Reusable Janus Self-Cleaning Nanofibrous Air Filters

Air pollution by fine dust/Particulate Matter (PM) particles has been rising with the recent industrialization [1]. As the PM concentration grows in air including membrane-based filtration technologies for filtration PM are gaining much attention. Among membrane-based filters, electrospun membranes exhibit high porosity, pore interconnections, and high specific surface area which are all advantageous features for the filtration of PM [2]. Most previous studies of filtration of PM focused only on the filtration performance of the membrane [3-4]. They did not deeply seek the reusability or the self-cleaning capability of such filters, although these are vital maintenance aspects that become relevant when considering practical reuse and real-life application. Previous works on membrane-based PM filters mostly utilize materials with high dipole moment, a characteristic commonly observed in hydrophilic polymers for better capturing of PM particles [5]. Hydrophilic materials with high dipole moment are usually very inclinable to wetting. However, implementing the hydrophobic self-cleaning surface technology can largely improve the already studied dust filtration membranes [6].<br/>Here, we report micro-beads coated nanofibrous membrane (MB-NFM) filters that had a dual layer structure consisting of hydrophilic polyacrylonitrile (PAN) nanofibers coated with hydrophobic micro-beads; this novel structure allows both high filtration efficiency and self-cleaning capability. This surface exhibited water contact angles of about 150° (sliding angle ≈ 10°), which was sufficient to allow water droplets to roll off its surface and pick up the PM particles with it. For PM_2.5dust particles, the MB-NFMs filter showed removal efficiency of more than 99.8%, achieving a quality factor was similar of commercial HEPA filter, H13. To evaluate the self-cleaning capability and reusability of the MB-NFMs filter, numerous dust-filtering/cleaning cycles were conducted. The filtration efficiency was still over 99.8% throughout the tests, and the pressure drop was recovered by 99% after every cleaning cycle. Owing to self-cleaning capability, the MB-NFMs filter would not require periodic maintenance, thus providing an economic benefit over conventional air filter. To the best our knowledge, this work is the first to apply the self-cleaning on hydrophilic membrane-based dust/PM filters to suggest a possible solution to enhancing filter reusability.<br/>Referance<br/>[1] G. Li, C. Fang, S. Wang, S. Sun, The Effect of Economic Growth, Urbanization, and Industrialization on Fine Particulate Matter ate Matter (PM2.5) Concentrations in China, Environ. Sci. Technol. 50 (2016) 11452–11459. https://doi.org/10.1021/acs.est.6b02562.<br/>[2] S.J. Cho, B. Kim, T. An, G. Lim, Replicable multilayered nanofibrous patterns on a flexible film, Langmuir. 26 (2010) 14395–14399. https://doi.org/10.1021/la102467u.<br/>[3] S. Shi, Y. Bian, L. Zhang, C. Chen, A method for assessing the performance of nanofiber films coated on window screens in reducing residential exposures to PM2.5 of outdoor origin in Beijing, Indoor Air. 27 (2017) 1190–1200. https://doi.org/10.1111/ina.12391.<br/>[4] X. Li, X.X. Wang, T.T. Yue, Y. Xu, M.L. Zhao, M. Yu, S. Ramakrishna, Y.Z. Long, Waterproof-breathable PTFE nano- and microfiber membrane as high efficiency PM2.5 filter, Polymers (Basel). 11 (2019) 1–14. https://doi.org/10.3390/polym11040590.<br/>[5] C. Liu, P.C. Hsu, H.W. Lee, M. Ye, G. Zheng, N. Liu, W. Li, Y. Cui, Transparent air filter for high-efficiency PM 2.5 capture, Nat. Commun. 6 (2015). https://doi.org/10.1038/ncomms7205. 26<br/>[6] N.A. Patankar, Mimicking the lotus effect: Influence of double roughness structures and slender pillars, Langmuir. 20 (2004) 8209–8213. https://doi.org/10.1021/la048629t.