Composite nanofiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a composite nanofiber membrane and a preparation method and application thereof.The method comprises the steps that a base membrane casting solution and a seed solution are prepared, the base membrane casting solution is firstly used for single-needle electrostatic spinning, then the base membrane casting solution and the seed solution are respectively used for double-needle electrostatic spinning, then the seed solution is used for single-needle electrostatic spinning, an original membrane is obtained, and the composite nanofiber membrane is obtained. And enabling the original membrane to be in contact with an aqueous solution with the front face facing downwards for hydrothermal reaction to prepare the composite nanofiber membrane provided by the invention. According to the partial double-needle electrostatic spinning technology, more seeds are concentrated on one side of the membrane, flourishing Ag / ZnO nanofiber rods similar to aquatic plant structures grow on the surface in a concentrated mode, the other side of the membrane keeps the original membrane morphology, the hydrophilic difference of the two sides of the membrane is well guaranteed, the oil-water separation efficiency of the membrane material is improved, and the oil-water separation efficiency of the membrane material is improved. The single-sided concentrated growth nanofiber rod is beneficial to improving the photocatalytic performance, and has a relatively good application prospect in the fields of oil-water separation and photocatalytic degradation.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and in particular relates to a composite nanofiber membrane and a preparation method and application thereof. Background Art

[0002] Nano-photocatalytic fiber membrane technology is a new environmental protection technology that combines nanotechnology and photocatalytic technology. ZnO (zinc oxide) is a typical II-VI oxide semiconductor material, and its crystal structure includes three types: hexagonal wurtzite, sodium chloride octahedron and cubic sphalerite. Under natural conditions, the stable phase of ZnO is the hexagonal wurtzite structure. ZnO has the advantages of excellent chemical stability, non-toxicity, low cost and high photocatalytic efficiency. Therefore, it is considered to be one of the most promising photocatalytic materials, and has application potential in air purification, water pollution control, oil-water separation, antibacterial disinfection, biomedicine and other fields. ZnO nano-photocatalytic fiber membrane is usually prepared by electrospinning. Electrospinning is a method of using electric field to make solvent molecules or ions in the solution move in a directional manner to form a fibrous substance. By adjusting parameters such as electric field strength, voltage, current, etc., the preparation of nanofibers of different diameters, lengths and shapes can be achieved. During the preparation process, it is necessary to select appropriate solution formula, spinning solution concentration, spinning temperature and other parameters to obtain high-quality ZnO nanofiber membranes.

[0003] The construction of ZnO nanofiber composite membranes with Janus structure and their application in the fields of oil-water separation and organic pollutant degradation is a hot topic of research. Janus membrane is a special membrane material, and its notable feature is that the two sides of the membrane have completely different properties. These properties can be hydrophobic and hydrophilic, conductive and insulating, magnetic and non-magnetic, etc. In a narrow sense, Janus membrane requires that the properties of the two sides must be opposite, such as one side is hydrophobic and the other side is hydrophilic. This membrane material has a distinct interface and can also transition evenly from one side to the other. The hydrophobic side of the Janus membrane can adsorb oil substances, while the hydrophilic side can adsorb water molecules. This difference in properties enables the Janus membrane to form a stable oil-water interface in water, thereby achieving efficient oil-water separation. When the oil-water mixture contacts the Janus membrane, due to the adsorption of oil droplets on the hydrophobic side and the adsorption of water molecules on the hydrophilic side, the oil droplets will be spontaneously transported to the hydrophobic side, while the water molecules are blocked by the hydrophilic side. This spontaneous transport process reduces the additional energy required to pass the liquid through the membrane, thereby reducing external energy input. Traditional hydrophobic membranes may have the problem of secondary mixing of oil and water during the oil-water separation process. However, due to its unique configuration and properties, the Janus membrane can theoretically completely avoid the secondary mixing of oil and water, thereby improving the efficiency of oil-water separation. The different properties of the two sides of the Janus membrane produce a significant interfacial effect in the photocatalytic reaction. This effect helps to promote the separation and transfer of photogenerated charges, thereby improving the efficiency and stability of the photocatalytic reaction. The preparation process of the Janus membrane is relatively complicated, and how to obtain the ideal membrane structure and properties is a technical difficulty. The nanofibers generated by the existing Janus membrane preparation process are relatively dispersed and are present on both sides of the membrane, resulting in little difference in the properties of the two sides of the membrane, which greatly reduces the performance advantages of the Janus membrane. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a composite nanofiber membrane with significant differences in properties on both sides and a preparation method and application thereof.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A method for preparing a composite nanofiber membrane comprises the following steps:

[0007] (1) mixing an amide polar aprotic solvent with acetone to obtain a mixed solvent, and dividing the mixed solvent into two parts, respectively referred to as mixed solvent a and mixed solvent b;

[0008] (2) dissolving a fiber-forming polymer in the mixed solvent a, wherein the mass percentage of the fiber-forming polymer to the mixed solvent a is 17% to 21%, heating and stirring to obtain a base film casting solution;

[0009] (3) Zn(Ac) 2 AgNO 3 and fiber-forming polymer are added to the mixed solvent b, the Zn(Ac) 2 The mass percentage of the fiber-forming polymer and the mixed solvent b is 1.2wt% to 1.6wt%, the mass percentage of the fiber-forming polymer and the mixed solvent b is 5% to 7%, and the mixture is heated and stirred to obtain a seed solution. The seed solution contains Ag + With Zn 2+ The atomic percentage is 0.04at% to 0.12at%;

[0010] (4) firstly use the base film casting solution to perform single-needle electrospinning for 0.5h to 1h, then use the base film casting solution and the seed solution to perform double-needle electrospinning for 1h to 1.5h, and then use the seed solution to perform single-needle electrospinning for 0.5h to 1.5h to obtain the original film, with the side of the original film facing the drum as the back side and the other side as the front side;

[0011] During the double-needle electrospinning process, the base film casting solution and the seed solution are ejected simultaneously from two needles located opposite to each other;

[0012] (5) The original membrane is heat-treated and then placed in an aqueous solution containing ammonia water, zinc nitrate hexahydrate and hexamethylenetetramine, with the front side of the original membrane facing downward in contact with the aqueous solution to undergo a hydrothermal reaction, so that Ag / ZnO nanofiber rods grow on the front side of the original membrane, thereby obtaining a composite nanofiber membrane.

[0013] In the above-mentioned method for preparing the composite nanofiber membrane, preferably, the volume ratio of the amide polar aprotic solvent to acetone is 3-7:1-3, the amide polar aprotic solvent is one or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc); and the fiber-forming polymer is one or more of polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN).

[0014] In the above-mentioned method for preparing the composite nanofiber membrane, preferably, in step (2) and step (3), the heating and stirring is water bath heating, the heating and stirring temperature is 50° C. to 70° C., and the heating and stirring time is 4 h to 7 h.

[0015] In the above-mentioned method for preparing the composite nanofiber membrane, preferably, in step (4), the emitting end of the electrospinning maintains a positive voltage of 17kV to 17.5kV, the collecting end maintains a negative voltage of 0.5kV to 0.7kV, the feed rate of the base membrane liquid is controlled to 1.8mL / h to 2mL / h, and the feed rate of the seed liquid is controlled to 1mL / h to 1.2mL / h.

[0016] In the above-mentioned method for preparing the composite nanofiber membrane, preferably, in step (4), a non-woven fabric is wrapped around the periphery of the drum before electrospinning to receive the membrane filaments, the distance between the needle tip of the base membrane liquid emission end and the non-woven fabric is 14cm to 17cm, the distance between the needle tip of the seed liquid emission end and the non-woven fabric is 8cm to 10cm, and the rotation speed of the drum during the electrospinning process is 100rpm to 120rpm.

[0017] The above-mentioned method for preparing the composite nanofiber membrane, preferably, in step (5), the temperature of the heat treatment is 100°C to 130°C, and the time of the heat treatment is 9h to 12h; the temperature of the hydrothermal reaction is 90°C to 105°C, and the time of the hydrothermal reaction is 1h to 6h; the volume percentage of ammonia water in the aqueous solution is 4% to 6%, the concentration of zinc nitrate hexahydrate in the aqueous solution is 0.01mol / L to 0.03mol / L, and the molar concentration ratio of zinc nitrate hexahydrate to hexamethylenetetramine is 1 to 2:1 to 3.

[0018] As a general inventive concept, the present invention also provides a composite nanofiber membrane obtained by the above preparation method, wherein Ag / ZnO nanofiber rods are directionally grown on the front side of the original membrane, and the back side of the original membrane remains original, the front side is light yellow, and the back side is white.

[0019] As a general inventive concept, the present invention also provides an application of the above-mentioned composite nanofiber membrane in the field of photocatalytic degradation or oil-water separation.

[0020] In the above application, preferably, the steps of using the composite nanofiber membrane for photocatalytic degradation include: laying the composite nanofiber membrane with the front side facing upward in an ultrafiltration cup, adding a solution to be degraded into the ultrafiltration cup, and first performing a dark reaction and then performing a light reaction under stirring conditions;

[0021] In the above application, preferably, the steps of using the composite nanofiber membrane for oil-water separation include: laying the composite nanofiber membrane with its front side facing upward in an ultrafiltration cup, wetting the surface of the composite nanofiber membrane, and then pouring the oil-water mixture into the ultrafiltration cup for separation.

[0022] In the above application, preferably, in the photocatalytic degradation, the solution to be degraded is a tetracycline hydrochloride solution, the concentration of the tetracycline hydrochloride solution is 30 mg / L to 50 mg / L, the dark reaction lasts for 0.4 h to 0.6 h, and the light reaction lasts for 2 h to 4 h.

[0023] In the above application, preferably, in the oil-water separation, the oil-water mixture is a mixture of light oil and water in a mass ratio of 1:2-3, and the density of the light oil is less than that of water.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] (1) In view of the defect that the seeds in the prior art are unevenly distributed and randomly distributed on the surface or inside of the membrane, resulting in the irregular growth of nanofiber rods on the membrane surface, the present invention creatively proposes a partial double-needle electrospinning process, wherein the reagents usually mixed and used in single-needle electrospinning are respectively prepared into a base film casting liquid and a seed solution, and the base film casting liquid is first sprayed, and then the base film casting liquid and the seed solution are simultaneously sprayed from opposite directions, and then the seed solution is sprayed separately to obtain the original membrane by the partial double-needle electrospinning process, and the original membrane is subjected to a hydrothermal reaction with the front side facing down after heat treatment to obtain the composite nanofiber membrane of the present invention. The partial double-needle electrospinning process of the present invention allows more seeds to be concentrated on one side of the membrane, and the Ag / ZnO nanofiber rods with a lush water grass structure are concentrated on the side, while the other side maintains the original membrane morphology, which better ensures the difference in hydrophilicity on both sides of the membrane, and is beneficial to improving the efficiency of the membrane material for oil-water separation. Since the Ag / ZnO nanofiber rods are highly concentrated on one side of the membrane, it can be used as the light-seeing side of the photocatalytic material to improve the photocatalytic performance. The present invention uses Ag-doped zinc oxide nanofiber rods to prepare Janus membranes, which can further improve the photocatalytic performance of the concentrated surface of the nanofiber rods. The present invention uses a partial double-needle electrospinning process to not only obtain a Janus membrane with better performance, but also make the membrane surface smoother, reduce particle size, and shorten the overall membrane preparation time while the size and size of the finished membrane remain unchanged.

[0026] (2) The composite nanofiber membrane of the present invention overcomes the problem of unconcentrated nanofiber growth in the prior art. It can densely grow Ag / ZnO nanofiber rods on one side and retain the original membrane fibers on the other side. Since the nanofiber rods have good hydrophilicity and photocatalytic properties, there is a significant difference in hydrophilicity between the side with densely grown Ag / ZnO nanofiber rods and the side without Ag / ZnO nanofiber rods, and the photocatalytic performance of the side with concentrated Ag / ZnO nanofiber rods is excellent.

[0027] (3) The composite nanofiber membrane of the present invention has greater performance advantages than the Janus membrane and has good application prospects in the fields of oil-water separation and photocatalytic degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a photograph of the electrospinning device in the method for preparing the composite nanofiber membrane in Example 1 of the present invention.

[0029] Figure 2 The photos are of the original membrane (a) and the finished membrane after hydrothermal treatment (b) in Example 1 of the present invention.

[0030] Figure 3 This is a SEM comparison diagram of the composite nanofiber membrane of Example 1 of the present invention and the composite membrane of Comparative Example 1.

[0031] Figure 4 This is a comparison diagram of the water contact angles of the composite nanofiber membrane of Example 1 of the present invention and the composite membrane of Comparative Example 1.

[0032] Figure 5 Schematic diagram of the photocatalytic reaction device of the composite nanofiber membrane in Example 2 of the present invention.

[0033] Figure 6 Different Ag prepared by the method of the present invention + / Zn 2+ Removal efficiency of TC by composite nanofiber membrane with atomic ratio.

[0034] Figure 7 The removal efficiency of TC by the composite nanofiber membrane prepared by different hydrothermal times in the present invention.

[0035] Figure 8 Different Ag prepared by the method of Comparative Example 1 + / Zn 2+ Removal efficiency of TC by composite nanofiber membrane with atomic ratio.

[0036] Legend: 1. Nitrogen cylinder; 2. Buffer bottle; 3. Ultrafiltration cup; 31. Air inlet; 32. Liquid inlet; 4. Sampling cup; 5. Regulating valve; 6. Pressure gauge; 7. Light source; 8. Magnetic stirrer. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. In the following examples, unless otherwise specified, the raw materials, reagents and instruments used are all commercially available.

[0038] Example 1

[0039] A method for preparing a composite nanofiber membrane of the present invention comprises the following steps:

[0040] (1) N,N-dimethylformamide (DMF) and acetone are mixed at a volume ratio of 3:1 to obtain a mixed solvent, and the mixed solvent is divided into two parts for standby use, respectively denoted as mixed solvent a and mixed solvent b.

[0041] (2) According to the mass ratio of polyvinylidene fluoride (PVDF) to mixed solvent a being 19%, PVDF was dissolved in mixed solvent a, and the mixture was placed in a water bath at 60° C. and stirred for 4 h to obtain a base film casting solution.

[0042] (3) Zn(Ac) 2 and 0.17 g AgNO 3 , and PVDF were added to the mixed solvent b, placed in a water bath at 60°C and stirred for 4 h to obtain a seed solution.

[0043] Among them, Zn(Ac) 2 That is, Zn(CH 3 COO 2 , Zn(Ac) 2 The mass percentage of PVDF and mixed solvent b is 1.5%, the mass percentage of PVDF and mixed solvent b is 5%, and the Ag in the seed solution + With Zn 2+ The atomic percentage is 0.08at%.

[0044] (4) Wrap a layer of non-woven fabric on the outside of the metal roller before electrospinning to receive the membrane filaments. First, put the base membrane casting solution into the syringe and spray it for 1 hour; take another syringe filled with seed solution, spray it with both needles for 1 hour at the same time, stop spraying the base membrane casting solution, and spray the seed solution alone for another hour to obtain the original membrane. Figure 2 As shown in (a).

[0045] The side of the original film facing the drum is the reverse side, and the other side is the front side. When the two needles spray at the same time, the directions are opposite, that is, the two needles are in opposite directions. Figure 1 As shown. The relevant parameters of electrospinning are as follows: the transmitting end maintains a positive voltage of 17kV, the collecting end maintains a negative voltage of 0.5kV, the base film liquid feed rate is controlled at 1.9mL / h, the seed liquid feed rate is controlled at 1mL / h, the distance between the base film liquid transmitting end needle tip and the non-woven fabric is 15cm, the distance between the seed liquid transmitting end needle tip and the non-woven fabric is 9cm, and the drum speed is set to 100rpm. The working environment temperature in the glass cover of the electrospinning host is maintained at 22℃~28℃, and the humidity is maintained at 28%~32%.

[0046] (5) The original membrane was peeled off from the non-woven fabric, placed in a 130°C oven for heat treatment for 12 hours, and then placed in a 500 mL aqueous solution containing ammonia water, zinc nitrate hexahydrate and hexamethylenetetramine, so that the original membrane floated on the surface of the aqueous solution with the front side facing down in contact with the aqueous solution, the opening of the reaction container was sealed with plastic wrap, and the reaction container was placed in a 95°C oven for hydrothermal growth for 3 hours to obtain a composite nanofiber membrane with Ag / ZnO nanofiber rods grown on the front side. The prepared composite nanofiber membrane was rinsed with distilled water and dried at room temperature (30°C to 40°C) to obtain a finished membrane, such as Figure 2 as shown in (b).

[0047] Among them, 500 ml of the aqueous solution contains 20 ml of ammonia water (commercially purchased, with a mass concentration of 25% to 28%), 2.97 g of zinc nitrate hexahydrate, and 0.71 g of hexamethylenetetramine. The molar concentration ratio of zinc nitrate hexahydrate (ZHN) to hexamethylenetetramine (HMTA) is 2:1.

[0048] Comparative Example 1

[0049] A method for preparing a composite nanofiber membrane, the preparation steps are basically the same as those in Example 1, the main difference being that this comparative example adopts single-needle electrospinning to prepare the composite nanofiber membrane, and the specific steps include:

[0050] (1) DMF and acetone are mixed at a volume ratio of 3:1 to obtain a mixed solvent, and PVDF is dissolved in the mixed solvent at a mass ratio of PVDF to the mixed solvent of 19% to obtain a PVDF solution.

[0051] (2) Zn(Ac) 2 and 0.17 g AgNO 3 Add to PVDF solution, stir in a 60℃ water bath for 4h to prepare spinning solution. 2 The mass percentage of the mixed solvent is 1.5%, Ag + With Zn 2+ The atomic percentage is 0.08at%.

[0052] (3) Before electrospinning, a layer of non-woven fabric was wrapped around the outside of the metal drum to receive the membrane filaments. The spinning solution was loaded into the syringe. The positive voltage at the transmitting end was maintained at 17 kV, and the negative voltage at the collecting end was maintained at 0.5 kV. The feed rate was controlled at 1.9 mL / h. The distance between the transmitting end and the non-woven fabric was 15 cm. The drum speed was set to 100 rpm. The spinning was performed for 4 hours to obtain the original membrane.

[0053] The side of the original film facing the drum is the back side, and the other side is the front side. The temperature of the working environment in the glass cover of the electrospinning host is maintained at 22℃~28℃, and the humidity is maintained at 28%~32%.

[0054] (4) The original membrane was peeled off from the non-woven fabric, placed in a 130°C oven for heat treatment for 12 h, and then placed in a 500 mL aqueous solution containing ammonia water, zinc nitrate hexahydrate, and hexamethylenetetramine, so that the original membrane floated on the surface of the aqueous solution and contacted with the aqueous solution with its front side facing down, and the opening of the reaction container was sealed with plastic wrap, and the reaction container was placed in a 95°C oven for hydrothermal growth for 3 h to obtain a composite membrane with Ag / ZnO nanofibers grown thereon. The obtained composite membrane was rinsed with distilled water and dried at room temperature (30°C to 40°C).

[0055] Among them, 500 ml of the aqueous solution contains 20 ml of ammonia water (commercially purchased, with a mass concentration of 25% to 28%), 2.97 g of zinc nitrate hexahydrate, and 0.71 g of hexamethylenetetramine. The molar concentration ratio of zinc nitrate hexahydrate (ZHN) to hexamethylenetetramine (HMTA) is 2:1.

[0056] The membrane materials obtained in Example 1 and Comparative Example 1 were characterized by SEM. Figure 3The SEM comparison diagram of the composite nanofiber membrane of Example 1 of the present invention and the composite membrane of Comparative Example 1, (a) and (b) are the front and back sides of the composite nanofiber membrane of Example 1, respectively, and (c) and (d) are the front and back sides of the composite membrane of Comparative Example 1, respectively. Figure 3 As can be seen from (a), the front side of the composite nanofiber membrane of Example 1 has Ag / ZnO nanofiber rods like "water grass" and they are dense and can almost completely cover the surface of the original membrane without exposing a large area of ​​the original membrane fibers. Figure 3 As can be seen from (b), the fibers of the original membrane on the reverse side are smooth and clear, with uniform thickness, and no "water grass" nanofiber rods at all. The morphology of the front and back sides is obviously different. Figure 3 It can be seen from (c) and (d) that the morphological differences between the front and back sides of the finished membrane of Comparative Example 1 are not obvious enough. Both have scattered and randomly distributed Ag / ZnO nanofiber rods. The Ag / ZnO nanofiber rods on the front side are sparse, and a large area of ​​the original membrane fibers are exposed, which is not conducive to improving the efficiency of the photocatalytic reaction. The original membrane fibers on the back side are partially covered by the Ag / ZnO nanofiber rods, which is not conducive to the efficient separation of the oil-water mixture.

[0057] The membrane materials prepared in Example 1 and Comparative Example 1 were tested for water contact angle. Figure 4 The water contact angle comparison diagram of the composite nanofiber membrane of Example 1 of the present invention and the composite membrane of Comparative Example 1, (a) and (b) are the front and back sides of the composite nanofiber membrane of Example 1, respectively, and (c) and (d) are the front and back sides of the composite membrane of Comparative Example 1, respectively. Figure 4 It can be seen that the difference in hydrophilicity between the front and back sides of the composite nanofiber membrane prepared in Example 1 is more obvious, and the difference in hydrophilicity between the front and back sides of the composite nanofiber membrane is greater, which is more conducive to the efficient separation of oil-water mixture.

[0058] Example 2

[0059] The application of a composite nanofiber membrane of the present invention in a photocatalytic reaction comprises the following steps:

[0060] The composite nanofiber membrane prepared in Example 1 is laid with the front side facing upward in the ultrafiltration cup 3, and a tetracycline hydrochloride TC solution with a concentration of 40 mg / L is prepared and added to the ultrafiltration cup 3, so that the TC solution is in contact with the front side of the composite nanofiber membrane (i.e., the side where the Ag / ZnO nanofiber rods are grown). Then, the ultrafiltration cup 3 containing the TC solution is placed on a magnetic stirrer 8 for stirring, and a dark reaction is carried out under stirring conditions for a duration of 0.5 hours. The dark reaction is to examine and eliminate the adsorption of the membrane material, so as to more objectively evaluate its photocatalytic performance; then the reaction is transferred to a 20A xenon lamp, and a photocatalytic reaction is carried out under stirring conditions for continuous irradiation for 3 hours. Every 0.5 hours of the experiment, a certain pressure is applied to the nitrogen bottle and sampled once. The water outlet of the ultrafiltration cup 3 is provided with a switch, which is opened only when sampling. The sample is measured for its absorbance A under visible light with a wavelength of 400nm, and its degradation rate is calculated.

[0061] like Figure 5 As shown, the photocatalytic reaction device includes a nitrogen cylinder 1, a buffer bottle 2, an ultrafiltration cup 3 and a sampling cup 4 which are connected in sequence by pipelines. A regulating valve 5 and a pressure gauge 6 are provided on the connecting pipe between the nitrogen cylinder 1 and the buffer bottle 2. An air inlet 31 and a liquid inlet 32 ​​are provided on the top of the ultrafiltration cup 3. The air inlet 31 is connected to the buffer bottle 2. The liquid inlet 32 ​​is used to inject a solution to be reacted. A light source 7 is provided above the ultrafiltration cup 3. A magnetic stirrer 8 is provided below the ultrafiltration cup 3. The composite nanofiber membrane ( Figure 5 As shown in A in the middle, it is laid face up on the bottom of the ultrafiltration cup 3, and the nitrogen cylinder 1 and the buffer bottle 2 are used to provide air pressure to the ultrafiltration cup 3 to control the reaction solution to flow into the sampling cup 4 through the composite nanofiber membrane to achieve sampling.

[0062] Prepare different Ag by referring to the preparation method of Example 1 + Composite nanofiber membranes with different doping concentrations and experimental comparison of different Ag + The effect of the composite nanofiber membrane with different doping concentrations on the removal of TC in the photocatalytic reaction is shown in the following figure. Figure 6 As shown, when Ag + / Zn 2+ When the doping ratio is 0.04at%, 0.08at% and 0.12at%, the degradation rates are 75.4%, 87.2% and 70.1% respectively. It can be seen that when the doping ratio is 0.08at%, the photocatalytic degradation efficiency of the composite nanofiber membrane is optimal.

[0063] Referring to the preparation method of Example 1, the composite nanofiber membranes were prepared using hydrothermal reaction times of 1 hour, 3 hours and 6 hours, and the photocatalytic properties of the three composite nanofiber membranes were investigated. The results are as follows: Figure 7As shown in the figure, the composite nanofiber membrane prepared by 3 hours of hydrothermal reaction has the highest degradation rate constant for TC antibiotics, indicating that the composite nanofiber membrane prepared by 3 hours of hydrothermal reaction has the best photocatalytic performance, and 3 hours is the optimal hydrothermal time. During the hydrothermal synthesis process, the formation and growth of Ag / ZnO nanofiber rods on the membrane substrate are significantly affected by the hydrothermal time. First, with the extension of the hydrothermal time, the interaction time between the zinc oxide precursor and the growth solution increases, which promotes the full contact and growth of the zinc oxide crystals, thereby facilitating the formation of nanofiber rods. Secondly, with the further increase of the hydrothermal time, the density of the zinc oxide nanofiber rods increases significantly, which leads to a significant increase in the specific surface area of ​​the membrane substrate. This change not only increases the number of active sites, but also improves the catalytic activity of the zinc oxide nanofiber rods, thereby accelerating the degradation rate of pollutants.

[0064] Prepare different Ag by referring to the method of Comparative Example 1 + / Zn 2+ Composite films with different doping ratios were investigated. + / Zn 2+ The removal effect of TC on the composite film with different doping ratios in the photocatalytic reaction. Figure 8 As shown, Ag was prepared by hydrothermal reaction for 3 h after single-needle electrospinning. + / Zn 2+ The degradation rates of TC for the composite films with doping ratios of 0.04at%, 0.08at%, and 0.12at% were 45.9%, 45.1%, and 41.2%, respectively, under the same photocatalytic reaction conditions, which were comparable to those of the Ag prepared by hydrothermal reaction for 3 h in Example 1. + / Zn 2+ The degradation rate of TC of the composite nanofiber membrane with a doping ratio of 0.08at% (87.2%) is at least 40% lower than that of the composite nanofiber membrane.

[0065] Example 3

[0066] The application of a composite nanofiber membrane of the present invention in oil-water separation is to use the composite nanofiber membrane prepared in Example 1 to carry out a water / light oil separation experiment, where the light oil refers to oil with a density less than 1, comprising the following steps:

[0067] When separating the water / light oil two-phase system, first, the surface of the membrane material is wetted, and then the gravity of the phase to be separated is used as the driving force for separation. In the experiment, light oil and water were mixed in a mass ratio of 1:2, the light oil was paraffin oil, and the water was dyed blue with methylene blue for easy observation. Then the oil-water mixture was poured into the ultrafiltration cup 3 with the composite nanofiber membrane laid, and the front of the membrane was in contact with the mixture. Nitrogen was introduced for 5s and then turned off to initially pressurize the solution to make it seep out faster. After that, through the action of its own gravity, water molecules gradually passed through the composite nanofiber membrane and were collected in the measuring cylinder, while the paraffin oil remained in the ultrafiltration cup 3.

[0068] The device used for the water / light oil separation experiment in this embodiment is basically the same as the photocatalytic reaction device in Example 2, with the only difference being that the sampling cup 4 is replaced by a measuring cylinder in the water / light oil separation experiment device in this embodiment, and the light source 7 and the magnetic stirrer 8 are not required.

[0069] In the oil-water separation process, the composite nanofiber membrane of Example 1 of the present invention showed a high -2 h -1 In addition, the composite membrane has excellent performance in separation efficiency, which is stable in the high separation efficiency range of 98% to 99%.

[0070] Under the same conditions, the composite membrane prepared in Comparative Example 1 was used to perform water / light oil separation experiments, and the permeation flux was only 994 L m -2 h -1 The oil-water separation efficiency is maintained between 82% and 91%. Compared with Example 1, not only the permeation flux and separation efficiency are significantly reduced, but also the stability during the separation process is poor, which is specifically manifested in that the permeation flux changes greatly during use, the fraction efficiency difference is large, and it cannot be maintained within a narrow range of variation.

[0071] The contact angle measurement revealed that the composite nanofiber membrane of the present invention has significant Janus heterogeneity. Specifically, the front and back sides of the composite nanofiber membrane exhibit different wettability characteristics: one side is hydrophilic, while the other side is hydrophobic. This property gives the composite nanofiber membrane a function similar to that of an oil-water separation fluid diode, that is, it allows water molecules to pass through while repelling oil molecules, thus playing a key role in the oil-water separation process. In addition, by increasing the roughness of the front side of the composite nanofiber membrane, not only the hydrophilicity of the membrane is improved, but also the mechanical strength and wear resistance of the membrane are enhanced to a certain extent.

[0072] The membrane material of the Janus structure exhibits different physical or chemical properties on both sides. The composite nanofiber membrane prepared by the process method of the present invention has lush Ag / ZnO nanofiber rods with a waterweed structure growing on one side, and the composite nanofiber membrane retains the original membrane morphology on the other side, thereby ensuring that the hydrophilicity on both sides of the fiber membrane is different, which is beneficial to improving the oil-water separation efficiency, and the Ag / ZnO nanofiber rods are highly concentrated on the light-seeing side, which can greatly improve the photocatalytic performance of the composite nanofiber membrane, thereby overcoming the defects that the nanofiber rods prepared by the previous process are relatively dispersed, and there are both sides of the membrane, and the difference in hydrophilicity on both sides is not large. The present invention adopts a partial double-needle electrospinning process, which not only obtains a Janus membrane with better performance, but also shortens the overall membrane preparation time. Compared with Example 1, the same spinning solution is completed once from 4 hours to 3 hours.

[0073] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a composite nanofiber membrane, characterized in that: The following steps are involved: (1) mixing an amide polar aprotic solvent with acetone to obtain a mixed solvent, and dividing the mixed solvent into two parts, respectively referred to as mixed solvent a and mixed solvent b; (2) dissolving a fiber-forming polymer in the mixed solvent a, wherein the mass percentage of the fiber-forming polymer to the mixed solvent a is 17% to 21%, heating and stirring to obtain a base film casting solution; (3) adding Zn(Ac)2, AgNO3 and a fiber-forming polymer to the mixed solvent b, wherein the mass percentage of Zn(Ac)2 to the mixed solvent b is 1.2wt% to 1.6wt%, and the mass percentage of the fiber-forming polymer to the mixed solvent b is 5% to 7%, and heating and stirring are performed to obtain a seed solution, wherein the seed solution contains AgNO3. + With Zn 2+ The atomic percentage is 0.04at% to 0.12at%; (4) firstly use the base film casting solution to perform single-needle electrospinning for 0.5h to 1h, then use the base film casting solution and the seed solution to perform double-needle electrospinning for 1h to 1.5h, and then use the seed solution to perform single-needle electrospinning for 0.5h to 1.5h to obtain the original film, with the side of the original film facing the drum as the back side and the other side as the front side; During the double-needle electrospinning process, the base film casting solution and the seed solution are ejected simultaneously from two needles located opposite to each other; (5) The original membrane is heat-treated and then placed in an aqueous solution containing ammonia water, zinc nitrate hexahydrate and hexamethylenetetramine, with the front side of the original membrane facing downward in contact with the aqueous solution to undergo a hydrothermal reaction, so that Ag / ZnO nanofiber rods grow on the front side of the original membrane, thereby obtaining a composite nanofiber membrane.

2. The method for preparing the composite nanofiber membrane according to claim 1, characterized in that: The volume ratio of the amide polar aprotic solvent to acetone is 3-7:1-3, the amide polar aprotic solvent is one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide and N,N-dimethylacetamide; the fiber-forming polymer is one or more of polyvinylidene fluoride and polyacrylonitrile.

3. The method for preparing the composite nanofiber membrane according to claim 1, characterized in that: In step (2) and step (3), the heating and stirring is water bath heating, the heating and stirring temperature is 50° C. to 70° C., and the heating and stirring time is 4 h to 7 h.

4. The method for preparing the composite nanofiber membrane according to claim 1, characterized in that: In step (4), the emitting end of the electrospinning maintains a positive voltage of 17 kV to 17.5 kV, the collecting end maintains a negative voltage of 0.5 kV to 0.7 kV, the feed rate of the base membrane liquid is controlled to 1.8 mL / h to 2 mL / h, and the feed rate of the seed liquid is controlled to 1 mL / h to 1.2 mL / h.

5. The method for preparing the composite nanofiber membrane according to claim 4, characterized in that: In step (4), a non-woven fabric is wrapped around the periphery of the drum before electrospinning to receive the membrane filaments. The distance between the needle tip of the base membrane liquid emission end and the non-woven fabric is 14 cm to 17 cm, and the distance between the needle tip of the seed liquid emission end and the non-woven fabric is 8 cm to 10 cm. The rotation speed of the drum during the electrospinning process is 100 rpm to 120 rpm.

6. The method for preparing the composite nanofiber membrane according to claim 1, characterized in that: In step (5), the heat treatment temperature is 100° C. to 130° C., and the heat treatment time is 9 h to 12 h; the hydrothermal reaction temperature is 90° C. to 105° C., and the hydrothermal reaction time is 1 h to 6 h; the volume percentage of ammonia water in the aqueous solution is 4% to 6%, the concentration of zinc nitrate hexahydrate in the aqueous solution is 0.01 mol / L to 0.03 mol / L, and the molar concentration ratio of zinc nitrate hexahydrate to hexamethylenetetramine is 1 to 2:1 to 3.

7. A composite nanofiber membrane, characterized in that: The composite nanofiber membrane is prepared according to the preparation method of any one of claims 1 to 6, wherein Ag / ZnO nanofiber rods are directionally grown on the front side of the original membrane, and the back side of the original membrane remains original, the front side is light yellow, and the back side is white.

8. Use of the composite nanofiber membrane as claimed in claim 7 in the field of photocatalytic degradation or oil-water separation.

9. The use according to claim 8, characterized in that: The steps of using the composite nanofiber membrane for photocatalytic degradation include: laying the composite nanofiber membrane with the front side facing upward in an ultrafiltration cup, adding a solution to be degraded into the ultrafiltration cup, and first performing a dark reaction and then performing a light reaction under stirring conditions; The steps of using the composite nanofiber membrane for oil-water separation include: laying the composite nanofiber membrane face up in an ultrafiltration cup, wetting the surface of the composite nanofiber membrane, and then pouring the oil-water mixture into the ultrafiltration cup for separation.

10. The use according to claim 9, characterized in that: In the photocatalytic degradation, the solution to be degraded is a tetracycline hydrochloride solution, the concentration of the tetracycline hydrochloride solution is 30 mg / L to 50 mg / L, the dark reaction lasts for 0.4 h to 0.6 h, and the light reaction lasts for 2 h to 4 h; In the oil-water separation, the oil-water mixture is a mixture of light oil and water in a mass ratio of 1:2-3, and the density of the light oil is smaller than that of water.

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