阅读说明：本技术 一种在聚丙烯熔喷布纤维表面原位生长纳米级金属有机框架zif-8的方法 (Method for in-situ growth of nanoscale metal organic framework ZIF-8 on surface of polypropylene melt-blown fabric fiber ) 是由 徐志伟 成颖 李秋昱 王维 邵瑞琪 裴晓园 刘胜凯 荆妙蕾 邓辉 于 2021-10-20 设计创作，主要内容包括：本发明属于纤维复合膜制备方法领域,公开了一种在惰性的聚丙烯熔喷布纤维表面原位生长纳米级(＜100nm)的ZIF-8晶体的制备方法。本发明首先用聚丙烯酰胺改性聚丙烯纤维,使其带有活性基团,再调节ZIF-8的金属及其有机配体的比例进而控制晶体的尺寸,通过原位生长的方法将纳米级的ZIF-8晶体均匀地生长在聚丙烯纤维表面。由于纳米级ZIF-8晶体具有较大比表面积和较高孔隙率以及丰富的活性官能团,可以有助于气体流通和捕获颗粒物。超小尺寸的ZIF-8颗粒牢固地结合在纤维表面,且不会堵塞纤维之间原有的孔洞,具有较好过滤效率的同时,能极大地抑制了过滤阻力的提升,有效减小了纤维过滤膜的Trade-off效应,且该方法反应条件温和,制备过程简单,适于放大合成和实际生产应用。(The invention belongs to the field of preparation methods of fiber composite membranes, and discloses a preparation method for in-situ growth of a nano-scale (< 100nm) ZIF-8 crystal on the surface of an inert polypropylene melt-blown fabric. The invention firstly uses polyacrylamide to modify polypropylene fiber to enable the polypropylene fiber to have active groups, then adjusts the proportion of metal of ZIF-8 and organic ligand thereof to further control the size of crystal, and uniformly grows the nano-scale ZIF-8 crystal on the surface of the polypropylene fiber by an in-situ growth method. The nanoscale ZIF-8 crystal has large specific surface area, high porosity and abundant active functional groups, and can be used for facilitating gas circulation and capturing particulate matters. The ZIF-8 particles with ultra-small sizes are firmly combined on the surfaces of the fibers, original holes among the fibers cannot be blocked, the filtration efficiency is high, meanwhile, the improvement of filtration resistance can be greatly inhibited, the Trade-off effect of a fiber filtration membrane is effectively reduced, and the method is mild in reaction conditions, simple in preparation process and suitable for amplification synthesis and practical production application.)

1. A method for growing ZIF-8 on the surface of a PP fiber modified by polyacrylamide is characterized by comprising the following steps:

firstly, carrying out ultrasonic pretreatment on a polypropylene fiber film in a methanol solution to remove redundant impurities and the electret effect of the fiber film;

putting the dried polypropylene fiber membrane into a polyacrylamide solution to obtain a modified polypropylene fiber membrane;

step three, putting the treated polypropylene fiber membrane into a ZIF-8 metal precursor solution to uniformly load metal ions on the surface of the fiber;

and step four, mixing the precursor solution of the ZIF-8 organic ligand with the metal precursor solution and then reacting.

2. The method of claim 1, wherein: the methanol solution for treating the polypropylene fiber membrane in the step one is 500mL, and the ultrasonic power is 300-600W.

3. The method of claim 1, wherein: in the second step, the concentration of the polyacrylamide aqueous solution is 0.5-2%, the time is 8-12 hours, and the temperature is 25 ℃.

4. The method of claim 1, wherein: in the third step, the mol ratio of zinc nitrate hexahydrate and methanol is 1: 560, the stirring time is 30 minutes, the temperature is 25 ℃, and the standing time is 3 hours.

5. The method of claim 1, wherein: in the fourth step, the molar ratio of the dimethyl imidazole to the methanol is 6: 560-8: 560, the stirring time is 30 minutes, the temperature is 25 ℃, and the reaction time is 3-12 hours.

Technical Field

The invention belongs to the field of preparation of fiber composite membranes, and particularly relates to a preparation method for stably combining a metal organic framework and inert fibers.

Background

Currently, due to the improvement of living standard and the rapid deterioration of environmental quality, people have rapidly raised attention to air quality, and the content of PM2.5 in air becomes an important standard for judging air quality. The removal of particulate matter from the air is therefore very important to our health. Air filters have been developed rapidly to date. However, further improvements are needed in terms of high removal efficiency, low pressure drop, stability, etc.

Porous materials that can be used in air filters have rapidly developed, in particular Metal Organic Frameworks (MOFs), which are generated by coordination bonds between metals (or metal clusters) and organic species with which they are called ligands. Thus, MOFs consist of both inorganic and organic species. Importantly, the MOFs have the advantages of simple synthesis, large porosity, designable pore size, rich functional groups and the like. Ordinary polypropylene filter materials can be produced industrially, but the filtration performance thereof decreases with the decay of the charge. There is a need for functionalized polypropylene fibers that provide stable filtration properties in various complex environments, thereby protecting the user. One difficulty in using MOFs materials in combination with surface inert polypropylene (PP) fibers as air filters is: there is a need to increase the MOFs loading while keeping the PP fiber network from becoming clogged so that it still possesses good air permeability. In addition, the MOFs particles loaded on the PP fibers are easy to fall off, so that the practicability is poor. Here we can achieve the growth of ZIF-8 crystals at nanometer level (< 100nm) by modifying PP fibers with polyacrylamide and then carrying out in-situ growth, and the ZIF-8 crystals and the fibers are firmly combined together.

Based on the research, the polyacrylamide is utilized to uniformly wrap a layer of active molecular layer on the surface of the PP fiber which is originally inert, so that the ZIF-8 material and the PP fiber are tightly combined together. Therefore, the porous, multifunctional and designable performances of the ZIF-8 material can be perfectly combined with PP fibers, and the filtering performance of the material can be remarkably improved. Meanwhile, the introduced preparation method has mild conditions, short reaction time and simple steps and can be used for large-scale preparation. In the aspect of material selection, the ZIF-8 crystal with large specific surface area can be loaded on the surface of the fiber, and due to the multifunctional property of the ZIF-8, the ZIF-8 crystal can be applied to different application scenes such as air filtration, gas separation, dye adsorption and the like. In general, this is a preparation method with a wide application range.

Publication number CN106582319B discloses a method for preparing a crystal film on a non-woven fabric support for use in the field of membrane separation. The method mixes crystal seed particles, a dispersing agent and a solution of a high molecular organic material in proportion to form a high-concentration crystal suspension, and then obtains the MOFs molecular membrane through a hydrothermal reaction. Thus, the steps are complicated and poor bonding between the nonwoven fibers can occur, which can block the holes. The publication number CN104841289A discloses a method for synthesizing NaA type molecular sieve membrane on the surface of organic hollow fiber, but the molecular membrane formed by the method is too dense and the conditions of hydrothermal reaction are harsh, so the method is not suitable for textile use. The publication number CN108295672B discloses a preparation method of a metal organic framework ZIF-8 membrane, but the method is synthesized in two steps, wherein the hydrothermal reaction conditions can limit the selection range of a base material, and the synthesized ZIF-8 membrane covers the original pore channel of the non-woven fabric, so that the permeability of the non-woven fabric is lost. In order to overcome the defects of the method, the prepared PP fiber membrane can uniformly load nanoscale ZIF-8 on the surface of the fibers, cannot block the original gaps among the fibers, and has the advantages of mild conditions and wide application range. The ZIF-8 is loaded on the surface of the PP fiber, so that the fiber can be functionalized, the filtering performance is improved, and the prepared air filter is firm and stable and can be suitable for various scenes.

According to the invention, polyacrylamide is utilized to modify inert PP fibers, and nanoscale ZIF-8 crystal particles are grown in situ on the PP fibers by adjusting the proportion of a ZIF-8 metal ligand to an organic ligand, so that the composite fiber membrane which is firmly combined with the fibers and has good filtering performance is prepared.

Disclosure of Invention

The invention aims to provide a method for growing ZIF-8 on the surface of a PP fiber modified by polyacrylamide aiming at the technical analysis, and the fiber composite membrane prepared by the method can be used for air filtration, has the characteristic of firm combination of nanocrystals and fibers, is simple to prepare, and is suitable for amplification synthesis and practical production application.

The technical scheme of the invention is as follows: the method for loading the nanoscale ZIF-8 material on the surface of the polypropylene (PP) fiber is characterized by comprising the following specific steps of:

(1) and (3) carrying out ultrasonic pretreatment on the PP fiber film by using a methanol solution to remove redundant impurities and the electret effect of the PP fiber film.

(2) And putting the dried PP fiber membrane into a polyacrylamide solution to obtain the modified PP fiber membrane.

(3) And (3) putting the treated PP fiber membrane into a ZIF-8 metal precursor solution, so that metal ions are uniformly loaded on the surface of the fiber.

(4) And mixing the precursor solution of the ZIF-8 organic ligand with the metal precursor solution for reaction.

After the reaction is finished, carrying out structural characterization and air filtration performance test on the sample;

in the invention, the methanol solution for treating the PP fiber membrane is 500mL, and the ultrasonic power is 300-600W.

In the invention, the concentration of the polyacrylamide aqueous solution is 0.5-2%, the time is 8-12 hours, and the temperature is 25 ℃.

In the invention, the molar ratio of zinc nitrate hexahydrate to methanol is 1: 560, the stirring time is 30 minutes, the temperature is 25 ℃, and the mixture is kept stand for 3 hours.

In the invention, the molar ratio of the dimethyl imidazole to the methanol is 6: 560-8: 560, the stirring time is 30 minutes, the temperature is 25 ℃, and the reaction time is 3-12 hours.

The invention has the beneficial effects that: a method for growing a nano-scale (< 100nm) ZIF-8 crystal on the surface of an inert PP fiber is designed.

The method is different from the common preparation method of the fiber-loaded MOFs crystal in that the common method needs various raw materials and auxiliary agents, and has the disadvantages of complicated steps and harsh conditions. However, the preparation method designed by the invention has simple preparation process, does not need various chemical reagents, is easy to meet the reaction conditions, and the prepared nano-crystal has small grain diameter, large specific surface area and very firm combination with the fiber.

The preparation method of the ZIF-8-loaded material designed by the invention has uniform load, can be used for large-scale production, is not limited to laboratory preparation, and is beneficial to industrial large-scale production.

According to the invention, a small amount of polyacrylamide is used for modifying PP fibers with inert surfaces, and a ZIF-8 material with controllable structure and function is introduced. The method has the characteristics of mild conditions and easy operation, can greatly improve the filtering performance under extremely low filtering resistance, and has good stability. The invention is not limited by complex instruments and equipment, improves the universality to a great extent and is suitable for popularization and production.

The ZIF-8 crystal supported by the PP fiber membrane is tightly grown around the PP fiber, and compared with other methods, the ZIF-8 crystal can expose MOFs materials to a greater extent and has a larger specific surface area, so that the resistance is reduced to the greatest extent in the filtering process, and the filtering efficiency is stably improved. The fiber membrane prepared by the invention has high-efficiency filtering performance, wherein the filtering resistance is 47.5Pa, the PM2.5 filtering efficiency is 98.35 percent, and the quality factor is 0.0230. The ZIF-8 nanocrystals are stably combined with the fibers, and the ratio of the ZIF-8 nanocrystals remaining on the fibers after continuous ultrasonic treatment for 30 minutes in an ultrasonic water bath with the maximum power of 600W is 68.09%.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Drawings

FIG. 1 is a simplified schematic diagram of a process for preparing nano-sized ZIF-8 supported on the surface of a PP fiber.

FIG. 2(a) is a Scanning Electron Microscope (SEM) image of a PP fiber without loading ZIF-8;

FIG. 2(b) is a Scanning Electron Microscope (SEM) image of PP fiber modified by polyacrylamide;

FIG. 2(c) is a Scanning Electron Microscope (SEM) of a PP fiber loaded ZIF-8;

FIG. 3 is a Transmission Electron Micrograph (TEM) of the prepared nanoscale ZIF-8;

FIG. 4 is an X-ray diffraction pattern XRD of ZIF-8 nanoparticles, PP fiber and PP @ ZIF-8 prepared in example 1;

FIG. 5 is a comparison of the filtration performance of examples 1-3 with the performance of an unloaded PP meltblown;

FIG. 6 is a graph of the retention of ZIF-8 nanoparticles for examples 1-3 at different ultrasonic powers;

Detailed Description

The preparation method for loading the ZIF-8 material on the PP fiber provided by the invention is further described in detail by combining specific embodiments. It should be understood that the specific examples are included merely for purposes of explanation and description and are not intended to limit the scope of the invention. Any modification and variation of the present invention can be made without departing from the object and scope of the present invention.

Examples 1-3 the protocol was as follows:

example 1:

firstly, the gram weight is 45g/m²The PP fiber film was cut into a circle having a radius of 9 cm. The cut PP fiber membrane was then placed in a methanol solution (500mL) and then pre-treated for 30 minutes at 300W ultrasonic power. And finally, washing the sample for three times by using distilled water, and then putting the sample into a conventional oven at the temperature of 80 ℃ for drying for 12 hours to remove redundant impurities and the electret effect of the fiber film.

And secondly, putting the dried sample into a solution with polyacrylamide concentration of 0.5%, and keeping for 8 hours after immersion. The sample was then removed and dried in a conventional oven at 80 ℃ for 12 hours.

Thirdly, putting the dried PP fiber membrane sample into Zn (NO) with the molar ratio of 1: 560₃)₂·6H₂In an O/methanol solution, the solution was maintained for 3 hours and referred to as solution A.

Fourthly, uniformly mixing dimethyl imidazole/methanol solution with the molar ratio of 8: 560, slowly pouring the mixture into the solution A, and reacting for 3 hours.

And fifthly, taking the reacted ZIF-8 fiber membrane out of the solution, washing the membrane for 3 times by using distilled water, drying the membrane for 3 hours in a conventional oven at the temperature of 80 ℃, and then carrying out filtration test and stability test. FIGS. 2(a), (b), and (c) are Scanning Electron Micrographs (SEM) of an unmodified PP fiber, a polyacrylamide-modified PP fiber, and a ZIF-8 nanoparticle-loaded PP fiber, respectively. From fig. 2(a), (b), it can be seen that the morphology of the PP fiber is not changed before and after the modification, so that the modification of the polyacrylamide does not block the pores between the fiber network. From 2(c), it can be seen that ZIF-8 is uniformly supported on the surface of the PP fiber. FIG. 3 is a transmission electron microscope image of ZIF-8 nanoparticles, and it can be seen that the size of ZIF-8 crystals is within 100nm, and such a structure can fully exert the advantage of the specific surface area of ZIF-8 and improve the capture of Particulate Matter (PM) by a fiber membrane. FIG. 4 is an XRD pattern of ZIF-8, PP, PP @ ZIF-8, and from FIG. 4, it can be seen that there are distinct ZIF-8 diffraction peaks near 7.5 and 12.5 degrees, indicating that the ZIF-8 crystal particles are successfully loaded on PP fibers. Fig. 5 is a graph of the filtration efficiency of examples 1-3 and PP blanks for different sizes of PM particles. It can be seen therein that the filtration efficiency is improved in all intervals after the PP fibers are loaded with ZIF-8 crystal particles, wherein the filtration efficiency for PM2.5 is 99.7%. It can also be seen from the figure that for the more difficult PM1.0 to filter, the filtration efficiency of PP @ ZIF-8 is increased 56.29% compared to the PP blank, which is due to the loading of the ZIF-8 nanoparticles. FIG. 6 is a graph showing the exfoliation of ZIF-8 crystals loaded on PP fibers at different ultrasonic powers. It can be seen from the figure that examples 1-3 conform to a substantially uniform law: as the power is increased, the ZIF-8 crystals gradually fall off, and about 80% of ZIF-8 crystals still remain on the surface of the fiber when the power is 420W. It can be shown that the connection between the fibers and the ZIF-8 crystals constructed in this way is very tight. Meanwhile, the PP fiber membrane prepared by the method has stable and efficient filtering performance.

Example 2:

firstly, the gram weight is 45g/m²The PP fiber film was cut into a circle having a radius of 9 cm. The cut PP fiber membrane was then placed in a methanol solution (500mL) and then pre-treated for 30 minutes at 450W ultrasonic power. And finally, washing the sample for three times by using distilled water, and then putting the sample into a conventional oven at the temperature of 80 ℃ for drying for 12 hours to remove redundant impurities and the electret effect of the fiber film.

And secondly, putting the dried sample into a solution with the polyacrylamide concentration of 1%, and keeping for 10 hours after immersion. The sample was then removed and dried in a conventional oven at 80 ℃ for 12 hours.

Thirdly, putting the dried PP fiber membrane sample into Zn (NO) with the molar ratio of 1: 560₃)₂·6H₂In an O/methanol solution, for 3 hours, this solution was designated as solution B.

And fourthly, uniformly mixing the dimethyl imidazole/methanol solution with the molar ratio of 7: 560, slowly pouring the mixture into the solution B, and reacting for 6 hours.

And fifthly, taking the reacted ZIF-8 fiber membrane out of the solution, washing the membrane for 3 times by using distilled water, drying the membrane in a conventional oven at 80 ℃ for 12 hours, and then carrying out filtration test and stability test.

Example 3:

firstly, the gram weight is 45g/m²The PP fiber film was cut into a circle having a radius of 9 cm. The cut PP fiber membrane was then placed in a methanol solution (500mL) and then pre-treated for 30 minutes at 600W ultrasonic power. And finally, washing the sample for three times by using distilled water, and then putting the sample into a conventional oven at the temperature of 80 ℃ for drying for 12 hours to remove redundant impurities and the electret effect of the fiber film.

And secondly, putting the dried sample into a solution with the polyacrylamide concentration of 2%, and keeping for 12 hours after immersion. The sample was then removed and dried in a conventional oven at 80 ℃ for 12 hours.

Thirdly, putting the dried PP fiber membrane sample into Zn (NO) with the molar ratio of 1: 560₃)₂·6H₂In an O/methanol solution, for 3 hours, this is called solution C.

Fourthly, uniformly mixing the dimethyl imidazole/methanol solution with the molar ratio of 6: 560, slowly pouring the mixture into the solution C, and keeping the mixture for 12 hours.

And fifthly, taking the reacted ZIF-8 membrane out of the solution, washing the membrane for 3 times by using distilled water, drying the membrane in a conventional oven at 80 ℃ for 12 hours, and then carrying out filtration test and stability test.

While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable in various fields of endeavor to which the invention pertains, and further modifications may readily be made by those skilled in the art, it being understood that the invention is not limited to the details shown and described herein without departing from the general concept defined by the appended claims and their equivalents.