Towards green, lightweight and highly efficient silk nanofiber-based air filters

Posted: Nanowerk,Jul 13, 2016

 

Summary:

Membranes of electrospun silk nanofibers made from silkworm cocoons, which is a kind of green and biocompatible natural material, are used as high performance air filters. The silk nanofiber air filters showed combined features of high filtration efficiency for both PM2.5 and more harmful submicron particles, low air flow resistance and lightweight, making them very attractive for fabrication of personal air filtration devices.

 

 

It is calling for new type of filter technology because of the serious threat of Particulate matter (PM) air pollution to human health. Efforts have been made in developing air filters with both high filtration efficiency and low airflow resistance by utilizing nanofibers, such as carbon nanotubes (CNTs) and electrospun polymer and inorganic nanofibers. To date, the development of CNT-based air filters is confronted by two main challenges: difficulty in fabrication and, more critically, unclear toxicity of CNTs. The fabrication of the abovementioned electrospun nanofibers lacks environmental safety and biological compatibility.

To address these issues, the team led by Yingying Zhang, an assistant professor in the Department of Chemistry and the Center for Nano and Micro Mechanics, Tsinghua University, have utilized the biocompatible, environmentally sustainable, and widely available natural silk fibers to fabricate silk nanofibers through the electrospinning approach and explored the performance of silk nanofiber membranes as air filters, which showed both of lightweight and high efficient features. They reported their findings in the June 27, 2016 online edition of Nano Research (“Silk Nanofibers as High Efficient and Lightweight Air Filter”).

 

 

Fabrication of the silk nanofiber-based air filter. (a) Silkworm cocoons are used as raw materials, and the molecular formula of silk protein is shown. (b) Schematic showing fabrication of the silk nanofiber-based air filter by electrospinning. (c) Example photographs of silk nanofiber-coated silk scarves as lightweight wearable air filters. (d) Optical image of silk nanofibers. (e) and (f) Scanning electron microscope (SEM) images of silk nanofibers, showing the detailed morphologies.

The team showed the superior performance of the silk nanofiber air fibers. The most attracted feature is that the silk nanofiber based air filter showed combined features of superior filtration efficiency and low air flow resistance (low pressure drop). In detail, by controlling electrospinning time, the silk nanofiber membranes could show filtration efficiency of 98.8% for PM2.5 and 96.2% for 300-nm particles with a lower pressure drop than commercial microfiber membranes with comparable filtration efficiency. In addition, the silk nanofiber membrane is lightweight with a basis weight of only 3.4 g/m2, about 1/60th of a typical commercial respirator with similar filtration efficiency, which is highly desired for personal air filtration devices such as respirators.

Furthermore, multifunctional silk nanofiber filters could be designed and fabricated by introducing functional components into the spinning solution. As a proof of concept, the silver nanoparticles, as the well-known broad-spectrum antibacterial agents, could be in-situ incorporated into spinning solution and subsequently electrospun into silk nanofibers to introduce antibacterial activity into the silk nanofiber based air filters.

Going forward, the team will work on the development of technology for the fabrication of low-cost and large-scale silk nanofiber air filter, further improving the filtration performance and the incorporation of other functionality (such as degradation of formaldehyde).

 

 

 

Draft by Chunya Wang (the first author of the original article), Tsinghua University

Email:

Ms. Chunya Wang, chywang1991@sina.com

Prof. Yingying Zhang, Yingyingzhang@tsinghua.edu.cn