CN108816064A - A kind of preparation method of the chitosan nano fiber membrane of growth in situ metal-organic framework material - Google Patents

Abstract

The invention belongs to the technical field of polymer composite material preparation, and specifically relates to a preparation method of a chitosan nanofiber film grown in-situ as a metal-organic framework material. Chitosan nanofiber membrane is obtained by electrospinning chitosan; then it is chelated with metal nodes in MOFs material in an acidic environment; after chelation, ligands are added to grow in situ on the surface of chitosan fibers MOFs material, obtained in situ growth MOFs material chitosan nanofiber membrane. The invention not only solves the problem that the composite of MOFs material and chitosan is difficult to uniformly disperse, but also improves the bonding strength of the two, and avoids the falling off of the MOFs material. The composite material has the advantages of simple preparation process, high adsorption efficiency, uniform surface and good stability, and can be applied to the adsorption of various dyes. At the same time, it also has potential application value in gas filtration, organic solvent separation and water treatment.

Description

Preparation of Chitosan Nanofibrous Membranes of Metal-Organic Frameworks Grown in Situ method

technical field

The invention belongs to the technical field of polymer composite material preparation, and specifically relates to a preparation method of a chitosan nanofiber film grown in-situ as a metal-organic framework material.

Background technique

Metal-organic frameworks (MOFs) materials are a class of materials with shapes and structures that only allow specific molecules to enter the pores. Due to the obvious directionality of the arrangement of organic ligands and metal ions or clusters, different framework pore structures can be formed. Depending on the selected organic ligands or metal ions, the crystal structure of MOFs materials is also different. Usually transition metal ions are used as nodes, such as Zn, Cu, Ni, Co, etc., combined with multifunctional organic ligands to prepare (Nature, 2015, 520:148-150).

MOFs materials are solid powders with low mechanical strength, and usually need to be combined with other materials that are easy to process and shape to prepare composite materials (Advanced Engineering Materials, 2008, 10(12):1151-1155). Among them, patent CN 107051398A discloses a method of growing MOFs on silk protein in situ, and prepares a film material with high filtration efficiency, high load capacity and good stability; A method for in situ growth of MOFs on the surface of silk fibers. In addition, in situ growth of MOFs on carboxycellulose (Cellulose, 2012, 19(5): 1771-1779) and carboxymethylcellulose (Nanoscale, 2017, 9(35): 12850-12854) has been reported.

Chitosan (Chitosan, CS) is an alkaline polysaccharide obtained by deacetylating chitin, and it is also the only naturally occurring cationic polymer in nature. In recent years, it has been recognized as a green material with great development potential in the future. However, it is only widely used in the fields of tissue engineering and drug delivery (Nanoscale, 2017, 9(12): 4154-4161).

Although the in situ compounding of MOFs with cellulose, alginic acid and other natural polymers of silk protein has been studied, the in situ growth mechanism of MOFs is the negative charge of the carboxyl group on the surface of the natural polymer and the positive charge on the surface of the metal ion. The charge produces a certain electrostatic attraction, which in turn promotes the initial coordination between the polymer and the metal ion, making the metal ion form a crystal nucleus on the surface of the cellulose, and the introduction of the ligand promotes the growth of the crystal. However, the in situ growth of MOFs on the surface of chitosan to prepare composite materials has not been reported.

Contents of the invention

The object of the present invention is to provide a preparation method of a chitosan nanofiber membrane of a metal organic framework material grown in situ.

In order to achieve the above object, the technical solution adopted by the present invention is:

A preparation method of chitosan nanofibrous membrane of in-situ growth metal-organic framework (MOFs): chitosan is electrospun to obtain chitosan nanofiber membrane; The metal node chelation; after chelation, ligands are added to grow MOFs materials in situ on the surface of chitosan fibers to obtain in situ growth MOFs material chitosan nanofiber membranes.

Furthermore, the chitosan nanofiber membrane and the metal salt are added to the organic solvent, and a concentrated acid solution is added to the system; then stirred at a rate of 100r/min-300r/min for 0.5h-3.5h , and then stand still for 1h-3h; after standing for precipitation, wash with organic solvent for 3-5 times, add to alkaline solution after washing, add ligand and stir evenly, wash with organic solvent, and dry to get the shell of MOFs grown on the surface Polysaccharide nanofiber membranes.

The metal salt refers to one or more of the water-soluble salts with main group elements, transition elements or lanthanides as metal cations; its consumption is 1-10 times of the chitosan fiber membrane quality, and the The ligand refers to one or more of the carboxyl-containing organic anion ligands containing oxygen or nitrogen, or used together with the nitrogen-containing heterocyclic organic neutral ligand, and the amount of the ligand added is 1% of the mass of the chitosan fiber membrane. -20 times,

Preferably, the amount of the metal salt is 3-5 times the mass of the chitosan fiber membrane, and the preferred addition of the ligand is 2-10 times the mass of the chitosan fiber membrane.

Preferably, the metal salt is zinc nitrate, cobalt chloride, copper acetate, chromium nitrate, zirconium tetrachloride or nickel chloride; the ligand is 2-methylimidazole, trimesic acid, terephthalic acid, 2 - aminoterephthalic acid or terephthalic acid.

At the same time, the amount relationship between the metal salt and the ligand when forming the MOFs material can be carried out and formulated according to the existing preparation method.

Described organic solvent refers to absolute methanol and/or absolute ethanol; The volume mass (mL/g) ratio of organic solvent and chitosan fiber film is 200-1000: 1, is preferably 300-700: 1; The organic solvent used for washing is absolute methanol and/or absolute ethanol;

Described alkali solution is the ammonia solution that concentration is 0.05mol/L-0.3mol/L; The volume mass (mL/g) ratio of ammonia solution and chitosan fiber membrane is 100-2000: 1, is preferably 500-1000: 1.

After the ligand is added, the system is stirred for 0.5h-5h at a rotational speed of 100-300r/min, then washed with an organic solvent for 3-5 times and then dried. The drying condition is 30°C-50°C, 5min-30min.

The chitosan nanofiber is a fiber with a diameter of less than 200nm obtained by electrospinning chitosan as a raw material. Among them, the electrospinning method _{, for example, wet spinning, dry spinning, etc.}

The chitosan nanofibers are prepared by electrospinning with chitosan as a raw material. Chitosan and polyethylene oxide are slowly added to a concentrated acid solution and mixed, and then water is added to obtain a uniform and viscous shell. The solution of polysaccharide to be spun is then subjected to electrospinning after ultrasonic treatment, and chitosan fibers are obtained after peeling off; wherein, the final concentration (mass concentration) of the acid solution is 1%-10%, and chitosan accounts for 1% of the acid solution quality. 0.5%-5%, polyethylene oxide accounts for 0.1%-10% of the acid solution mass.

The preferred final concentration (mass concentration) of the acid solution is 3%-5%, chitosan accounts for 1%-3% of the mass of the acid solution, and polyethylene oxide accounts for 0.1%-1% of the mass of the acid solution.

After ultrasonicating the solution, extract the solution with a syringe for electrospinning, using tin foil as the receiving plate, the spinning conditions are: positive pressure 2.0KV-13.0KV, negative pressure -5.0KV-10.0KV, injection speed 0.02 mm/min-0.15mm/min, the translational speed is 100mm/min-500mm/min, and the rotational speed of the receiving drum is 5r/min-30r/min.

The preparation of the chitosan nanofibrous membrane of MOFs grown in situ of the present invention has the following advantages:

(1) Under acidic conditions, the amino groups on the molecular chain have a good chelation effect on metal ions in MOFs, thereby providing suitable and uniform nucleation sites for MOFs crystals, and then adjusting the system to Alkaline, metal ions react with ligands to obtain MOFs, and then grow uniformly on the surface of chitosan nanofiber membrane. This effectively solves the problem that MOFs are difficult to grow in situ on the surface of chitosan, and avoids the technical problems of poor dispersion of MOFs, low loading rate and poor binding fastness of MOFs caused by blending MOFs and chitosan.

(2) compared with chitosan, the chitosan nanofibers adopted by the present invention have larger specific surface area and porous structure, which can effectively promote the chelation between its surface amino groups and metal ions, and its pore structure can be changed by changing The preparation process is adjusted, and MOFs particles have a mesoporous or microporous structure, and MOFs with different pore sizes can also be screened according to different uses. This adjustable hierarchical porous structure is conducive to the adsorption or filtration of MOFs-chitosan composites. application and improve efficiency.

(3) The method used in the present invention is simple and easy to implement, and is easy to produce on a large scale.

Description of drawings

Fig. 1 is a flowchart of preparation of chitosan fiber membranes for in-situ growth of MOFs provided by an example of the present invention.

Fig. 2 is the SEM image of the chitosan nanofiber membrane prepared in Example 1 of the present invention.

Fig. 3 is the actual picture of the ZIF-8@chitosan fiber membrane prepared in Example 1 of the present invention.

Fig. 4 is the SEM image of the ZIF-8@chitosan fiber membrane prepared in Example 1 of the present invention.

Fig. 5 is the absorbance curve of the ZIF-8@chitosan fiber membrane prepared in Example 1 of the present invention.

Fig. 6 is the variation of rhodamine b solution color (left: 0.1% rhodamine b solution, right: rhodamine b solution after composite membrane adsorption 24h) after ZIF-8@chitosan fiber film adsorption prepared by Example 1 of the present invention ).

Fig. 7 is the absorbance curve of the ZIF-67@chitosan fiber membrane prepared in Example 2 of the present invention.

Detailed ways

The feasibility of the method is further described below through specific implementation examples, but it does not mean that the present invention is limited to these examples.

The present invention uses chitosan nanofiber membrane as raw material, and there is no carboxyl group in chitosan molecular structure, although the amino group in chitosan molecule also can produce certain chelating action to metal ion under acidic conditions, but the introduction of ligand Finally, metal ions and ligands need to be under alkaline conditions to form MOFs crystals; and then MOFs are loaded on the surface of chitosan fiber membrane by in situ growth method, and a uniform porous chitosan fiber membrane material is prepared. Under the premise of not affecting the properties of chitosan fibers, it enables MOFs materials to be firmly combined with chitosan fiber membranes, and solves the problem that MOFs are easy to aggregate in polymers. In addition, MOFs loaded on the chitosan nanofiber membrane to form an adjustable porous structure has a large specific surface area, which is expected to be used as an adsorption or filter material in the fields of separation and gas storage.

The invention not only solves the problem that the composite of MOFs material and chitosan is difficult to uniformly disperse, but also improves the bonding strength of the two, and avoids the falling off of the MOFs material. The composite material has the advantages of simple preparation process, high adsorption efficiency, uniform surface and good stability, and can be applied to the adsorption of various dyes. At the same time, it also has potential application value in gas filtration, organic solvent separation and water treatment.

Example 1

Preparation of ZIF-8@chitosan nanofibrous membrane by in situ growth method

1) Preparation of chitosan nanofibers: Slowly add chitosan and polyethylene oxide respectively in glacial acetic acid to obtain a mixed solution, wherein the final concentration (mass concentration) of the glacial acetic acid solution in the mixed solution is 3%, and the chitosan Accounting for 1% of the mass of the acid solution, polyethylene oxide accounts for 0.1% of the mass of the acid solution; after adding, turn on the magnetic stirrer at a speed of 500r/min, and stir for 30 minutes to completely dissolve the solid; after dissolution, ultrasonicate the solution at 300W for 10 minutes Finally, use a 5mL syringe to extract the solution for electrospinning, using tin foil as the receiving plate, the spinning conditions are: positive pressure 2.0KV, negative pressure -10.0KV, injection speed 0.02mm/min, translation speed 100mm /min, the rotating speed of receiving drum is 5r/min; After spinning finishes, tinfoil is taken off, is cut into the fritter of 2cm * 2cm, and chitosan fiber film is peeled off from tinfoil (referring to Fig. 2);

2) Preparation of Zn-chitosan nanofiber membrane: take chitosan nanofiber membrane and zinc nitrate and add them to methanol, then add 1 g of glacial acetic acid dropwise. Among them, the dosage of zinc nitrate is 3 times of the mass of chitosan fiber membrane, that is, 0.15 g; the volume mass (mL/g) ratio of methanol to chitosan fiber membrane is 300:1. The system was stirred at a speed of 100r/min for 0.5h, and after standing for 1h, it was washed 3 times with methanol to remove unchelated Zn ^ions on the fiber surface to obtain a Zn-chitosan nanofiber membrane;

3) Add the Zn-chitosan nanofiber membrane to ammonia water (the concentration of ammonia water is 0.05mol/L, and the volume mass (mL/g) ratio of it to the chitosan fiber membrane is 500:1), and then add 2-formazan imidazole (2-methylimidazole 0.1g, the dosage is 2 times the mass of the chitosan fiber membrane), the system was stirred at 100r/min for 0.5h; then washed with methanol for 3 times, then air-dried at 30°C After 5 minutes, the chitosan nanofiber membrane with ZIF-8 grown on the surface can be obtained. After testing, the loading of ZIF-8 in the ZIF-8@chitosan nanofiber membrane is relatively high (8.3%). It can be seen from the SEM images that the crystal structure formed by ZIF-8 in chitosan fibers is regular and uniformly dispersed. (See Figures 3 and 4).

Verification 1

Adsorption of rhodamine b by ZIF-8@chitosan fiber composite membrane

Weigh 0.05g ZIF-8@chitosan fiber composite membrane, 0.05g chitosan nanofiber membrane and 1mg ZIF-8 prepared in Example 1, respectively place them in 0.1% rhodamine b-ethanol solution, and seal. After 24 hours of adsorption, 200 μL of the supernatant was added to a cuvette, and the absorbance value at 554 nm was measured by a UV-visible spectrophotometer (Figure 5), and then the concentration of rhodamine b after adsorption was calculated. Figure 6 is the color change of rhodamine b solution before and after adsorption. After testing, after adsorption of chitosan nanofiber membrane, ZIF-8 and ZIF-8@chitosan fiber membrane, the concentration of rhodamine b solution decreased from 0.1% to 0.08%, 0.004% and 0.008%, respectively. The ratios were 20%, 96%, and 92%, respectively, that is, the chitosan nanofibrous membrane significantly improved the adsorption capacity of rhodamine b after growing MOFs in situ.

Example 2

Preparation of ZIF-67@chitosan nanofiber membrane by in situ growth method

1) Preparation of chitosan nanofibers: Slowly add chitosan and polyoxyethylene respectively in glacial acetic acid to obtain a mixed solution, wherein the final concentration (mass concentration) of the glacial acetic acid solution in the mixed solution is 5%, and the chitosan It accounts for 3% of the mass of the acid solution, and polyethylene oxide accounts for 1% of the mass of the acid solution. After mixing, turn on the magnetic stirrer with a rotation speed of 700r/min. After stirring for 30 minutes, the solids are completely dissolved; after dissolution, the solution is ultrasonicated for 30 minutes at a strength of 1500W, and the solution is extracted with a 5mL syringe for electrospinning, and tin foil is used as a receiving plate. The spinning conditions are as follows: positive pressure is 5.0KV, negative pressure is -6.0KV, injection speed is 0.15mm/min, translational speed is 500mm/min, and the rotating speed of the receiving drum is 30r/min; Take it off, cut it into small pieces of 2cm×2cm, and peel off the chitosan fiber membrane from the tin foil;

2) Preparation of Co-chitosan nanofiber membrane: 0.5 g of chitosan nanofiber membrane and cobalt chloride were added to absolute ethanol, and then 0.05 g of glacial acetic acid was added dropwise. Wherein, the dosage of cobalt chloride is 10 times of the mass of chitosan fiber membrane, and the volume mass (mL/g) ratio of absolute ethanol to chitosan fiber membrane is 700:1. The system was stirred for 3 hours at a speed of 300 r/min, and after standing for 3 hours, it was washed 5 times with absolute ethanol to remove unchelated Co ^ions on the surface of the fiber membrane to obtain a Co-chitosan nanofiber membrane;

3) Add the Co-chitosan nanofiber membrane to ammonia water (the concentration of ammonia water is 0.3mol/L, and the volume mass (mL/g) ratio of the chitosan fiber membrane is 1000:1), and then add 2-formazan imidazole (2-methylimidazole dosage is 0.5g, which is 10 times the mass of chitosan fiber membrane), the system was stirred at 300r/min for 5h; Blast drying for 30 minutes, the ZIF-67@chitosan nanofiber membrane with ZIF-67 loading of 5.9% can be obtained.

Verification 2

ZIF-67@chitosan fiber membrane for adsorption of malachite green

Weigh 0.05g ZIF-67@chitosan fiber membrane, 0.05g chitosan nanofiber membrane and 1mg ZIF-8 prepared in Example 2, respectively place them in 1% malachite green aqueous solution, and seal. Stir slowly, and after 24 hours of adsorption, take 200 μL of the supernatant and add it to a cuvette, and measure its absorbance at 616.9 nm by using a UV-visible spectrophotometer (Figure 7), and then calculate the malachite after adsorption. Concentration of green. After testing, after ZIF-67@chitosan fiber membrane is adsorbed, the concentration of malachite green solution drops from 1% to 0.12%, and the removal efficiency is 88%, which can be completely removed by secondary adsorption. Since malachite green is a toxic triphenylmethane chemical, which has the disadvantages of high toxicity and high residue, and ZIF-67@chitosan fiber membrane has a better adsorption effect on such dyes, therefore, ZIF-67@chitosan Sugar fiber membrane has a great application prospect in the water treatment industry.

Example 3

Preparation of HKUST-1@chitosan nanofiber membrane by in situ growth method

1) Preparation of chitosan nanofibers: chitosan and polyoxyethylene were slowly added respectively in glacial acetic acid to obtain a mixed solution, wherein the final concentration (mass concentration) of glacial acetic acid in the mixed solution was 4.5%, and chitosan accounted for 1.5% of the mass of the acid solution, polyethylene oxide accounts for 0.7% of the mass of the acid solution. After mixing, turn on the magnetic stirrer with a rotation speed of 500r/min. After stirring for 30min, the solids are completely dissolved; after the solution is ultrasonicated for 30min at a strength of 700W, the solution is extracted with a 5mL syringe for electrospinning, using tin foil as a receiving plate, and spinning The conditions are: the positive pressure is 3.0KV, the negative pressure is -9.0KV, the injection speed is 0.10mm/min, the translational speed is 400mm/min, the speed of the receiving drum is 10r/min; after the spinning is finished, remove the tin foil , cut into small pieces of 2cm×2cm, and peel off the chitosan fiber membrane from the tin foil;

2) Preparation of Cu-chitosan nanofiber membrane: 0.4 g of chitosan nanofiber membrane and anhydrous copper acetate were added to absolute ethanol, and then 1 g of glacial acetic acid was added dropwise. Among them, the dosage of anhydrous copper acetate is 8 times of the mass of chitosan fiber membrane, and the volume mass (mL/g) ratio of absolute ethanol to chitosan fiber membrane is 500:1. The system was stirred at a speed of 500r/min for 2.5h, and after standing for 2h, it was washed 5 times with methanol to remove unchelated Cu ²⁺ ions on the fiber surface to obtain a Cu-chitosan nanofiber membrane;

3) Add the Cu-chitosan nanofiber membrane to ammonia water (the concentration of ammonia water is 0.11mol/L, and the volume mass (mL/g) ratio of it to chitosan fiber membrane is 700:1), and then add trimesis acid (the amount of trimesic acid is 0.2g, which is 4 times the mass of the chitosan fiber membrane); the system was stirred at 200r/min for 2h; after washing with methanol for 5 times, it was air-dried at 40°C for 10min , the HKUST-1@chitosan nanofiber membrane with a loading of 6.2% can be obtained.

The HKUST-1@chitosan nanofiber membrane obtained above was adsorbed on Sudan Red (initial concentration 2%), and the removal efficiency of Sudan Red after adsorption by HKUST-1@chitosan nanofiber membrane was 74%. Secondary adsorption can be completely removed.

Example 4

Preparation of MIL-101(Cr)@chitosan nanofiber membrane by in situ growth method

1) Preparation of chitosan nanofibers: Slowly add chitosan and polyoxyethylene respectively in glacial acetic acid to obtain a mixed solution, wherein the final concentration (mass concentration) of the glacial acetic acid solution in the mixed solution is 4%, and the chitosan Accounting for 2% of the mass of the acid solution, polyethylene oxide accounts for 0.5% of the mass of the acid solution. Turn on the magnetic stirrer with a rotation speed of 400r/min. After stirring for 30min, the solids are completely dissolved; after ultrasonicating the solution for 30min at a strength of 700W, extract the solution with a 5mL syringe for electrospinning, using tin foil as the receiving plate, and the spinning conditions are: : The positive pressure is 10.0KV, the negative pressure is -8.0KV, the injection speed is 0.08mm/min, the translational speed is 400mm/min, and the rotating speed of the receiving drum is 25r/min; into small pieces of 2cm × 2cm, and the chitosan fiber membrane is peeled off from the tin foil;

2) Preparation of Cr-chitosan nanofiber membrane: take chitosan nanofiber membrane and 0.25 g of chromium nitrate and add them to methanol, then add 1 g of glacial acetic acid dropwise. Among them, the dosage of chromium nitrate is 5 times of the mass of chitosan fiber membrane, and the volume mass (mL/g) ratio of methanol to chitosan fiber membrane is 600:1. The system was stirred at a speed of 200r/min for 1.5h, and after standing for 1h, it was washed 3 times with methanol to remove unchelated Cr ^ions on the surface of the fiber membrane to obtain a Cr-chitosan nanofiber membrane;

3) Add the Cr-chitosan nanofiber membrane to ammonia water (the concentration of ammonia water is 0.05mol/L, and the volume mass (mL/g) ratio of the chitosan fiber membrane is 1000:1), and then add terephthalic acid (0.4g of terephthalic acid), its consumption is 8 times of chitosan fiber film quality, this system is stirred 1.5h under 100r/min; After washing 5 times with methanol, blow dry 10min at 30 ℃ , the chitosan nanofiber membrane with MIL-101(Cr) grown on the surface can be obtained.

The MIL-101(Cr)@chitosan nanofiber membrane with a load of 8.9% obtained above was adsorbed on methylene blue (initial concentration 1%), and after being adsorbed by MIL-101(Cr)@chitosan nanofiber membrane The removal efficiency of methylene blue was 90.1%.

Example 5

Preparation of UiO-66-NH ₂ @chitosan nanofibrous membrane by in situ growth method

1) Preparation of chitosan nanofibers: Slowly add chitosan and polyoxyethylene respectively in glacial acetic acid to obtain a mixed solution, wherein the final concentration (mass concentration) of the glacial acetic acid solution in the mixed solution is 3.5%, and the chitosan Accounting for 1.5% of the mass of the acid solution, polyethylene oxide accounts for 0.9% of the mass of the acid solution. Turn on the magnetic stirrer with a rotation speed of 700r/min. After stirring for 30min, the solids are completely dissolved; after ultrasonicating the solution for 30min at a strength of 700W, extract the solution with a 5mL syringe for electrospinning, using tin foil as the receiving plate, and the spinning conditions are: : The positive pressure is 10.0KV, the negative pressure is -8.0KV, the injection speed is 0.08mm/min, the translational speed is 400mm/min, and the rotating speed of the receiving drum is 15r/min; into small pieces of 2cm × 2cm, and the chitosan fiber membrane is peeled off from the tin foil;

2) Preparation of Zr-chitosan nanofiber membrane: take chitosan nanofiber membrane and 0.3 g of zirconium tetrachloride and add them to methanol, then add 1 g of glacial acetic acid dropwise. Among them, the dosage of zirconium tetrachloride is 6 times of the mass of chitosan fiber membrane, and the ratio of methanol to chitosan fiber membrane volume mass (mL/g) is 550:1. Stir at 300r/min speed for 3h, after standing for 3h, wash 5 times with dehydrated alcohol, remove the ^unchelated Zr ions on the fiber membrane surface, obtain Zr-chitosan nanofibrous membrane;

3) Add the Zr-chitosan nanofiber membrane to ammonia water (the concentration of ammonia water is 0.3mol/L, and the volume mass (mL/g) ratio of the chitosan fiber membrane is 900:1), and then add 2-amino p- 0.35g of phthalic acid, the amount of which is 7 times the quality of the chitosan fiber membrane, the system was stirred at 300r/min for 3h; then washed with absolute ethanol for 5 times, and then air-dried at 50°C for 30min. A chitosan nanofibrous membrane (loaded at 7.8%) with UiO-66-NH ₂ grown on the surface was obtained. It has been verified that the removal efficiency of the UiO-66-NH ₂ -chitosan nanofiber membrane for methylene orange (initial concentration 1.5%) is 82%, and can be completely removed by secondary adsorption.

Example 6

Preparation of MOFs-74(Ni)@chitosan nanofibrous membrane by in situ growth method

1) Preparation of chitosan nanofibers: Slowly add chitosan and polyoxyethylene respectively in glacial acetic acid to obtain a mixed solution, wherein the final concentration (mass concentration) of the glacial acetic acid solution in the mixed solution is 10%, and the chitosan It accounts for 5% of the mass of the acid solution, and polyethylene oxide accounts for 10% of the mass of the acid solution. Turn on the magnetic stirrer at a speed of 550r/min, and stir for 30 minutes to dissolve the solid completely; after ultrasonicating the solution for 30 minutes at a strength of 700W, use a 5mL syringe to extract the solution for electrospinning, using tin foil as the receiving plate, and the spinning conditions are: : The positive pressure is 13.0KV, the negative pressure is -10.0KV, the injection speed is 0.15mm/min, the translation speed is 500mm/min, and the rotating speed of the receiving drum is 5r/min; after spinning, remove the tin foil, cut into small pieces of 2cm × 2cm, and the chitosan fiber membrane is peeled off from the tin foil;

2) Preparation of MOFs-74(Ni)-chitosan nanofiber membrane: take chitosan nanofiber membrane and nickel chloride 0.5 g and add them to absolute ethanol, then add 1 g of glacial acetic acid dropwise. Wherein, the dosage of nickel chloride is 10 times of the mass of chitosan fiber membrane, and the volume mass (mL/g) ratio of absolute ethanol to chitosan fiber membrane is 1000:1. The system was stirred at a speed of 100r/min for 0.5h, and after standing for 1h, it was washed 3 times with methanol to remove unchelated Ni ²⁺ ions on the fiber surface to obtain a Ni-chitosan nanofiber membrane;

3) Add the Ni-chitosan nanofiber membrane to ammonia water (the concentration of ammonia water is 0.05mol/L, and the volume mass (mL/g) ratio of the chitosan fiber membrane is 2000:1), and then add terephthalic acid 1g, the amount of which is 20 times the mass of chitosan fiber membrane, the system was stirred at 100r/min for 1h; then washed with methanol for 3 times, and air-dried at 30°C for 5min to obtain surface-grown MOFs-74 (Ni) chitosan nanofiber membrane (2.9% loading).

The MOFs-74(Ni)@chitosan nanofiber membrane obtained above was adsorbed on rhodamine b (initial concentration 1.2%), and the removal efficiency after membrane adsorption was 32.4%.

Based on the above examples, the present invention obtains chitosan nanofiber membranes based on electrospinning, and successfully prepares MOFs@chitosan nanofiber membranes by using the in-situ growth method. Examples have proved that the membranes are effective against dyes in water or organic solvents. Better adsorption, the adsorption capacity is equivalent to that of MOFs materials, and the removal rate can reach up to 92%. Therefore, the membrane has broad application prospects in dye wastewater treatment.

Claims (9)

1. a kind of preparation method of the chitosan nanofiber membrane of metal-organic framework material (MOFs) in situ growth, it is characterized in that: chitosan is obtained chitosan nanofiber membrane by electrospinning; Chelate with the metal nodes in the MOFs material under the environment; add the ligand after chelation, grow the MOFs material in situ on the surface of the chitosan fiber, and obtain the in situ growth MOFs material chitosan nanofiber membrane. 2. by the preparation method of the chitosan nanofiber membrane of in-situ growth metal organic framework material (MOFs) described in claim 1, it is characterized in that: chitosan nanofiber membrane and metal salt are added in the organic solvent, And add a concentrated acid solution into the system; then stir for 0.5h-3.5h at a rate of 100r/min-300r/min, then stand still for 1h-3h; wash with an organic solvent for 3-5 times after standing for precipitation, After washing, adding to the alkali solution, adding the ligand and stirring evenly, washing with an organic solvent, and drying to obtain the chitosan nanofiber membrane with MOFs grown on the surface. 3. by the preparation method of the chitosan nanofiber membrane of the in-situ growth metal-organic framework material (MOFs) described in claim 1 and 2, it is characterized in that: described metal salt refers to with main group element, transition element or The lanthanide is one or more of the water-soluble salts of metal cations; its dosage is 1-10 times the quality of the chitosan fiber membrane: The ligand refers to one or more of the carboxyl-containing organic anion ligands containing oxygen or nitrogen, or used together with the nitrogen-containing heterocyclic organic neutral ligand, and the amount of the ligand added is the mass of the chitosan fiber membrane 1-20 times. 4. by the preparation method of the chitosan nanofiber membrane of in-situ growth metal organic framework material (MOFs) described in claim 3, it is characterized in that: described metal salt is zinc nitrate, cobalt chloride, copper acetate, nitric acid Chromium, zirconium tetrachloride or nickel chloride; the ligand is 2-methylimidazole, trimesic acid, terephthalic acid, 2-aminoterephthalic acid or terephthalic acid. 5. by the preparation method of the chitosan nanofiber film of in-situ growth metal organic framework material (MOFs) according to claim 2, it is characterized in that: described organic solvent refers to absolute methanol and/or dehydrated alcohol, The volume mass ratio of the organic solvent to the chitosan fiber membrane is 200-1000:1; the alkali solution is an ammonia solution with a concentration of 0.05mol/L-0.3mol/L; the volume mass of the ammonia solution and the chitosan fiber membrane The ratio is 100-2000:1. 6. by the preparation method of the chitosan nanofiber membrane of the in-situ growth metal-organic framework material (MOFs) described in claim 1 and 2, it is characterized in that: the system is 100-300r/ at the rotating speed after the described adding part Stir for 0.5h-5h under the condition of min, then wash with organic solvent for 3-5 times and then dry, the drying condition is 30°C-50°C, 5min-30min. 7. by the preparation method of the chitosan nanofiber membrane of the in-situ growth metal organic framework material (MOFs) described in claim 1 or 2, it is characterized in that: described chitosan nanofiber is to be raw material with chitosan Fibers with a diameter less than 200nm obtained by electrospinning. 8. by the preparation method of the chitosan nanofiber membrane of in-situ growth metal organic framework material (MOFs) described in claim 7, it is characterized in that: described chitosan nanofiber is to take chitosan as raw material by static electricity Prepared by spinning, chitosan and polyethylene oxide are slowly added to the concentrated acid solution and mixed, then water is added to obtain a uniform and viscous chitosan solution to be spun, and then electrostatic spinning is carried out after ultrasonic treatment to peel off After that, chitosan fibers are obtained; wherein, the final concentration of the acid solution is 1%-10%, chitosan accounts for 0.5%-5% of the mass of the acid solution, and polyethylene oxide accounts for 0.1%-10% of the mass of the acid solution. 9. by the preparation method of the chitosan nanofiber membrane of in-situ growth metal organic framework material (MOFs) described in claim 8, it is characterized in that: after solution ultrasonic, extract solution with syringe and carry out electrospinning, adopt tinfoil As a receiving plate, the spinning conditions are: positive pressure 2.0KV-13.0KV, negative pressure -5.0KV-10.0KV, injection speed 0.02mm/min-0.15mm/min, translational speed 100mm/min- 500mm/min, the speed of the receiving drum is 5r/min-30r/min.