetate-based phase conversion membrane, comprising the following steps:

[0007] S1, mixing cellulose acetate and a solvent, stirring, ultrasonicating, filtering, and standing for degassing in sequence to obtain a cellulose acetate casting solution;

[0008] S2, scraping the cellulose acetate casting liquid onto a support plate to form a liquid film, performing an air stagnation treatment, and then placing the liquid film in a coagulation bath for a non-solvent-induced phase inversion treatment to obtain a cellulose acetate film;

[0009] S3, mixing the cellulose acetate membrane with an alkaline aqueous solution and performing a hydrolysis treatment to obtain a hydrolyzed cellulose acetate membrane;

[0010] S4. Mixing the hydrolyzed cellulose acetate membrane with the amino quantum dot solution, performing an adsorption reaction, washing, and freeze-drying to obtain the amino quantum dot-doped cellulose acetate-based phase conversion membrane.

[0011] In one embodiment, in step S1:

[0012] The concentration of cellulose acetate in the cellulose acetate casting solution is 0.05 to 0.5 g / mL; and / or,

[0013] The solvent includes one or more of acetone, dichloromethane, and ethyl acetate; and / or,

[0014] The stirring temperature is 30-60° C., the stirring speed is 100-800 rpm, and the stirring time is 2-24 h; and / or,

[0015] The ultrasonic time is 10 to 40 minutes; and / or,

[0016] The temperature of the static degassing is 10 to 30° C., and the time of the static degassing is 24 to 72 hours.

[0017] In one embodiment, in step S2:

[0018] The thickness of the liquid film is 50 to 800 μm; and / or,

[0019] The coagulation bath comprises a water bath in at least one reagent selected from deionized water, anhydrous ethanol, and anhydrous methanol.

[0020] In one embodiment, in step S3:

[0021] The alkaline aqueous solution includes at least one of a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution and an ammonia solution; and / or,

[0022] The concentration of the alkaline aqueous solution is 2 to 15 g / L; and / or,

[0023] The hydrolysis treatment time is 2 to 24 hours.

[0024] In one embodiment, in step S4:

[0025] The amino quantum dots in the amino quantum dot solution are amino cadmium telluride quantum dots; and / or,

[0026] The emission wavelength of the amino quantum dots in the amino quantum dot solution is 525 nm, 565 nm or 605 nm; and / or,

[0027] The freeze-drying conditions are: drying at -20 to -40°C for 2 to 48 hours.

[0028] The present invention also provides an amino quantum dot-doped cellulose acetate-based phase conversion membrane, comprising a first membrane layer, a second membrane layer, and a third membrane layer arranged sequentially from bottom to top:

[0029] The materials of the first film layer, the second film layer and the third film layer are cellulose acetate adsorbed with amino quantum dots;

[0030] The average pore size of the second membrane layer is greater than the average pore size of the first membrane layer and greater than the average pore size of the third membrane layer;

[0031] The amino quantum dot-doped cellulose acetate-based phase conversion membrane is prepared by the aforementioned method for preparing the amino quantum dot-doped cellulose acetate-based phase conversion membrane.

[0032] In one embodiment, the average pore size of the first membrane layer is 100 nm to 5 μm; and / or,

[0033] The average pore size of the second membrane layer is 9 μm to 50 μm; and / or,

[0034] The average pore size of the third membrane layer is 1 nm to 100 nm.

[0035] The present invention also provides the aforementioned amino quantum dot-doped cellulose acetate-based phase conversion membrane or the use of the amino quantum dot-doped cellulose acetate-based phase conversion membrane prepared by the aforementioned method for preparing the amino quantum dot-doped cellulose acetate-based phase conversion membrane in the preparation of microfiltration separation membranes, heavy metal ion removal membranes or fuel cell membranes.

[0036] In the technical solution of the present invention, in step S1, cellulose acetate is dissolved in a solvent to form a uniform solution, and stirring is used to promote uniform dissolution. Ultrasound is used to accelerate dissolution and break small bubbles. Filtration is used to remove undissolved particles or impurities. Static degassing is used to allow large-sized bubbles to float up and escape, thereby preventing defects from forming during the film formation process. A uniformly dispersed, bubble-free, and moderately viscous casting liquid is obtained, ensuring the thickness uniformity in the subsequent film scraping process, which is conducive to the formation of a controllable pore structure in the subsequent non-solvent-induced phase separation process. In step S2, a scraper can be used to flatten the casting liquid on the support plate to form a liquid film to form a uniform initial structure. The air stagnation treatment can evaporate part of the solvent in the part of the liquid film that contacts the air, thereby reducing the solvent concentration in the surface liquid film, and regulating the thickness and pore structure of the third film layer in the later stage. The liquid film after the air stagnation treatment is subjected to a coagulation bath treatment, so that the solvent in the liquid film diffuses into the coagulation bath, and the non-solvent enters the liquid film, resulting in the precipitation of the cellulose acetate film. Since the solvent exchange rate on the side close to the support plate is the slowest, the pore size of the obtained membrane layer structure is smaller, and the solvent exchange rate in the middle layer is slower. The speed is fast, and the pore size of the obtained membrane structure is large. The cellulose acetate membrane obtained in this step has a precursor layer of three types of membrane layers; in step S3, the precipitated cellulose acetate membrane is hydrolyzed with an alkaline aqueous solution, so that a large number of acetyl groups (-OCOCH3) in the cellulose acetate undergo ester bond hydrolysis reaction under alkaline conditions to generate carboxyl groups (-COOH) and hydroxyl groups (-OH), thereby obtaining a hydrolyzed cellulose acetate membrane. The surface of the hydrolyzed cellulose acetate membrane has a large number of active hydrophilic functional groups, which enhances the hydrophilicity of the cellulose acetate membrane and can improve the flux of the final phase conversion membrane. Since these hydrophilic functional groups are negatively charged, they provide more electrostatic adsorption sites, which facilitates the stable binding of subsequent amino quantum dots; in step S4, the hydrolyzed cellulose acetate membrane is mixed with an amino quantum dot solution. The amino groups of the amino quantum dots in the amino quantum dot solution have a positive charge and will combine with the carboxyl groups or hydroxyl groups through electrostatic adsorption or hydrogen bonding to be stably connected to the cellulose acetate membrane. Finally, by freeze-drying, a phase conversion membrane with a three-layer membrane structure can be obtained. The phase conversion membrane prepared by the invention has high rejection rate and flux and can be used as a high-performance separation membrane material. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0038] Figure 1 IR spectra of the phase conversion films in Examples 1 to 3 of the present invention;

[0039] Figure 2 IR spectra of the phase conversion films in Examples 4 and 5 of the present invention;

[0040] Figure 3 IR spectra of the phase conversion films in Examples 7 to 9 of the present invention;

[0041] Figure 4 IR spectra of the phase conversion films in Comparative Examples 1 to 3 of the present invention;

[0042] Figure 5 CA in Comparative Example 2 of the present invention 0.11 Cross-sectional scanning electron microscopy image of the phase transition membrane;

[0043] Figure 6 605nm-NH2-CdTe-QDs / CA in Example 8 of the present invention 0.11 Cross-sectional scanning electron microscopy image of the phase transition membrane;

[0044] Figure 7 605nm-NH2-CdTe-QDs / CA in Example 9 of the present invention 0.12 Cross-sectional scanning electron microscopy image of the phase transition membrane;

[0045] Figure 8 Graphs showing membrane flux and separation performance of the phase conversion membranes in Comparative Examples 1 to 3 of the present invention;

[0046] Figure 9 Graphs showing membrane flux and separation performance of the phase conversion membranes in Examples 7 to 9 of the present invention.

[0047] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0049] Separation membranes are semipermeable membranes with selective permeability, capable of selectively transmitting different components in a mixture based on differences in their physical and chemical properties (such as size, shape, and charge). Separation membranes are widely used in water treatment, pharmaceuticals, and energy.

[0050] Methods for preparing separation membranes include phase inversion, interfacial polymerization, thermally induced phase separation, or electrospinning.

[0051] However, the separation performance of the separation membranes obtained by existing separation membrane preparation technologies is limited, and they have the following main defects: (1) Trade-off effect between selectivity and permeability: increasing the selectivity of the membrane often leads to a decrease in permeability, and vice versa; (2) Under harsh conditions such as high temperature, high pressure or strong acid and alkali, many traditional polymer membranes are prone to degradation, swelling or pore structure destruction, resulting in a decrease in separation performance; (3) The membrane surface is easily contaminated by organic matter, colloids or microorganisms, forming a fouling layer, which significantly reduces the flux and separation efficiency and increases operating costs; (4) Existing preparation methods (such as phase inversion method) are difficult to achieve a highly uniform pore size distribution, which affects the selectivity and mass transfer efficiency of the membrane.

[0052] In view of this, the present invention provides a preparation method of an amino quantum dot-doped cellulose acetate-based phase conversion membrane, comprising the following steps: S1, mixing cellulose acetate and a solvent, and sequentially performing stirring, ultrasonication, filtration, and static degassing treatment to obtain a cellulose acetate casting solution; S2, scraping the cellulose acetate casting solution onto a support plate to form a liquid film, and performing an air stagnation treatment to allow the solvent in the casting solution adjacent to the air to evaporate quickly, and the polymer concentration to increase continuously, so that the cellulose acetate in the subsequent casting solution adjacent to the air forms a relatively compact membrane structure, and then placing the film in a coagulation bath for non-solvent induced phase conversion. The method further comprises the steps of: performing a conversion treatment to rapidly exchange the solvent in the casting solution and the non-solvent in the coagulation bath to obtain a cellulose acetate membrane; S3, mixing the cellulose acetate membrane with an alkaline aqueous solution and performing a hydrolysis treatment to activate the cellulose acetate to obtain an activated cellulose acetate membrane rich in hydroxyl groups (hydrolyzed cellulose acetate membrane); S4, mixing the hydrolyzed cellulose acetate membrane with an amino quantum dot solution and performing an adsorption reaction to fully complex the amino quantum dots with the activated cellulose acetate membrane, washing, and freeze-drying to obtain the amino quantum dot-doped cellulose acetate-based phase conversion membrane.

[0053] In the technical solution of the present invention, in step S1, cellulose acetate is dissolved in a solvent to form a uniform solution, and stirring is used to promote uniform dissolution. Ultrasound is used to accelerate dissolution and break small bubbles. Filtration is used to remove undissolved particles or impurities. Static degassing is used to allow large-sized bubbles to float up and escape, thereby preventing defects from forming during the film formation process. A uniformly dispersed, bubble-free, and moderately viscous casting solution is obtained, thereby ensuring thickness uniformity in the subsequent film scraping process and facilitating the formation of a controllable pore structure in the subsequent non-solvent-induced phase separation process. In step S2, a scraper can be used to flatten the casting solution on a support plate to form a liquid film to form a uniform initial structure. The air stagnation treatment can volatilize part of the solvent in the part of the liquid film that contacts the air, thereby reducing the solvent concentration in the surface liquid film, and regulating the thickness and pore structure of the third film layer in the later stage. The liquid film after the air stagnation treatment is subjected to a coagulation bath treatment, so that the solvent in the liquid film diffuses into the coagulation bath, and the non-solvent enters the liquid film, resulting in the precipitation of the cellulose acetate film. Since the solvent exchange rate on the side close to the support plate is the slowest, the pore size of the resulting membrane layer structure is smaller, and the solvent exchange rate in the middle layer is higher. The conversion speed is fast, and the pore size of the obtained membrane structure is large. The cellulose acetate membrane obtained in this step has a precursor layer of three types of membrane layers; in step S3, the precipitated cellulose acetate membrane is hydrolyzed with an alkaline aqueous solution, so that a large number of acetyl groups (-OCOCH3) in the cellulose acetate undergo ester bond hydrolysis reaction under alkaline conditions to generate carboxyl groups (-COOH) and hydroxyl groups (-OH), thereby obtaining a hydrolyzed cellulose acetate membrane. The surface of the hydrolyzed cellulose acetate membrane has a large number of active hydrophilic functional groups, which enhances the hydrophilicity of the cellulose acetate membrane and can improve the flux of the final phase conversion membrane. Since these hydrophilic functional groups are negatively charged, they provide more electrostatic adsorption sites, which facilitates the stable binding of subsequent amino quantum dots; in step S4, the hydrolyzed cellulose acetate membrane is mixed with an amino quantum dot solution. The amino groups of the amino quantum dots in the amino quantum dot solution have a positive charge and will combine with the carboxyl groups or hydroxyl groups through electrostatic adsorption or hydrogen bonding to be stably connected to the cellulose acetate membrane. Finally, by freeze-drying, a phase conversion membrane with a three-layer membrane structure can be obtained. The phase conversion membrane prepared by the invention has high rejection rate and flux and can be used as a high-performance separation membrane material.

[0054] It's understandable that the most basic three-layer membrane structure is formed during the non-solvent phase transition. That is, after the film is placed in a non-solvent, the solvent in the casting solution and the non-solvent are completely exchanged, and the film peels off from the glass plate, forming a three-layer membrane structure. Finally, after the quantum dot adsorption treatment, all membrane layers contain quantum dots.

[0055] In some embodiments, in step S1, the cellulose acetate casting solution has a cellulose acetate concentration of 0.05 to 0.5 g / mL, preferably 0.1 to 0.2 g / mL. A cellulose acetate casting solution concentration within this range can achieve a good balance between film thickness and pore structure, and is suitable for constructing gradient porous membranes.

[0056] In some embodiments, in step S1, the solvent includes one or more of acetone, dichloromethane, and ethyl acetate. The above solvents can be any one or a mixture of two or three solvents, all of which are within the scope of the present invention.

[0057] In some embodiments, in step S1, the stirring temperature is 30-60°C, the stirring speed is 100-800 rpm, and the stirring time is 2-24 hours. Preferably, the stirring temperature is 30-40°C, the stirring speed is 500-700 rpm, and the stirring time is 10-20 hours. Stirring temperature, speed, and time within these ranges can ensure good initial dissolution of cellulose acetate.

[0058] In some embodiments, in step S1, the ultrasonic treatment time is 10 to 40 minutes, preferably 20 to 30 minutes. The ultrasonic treatment time within the above range can ensure that the cellulose acetate is further and more thoroughly dissolved in the solvent.

[0059] In some embodiments, in step S1, the degassing temperature is 10-30°C, and the degassing time is 24-72 hours. Preferably, the degassing conditions are: an ambient temperature of 20-30°C, and a time of 24-48 hours. Degassing time and temperature within the above ranges can ensure that there are fewer bubbles in the casting solution, and the pore size and pore density of each layer of the ultimately formed phase change membrane are relatively uniform.

[0060] In some embodiments, in step S2, the liquid film has a thickness of 50 to 800 μm; and / or the coagulation bath comprises a water bath in at least one of deionized water, anhydrous ethanol, and anhydrous methanol. A liquid film thickness within this range ensures good mechanical properties of the final phase conversion membrane and facilitates the formation of a three-layer membrane structure. The casting liquid can be smoothed using a scraper. The thickness of the stainless steel scraper is 50 to 800 μm, preferably 200 to 500 μm.

[0061] In some embodiments, in step S3: the alkaline aqueous solution includes at least one of a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, and ammonia water; and / or the concentration of the alkaline aqueous solution is 2 to 15 g / L; and / or the hydrolysis treatment time is 2 to 24 hours. Simultaneously controlling the type, concentration, and hydrolysis treatment time of the alkaline aqueous solution within the above ranges can ensure that the surface of the hydrolyzed cellulose acetate membrane has a large number of negatively charged active hydrophilic functional groups, thereby enhancing the hydrophilicity of the cellulose acetate membrane and improving the flux of the final phase conversion membrane. Preferably, the alkaline aqueous solution is a sodium hydroxide aqueous solution, the concentration of the alkaline aqueous solution is 5 to 12 g / L, and the hydrolysis treatment time is 6 to 18 hours.

[0062] In some embodiments, in step S4, the amino quantum dots in the amino quantum dot solution are amino cadmium telluride quantum dots (CdTe-QDs); and / or the emission wavelength of the amino quantum dots in the amino quantum dot solution is 525 nm, 565 nm, or 605 nm; and / or the freeze-drying conditions are: drying at -20°C to -40°C for 2 to 48 hours. The type and emission wavelength of the amino quantum dots in the amino quantum dot solution within the above ranges can ensure that a relatively uniform and stable amino quantum dot film layer is formed on the surface of the hydrolyzed cellulose acetate membrane. The freeze-drying conditions are preferably: drying at -20°C to -30°C for 6 to 24 hours.

[0063] The present invention also proposes an amino quantum dot-doped cellulose acetate-based phase conversion membrane, comprising a first membrane layer, a second membrane layer, and a third membrane layer arranged in sequence from bottom to top: the materials of the first membrane layer, the second membrane layer, and the third membrane layer are cellulose acetate adsorbed with amino quantum dots; the average pore size of the second membrane layer is greater than the average pore size of the first membrane layer, which is greater than the average pore size of the third membrane layer; the amino quantum dot-doped cellulose acetate-based phase conversion membrane is prepared by the aforementioned preparation method of the amino quantum dot-doped cellulose acetate-based phase conversion membrane.

[0064] In the technical solution of the present invention, the first membrane layer, the second membrane layer and the third membrane layer are respectively a uniform sponge-like support layer, a finger-like macroporous layer and a dense cortex layer in appearance. The three membrane layers are arranged from bottom to top and the materials and average pore sizes of the three membrane layers are controlled within the above range to ensure that the phase conversion membrane has a higher retention rate and flux, and can be used as a high-performance separation membrane material.

[0065] It can be understood that, in terms of average pore size, when the average pore size of the finger-like pore layer is greater than the average pore size of the uniform sponge-like support layer and greater than the average pore size of the dense cortex, step-by-step filtration can be ensured. The dense cortex is used to intercept small molecules, thereby improving the selectivity and retention rate of the phase conversion membrane; the sponge-like support layer provides mechanical support to prevent the membrane from rupturing or collapsing; the middle finger-like macroporous layer and the sponge-like support layer provide fast mass transfer channels. Therefore, the amino quantum dot-doped cellulose acetate-based phase conversion membrane provided by the present invention breaks the "flux-retention rate trade-off effect" in traditional membranes.

[0066] In some embodiments, the average pore size of the first membrane layer is 100 nm to 5 μm. Controlling the average pore size of the first membrane layer within the above range can ensure that the phase conversion membrane has good mechanical strength and is not prone to collapse; it also serves as part of the mass transfer channel.

[0067] In some embodiments, the average pore size of the second membrane layer is 9 μm to 50 μm. The average pore size of the second membrane layer within the above range can ensure that the phase conversion membrane has a good mass transfer channel, significantly reduce flow resistance, and thus improve the flux performance of the membrane.

[0068] In some embodiments, the average pore size of the third membrane layer is 1 nm to 100 nm. The average pore size of the third membrane layer within the above range can ensure that the phase conversion membrane has excellent selective separation ability, effectively intercepts target molecules or particles, and maintains a high permeation flux.

[0069] The present invention also provides the use of the aforementioned amino-quantum-dot-doped cellulose acetate-based phase conversion membrane or the amino-quantum-dot-doped cellulose acetate-based phase conversion membrane prepared by the aforementioned method for preparing the same, in the preparation of microfiltration separation membranes, heavy metal ion removal membranes, or fuel cell membranes. Therefore, the membrane possesses all the beneficial effects of the aforementioned amino-quantum-dot-doped cellulose acetate-based phase conversion membrane or the aforementioned method for preparing the same, and no further details are given here.

[0070] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0071] Example 1

[0072] A quantum dot-doped cellulose acetate-based phase conversion membrane is prepared by the following steps:

[0073] Step 1. Weigh 5 g of cellulose acetate (CA) (purchased from Wuhan Shenshi, 300.0-500.0 mPa·s, product number: C49830-250 g) and place it in a clean 100 mL beaker. Then use a graduated cylinder to measure 50 mL of acetone and place it in the above beaker. After stirring thoroughly at 35°C for 24 hours, transfer it to an ultrasonic bath and continue ultrasonication for 30 minutes. Then, let it stand for degassing for 24 hours until the above system becomes a uniform, transparent, and bubble-free solution, thereby preparing a CA / acetone solution with a concentration of 0.10 g / mL, which is also the casting solution; wherein, CA:acetone = 5:50 (mass ratio);

[0074] Step 2: Place a clean 10 cm × 10 cm glass plate at 30°C on a horizontal laboratory table, slowly pour 50 mL of the above casting solution, and use a stainless steel scraper at 30°C and 500 μm thick to slowly push the casting solution to form a liquid film of uniform thickness, and leave it in the air for 1 minute;

[0075] Step 3: Take 1L of clean deionized water bath (30℃), place the glass plate with the unsolidified liquid film horizontally in it to fully transform the phase. After it falls off naturally, use clean tweezers to remove the floating CA film to obtain the wet CA film. 0.10 membrane;

[0076] Step 4. Preparation of quantum dot solution: Use a 5mL graduated cylinder to measure 1mL of 525nm emission wavelength NH2-CdTe-QDs solution (purchased from Wuhan Shenshi, 0.05μmol / L, catalog number: F122251-5mL) and place it in a 100mL beaker. Then measure 99mL of deionized water and place it in the beaker. Stir thoroughly with a glass rod and set aside. The concentration of the 525nm-NH2-CdTe-QDs aqueous solution is 0.0005μmol / L.

[0077] Step 5, preparation of sodium hydroxide solution: 2.5 g of NaOH was weighed using an electronic analytical balance and placed in a 500 mL beaker. 250 mL of deionized water was then measured and poured into the beaker, stirred, and set aside to obtain a NaOH aqueous solution; wherein the concentration of the NaOH aqueous solution was 0.01 g / mL;

[0078] Step 6, Preparation of 525nm-NH2-CdTe-QDs / CA0.10 phase conversion film: First, wet the CA 0.10 The membrane was immersed in 0.01g / mL NaOH solution for 2 minutes and hydrolyzed to fully expose -COOH. The treated membrane was then taken out and placed in 30mL of prepared 525nm-NH2-CdTe-QDs solution and immersed for 24 hours. Finally, the treated membrane was taken out again, rinsed with deionized water several times, and placed in a ceramic basin filled with a small amount of deionized water to fully replace the residual solvent in the membrane. The replaced film was then placed in a freeze drying oven at -30°C and dried for 24 hours to prepare 525nm-NH2-CdTe-QDs / CA 0.10 Phase conversion membrane.

[0079] Example 2

[0080] Compared with Example 1, Example 2 is different in that:

[0081] Step 1: Weigh 5.5 g of cellulose acetate to prepare a 0.11 g / mL CA / acetone solution; wherein the CA:acetone ratio is 5.5:50 (mass ratio);

[0082] The other steps were the same as in Example 1, and finally 525 nm-NH2-CdTe-QDs / CA was prepared. 0.11 Phase conversion membrane.

[0083] Example 3

[0084] Compared with Example 1, Example 3 is different in that:

[0085] Step 1: Weigh 6.0 g of cellulose acetate to prepare a 0.12 g / mL CA / acetone solution; wherein the CA:acetone ratio is 6.0:50 (mass ratio);

[0086] The other steps were the same as in Example 1, and finally 525 nm-NH2-CdTe-QDs / CA was prepared. 0.12 Phase conversion membrane.

[0087] Example 4

[0088] Compared with Example 1, Example 4 is different in that:

[0089] In step 4, 1 mL of 565 nm emission wavelength NH2-CdTe-QDs solution (purchased from Wuhan Shenshi, 0.05 μmol / L, product number: F122257-5 mL) was measured using a 5 mL graduated cylinder.

[0090] The other steps were the same as in Example 1, and finally 565 nm-NH2-CdTe-QDs / CA was prepared. 0.10 Phase conversion membrane.

[0091] Example 5

[0092] Compared with Example 4, Example 5 is different in that:

[0093] Step 1: Weigh 5.5 g of cellulose acetate to prepare a 0.11 g / mL CA / acetone solution; wherein the CA:acetone ratio is 5.5:50 (mass ratio);

[0094] The other steps were the same as in Example 4, and finally 565nm-NH2-CdTe-QDs / CA was prepared. 0.11 Phase conversion membrane.

[0095] Example 6

[0096] Compared with Example 4, Example 6 is different in that:

[0097] Step 1: Weigh 6.0 g of cellulose acetate to prepare a 0.12 g / mL CA / acetone solution; wherein the CA:acetone ratio is 6.0:50 (mass ratio);

[0098] The other steps were the same as in Example 1, and finally 565 nm-NH2-CdTe-QDs / CA was prepared. 0.12 Phase conversion membrane.

[0099] Example 7

[0100] Compared with Example 1, Example 7 is different in that:

[0101] In step 4, 1 mL of NH2-CdTe-QDs solution (purchased from Wuhan Shenshi, 0.05 μmol / L, product number: R138880-5 mL) with an emission wavelength of 605 nm was measured using a 5 mL graduated cylinder.

[0102] The other steps were the same as in Example 1, and finally 605 nm-NH2-CdTe-QDs / CA was prepared. 0.10 Phase conversion membrane.

[0103] Example 8

[0104] Compared with Example 7, Example 8 is different in that:

[0105] Step 1: Weigh 5.5 g of cellulose acetate to prepare a 0.11 g / mL CA / acetone solution; wherein the CA:acetone ratio is 5.5:50 (mass ratio);

[0106] The other steps were the same as in Example 7, and finally 605 nm-NH2-CdTe-QDs / CA was prepared. 0.11 Phase conversion membrane.

[0107] Example 9

[0108] Compared with Example 7, Example 9 is different in that:

[0109] Step 1: Weigh 6.0 g of cellulose acetate to prepare a 0.12 g / mL CA / acetone solution; wherein the CA:acetone ratio is 6.0:50 (mass ratio);

[0110] The other steps were the same as in Example 7, and finally 605 nm-NH2-CdTe-QDs / CA was prepared. 0.12 Phase conversion membrane.

[0111] Comparative Example 1

[0112] Comparative Example 1 is different from Example 1 in that:

[0113] Steps 4, 5, and 6 are omitted, and step 3 is specifically as follows: take a 1L clean deionized water bath (30°C), place the glass plate with the unsolidified liquid film on the surface in step 2 horizontally in it to fully invert the phase. After it falls off naturally, use clean tweezers to remove the floating CA film, place it in a ceramic basin with clean deionized water, and fully replace the residual solvent in the film to obtain a wet CA film. 0.10 Then wet CA 0.10 The membrane was placed in a freeze drying oven at -30°C and dried for 24 hours to prepare CA. 0.10 Phase conversion membrane.

[0114] Comparative Example 2

[0115] Comparative Example 2 is different from Comparative Example 1 in that:

[0116] Step 1: Weigh 5.5 g of cellulose acetate to prepare a 0.11 g / mL CA / acetone solution; wherein CA:acetone = 5.5:50 (mass ratio). The other steps are the same as those in Comparative Example 1, and finally CA is prepared. 0.11 Phase conversion membrane.

[0117] Comparative Example 3

[0118] Comparative Example 3 is different from Comparative Example 1 in that:

[0119] Step 1: Weigh 6.0 g of cellulose acetate to prepare a 0.12 g / mL CA / acetone solution; wherein CA:acetone = 6.0:50 (mass ratio). The other steps are the same as those in Comparative Example 1, and finally CA is prepared. 0.12 Phase conversion membrane.

[0120] Performance Testing

[0121] The phase conversion membranes in Examples 1 to 9 and Comparative Examples 1 to 3 were tested by infrared spectroscopy. Figure 1 、 Figure 2 、 Figure 3 and Figure 4 shown.

[0122] Figure 1 From top to bottom are 525nm-NH2-CdTe-QDs / CA 0.10 、525nm-NH2-CdTe-QDs / CA 0.11 and 525nm-NH2-CdTe-QDs / CA 0.12 Infrared spectrum of cellulose acetate membrane; Figure 2 From top to bottom are 565nm-NH2-CdTe-QDs / CA 0.10 、565nm-NH2-CdTe-QDs / CA 0.11 and 565nm-NH2-CdTe-QDs / CA 0.12 Infrared spectrum of cellulose acetate membrane; Figure 3 From top to bottom are 605nm-NH2-CdTe-QDs / CA 0.10 、605nm-NH2-CdTe-QDs / CA 0.11 and 605nm-NH2-CdTe-QDs / CA 0.12 Infrared spectrum of cellulose acetate membrane; Figure 4 From bottom to top, CA 0.10 , CA0.11 and CA 0.12 Infrared spectrum of cellulose acetate membrane.

[0123] Depend on Figures 1 to 4 It can be seen that the amino quantum dots with different absorption wavelengths form chemical bonds with the activated cellulose acetate after hydrolysis, that is, at 1585 cm -1 and 3405cm -1 The stretching vibration peaks of C=O and -OH of CdTe-QDs and -NH2 are at 3100 cm -1 -3700cm -1 Within the range, the stretching vibration peak intensity gradually broadens with the increase of the quantum dot emission wavelength, indicating that the amino quantum dots can be well loaded in the cellulose acetate membrane.

[0124] The phase transition films in Examples 8, 9 and Comparative Example 2 were observed by cross-sectional scanning electron microscopy. The specific process was as follows: the film was quenched in liquid nitrogen, taken out after a few seconds and cut with a glass knife, and then sprayed with gold to obtain a cross-sectional electron microscopy sample of the film for electron microscopy detection. The results are shown in Figure 2. Figure 5 、 Figure 6 and Figure 7 shown.

[0125] Depend on Figures 5 to 7 It can be seen that after adding quantum dots, the membrane skin is denser, the finger-like pores are smaller, and the membrane separation performance is better. An excellent microfiltration membrane material with uniform sponge pores, high membrane porosity, smaller mass transfer resistance, and better hydrophilicity can be prepared.

[0126] The separation performance of the phase conversion membranes in Examples 7 to 9 and Comparative Examples 1 to 3 was tested by measuring the flux and rejection of the Rhodamine B aqueous solution through the membrane per unit area per unit time, and then judging the separation performance of the ultrafiltration membrane. The specific test method is as follows:

[0127] A uniform, defect-free membrane area was placed in an ultrafiltration cup and a transmembrane pressure difference of 0.5 bar was applied. Pre-pressurization was performed for 30 minutes, and the time required to transfer 10 mL of water was recorded with a stopwatch. The flow rate was then calculated according to the formula: J = V / (S·t), where J is the pure water flux of the membrane (L·m -2 h -1 ), V is the total volume of water passing through a certain membrane surface (L), S is the effective pressure area of ​​the membrane during separation test (m 2 , effective radius r = 2.1 cm), t is the time (h) for the liquid to flow through the separation membrane during a separation test, the flux of the Rhodamine B aqueous solution is obtained, and the filtrate is placed in an ultraviolet absorption spectrometer to measure its concentration, and then the retention rate R is calculated to be (C0-C t ) / C0×100%, where R is the membrane to 10mg·L -1The retention rate of Rhodamine B / H2O solution, C0 is the initial feed concentration (10 mg·L -1 ), C t is the concentration of the permeate after separation test. Figure 8 and Figure 9 shown.

[0128] Depend on Figure 8 and Figure 9 It can be seen that the flux of the cellulose acetate film is significantly improved after the adsorption of amino quantum dots, and the retention rate is also improved to a certain extent. The maximum pure water flux of the NH2-CdTe-QDs / CA phase conversion membrane prepared in this example is 1412 L / (m 2 h), with a retention rate of 47.03%.

[0129] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A method for preparing an amino quantum dot-doped cellulose acetate-based phase conversion membrane, characterized in that: The following steps are involved: S1, mixing cellulose acetate and a solvent, stirring, ultrasonicating, filtering, and standing for degassing in sequence to obtain a cellulose acetate casting solution; S2, scraping the cellulose acetate casting liquid onto a support plate to form a liquid film, performing an air stagnation treatment, and then placing the liquid film in a coagulation bath for a non-solvent-induced phase inversion treatment to obtain a cellulose acetate film; S3, mixing the cellulose acetate membrane with an alkaline aqueous solution and performing a hydrolysis treatment to obtain a hydrolyzed cellulose acetate membrane; S4. Mixing the hydrolyzed cellulose acetate membrane with the amino quantum dot solution, performing an adsorption reaction, washing, and freeze-drying to obtain the amino quantum dot-doped cellulose acetate-based phase conversion membrane.

2. The method for preparing an amino quantum dot-doped cellulose acetate-based phase conversion membrane according to claim 1, wherein: In step S1: The concentration of cellulose acetate in the cellulose acetate casting solution is 0.05 to 0.5 g / mL; and / or, The solvent includes one or more of acetone, dichloromethane, and ethyl acetate; and / or, The stirring temperature is 30-60° C., the stirring speed is 100-800 rpm, and the stirring time is 2-24 h; and / or, The ultrasound duration is 10 to 40 minutes; and / or, The temperature of the static degassing is 10 to 30° C., and the time of the static degassing is 24 to 72 hours.

3. The method for preparing an amino quantum dot-doped cellulose acetate-based phase conversion membrane according to claim 1, wherein: In step S2: The thickness of the liquid film is 50 to 800 μm; and / or, The coagulation bath comprises a water bath in at least one reagent selected from deionized water, anhydrous ethanol, and anhydrous methanol.

4. The method for preparing an amino quantum dot-doped cellulose acetate-based phase conversion membrane according to claim 1, wherein: In step S3: The alkaline aqueous solution includes at least one of a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution and an ammonia solution; and / or, The concentration of the alkaline aqueous solution is 2 to 15 g / L; and / or, The hydrolysis treatment time is 2 to 24 hours.

5. The method for preparing an amino quantum dot-doped cellulose acetate-based phase conversion membrane according to claim 1, wherein: In step S4: The amino quantum dots in the amino quantum dot solution are amino cadmium telluride quantum dots; and / or, The emission wavelength of the amino quantum dots in the amino quantum dot solution is 525 nm, 565 nm or 605 nm; and / or, The freeze-drying conditions are: drying at -20 to -40°C for 2 to 48 hours.

6. An amino quantum dot-doped cellulose acetate-based phase conversion membrane, characterized in that: It includes a first film layer, a second film layer and a third film layer arranged in sequence from bottom to top: The materials of the first film layer, the second film layer and the third film layer are cellulose acetate adsorbed with amino quantum dots; The average pore size of the second membrane layer is greater than the average pore size of the first membrane layer and greater than the average pore size of the third membrane layer; The amino quantum dot-doped cellulose acetate-based phase conversion membrane is prepared by the preparation method of the amino quantum dot-doped cellulose acetate-based phase conversion membrane according to any one of claims 1 to 5.

7. The amino quantum dot-doped cellulose acetate-based phase conversion membrane according to claim 6, wherein: The average pore size of the first membrane layer is 100 nm to 5 μm; and / or, The average pore size of the second membrane layer is 9 μm to 50 μm; and / or, The average pore size of the third membrane layer is 1 nm to 100 nm.

8. Use of an amino quantum dot-doped cellulose acetate-based phase conversion membrane prepared by the method for preparing the amino quantum dot-doped cellulose acetate-based phase conversion membrane according to any one of claims 1 to 2 or the amino quantum dot-doped cellulose acetate-based phase conversion membrane according to any one of claims 3 to 7 in the preparation of a microfiltration separation membrane, a heavy metal ion removal membrane, or a fuel cell membrane.

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