In-situ Construction And Protective Properties Of PI-based Zr-MOFs Flexible Membrane Materials

With rapid economic development and global industrialization,air pollution has become one of the most serious threats facing mankind.In the real world,air pollutants are complex mixtures of particles,droplets,and gases.Compared with conventional fine particle pollutants（PMs）,toxic and harmful gaseous pollutants have a greater negative impact on human health.Among them,sulfur dioxide（SO₂）harmful gas will cause acid rain and then increase the incidence rate of lung cancer.In addition,the highly toxic chemicals dropped on the battlefield,known as chemical warfare agents（CWAs）,are more concealed,spread more quickly,are more difficult to prevent,and even cause irreversible environmental degradation.Traditional adsorbents such as porous carbon and zeolite have poor reaction strength due to lack of specific adsorption sites.In addition,it is difficult to self-detoxify will cause secondary pollution.However,zirconium-based metal organic frameworks（Zr-MOFs）have large specific surface area and porosity,adjustable skeleton structure and abundant adsorption sites.In this paper,Zr-MOFs are used as novel porous adsorbents,combined with the electrospinning nanofiber technology,and self-assembled on the surface of nanofibers uniformly loaded with Zr-MOFs crystals using in-situ growth method to construct a multifunctional composite material with fast and efficient filtration,adsorption,and catalytic degradation.The main research is as follows:（1）Based on high temperature resistant polyimide（PI）nanofiber membrane,Zr-MOFs（Ui O-66-NH₂）composite membrane material based on PI fiber was prepared by simple in situ growth method to realize multifunctional air protection by filtration and adsorption of toxic substances in one,named as T/Ui O-66-NH₂@PI composite membrane protective material.Under the action of trifluoroacetic acid（TFA）,the synthesized Ui O-66-NH₂ crystal has abundant defect sites,and it also carries a large number of amino active groups（-NH₂）to achieve efficient performance.By discussing the variation of Ui O-66-NH₂ growth time on PI fiber surface,T/Ui O-66-NH₂@PI composite membrane with the best structure and performance was constructed,and the PI fiber’s ability to filter PMs and adsorb SO₂ was optimized.The results show that the PM_0.3 filtration efficiency of T/Ui O-66-NH₂@PI composite membrane with growing 4 h is 96.3%at room temperature,the pressure drop is 76.7 Pa,and the quality factor of 2.7764 times higher than of PI membrane.Even when tested at a constant temperature of 200°C for 120 minutes,the filtration efficiency remained at 93.6%.In addition,the composite membrane can fast and efficiently adsorb SO₂,the penetration time is as long as 210min,the adsorption capacity is as high as 0.29 g/g.After three adsorption-desorption regeneration experiments,it still has an adsorption capacity of 0.24 g/g.（2）Zirconium tetrachloride（Zr Cl₄）in different proportions was introduced into the chemically stable PI precursor polyamide acid（PAA）polymer solution to provide Zr metal seeds.Then,PAA/Zr Cl₄ film was prepared by electrospinning technology,which was transformed into PI/Zr Cl₄ film by imide.Further,the ideal PI/Zr Cl₄ fiber-based Zr-MOFs（Ui O-66-NH₂）composite membrane was designed by exploring the addition of Zr Cl₄ in the growth solution and the reaction time through in-situ growth method for wearing comfortable while catalyzing the degradation of highly toxic CWAs,named Z/Ui O-66-NH₂@PI composite membrane protective material.The results show that 16 wt.%was selected as the optimal concentration of PI spinning solution,and the introduction of 15%Zr Cl₄ seed could better assist the growth of Ui O-66-NH₂ crystal.Secondly,adding 0.0885 g Zr Cl₄ into the growth solution and growing for 24 h can promote the assembly of metal sites and ligands,so that the surface of the nanofibers is uniformly and intensively loaded with Ui O-66-NH₂.Due to the large number of Zr Lewis acidic metal sites and-NH₂ active sites in Ui O-66-NH₂,this composite membrane catalyzes the degradation of CWAs mimics（CEES）with a conversion rate of 96.96%.Moreover,the crystal structure of the composite membrane did not change after the reaction and possessed good stability.The degradation capacity remained stable and constant at 96.06%through multiple re-use.Meanwhile,its composite film has a high water contact angle of 152.8°and a moisture permeability of 4897 g/m²/d,demonstrating comfortable wearability.