ELECTROSPUN NANOFIBERS FOR AIR FILTRATION

Air pollution has become one of the most serious environmental issues, particularly fog and haze pollution, resulting in a growing impact on public health, production effificiency, and even ecosystems. Atmospheric particulate matter (PM) pollution, including solid and liquid particles emitted into the air, is the major noxious form of pollutant, and can cause adverse effects on human health due to its ability to penetrate deep into the lungs and cardiovascular system, causing minor irritation to chronic respiratory and lung cancer and making preexisting heart and lung diseases worse (Kampa and Castanas, 2008; Rodrıguez et al., 2004; Querol et al., 2001). The major sources of PM pollution are industrial emissions (e.g., mineral powder, coal, and carbon powder), combustion from daily life, intensive road transport, secondary nitrates, and secondary sulfates. Furthermore, certain contaminants attached to PM, such as bacteria, pollen, microorganisms, and viruses, may also badly inflfluence the environment and the aforementioned diseases (Montefusco, 2005; Chuanfang, 2012; Peukert, 1998). For example, according to the report provided by the World Health Organization in 2014, PM pollution was the main cause of death around the world for 7 million people (Wang et al., 2016a).

The size of PM particles is responsible for various health hazards; for example, thoracic particles (diameter <10 mm, PM10) can be mostly blocked by our nasal cavity (Brook et al., 2010); but the fifine particles (diameter <2.5 mm, PM2.5) are small enough to enter the lungs, leading to various serious health issues (Mannucci et al., 2015; Yoon et al., 2008). The larger particles (diameter >10 mm) are easier to fifilter by using air cleaners, such as scrubbers, cyclones, sedimentation tanks, etc.; however, the fifine particles, especially the PM2.5, are technically more diffificult to remove from air. Taking into account the well-known hazards of ultrafifine airborne particles to ecosystems and public health, a number of strategies have been developed to prevent this problem, such as source governance, new energy development, fifiltration technologies, and so on (Song et al., 2006). Among them, air fifiltration technology has prime importance because of its various advantages, including economy with low consumption of energy, robust performance, and a broad range of applications. For instance, Huang et al. have reported that the fifiltration market will increase to an estimate of US$700 billion by 2020(Huang et al., 2003). By virtue of their porous structures and tortuous channels, which can synchronously realize PM capture and air transmission, fifiber-based fifiltration media have become a feasible, effificient, and promising technology for PM pollution. Conventional fifiber-based fifilters, such as meltblown, spunbonded, and glass fifibers, have been extensively used in various fifiltration applications (Wang and Otani, 2012); however, their fifiltration effificiency for fifine particles is still low, which can be attributed to their structural disadvantages, like microsized fifiber diameter, large pore size, and low porosity (Adiletta, 1999; Wang et al., 2016a; Park and Park, 2005; Hung and Leung, 2011). Considering that the thickness and basis weight of these air fifilters must be increased to reduce the pore size, and thus increase the fifiltration effificiency, their applications are still restricted because of high energy consumption and high pressure drop (Wang et al., 2016a).

Taking into account that a decrease in fifiber diameter would greatly improve the fifiltration performance of the fifiber fifilters, the nanofifibers emerge as a promising fifiltration medium because of their small diameter, open pore structure, and high porosity. Different from other techniques for the fabrication of nanofifibers, electrospinning can fabricate nanofifibers with a wide range of fifiber diameters, from 50 to 2000 nm, by regulating solution properties and processing parameters (Park and Park, 2005; Graham et al., 2002; Kosmider and Scott, 2002; Grafe and Graham, 2003a). The resultant electrospun nanofifiber membranes possess various outstanding characteristics, such as small diameter, large specifific surface area, interconnected porous structures, and controllable morphologies, which differentiate them with conventional fifibrous fifilters (Lu and Ding, 2008; Bhardwaj and Kundu, 2010; Wang et al., 2013b; Fanet al., 2016; Sridhar et al., 2015). These remarkable characteristics would endow air fifilters with admirable fifiltration performance and provide a new strategy for controllable fabrication of novel fifilters at low cost. This chapter will present a brief overview of recent advances in electrospun nanofifiber membranes used in air fifiltration. After brieflfly introducing the technique and materials for air fifiltration and the structural advantages and fifiltration mechanisms of fifibrous fifiltration, we highlight the types, structural characters, and application performance of the existing electrospun nanofifiber fifilters for various fifiltration applications. In addition,concluding remarks are also presented in terms of current and future perspectives.

Scanning electron microscopy images of (A) a polyacrylic acid nanonet membrane and (B) a polyamide-6 nanonet membrane.

Paper link：https://www.sciencedirect.com/book/9780323512701/electrospinning-nanofabrication-and-applications