Preparation method of polynorbornene spinning nanofiber adsorption separation membrane

Abstract

The invention belongs to the technical field of nanofiber membrane material preparation, and provides a preparation method of a polynorbornene spinning nanofiber adsorption separation membrane, which comprises the following steps: step 1, adding calcium hydride as a drying agent into a round-bottom flask, and adding dichloromethane with the content of more than 95%; step 2, adding 5-norbornene-2-carboxylic acid and anhydrous dichloromethane into the reaction flask, and introducing inert gas; step 3, dissolving the PNB-COOH polymer powder and PVDF powder in a DMF solution according to different mass ratios; according to the method, the stable performance and the consistent quality of the nanofiber membrane are ensured by accurately controlling the preparation process; after the polynorbornene is introduced, the selectivity and the adsorption capacity of the membrane on refractory pollutants such as organic dyes are remarkably improved; meanwhile, the steps are clear, operation is easy and convenient, industrial production is easy to achieve, an efficient and novel nanofiber membrane material is provided for the field of water treatment, and wide market application prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of nanofiber membrane materials, and particularly relates to a method for preparing a poly(norbornene) electrospun nanofiber adsorption and separation membrane. Background Art

[0002] The nanofiber membrane materials prepared by electrospinning are widely used in the field of water treatment due to their high specific surface area, high porosity and good mechanical properties.

[0003] However, for the separation of refractory pollutants such as organic dyes, traditional nanofiber membrane materials often have problems such as low selectivity and limited adsorption capacity. As a porous polymer material, poly(norbornene) has the characteristics of easy processing and stable chemical properties. However, its application in the field of water treatment, especially the preparation of functionalized nanofiber membrane materials for the separation of organic dyes, still needs to be further studied.

[0004] Therefore, the technical personnel in this field have proposed a method for preparing a poly(norbornene) electrospun nanofiber adsorption and separation membrane to solve the problems raised in the background art. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a poly(norbornene) electrospun nanofiber adsorption and separation membrane to solve the problems existing in the prior art.

[0006] A method for preparing a poly(norbornene) electrospun nanofiber adsorption and separation membrane includes:

[0007] Step 1: Prepare anhydrous dichloromethane solvent: Add calcium hydride as a desiccant to a round-bottom flask, add dichloromethane with a content of more than 95%, heat under reflux under nitrogen protection, collect the reflux liquid, let it stand and cool before use. Among them, the temperature of heating under reflux is 50-60 °C, and the reflux time is 2-4 hours;

[0008] Step 2: Prepare PNB-COOH polymer: Add 5-norbornene-2-carboxylic acid and anhydrous dichloromethane to a reaction flask, introduce an inert gas, add Grubbs II generation catalyst, and carry out a homopolymerization reaction to obtain a carboxyl norbornene homopolymer. Among them, the temperature of the homopolymerization reaction is 25-35 °C, and the reaction time is 40-80 minutes;

[0009] Step 3: Prepare an electrospinning precursor solution: Dissolve the PNB-COOH polymer powder and PVDF powder in a DMF solution according to different mass ratios, and stir and dissolve at 50 °C to obtain a uniform electrospinning precursor solution with a total mass fraction of 20%-25%. Among them, the mass ratio of PVDF to PNB-COOH is 10:0 to 0:10;

[0010] Step 4. Preparation of nanofiber membrane by electrospinning: The precursor solution is electrospun under the conditions of a set voltage, injection flow rate, receiver distance, ambient temperature, and relative humidity. After electrospinning, the receiver covered with the nanofiber membrane is removed and dried to obtain a poly(norbornene) electrospun nanofiber adsorption separation membrane. Among them, the voltage for electrospinning is 15 - 20 kV, the injection flow rate is 15 - 20 μL / min, the distance between the receiver and the needle tip is 15 - 25 cm, the ambient temperature is 25 ± 5 °C, the relative humidity is 25 ± 5%, and the electrospinning time is 6 - 10 hours.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] 1. The present invention provides a preparation method of a poly(norbornene) electrospun nanofiber adsorption separation membrane. By precisely controlling the preparation process, poly(norbornene) is successfully introduced into the nanofiber membrane, improving the selectivity and adsorption capacity of the membrane for refractory pollutants such as organic dyes.

[0013] 2. The method steps of the present invention are clear and highly controllable, and are easy to realize industrial production, providing a new and efficient nanofiber membrane material for the water treatment field. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of the reaction structure of the finished polymer PNB-COOH of the present invention;

[0015] Figure 2 It is the nuclear magnetic resonance hydrogen spectrum of NB-COOH and PNB-COOH of the present invention;

[0016] Figure 3 It is the infrared spectrum of NB-COOH and PNB-COOH of the present invention;

[0017] Figure 4 It is the infrared spectrum of six different ratios of PNB-COOH nanofiber membranes of the present invention;

[0018] Figure 5 It is the scanning electron microscope image of different ratios of PNB-COOH nanofiber membranes of the present invention;

[0019] Figure 6 It is the contact angle test image of different ratios of PNB-COOH nanofiber membranes of the present invention;

[0020] Figure 7 It is the scanning electron microscope image of different ratios of PNB-COOH nanofiber membranes after soaking in water for 24 h of the present invention;

[0021] Figure 8Schematic diagram of the adsorption capacity of PNB-COOH nanofiber membranes with different ratios of the present invention;

[0022] Figure 9 Schematic photo of the selective adsorption of MB by the VN-2-8 membrane of the present invention in a methylene blue (MB) / methyl orange (MO) mixed solution;

[0023] Figure 10 UV-visible spectrogram of the MB / MO mixed solution before and after adsorption of the present invention. Detailed implementation manners

[0024] The following further describes in detail the implementation manners of the present invention in conjunction with the drawings and embodiments. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0025] A preparation method of a polynorbornene spinning nanofiber adsorption separation membrane includes:

[0026] Step 1, prepare anhydrous solvent dichloromethane: Add calcium hydride as a desiccant to a round-bottom flask, add dichloromethane with a content of more than 95%, heat and reflux under nitrogen protection, collect the reflux liquid, let it stand and cool before use. Among them, the temperature of heating and reflux is 50 - 60 °C, and the reflux time is 2 - 4 hours;

[0027] Step 2, prepare PNB-COOH polymer: Add 5-norbornene-2-carboxylic acid and anhydrous dichloromethane to a reaction flask, introduce an inert gas, add Grubbs II generation catalyst, and carry out a homopolymerization reaction to obtain a carboxyl norbornene homopolymer. Among them, the temperature of the homopolymerization reaction is 25 - 35 °C, and the reaction time is 40 - 80 minutes;

[0028] Step 3, prepare an electrospinning precursor solution: Dissolve the PNB-COOH polymer powder and PVDF powder in a DMF solution according to different mass ratios, and stir and dissolve at 50 °C to obtain a uniform electrospinning precursor solution with a total mass fraction of 20% - 25%; among them, the mass ratio of PVDF to PNB-COOH is 10:0 to 0:10;

[0029] Step 4, prepare a nanofiber membrane by electrospinning: Carry out electrospinning on the precursor solution under the conditions of a set voltage, injection flow rate, receiver distance, ambient temperature and relative humidity. After electrospinning, remove the receiver covered with the nanofiber membrane, and dry it to obtain a polynorbornene spinning nanofiber adsorption separation membrane. Among them, the voltage of electrospinning is 15 - 20 kV, the injection flow rate is 15 - 20 μL / min, the distance between the receiver and the needle tip is 15 - 25 cm, the ambient temperature is 25 ± 5 °C, the relative humidity is 25 ± 5%, and the electrospinning time is 6 - 10 hours.

[0030] Example: The present invention provides a method for preparing a poly(norbornene) spun nanofiber adsorption and separation membrane, comprising the following steps:

[0031] S1. To ensure that the ROMP reaction of norbornene proceeds under strictly anhydrous and anaerobic conditions, it is necessary to prepare anhydrous dichloromethane. Add 3 g of calcium hydride as a desiccant to a 500 ml round-bottom flask, then add 300 mL of dichloromethane with a content of 95%. Under nitrogen protection, heat under reflux in an oil bath at 56 °C for 3 h, collect the reflux liquid, and use it after standing and cooling.

[0032] S2. Homopolymerization reaction of NB-COOH: Add 1.382 g of 5-norbornene-2-carboxylic acid (10 mmol) to a 100 ml Schlenk reaction flask, add 50 ml of anhydrous dichloromethane, introduce argon into the flask, and then add 0.0424 g of Grubbs II generation catalyst (0.05 mmol). Perform freeze-degassing three times in a cycle, and stir and react at 30 °C for 60 min. After the reaction, a large amount of white flocculent precipitate is formed. Filter, and wash the filter cake with dichloromethane multiple times to obtain a carboxyl norbornene homopolymer.

[0033] S3. Electrospinning to prepare VN series nanofiber membranes: Dissolve the PNB-COOH polymer powder and PVDF powder in a DMF solution at different mass ratios, and stir and dissolve at 50 °C for 12 hours to obtain a uniform electrospinning precursor solution with a total mass fraction of 22 wt%. The mass ratio of PVDF to the polymer PNB-COOH in the spinning solution is 10:0, 8:2, 6:4, 4:6, 2:8, 0:10, as shown in Table 1 below;

[0034] Table 1 Composition of spinning solutions for PNB-COOH nanofiber membranes with different mass ratios

[0035]

[0036] Subsequently, let the solution stand at room temperature for 6 hours to fully eliminate the bubbles in the solution.

[0037] Among them, the spinning parameters are as follows: voltage 17 kV; injection flow rate of the syringe pump is 17 μL / min; the receiver is a metal roller wrapped with silicon oil paper, and the distance between the receiver and the needle tip is 20 cm; control the environmental temperature at 28 ± 2 °C; relative humidity at 30 ± 5%; continuously spin for 8 h.

[0038] Finally, remove the silicon oil paper covering the nanofiber membrane from the roller, and place them together in a vacuum oven at 45 °C for drying for 24 h to obtain a dried poly(norbornene) fiber membrane.

[0039] As can be seen from the above, the following beneficial effects can be summarized:

[0040] Precise and controllable preparation process: By strictly controlling the reaction conditions and operation process of each step in the present invention, it is ensured that the prepared nanofiber membrane has stable performance and consistent quality.

[0041] Excellent material properties: After introducing polynorbornene, the selectivity and adsorption capacity of the nanofiber membrane have been significantly improved, and it can better treat refractory pollutants such as organic dyes.

[0042] Great potential for industrial production: The preparation method of the present invention has clear steps and is easy to operate, making it easy to realize industrial production and having broad market application prospects.

[0043] The content of the above embodiments will be further described below in conjunction with the accompanying drawings.

[0044] Among them, the reaction structural formula of the obtained finished polymer PNB-COOH in the preparation method of the polynorbornene-spun nanofiber adsorption separation membrane is as Figure 1 shown.

[0045] As Figure 2 shown, through Figure 2 1H NMR, it can be confirmed that PNB-COOH is successfully synthesized, the main chain structure is complete, and the polymerization reaction is highly efficient and controllable. The two olefin hydrogen characteristic peaks of the norbornene monomer near 6.1 - 5.9 ppm disappear, and a broad peak appears near 5.2 - 5.4 ppm, which is the double bond (-CH=CH-) peak of the polymer formed after the ring-opening of norbornene, indicating the synthesis of the polymer double bond main chain. The multiplet peaks at 1.0 - 2.5 ppm are the signals of the bridgehead hydrogen and the saturated hydrogen on the ring of norbornene.

[0046] As Figure 3 shown, through the infrared spectrogram, it can be seen that the characteristic peak of the carbon-carbon double bond at 1707 cm -1 -1 proves the success of the ring-opening metathesis polymerization reaction. The bending vibrations of CH2 and CH exist within 1465 - 1375 cm -1 , indicating that the structure of the cycloalkane is not damaged.

[0047] As Figure 4 shown, in Figure 4 , the characteristic absorption peaks of the functional group -CF2 of PVDF are at 883 cm -1 and 1180 cm -1 . There are no obvious absorption peaks in the infrared spectrogram of PNB-COOH at these two places. The other five blend membranes all have characteristic absorption peaks of varying degrees at these two places, and the intensity of the absorption peaks is consistent with the mass ratio of PVDF. In summary, it shows that the ring-opening metathesis polymerization of carboxynorbornene is successful, and the blend membrane of the polymer and PVDF is successfully prepared.

[0048] As Figure 5 shown, Figure 5The SEM images show that all the membrane materials exhibit typical electrospun fiber characteristics, featuring an elongated, continuous, and randomly oriented fiber network. However, there are significant differences in the fiber diameter and fiber morphology distribution for different polymer ratios. The fibers of PVDF are of uniform diameter and have a smooth surface without obvious bead defects, and their fibers form a dense network structure. The fibers of the PNB-COOH membrane are evenly distributed and have a smooth surface, showing excellent processability for electrospinning.

[0049] From VN-8-2 to VN-2-8, as the mass ratio of the PNB-COOH polymer changes, the average diameter of the nanofibers gradually increases. The fiber diameter distributions of the VN-6-4 membrane and the VN-4-6 membrane are extremely uneven. Due to the poor compatibility between the polynorbornene-based polymer and PVDF, the two components of the spinning solution are stratified during the spinning process, and phase separation occurs in the spun fibers. However, at the same time, the diameter distributions of VN-8-2 and VN-2-8 in the blend membranes are relatively uniform, without obvious phase separation, and the fibers are closely packed. The fiber diameter of VN-2-8 is approximately around 400 nm, and the fiber distribution is relatively loose with fewer nodes.

[0050] As Figure 6 shown, Figure 6 Pictures of the contact angle tests of six fiber membranes with different blend ratios of PNB-COOH. It can be seen from the figure that as the PNB-COOH content increases, the contact angle gradually decreases. The carboxyl groups in PNB-COOH improve the hydrophilicity of the material. The contact angle of pure PVDF is the largest. Since the PVDF molecular chain contains a large number of fluorocarbon groups (-CF2-), the low surface energy and high electronegativity significantly repel water molecules, forming a stable hydrophobic surface. The contact angle of the PNB-COOH membrane is 95°. The hydrophilicity of the carboxylic acid groups therein dominates. The strong polar -COOH easily forms hydrogen bonds with water molecules, significantly reducing the contact angle. Its hydrophilicity is conducive to the diffusion of pollutants on the membrane surface and in the internal pores, thus accelerating the capture of pollutants.

[0051] As Figure 7 shown, Figure 7The following are scanning electron microscope images of six nanofiber membranes with different blending ratios that were dried after being soaked in water for 24 hours. It is obvious that the overall structure of the fiber membrane structure of the nanofiber membranes PVDF, VN-8-2, VN-6-4, VN-4-6 and VN-2-8 containing the hydrophobic polymer PVDF can still remain relatively intact, and there is no collapse or adhesion. After the pure PNB-COOH membrane was soaked in water for 24 hours, some fibers collapsed and could not be used normally as an adsorption membrane. The reason is that the strong hydrophilic groups of the PNB-COOH fiber membrane easily form hydrogen bonds with water molecules, resulting in a large amount of water molecules adsorbed on the surface and inside of the membrane, increasing the distance between the chain segments, swelling the polymer membrane, weakening the interaction between the polymer chains, and eventually exceeding the swelling limit of the material. The structure cannot maintain its original state, showing fiber collapse and adhesion. Therefore, when the carboxyl norbornene polymer membrane is used for water treatment, hydrophobic PVDF is required to provide a three-dimensional structure to support the membrane.

[0052] Combined with the above, among the six fiber membranes with different blending ratios, PVDF is needed to provide hydrophobicity and three-dimensional structural support for the fiber membrane. Compared with fiber membranes blended in other ratios, VN-2-8 has more carboxyl groups with adsorption function, and its fiber spinnability is good and the diameter distribution is uniform. Therefore, VN-2-8 is selected as the best ratio material for adsorption experiments.

[0053] like Figure 8 As shown, from Figure 8 It can be seen that with the increase of the PNB-COOH blending ratio, the adsorption capacity of the adsorption membrane gradually increases. The reason is that the number of carboxyl groups of the adsorption functional group gradually increases. The carboxyl group is easily dissociated into carboxylate COO- and proton H+ in aqueous solution, making the surface of the adsorption membrane negatively charged. The dye methylene blue molecules exist in the form of cations in aqueous solution and can be combined with negatively charged carboxyl groups through electrostatic attraction. Therefore, with the increase of the number of carboxyl groups, the hydrophilicity of the membrane material is improved, and the density of surface negative charges is gradually increased, so the electrostatic attraction of the membrane to the methylene blue cation is enhanced, and the adsorption capacity is significantly improved. The adsorption amount of PVDF membrane is the lowest, which is 9.7 mg / g. There are no obvious characteristic groups in the membrane. The high specific surface area and rich pore structure of the electrospun membrane provide a large number of physical adsorption sites for the methylene blue molecules, allowing them to intercept a small amount of pollutant molecules.

[0054] like Figure 9 As shown, from Figure 9 As can be seen in the figure, after MB and MO dyes are mixed in a mass ratio of 1:1, the color of the mixed dye solution is dark green. After adsorption, the color of the solution is close to the yellow of MO. In order to prove the selective adsorption process, the UV-visible spectra of the solution before and after adsorption were monitored.

[0055] like Figure 10As shown, the peaks at 664 nm and 464 nm are the characteristic peaks of MB and MO, respectively. After adsorption, the peak value of MB decreased significantly, while the peak value of MO remained almost unchanged. The above experimental results confirmed that the MB dye was selectively adsorbed by the VN-2-8 nanofiber membrane, while the MO dye remained in the water. The high selective adsorption ability of the nanofiber membrane makes it possible to separate MB and MO dyes by the dynamic filtration method.

[0056] In summary, this method ensures the stable performance and consistent quality of the nanofiber membrane by precisely controlling the preparation process; after introducing polynorbornene, the selectivity and adsorption capacity of the membrane for refractory pollutants such as organic dyes are significantly improved; at the same time, the steps are clear, the operation is simple, and it is easy to realize industrial production, providing an efficient and novel nanofiber membrane material for the water treatment field, with broad market application prospects.

[0057] The embodiments of the present invention are given for purposes of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A preparation method of a poly(norbornene) spun nanofiber adsorption and separation membrane, characterized in that: It includes the following steps: Step 1: Add calcium hydride as a desiccant to a round-bottom flask, add dichloromethane with a content of more than 95%, heat under reflux under nitrogen protection, collect the reflux liquid, let it stand and cool before use; Step 2: Add 5-norbornene-2-carboxylic acid and anhydrous dichloromethane to a reaction flask, introduce an inert gas, add Grubbs II generation catalyst, and carry out a homopolymerization reaction to obtain a carboxyl norbornene homopolymer; Step 3: Dissolve the PNB-COOH polymer powder and PVDF powder in a DMF solution according to different mass ratios, stir and dissolve at 50 °C to obtain a uniform electrospinning precursor solution with a total mass fraction of 20% - 25%; among them, the mass ratio of PVDF to PNB-COOH is 10:0 to 0:10; Step 4: Carry out electrospinning on the precursor solution under the conditions of set voltage, injection flow rate, receiver distance, ambient temperature and relative humidity. After electrospinning, remove the receiver covered with the nanofiber membrane, and obtain a poly(norbornene) electrospun nanofiber adsorption separation membrane after drying.

2. The preparation method of a polynorbornene spinning nanofiber adsorption separation membrane as described in claim 1, characterized in that: In Step 1, the temperature of heating under reflux is 50 - 60 °C, and the reflux time is 2 - 4 hours.

3. The preparation method of a polynorbornene spun nanofiber adsorption and separation membrane according to claim 1, characterized in that: In Step 2, the temperature of the homopolymerization reaction is 25 - 35 °C, and the reaction time is 40 - 80 minutes.

4. The preparation method of a poly(norbornene) spinning nanofiber adsorption and separation membrane according to claim 1, characterized in that: In Step 3, the mass ratio of PVDF to PNB-COOH includes any one of 10:0, 8:2, 6:4, 4:6, 2:8, 0:

10.

5. The preparation method of a poly(norbornene) spun nanofiber adsorption and separation membrane according to claim 1, characterized in that: In Step 4, the voltage of electrospinning is 15 - 20 kV, the injection flow rate is 15 - 20 μL / min, the distance between the receiver and the needle tip is 15 - 25 cm, the ambient temperature is 25 ± 5 °C, the relative humidity is 25 ± 5%, and the electrospinning time is 6 - 10 hours.

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