Construction And Performance Of Multifunctional Polyaniline Air Filter

In recent years,with the rapid development of industry,the pollution problem of inhalable particulate matter（PM）in the air has become increasingly serious.Due to the long residence time and large surface area of PM particles smaller than 2.5μm,PM2.5can easily enter the human body through the respiratory system and cause cardiovascular and respiratory diseases.Moreover,studies have shown that during the COVID-19 pandemic worldwide,air particles or dust can act as viral vectors for the spread of the virus among people,posing a threat to human health and society.Therefore,air filters are urgently needed to protect people from respiratory virus infection and air pollution during outdoor activities.Traditional micrometer-sized fiber air filters have good filtration efficiency for large PM（2.5μm-10μm）,however,these filters efficiency of small particles（≤2.5μm）is low because the fiber membrane has a large pore size due to the disordered accumulation of fibers.Researchers usually improve the filter efficiency by increasing the thickness of the membrane,however,the accumulation of these fibers will reduce the porosity of the membrane,so that the air resistance of the filter increases sharply.In recent years,electrospinning nanofibers have attracted the attention of researchers because of their advantages of fine diameter,small pore size and high porosity,which can effectively improve the filtration efficiency of the fiber on PM particles.However,nanofibers with sub-micron size are less efficient in filtering 300 nm particles（PM0.3）,and their poor mechanical strength further limits their application in real life.Therefore,in this paper,new composite fiber membranes based on nanofibers were prepared by electrostatic spinning technology,which have higher PM0.3 filtration efficiency,lower air resistance and excellent mechanical properties.The main research contents of this paper are as follows:（1）Using high dipole moment PAN as raw material,pure PAN nanofiber membrane was obtained by electrospinning technology,and PAN/PANI composite nanofiber membrane was formed by in-situ polymerization of PANI.The interaction between fiber and PM was enhanced by optimizing fiber structure and regulating polar functional groups on fiber surface.The results showed that the addition of PANI improved the filtration efficiency of PM0.3,and the PAN/PANI-1.0 membrane had the best filtration efficiency（99.66%）for PM0.3 and low air resistance（96 Pa）.Its quality factor(0.0592 Pa^-1)is about twice of pure PAN nanofiber membrane(0.025 Pa^-1).Moreover,PAN/PANI-1.0 membrane has excellent tensile properties（8.98 MPa）,which is much higher than pure PAN nanofiber membrane（3.9 MPa）.In addition,as an excellent photothermal conversion material,PANI has good light absorption in the range of visible light,which can make PAN/PANI films rapidly heated up to 150℃under sunlight irradiation.Then the virus or bacteria attached to the surface can be destroyed at high temperature.（2）In order to further optimize the pressure drop of the filter,thinner carbon-based Ti O₂/PANI composite nanofiber membranes were prepared by electrostatic spinning,heat treatment and chemical in-situ polymerization.According to the energy band bending theory of the semiconductor composite and combining with UPS test,it indicated that the heterojunction of semiconductor Ti O₂ and carbon,PANIand carbon can form built-in electric fields under the action of the Schottky barrier.In addition,N-type semiconductor Ti O₂ and P-type semiconductor PANI form a space charge region at the junction through diffusion.Multiple electrostatic fields were used to enhance the electrostatic attraction of fiber to PM,so as to improve the filtration efficiency of C/Ti O2/PANI composite membrane for PM0.3.The results show that the filtration efficiency of PM0.3 can reach 99.07%and the quality factor is 0.1264 Pa^-1（about 2.5times of PAN/PANI composite membrane）.When the flow velocity is 5.5 cm s^-1,the pressure drop is only 37 Pa.Meanwhile,the addition of nano Ti O₂ increases the flexibility of carbon fiber membrane,which makes C/Ti O₂/PANI membrane meet the requirements of practical application.Moreover,Ti O₂ as a photocatalytic material can can be used to photodegrade the adsorbed PM particles,realizing the self-cleaning recycling of C/Ti O₂/PANI fiber membrane.