Direct MOF (Metal Organic Framework) polymer fiber as well as preparation method and application thereof

Abstract

The invention provides a direct MOF polymer fiber as well as a preparation method and application thereof, and belongs to the technical field of polymer fibers. The preparation method of the direct MOF polymer fiber comprises the following steps: uniformly mixing an organic ligand, a metal salt, a growth regulator and an organic solvent, and carrying out a microwave heating reaction to obtain MOFs nanocrystals; the MOFs nanocrystals are uniformly dispersed in a dispersing agent solution, and MOFs dispersion liquid is obtained; the MOFs dispersion liquid is used for modification in / after polymer fiber preparation, and the direct MOF polymer fiber is obtained. The MOFs are directionally anchored to the polymer to prepare the direct MOF polymer fiber, the fiber has high electroactivity, high mechanical property, low air resistance, high filtering efficiency and high catalytic performance, and fine particles and harmful gas in air are efficiently purified.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer fibers, and particularly relates to a directly MOF-modified polymer fiber, a preparation method thereof, and an application thereof. Background Art

[0002] Respiratory health problems have always been a global focus. With the continuous development of society and the continuous improvement of the mechanization level, in the construction sites of many industries and even in people's daily lives, the exhaust gases emitted by production machines mostly have problems of high concentrations of particulate matter and toxic gases. Such exhaust gases not only seriously damage the natural environment, but as the concentration increases, they even pose a threat to people's lives. The exhaust gases contain many substances harmful to the human body, such as PM 2.5 , SO 2 , nitrogen oxides (NO x ) and so on. Working and living in such an environment for a long time will continuously inhale a large amount of fine particulate matter and toxic gases into the body. The fine particulate matter and toxic gases will directly enter the human respiratory tract and alveoli, which can cause respiratory system inflammation, and severe cases can turn into pneumoconiosis. The inhalation of toxic gases will erode the human kidneys and seriously threaten people's lives.

[0003] Although there are currently particulate matter treatment measures such as spray dust suppression and dust removal by dust collectors, they still cannot meet the needs of treating fine particulate matter in factory exhaust gases and daily living environments. In particular, the treatment effect for ultrafine particulate matter with a particle size less than 2.5 μm is poor, and the respirable particulate matter with a smaller particle size can enter the human alveolar area, which is the main cause of pneumoconiosis. There are even fewer treatment methods for toxic gases in exhaust gases.

[0004] Currently, most filter materials for fine particulate matter use polymers as the main material and make them into fibers with micron or even nanometer sizes through technologies such as electrospinning or melt spinning as the filter layer of protective masks. However, since polymer fibers only have filtration means such as physical adsorption, they cannot efficiently filter out fine particulate matter such as PM 2.5 and so on, and also do not have the ability to catalytically degrade harmful gases.

[0005] Therefore, developing protective materials that can effectively purify ultrafine particulate matter and toxic gases contained in exhaust gases is of great significance for preventing the occurrence of pneumoconiosis and protecting life and health. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a directly MOF-modified polymer fiber, a preparation method thereof, and an application thereof. The fiber provided by the present invention has the advantages of high surface activity, high electroactivity, excellent mechanical properties, low air resistance, high filtration efficiency, and high catalytic conversion efficiency.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention is a method for preparing a directly MOF-functionalized polymer fiber, comprising the following steps:

[0009] After uniformly mixing an organic ligand, a metal salt, a growth regulator, and an organic solvent, subjecting the mixture to microwave heating reaction to obtain MOFs nanocrystals;

[0010] Uniformly dispersing the MOFs nanocrystals in a dispersant solution to obtain a MOFs dispersion;

[0011] Using the MOFs dispersion to modify during / after the preparation of a polymer fiber to obtain the directly MOF-functionalized polymer fiber.

[0012] Another technical solution of the present invention is a directly MOF-functionalized polymer fiber prepared by the above preparation method.

[0013] Another technical solution of the present invention is an application of the above directly MOF-functionalized polymer fiber in filtering PMs in air or catalytically degrading harmful gases in air.

[0014] The present invention discloses the following technical effects:

[0015] The preparation method provided by the present invention uses microwave-assisted synthesis to obtain MOFs nanocrystals with high structural regularity (the diameter of the nanocrystals is 300 - 800 nm, and the purity is 95.0 - 99.9%), and realizes the directional anchoring of MOFs on a polymer to form a directly MOF-functionalized polymer fiber. This fiber has advantages such as high surface activity, high electroactivity, high mechanical properties, low air resistance, high filtration efficiency, and high catalytic performance, and realizes the efficient purification of fine particulate matter in air (such as PM 0.3 , PM 2.5 ) and harmful gases (such as SO 2 , nitrogen oxides, etc.).

[0016] The directly MOF-functionalized polymer fiber obtained by the present invention has a pore size of 300 nm - 5 μm, a specific surface area (SSA) of 500 - 5000 g / m 2 , a breaking strength of 10 - 20 MPa, a dielectric constant of 1.01 - 5.04, a surface potential of 10 - 20 kV. At a high flow rate of 85 L / min, the filtration efficiency for PM 2.5 , PM 0.3 reaches more than 98%, and for SO 2 , NO, and NO 2The catalytic efficiency reaches over 94%, and can reach up to 98.7% at most. It has the advantages of high electroactivity, excellent mechanical properties, high filtration efficiency and high catalytic performance, and can be used for the efficient filtration and interception of ultrafine particles and the effective catalytic treatment of toxic gases in the waste gas discharged from industrial production and daily life. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 is the process flow chart for preparing directly MOF-functionalized polymer fibers of the present invention;

[0019] Figure 2 is the scanning electron microscope image of MOF(Fe) nanocrystals in Example 3;

[0020] Figure 3 is the scanning electron microscope observation image of directly MOF-functionalized polymer fibers in Example 4;

[0021] Figure 4 is the catalytic efficiency of directly MOF-functionalized polymer fibers in Examples 1-4 for SO 2 gas. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded within the range.

[0024] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although only preferred methods and materials are described in this invention, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0025] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0026] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0027] In this invention, " / " means "or".

[0028] MOFs are a kind of porous crystalline materials, which are crystalline networks formed by the coordination of metal ions or metal clusters with organic ligands. They have high porosity and large specific surface area, and can be applied to catalytic treatment of some common toxic gases, for the degradation of organic pollutants and gases in the air. At the same time, due to their advantages such as high catalytic activity, high thermal stability and visible light response, they can be used for the filtration and catalysis of waste gas.

[0029] Electrospinning technology is one of the most effective methods for preparing one-dimensional nanostructured materials at present, with advantages such as simple equipment, controllable process parameters, fast preparation speed and low cost. Since the fibers prepared by electrospinning have characteristics such as small fiber diameter, many pores and small pore size, the formed fibers have advantages such as good air permeability, small air resistance and strong protection. Many new and practical strategies have been derived from electrospinning technology, such as electrospinning-spray strategy, coaxial electrospinning strategy, centrifugal spinning strategy, etc., and the fibers can be functionalized by compounding with other functional materials. Melt spinning is a large-scale spinning method, and its main process is to heat and melt the polymer, extrude it through a spinneret, and cool and solidify in the air to form fibers. The above two methods have shown great application potential in the fields of waste gas filtration and catalysis.

[0030] To achieve long-term filtration of fine particulate matter with a particle size less than 2.5 μm in engine exhaust gas and efficient catalysis of toxic gases, the present invention prepares directly MOF-functionalized polymer fibers based on electrospinning and melt spinning technologies. First, high-purity nanoscale metal-organic framework (MOFs) crystals are synthesized through microwave-ultrasonic assistance. Then, a stable and uniform MOFs dispersion is rapidly prepared by high-pressure homogenization dispersion. Finally, directly MOF-functionalized polymer fibers are prepared by directly MOF-functionalized modification using electrospinning or melt spinning technologies. The fibers have advantages such as high surface activity, high electroactivity, low air resistance, high filtration efficiency, and high catalytic conversion efficiency, and ultimately achieve efficient filtration of ultrafine particulate matter and effective catalytic degradation of toxic gases, showing good application prospects in the field of waste gas purification.

[0031] The first aspect of the present invention provides a method for preparing directly MOF-functionalized polymer fibers, comprising the following steps:

[0032] After uniformly mixing an organic ligand, a metal salt, a growth regulator, and an organic solvent, a MOFs nanocrystal is obtained through microwave heating reaction;

[0033] The MOFs nanocrystal is uniformly dispersed in a dispersant solution to obtain a MOFs dispersion;

[0034] The directly MOF-functionalized polymer fiber is obtained by using the MOFs dispersion for modification during / after the preparation of the polymer fiber.

[0035] In a preferred embodiment of the present invention, the organic ligand is terephthalic acid or 2-methylimidazole; the metal salt is zinc acetate, silver nitrate, or iron chloride; the growth regulator is cetyltrimethylammonium bromide, polyvinylpyrrolidone, carboxymethyl cellulose, or dopamine hydrochloride; the molar ratio of the organic ligand, the metal salt, and the growth regulator is 1-5:4-10:1. Only through the specific organic ligand, metal salt, and growth regulator in the present invention can MOFs nanocrystals with regular, uniform, and high purity be synthesized efficiently and with low consumption. The MOFs nanocrystals in the present invention have advantages such as a large specific surface area, strong electroactivity, and good catalytic performance compared with other MOFs.

[0036] In a preferred embodiment of the present invention, the organic solvent is N,N-dimethylformamide, dichloromethane, or chloroform. The present invention does not make special limitations on the dosage of the organic solvent, and the dosage well-known to those skilled in the art and capable of meeting the requirements of microwave heating reaction can be selected.

[0037] The present invention does not make special limitations on the way of uniform mixing, and conventional technical means well-known to those skilled in the art can be selected, such as ultrasonic.

[0038] In a preferred embodiment of the present invention, the parameters of the microwave heating reaction are set as follows: temperature 80 - 180 °C, power 300 - 1000 W, and time 10 - 120 min.

[0039] In a preferred embodiment of the present invention, the parameters of the microwave heating reaction are set as follows: temperature 80 - 130 °C or 130 - 180 °C, power 300 - 700 W or 700 - 1000 W, and time 10 - 40 min, 40 - 80 min, or 80 - 120 min.

[0040] In a preferred embodiment of the present invention, the parameters of the microwave heating reaction are set as follows: temperature 80 - 90 °C, 90 - 130 °C, or 130 - 180 °C, power 300 - 600 W, 600 - 700 W, or 700 - 1000 W, and time 10 - 20 min, 20 - 30 min, or 30 - 120 min.

[0041] In a preferred embodiment of the present invention, the parameters of the microwave heating reaction are set as follows: temperature 80 °C, 90 °C, 130 °C, or 180 °C, power 300 W, 600 W, 700 W, or 1000 W, and time 10 min, 20 min, 30 min, or 120 min.

[0042] In a preferred embodiment of the present invention, after the microwave heating reaction, the steps of centrifugation, washing, and drying are further included.

[0043] In a preferred embodiment of the present invention, the solute in the dispersant solution is cetyltrimethylammonium bromide, carboxymethyl cellulose, or dopamine hydrochloride; the concentration of MOFs nanocrystals in the dispersion is 1% - 20% (more preferably, 10% - 15%). The present invention does not make special limitations on the solvent in the dispersant solution, and a solvent well-known to those skilled in the art and capable of dissolving the solute can be selected. For example: when the solute is cetyltrimethylammonium bromide, the solvent is N,N - dimethylacetamide; when the solute is carboxymethyl cellulose, the solvent is ethanol; when the solute is dopamine hydrochloride, the solvent is water or N,N - dimethylformamide. In the dispersant solution of the present invention, the mass - volume ratio of the solute to the solvent is 0.01 - 0.02 g:10 mL.

[0044] The present invention does not make special limitations on the method of uniformly dispersing MOFs nanocrystals in the dispersant solution, and conventional technical means of those skilled in the art can be selected, such as: high - pressure homogenization; the parameters are: the pressure of homogeneous dispersion is 1 MPa - 100 MPa, and the time of homogeneous dispersion is 1 min - 3 h.

[0045] In a preferred embodiment of the present invention, the following three methods are included for modifying with the MOFs dispersion during / after the preparation of polymer fibers:

[0046] Method 1. When the preparation method of the polymer fiber is the melt spinning method: The polymer is prepared into polymer fibers by the melt spinning method, and then the MOFs dispersion is coated on the surface of the polymer fibers;

[0047] Method 2. When the preparation method of the polymer fiber is coaxial electrospinning or centrifugal electrospinning: After the polymer is formulated into a polymer solution, it is mixed evenly with the MOFs dispersion, and then coaxial electrospinning or centrifugal electrospinning is carried out;

[0048] Method 3. When the preparation method of the polymer fiber is electrospinning-spray method: The polymer is formulated into a polymer solution, and then electrospinning-spray is carried out with the MOFs dispersion.

[0049] The present invention does not make special limitations on the specific parameters of melt spinning, coaxial electrospinning, centrifugal electrospinning and electrospinning-spray, and the parameters well-known to those skilled in the art can be selected.

[0050] In a preferred embodiment of the present invention, the polymer is polyvinylidene fluoride, polyimide, polyphenylene sulfide, polypropylene, polylactic acid or polyethylene terephthalate; the mass fraction of the polymer in the polymer solution is 2 wt% to 30 wt%.

[0051] In a preferred embodiment of the present invention, the mass fraction of the polymer in the polymer solution is 15 wt% to 25 wt%.

[0052] In a preferred embodiment of the present invention, the mass ratio of the MOFs nanocrystals to the polymer in the MOFs dispersion is 1:1 to 1:100.

[0053] In a preferred embodiment of the present invention, the mass ratio of the MOFs nanocrystals to the polymer in the MOFs dispersion is 1:20 to 1:80.

[0054] In a preferred embodiment of the present invention, the mass ratio of the MOFs nanocrystals to the polymer in the MOFs dispersion is 1:30 to 1:70.

[0055] In a preferred embodiment of the present invention, the mass ratio of the MOFs nanocrystals to the polymer in the MOFs dispersion is 1:40 to 1:60.

[0056] The second aspect of the present invention provides a directly MOF-functionalized polymer fiber prepared by the above preparation method.

[0057] The third aspect of the present invention provides an application of the above directly MOF-functionalized polymer fiber in filtering PMs in the air or catalytically degrading harmful gases in the air.

[0058] In a preferred embodiment of the present invention, the harmful gas is SO 2 , NO and NO 2 at least one of them.

[0059] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art. The reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been made public.

[0060] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments.

[0061] Example 1

[0062] A method for preparing a directly MOF-functionalized polymer fiber, the steps are as follows:

[0063] S1. Prepare MOFs nanocrystals: Dissolve 1.5 g of carboxymethyl cellulose in 100 mL of N,N-dimethylformamide, stir for 2 min, then add 1.6 g of 2-methylimidazole thereto, and ultrasonicate the mixture for 3 min. Then slowly add 4.5 g of zinc acetate thereto, stir well, transfer the mixture to a metal reaction kettle after uniform dispersion, and set the microwave heating reaction at 80 °C and 300 W for 10 min. Then, the obtained product is centrifuged and washed with N,N-dimethylformamide, and placed in a constant temperature drying oven for drying to obtain high-purity MOF(Zn) nanocrystals with a purity of 95.5%, and the average size of MOF(Zn) nanoparticles is 420 nm;

[0064] S2. Prepare a MOF dispersion: Add 0.01 g of MOF(Zn) nanocrystals obtained in S1 and 0.01 g of dopamine hydrochloride to 10 mL of deionized water and mix evenly. Place it in a high-pressure homogenizer at a pressure of 10 MPa for 1 min to obtain a stable and uniform MOF dispersion;

[0065] S3. Prepare a directly MOF-functionalized polymer fiber: Feed the polypropylene melt into a screw extruder, send it to the heating zone by a rotating screw, extrude and melt it forward to a metering pump. The metering pump controls and ensures the stable flow of the polymer melt into the spinning box. In the box, the melt is filtered and pressed into a porous spinneret to eject a melt stream, and then cooled and solidified into a tow fiber by a conveyor belt in the air. The melting temperature is 100 °C and the output voltage is 10 kV. Then, the MOF dispersion is evenly coated on the fiber surface (the mass ratio of MOF nanocrystals to polypropylene in the MOF dispersion is 1:100), and placed in a vacuum oven at 40 °C for drying for 12 h to obtain a directly MOF-functionalized polymer fiber with an average pore size of 3.35 μm.

[0066] Example 2

[0067] A preparation method of directly MOF-functionalized polymer fibers is as follows:

[0068] S1. Prepare MOFs nanocrystals: Dissolve 2 g of dopamine hydrochloride in 100 mL of chloroform, stir for 3 min, then add 1.8 g of terephthalic acid thereto, and ultrasonicate the mixture for 15 min. Then slowly add 4.5 g of silver nitrate thereto, stir well, transfer it to a metal reaction kettle after being uniformly dispersed, and set the microwave heating reaction at 180 °C and 1000 W for 2 h. Then, centrifuge and wash the obtained product with N,N-dimethylformamide, and dry it in a constant temperature drying oven to obtain high-purity MOF(Ag) nanocrystals with a purity of 96.6% and an average size of 780 nm for the MOF(Ag) nanocrystal particles;

[0069] S2. Prepare a MOF dispersion: Add 0.2 g of the MOF(Ag) nanocrystals obtained in S1 and 0.02 g of carboxymethyl cellulose to 10 mL of ethanol and mix uniformly. Place it in a high-pressure homogenizer at a pressure of 30 MPa for 30 min to obtain a stable and uniform MOF dispersion;

[0070] S3. Prepare directly MOF-functionalized polymer fibers: Uniformly mix the MOF dispersion with a polyvinylidene fluoride solution (the mass fraction of the polyvinylidene fluoride solution is 15%, and the mass ratio of the MOFs nanocrystals to polyvinylidene fluoride in the MOF dispersion is 1:80), make and take 2 mL of the spinning dope, and use a coaxial electrospinning strategy at a flow rate of 1 mL / h, an output voltage of 50 kV, a spinning collector rotation speed of 2500 rpm, a spinning temperature of 35 °C, and a RH of 60% to prepare directly MOF-functionalized polymer fibers with an average pore size of 541 nm.

[0071] Example 3

[0072] A preparation method of directly MOF-functionalized polymer fibers is as follows:

[0073] S1. Prepare MOFs nanocrystals: Dissolve 2.5 g of cetyltrimethylammonium bromide in 100 mL of dichloromethane, stir for 4 min, then add 2 g of 2-methylimidazole thereto, ultrasonicate the mixture for 30 min, then slowly add 5 g of ferric chloride thereto, stir well, transfer it to a polytetrafluoroethylene reaction kettle after being uniformly dispersed, and set the microwave-assisted heating reaction at 90 °C and 600 W for 30 min. Then, centrifuge and wash the obtained product with N,N-dimethylformamide, and dry it in a constant temperature drying oven to obtain high-purity MOF(Fe) nanocrystals with a purity of 98.7% and an average size of 480 nm for the MOF(Fe) nanocrystal particles;

[0074] S2. Preparation of MOF dispersion: Add 0.3 g of MOF(Fe) nanocrystals obtained in S1 and 0.15 g of dopamine hydrochloride into 10 mL of N,N-dimethylformamide and mix evenly. Place it in a high-pressure homogenizer with a pressure of 60 MPa and a homogenization time of 2 h to obtain a stable and uniform MOF dispersion;

[0075] S3. Preparation of directly MOF-functionalized polymer fibers: Uniformly mix the MOF dispersion with a polyphenylene sulfide solution (the mass fraction of the polyphenylene sulfide solution is 25%, and the mass ratio of MOFs nanocrystals to polyphenylene sulfide in the MOF dispersion is 1:40). Prepare and take 3 mL of the spinning dope, and use the centrifugal electrospinning strategy to prepare directly MOF-functionalized polymer fibers under the parameter conditions of a flow rate of 1.5 mL / h, an output voltage of 25 kV, a spinning collector rotation speed of 1000 rpm, a spinning temperature of 20 °C, and an RH of 20%. The average pore diameter of the fibers is 735 nm.

[0076] Example 4

[0077] A method for preparing directly MOF-functionalized polymer fibers, the steps are as follows:

[0078] S1. Preparation of MOFs: Dissolve 3 g of polyvinylpyrrolidone in 100 mL of N,N-dimethylformamide, stir for 5 min, then add 2.2 g of terephthalic acid into it, ultrasonicate the mixture for 1 h, and then slowly add 5.5 g of zinc acetate into it. Stir well, and transfer it to a polytetrafluoroethylene reaction kettle after uniform dispersion. Set the microwave-assisted heating reaction at 130 °C and 700 W for 20 min. Then, centrifuge and wash the obtained product with N,N-dimethylformamide, and place it in a constant temperature drying oven for drying to obtain high-purity MOF(Zn) nanocrystals with a purity of 99.9%. The average size of MOF(Zn) nanocrystal particles is 380 nm;

[0079] S2. Preparation of MOF dispersion: Add 0.1 g of MOF(Zn) nanocrystals obtained in S1 and 0.02 g of cetyltrimethylammonium bromide into 10 mL of N,N-dimethylacetamide and mix evenly to obtain a MOF dispersion (spray stock solution);

[0080] S3. Preparation of directly MOF-functionalized polymer fibers: Take 2 mL of the spray stock solution and 3 mL of a polylactic acid solution (the mass fraction of the polylactic acid solution is 20%, and the mass ratio of MOFs nanocrystals to polylactic acid in the MOF dispersion is 1:10), and use the electrospinning-spraying strategy to prepare directly MOF-functionalized polymer fibers under the parameter conditions of flow rates of 1.5 mL / h and 2 mL / h respectively, an output voltage of 30 kV, a spinning collector rotation speed of 800 rpm, a spinning temperature of 25 °C, and an RH of 30%. The average pore diameter of the fibers is 328 nm.

[0081] Comparative Example 1

[0082] S1. The same as step S1 of Example 1;

[0083] S2. The polypropylene melt is uniformly mixed with MOF nanocrystals (the mass ratio of MOFs nanocrystals to polypropylene is 1:100), and fed into a screw extruder. It is sent to the heating zone by a rotating screw, and after extrusion and melting, it is sent forward to a metering pump. The metering pump controls and ensures the stable flow of the polymer melt into the spinning box. In the box, the melt is filtered and pressed into a porous spinneret to eject a melt stream, and then cooled and solidified into a tow fiber in the air by a conveyor belt. The melting temperature is 100 °C, and the output voltage is 10 kV. A directly MOF-functionalized polymer fiber is prepared, and the average pore size of the fiber is 3.96 μm. (That is, different from Example 1 in that the MOF (Zn) nanocrystals are not dispersed by adding a dispersant)

[0084] Comparative Example 2

[0085] S1. Dissolve 2 g of dopamine hydrochloride in 100 mL of chloroform, stir for 3 min, then slowly add 1.8 g of terephthalic acid and 4.5 g of silver nitrate thereto, stir well, transfer it to a metal reaction kettle after uniform dispersion, and water bath at 90 °C for 2 h. Then, the obtained product is centrifuged and washed with N,N-dimethylformamide, and placed in a constant temperature drying oven for drying to obtain high-purity MOF (Ag) nanocrystals with a purity of 85.6% and an average size of MOF (Ag) nanoparticles of 780 nm;

[0086] S2. Prepare a MOF dispersion: Add 0.2 g of MOF (Ag) obtained in S1 and 0.02 g of carboxymethyl cellulose to 10 mL of ethanol and mix uniformly. Place it in a high-pressure homogenizer at a pressure of 30 MPa for a homogenization time of 30 min to obtain a stable and uniform MOF dispersion;

[0087] S3. Prepare a directly MOF-functionalized polymer fiber: Uniformly mix the MOF dispersion with a polyvinylidene fluoride solution (the mass fraction of the polyvinylidene fluoride solution is 15%, and the mass ratio of MOFs nanocrystals to polyvinylidene fluoride in the MOF dispersion is 1:80), make and take 2 mL of spinning dope, and use a coaxial electrospinning strategy at a flow rate of 1 mL / h, an output voltage of 50 kV, a spinning collector rotation speed of 2500 rpm, a spinning temperature of 35 °C, and a RH of 60% to prepare a directly MOF-functionalized polymer fiber with an average pore size of 541 nm. (That is, different from Example 2 in that the preparation method of MOFs nanocrystals is replaced from the microwave heating method to the hydrothermal synthesis method)

[0088] Comparative Example 3

[0089] S1. Add iron chloride particles to 0.01 g of dopamine hydrochloride in 10 mL of N,N-dimethylformamide and mix evenly to obtain an iron chloride dispersion.

[0090] S2. Prepare 10 mL of diethylformamide and add 3 g of polyphenylene sulfide. After completely mixing and dispersing evenly, a polymer solution is obtained.

[0091] S3. Uniformly mix the iron chloride dispersion and the polymer solution, prepare and take 3 mL of spinning dope. Using the centrifugal electrospinning strategy, at a flow rate of 1.5 mL / h, an output voltage of 25 kV, a spinning collector rotation speed of 1000 rpm, a spinning temperature of 20 °C, and an RH of 20%, zinc oxide polymer fibers are prepared. The average pore size of the fibers is 803 nm. (That is, different from Example 3, replace the MOFs nanocrystals with iron chloride)

[0092] Characterization and performance testing:

[0093] Scanning electron microscope observation: Observe the microstructure of MOF nanoparticles and directly MOF-functionalized polymer fibers through a field emission scanning electron microscope (model JSM-7900F, JEOL, Japan) ( Figure 2 and 3 ).

[0094] Tensile property testing: Cut the obtained directly MOF-functionalized polymer fibers to obtain tensile specimens. According to the plastic tensile property testing standard in ASTM D638-2003 of the American Society for Testing and Materials, use a universal tensile testing machine (model 4403, sensor 100N) from Instron Corporation, USA, to test the tensile properties of the composite material. Ensure at least 3 parallel test samples in each group, and take the average value of the results.

[0095] Surface potential testing: Use a non-contact electrostatic meter (VM54XQS, Quatek Corporation, USA) to test the surface potential of the nanofibers. The testing height is 2 cm, and the temperature and humidity are kept constant at 25 °C and 45%. Randomly collect 20 data points for each sample and take the average value.

[0096] Dielectric constant testing: Test the dielectric constant of the directly MOF-functionalized polymer fibers through a dielectric constant tester (model WK-6500B, Wayne Kerr Company, UK).

[0097] Filtration performance testing: Use an LZC-K type automatic filter material tester (Suzhou Huada Instrument and Equipment Co., Ltd.) to test the fibers (area 100 cm 2) For the air filtration performance, the gas flow rate was set at 85 L / min, and the particle size range of the NaCl aerosol particles generated by the aerosol generator was 0.1 - 10 μm. At least 3 different positions of each group of fibers were tested, and the results were averaged.

[0098] Air resistance test: An AP800 micro - manometer from TSI, Inc., USA was used to test the air resistance.

[0099] Photocatalytic test for toxic gases: A diesel engine was used as the source of toxic gases, and a PLS - SXE 300 xenon lamp was used as the light source for photocatalysis and a multi - pollutant integrated portable detector BGMJ - 1 was used to test the content of toxic gases such as SO 2 , NO, NO 2 etc. before and after the fiber adsorption, so as to calculate the catalytic efficiency for the toxic gases in diesel exhaust.

[0100] Experimental results:

[0101] Table 1. Test results of the mechanical properties, dielectric constant, surface potential, filtration performance and air resistance of directly MOF - modified polymer fibers

[0102]

[0103]

[0104] Table 2. Test results of the catalytic performance of directly MOF - modified polymer fibers

[0105]

[0106] As Figure 2 shown, the MOFs nanocrystals synthesized by microwave - assisted method have regular structures. Figure 3 It can be found in the directly MOF - modified polymer fibers shown that the high - purity MOFs nanocrystals are well embedded in the fibers, the structure between the fibers is denser, there is no risk of falling off under external force, and it can be found that the fiber diameter becomes thinner and the pores become more, which is more conducive to the active adsorption and electrostatic trapping of fine particles by the fibers and MOF nanocrystals.

[0107] Table 1 compares the test results of the mechanical properties and dielectric constants of the directly MOF-functionalized polymer fibers obtained in the examples and comparative examples. Examples 1-4 and Comparative Example 2 all have relatively high breaking strengths (14.2 MPa - 19.9 MPa). This is because the addition of high-purity MOFs nanocrystals effectively improves the interfacial interaction between the fibers and the nanocrystals, thus exhibiting excellent mechanical properties and meeting the mechanical property requirements of the fibers in the field of air filtration. The breaking strengths of Comparative Examples 1 and 3 are less than those of Examples 1–4, mainly due to the easy aggregation of MOF nanoparticles in the solution without a dispersant and the lack of modification of the polymer fibers with MOF nanoparticles. Moreover, the dielectric constants of the directly MOF-functionalized polymer fibers in the examples are significantly higher than those of the comparative examples. This is because the anchoring of MOF nanocrystals improves the electret effect of the polymer matrix, thus significantly increasing the dielectric constant.

[0108] Meanwhile, through the real-time monitoring of the surface potentials of Examples 1–4 and Comparative Examples 1–3, it was found that the directly MOF-functionalized polymer fibers in Examples 1–4 all exhibited extremely high and persistent surface potentials (10.11 kV - 18.04 kV), with extremely high long-term stability. The main reason for the lower surface potential of Comparative Example 1 compared to Examples 1–4 is that the high-purity MOFs nanocrystals in the solution aggregated, so only part of the high-purity MOF nanoparticles were anchored in the fibers, resulting in weak charge retention ability and a decrease in surface potential. The low surface potential of Comparative Example 2 is mainly due to the incomplete reaction between the metal salt and the organic ligand prepared by the hydrothermal synthesis method, poor chemical bond binding, and uneven synthesis of MOFs nanocrystals, which leads to their inability to generate and store charges. The main reason for the low surface potential of Comparative Example 3 is that zinc oxide particles cannot provide a large amount of charges and have weak charge storage ability. The high dielectric constant and surface potential of the fibers exhibit excellent electroactivity, significantly enhancing their electrostatic trapping effect, thus bringing excellent air purification ability. The fibers prepared in Example 4 with the highest surface potential have the best filtration and catalytic effects. Their filtration efficiencies for PM 0.3 and PM 2.5 reach 99.95% and 99.97% respectively, which are much higher than those of Comparative Examples 1–3 with lower surface potentials (the filtration efficiencies for PM 0.3 and PM 2.5 are both < 90%). Meanwhile, according to the catalytic efficiencies of each sample for NO, NO 2 and SO 2 gases in Table 2, the catalytic efficiencies of the fibers in Example 4 for NO, NO 2 and SO 2 gases reach 99.73%, 99.58% and 99.61% respectively, which are much higher than those of Comparative Examples 1–3 with lower surface potentials (the catalytic efficiencies for NO, NO 2 and SO2 The catalytic efficiencies are all < 80%).

[0109] Figure 4 It shows the catalytic efficiencies of Examples 1 - 4 for SO 2 gas at different temperatures. Above 70 °C, the catalytic efficiency of Example 4 for SO 2 gas almost reaches 100%.

[0110] In addition, further exploration reveals that during the filtration experiment of directly MOF - modified polymer fibers, their surface potential increases compared to the initial state. The surface potential of the fibers in Examples 1 - 4 increases significantly (12.51 kV - 20.35 kV). This is mainly because the addition of high - purity MOFs nanocrystals greatly increases the dielectric constant of the fibers. And relying on the ferroelectricity of high - purity MOFs nanocrystals, when subjected to an external force, polarization occurs to form an electric dipole moment, thus showing polarity at both ends of the fiber, generating polar charges, and thereby increasing the surface potential.

[0111] Low air resistance is crucial for polymer fibers to be used for waste gas purification. At a high gas flow rate of 85 L / min, compared with the relatively high air resistances (213 Pa - 573 Pa) in Comparative Examples 1 - 3, the air resistances of Examples 1 - 4 are significantly lower (89 Pa - 182 Pa). This is mainly because during the electrospinning process, the addition of high - purity MOFs nanocrystals brings more charges to the fiber surface, resulting in an enhanced electrostatic repulsion force and stretching effect of the electric field on the fiber and a reduction in the surface tension of the fiber, significantly promoting fiber thinning. In Example 4, due to the increase in relative humidity during electrospray in the spinning process, the time of the charged jet is extended, thus the diameter of the fiber is thinned. At the same time, the conductivity of the electrosprayed MOF nanocrystal dispersion is enhanced. This change leads to an increase in the electrostatic repulsion force within the electric field, thereby resulting in significant thinning of the PLA fibers.

[0112] In summary, the high-purity MOFs nanocrystals prepared by the technical solution proposed in the present invention form a uniform MOFs dispersion with a dispersant and a solvent, and the polymer matrix and the solvent are mixed to form a polymer solution, so that the electrospinning technology can be used to make directly MOF-functionalized polymer fibers. The fibers have high surface potential, high mechanical properties, low air resistance, high filtration and catalytic properties. These are due to: (1) The microwave-assisted synthesis method has the characteristics of high efficiency and low energy consumption, greatly shortening the reaction time, and the obtained MOFs nanoparticles have the characteristics of high yield, high purity and structural integrity; (2) The addition of the dispersant effectively solves the problem that high-purity MOFs nanocrystals are prone to agglomeration, and can greatly improve the structural characteristics of the polymer fibers; (3) The directional anchoring of high-purity MOFs nanocrystals significantly improves the piezoelectric properties of directly MOF-functionalized polymer fibers, and the multi-level structural characteristics enable the dipole polarization generated by the rearrangement of dipoles in the directly MOF-functionalized polymer fibers when the exhaust gas in the factory or daily life is discharged to attract the generation of charges on the electrodes, so that a potential difference is generated between the charges aggregated on the fiber membrane, improving the surface potential, thereby achieving a better electrostatic adsorption effect on ultrafine particles in the air and greatly improving the filtration efficiency of the fibers. Due to the high porosity and large specific surface area of MOFs, MOFs also show very excellent effects in the photocatalysis of toxic gases. The directly MOF-functionalized polymer fibers with ultra-high air purification efficiency have good application prospects in the field of waste gas purification.

[0113] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a direct MOF polymer fiber, characterized in that: The following steps are involved: After the organic ligand, metal salt, growth regulator and organic solvent are uniformly mixed, MOFs nanocrystals are obtained by microwave heating reaction; Uniformly dispersing the MOFs nanocrystals in a dispersant solution to obtain a MOFs dispersion; The MOFs dispersion is used to modify the polymer fiber during / after the preparation to obtain the direct MOF-modified polymer fiber.

2. The method for preparing direct MOF polymer fiber according to claim 1, characterized in that: The organic ligand is terephthalic acid or 2-methylimidazole; the metal salt is zinc acetate, silver nitrate or ferric chloride; the growth regulator is hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, carboxymethyl cellulose or dopamine hydrochloride; the molar ratio of the organic ligand, the metal salt and the growth regulator is 1-5:4-10:

1.

3. The method for preparing direct MOF polymer fiber according to claim 1, characterized in that: The organic solvent is N,N-dimethylformamide, dichloromethane or chloroform.

4. The method for preparing direct MOF polymer fiber according to claim 1, characterized in that: The parameters of the microwave heating reaction are set as: temperature 80-180° C., power 300-1000 W, and time 10-120 min.

5. The method for preparing direct MOF polymer fiber according to claim 1, characterized in that: The solute in the dispersant solution is hexadecyltrimethylammonium bromide, carboxymethyl cellulose or dopamine hydrochloride; and the concentration of MOFs nanocrystals in the dispersion is 1% to 20%.

6. The method for preparing direct MOF polymer fiber according to claim 1, characterized in that: The MOFs dispersion is used to modify the polymer fiber during / after preparation, including the following three methods: Method 1. When the preparation method of the polymer fiber is a melt spinning method: preparing the polymer fiber by melt spinning the polymer, and then coating the MOFs dispersion on the surface of the polymer fiber; Method 2: When the preparation method of the polymer fiber is coaxial electrospinning or centrifugal electrospinning: after the polymer is prepared into a polymer solution, the polymer solution is uniformly mixed with the MOFs dispersion, and then coaxial electrospinning or centrifugal electrospinning is performed; Method 3: When the preparation method of the polymer fiber is the electrospinning-spraying method: the polymer is formulated into a polymer solution, and then electrospinning-spraying is performed with the MOFs dispersion.

7. The method for preparing direct MOF polymer fiber according to claim 6, characterized in that: The polymer is polyvinylidene fluoride, polyimide, polyphenylene sulfide, polypropylene, polylactic acid or polyethylene terephthalate; the mass fraction of the polymer in the polymer solution is 2wt% to 30wt%.

8. The method for preparing direct MOF polymer fiber according to claim 6, characterized in that: The mass ratio of the MOFs nanocrystals to the polymer in the MOFs dispersion is 1:1 to 1:

100.

9. A directly MOF-modified polymer fiber prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the direct MOF polymer fiber according to claim 9 in filtering PMs in the air or catalytically degrading harmful gases in the air.

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