Bacteria, viruses, or toxic substances widely spread in ambient temperature environments, carried by ultrafine particulate matter such as PM0.3, posing a threat to public health. Additionally, industrial high-temperature waste gases severely pollute the environment. There is an urgent need to develop filtration membranes applicable to both ambient sources containing bacteria and high-temperature sources for people's health and environmental optimization. Currently, most filtration membranes face technical bottlenecks, such as poor filtration durability and slow industrialization progress. To address these issues, the team led by Academician Xu Weilin at Wuhan Textile University has utilized centrifugal spinning technology. Without the need for an external electric field, polyimide spontaneously acquires a polarized molecular structure during the spinning process, generating strong self-sustained electrostatic forces on the surface of the formed fiber mats. By in-situ growth of silver nanoparticles, antibacterial properties are endowed, achieving antibacterial and long-term filtration. This technique also realizes the bulk preparation of filtration membranes. Their work, "Heat-Resistant Air Filters Based on Self-Sustained Electrostatic and Antibacterial Polyimide/Silver Fiber Mats," was published in Advanced Functional Materials. The co-first authors of the paper are Dr. Lv Pei from Wuhan Textile University and Ju Zheng, a master's student from the class of 2023, with Academician Xu Weilin and Professor Liu Xin as the corresponding authors.

The generation of strong self-sustained electrostatic forces on the surface of polyimide fiber mats is mainly attributed to macroscopic friction and microscopic dipole polarization during the centrifugal spinning process. The friction between fibers and air, as well as between fibers, creates a strong electrostatic field, which triggers the polarization of polyimide molecules, thereby further strengthening the electrostatic field. Due to the high insulation and excellent dielectric properties of polyimide, its electrostatic loss is minimal, slowing the dissipation of surface electrostatic forces. Compared with polyimide films obtained by casting, the strong electrostatic forces are only present on the surface of the centrifugal spun fiber mats. Further molecular simulations confirmed the different degrees of polarization of polyimide molecules obtained by centrifugal spinning and casting methods. The hydrogen bond energy of the centrifugal spun fiber mats and cast films were 28.54 kJ/mol and 19.50 kJ/mol, respectively, consistent with their thermal stability. Moreover, the absolute polarity parameter of the centrifugal spun fiber mats was higher than that of the cast films, further confirming that the centrifugal spinning process induces polarization of polyimide molecules, enhancing molecular polarity.

Analysis of the morphology and physicochemical properties of polyimide and its silver nanoparticle composite fiber mats shows that the in-situ growth method successfully attaches silver nanoparticles to the polyimide fiber mats. Within the thermal decomposition temperature range of 30-350 °C, the weight loss of polyimide/silver nanoparticle fiber mats (PI/Ag) does not exceed 5%; heat resistance tests show that PI/Ag fibers maintain their continuous form even after long-term heat treatment at 280 °C, with no significant change in fiber diameter. The excellent thermal stability of PI/Ag allows air filters based on this material to be used for long periods at environmental temperatures of 200-300 °C.

The filtration performance test of PI/Ag shows that the filtration efficiency for PM0.3 of a 260 µm thick fiber mat is 99.1%, and for a 180 µm thick fiber mat, it is 98.1%, with a pressure drop reduced to 73.67 Pa, and an average surface electrostatic voltage of -713 V. In contrast, commercial polyimide fiber mats only have a surface electrostatic voltage of -10 V, with a PM0.3 filtration efficiency of 58.5%. The ultra-high surface electrostatic voltage and the 3D network structure constructed by centrifugal spinning synergistically enhance the air filtration efficiency of PI/Ag. After 330 days, the surface electrostatic voltage of PI/Ag still remains above -700 V, and after 1 hour of high-temperature treatment at 280 °C, its filtration efficiency for PM0.3 remains above 91.3%. Therefore, PI/Ag can ensure low pressure drop while achieving long-term filtration in high-temperature environments. Antibacterial tests show that PI/Ag exhibits significant antibacterial activity against Escherichia coli and Staphylococcus aureus. Therefore, the PI/Ag prepared in this study can be used for air filtration of room temperature bacterial sources as well as industrial high-temperature source flue gas filtration.

Summary: The authors have prepared antibacterial, high-temperature resistant polyimide fiber mats with strong self-sustained electrostatic forces using centrifugal spinning technology, which, due to the effect of self-sustained electrostatic forces, have a high PM0.3 filtration efficiency while ensuring a low pressure drop. This work provides a new approach to the large-scale, continuous preparation of multifunctional, efficient air filtration fiber materials.