Fabrication of bead-on-string polyacrylonitrile nanofibrous air filters with superior filtration efficiency and ultralow pressure drop

The presence of ultrafine particle matter (PM) in air is one of the most hazardous environmental issues because of their severe threat to human health. Design and development of cost-effective and energy-efficient air filters to remove the PM by facile methods are highly demanded. Electrospun nanofibrous membranes have been explored for PM filtrations as they can achieve high removal efficiencies due to their ultrafine nanofibers. However, their enhanced particle removal efficiencies are at the cost of high pressure drops. In this work, porous bead-on-string filters with nanobeads along the nanofiber axis have been successfully fabricated by optimizing the polyacrylonitrile (PAN) concentration of electrospun dopes and ambient humidity condition during the electrospinning process. The combined effects of polymer concentration and humidity condition could achieve an unbalanced status between the repulsive and constrictive forces along the jets from the spinneret in the electrospinning process, which generated a filter with a desirable bead-on-string morphology. The nanobeads are able to reduce the packing density and alleviate the pressure drop through the filter while the ultrafine nanofibers guarantee the PM removal efficiency. Besides, the effects of nanofiber diameter, airflow rate and nanobead density on the filtration efficiency and pressure drop of NaCl solid and Paraffin oil aerosols with an average diameter of 300 nm have been investigated systematically. With the assistance of bead-on-string construction, the pristine PAN filter can easily achieve an excellent efficiency above 99% with a low pressure drop of 27 Pa at an airflow rate of 4.2 cm/s. This work suggests that transformation of electrospun filters from a nanofibrous structure to a bead-on-string morphology via the adjustments of polymer concentration and ambient humidity is sufficient to generate filter mediums with excellent efficiency and low airflow resistance for air filtration applications, which is also facile to be scaled up as no special equipment and costly chemicals are required.

空气中存在超细颗粒物（PM）是最危险的环境问题之一，因为它们对人类健康构成严重威胁。迫切需要设计和开发经济，节能的空气过滤器，以通过简便的方法去除PM。人们已经探索了电纺纳米纤维膜用于PM过滤的方法，因为它们的超细纳米纤维可以实现高去除效率。然而，它们提高的颗粒去除效率是以高压降为代价的。在这项工作中，通过优化静电纺丝原液的聚丙烯腈（PAN）浓度和静电纺丝过程中的环境湿度条件，成功地制造了沿纳米纤维轴具有纳米珠的多孔串珠式过滤器。聚合物浓度和湿度条件的共同作用可能会在静电纺丝过程中沿着喷丝头的射流产生排斥力和收缩力之间的不平衡状态，从而产生具有理想的串珠状形态的过滤器。纳米珠能够降低堆积密度并减轻通过过滤器的压降，而超细纳米纤维则保证了PM去除效率。此外，系统地研究了纳米纤维直径，气流速率和纳米珠密度对平均直径为300 nm的NaCl固体和石蜡油气雾剂的过滤效率和压降的影响。借助串串式构造，原始PAN过滤器可以轻松实现99％以上的出色效率，并且在4.2 cm / s的气流速率下具有27 Pa的低压降。这项工作表明，通过调节聚合物浓度和环境湿度，将电纺过滤器从纳米纤维结构转变为串珠状形态，足以为空气过滤应用生产出效率极高且气流阻力低的过滤介质，这也是由于不需要特殊设备和昂贵的化学品，因此易于扩展。

Published: 2020

Journal ：SEPARATION AND PURIFICATION TECHNOLOGY

Impact Factor：6195

Paper link: https://www.sciencedirect.com/science/article/abs/pii/S138358661933583X