A reusable electret filter media based on water droplet charging/cleaning

Particulate matter is a primary contributor to the problem of air pollution, which poses a substantial risk to public health. Particulate matter consists of tiny solid particles and liquid droplets suspended in the air, and it has the ability to absorb harmful substances such as bacteria and viruses. Long-term exposure to particulate matter has been associated with a variety of health risks, including respiratory and cardiovascular diseases, as well as early mortality. Effective air filtration systems are crucial for mitigating the adverse effects of air pollution. Due to their numerous advantages, electret filters have become a popular option for air filtration. These filters have quasi-permanent electric charges on the filter fibers, which substantially improves their filtration efficiency without causing a substantial pressure drop increase. This makes them exceptionally effective at capturing and removing airborne particles. Nonetheless, as particulate matter is deposited on the filter material, the filtration resistance increases. Therefore, the filters must be replaced or cleaned periodically to preserve their performance. Not only does frequent filter replacement incur additional expenses, but it also contributes to environmental degradation through the disposal of used filters. It is necessary to develop reusable electret filter media that can be cleaned without degrading filtration performance significantly.

In a new study published in the peer-reviewed Journal Chemical Engineering Science, Jiu-Si Wang, Professor Rong-Rong Cai, Shun-Jie Wu and Li-Zhi Zhang from South China University of Technology designed and manufactured a reusable PTFE electret filter membrane based on liquid–solid contact electrification theory and the self-cleaning property of hydrophobic surface. Using electrospinning, polytetrafluoroethylene electret filter membranes were produced. Sodium chloride and silica particles were also used to prepare hydrophilic and hydrophobic PM_2.5 particles for experimentation.

The research team analyzed the morphology and composition of PTFE electret membranes using characterization techniques. To examine the membrane’s structure and element distribution, a scanning electron microscope with an energy-dispersive X-ray spectroscopy detector was utilized. Image analysis software was used to determine the diameter of the fibers, whereas a non-contacting electrometer was used to measure the surface potentials of the charged membranes. The PTFE electret membranes produced a fibrous structure with erratically distributed fibers, and the addition of PEO to the spinning solution improved fiber diameter uniformity. The energy-dispersive X-ray spectroscopy analysis confirmed the presence of fluorine and carbon, which are characteristic of PTFE.

Through particle loading-droplet charging/cleaning cycles, the authors evaluated the filtration and regeneration efficiency of PTFE electret membranes. As test aerosols, sodium chloride and silica particles were used. During particle loading, the filtration efficiency, pressure decrease, and surface potential were monitored. After particle loading, the membranes were cleaned with water droplets, and additional parameters were measured. This cycle was repeated on numerous occasions. With increased particle deposition, the membranes demonstrated enhanced filtration efficiency, indicating effective particle capture. Dust loading increased the pressure decrease, but it remained acceptable. Cleaning with water droplets restored the surface potential, indicating successful charge regeneration and particle removal, thereby demonstrating the hydrophobic membrane’s self-cleaning properties. Due to triboelectrification, the membrane’s surface potential increased as the volume of water particles increased during a liquid-solid triboelectrification test. This provided support for the concept of charge recovery by liquid-solid contact electrification.

In nutshell, Professor Rong-Rong Cai and her colleagues designed and manufactured a PTFE-based reusable electret filter membrane. Through liquid-solid contact electrification and self-cleaning hydrophobic surfaces, the PTFE membranes were capable of regenerating their charge and removing deposited particles, prolonging filter life and thus reducing filtration energy consumption. This study’s findings and methods have the potential to advance electret membrane and air filtration technology.