Nanofibers, mainly fabricated by electrospinning, have exhibited great potential for many emerging environmental applications. They can be considered as one of the safest nanomaterials due to their extremely long length (can be up to hundreds of kilometers) and their ability to be embedded within other media. Their high surface-to-volume ratio, large porosity (up to over 80%) and adjustable functionality are also much more effective than conventional non-woven and polymeric membranes in particulate separation and liquid filtration. Technology advances such as multiple-jet electrospinning and electroblowing for mass production of nanofibers have made it practical to use nanofibrous scaffolds as a unique and breakthrough component in separation media for both gas and liquid filtration. In this review, the opportunities and challenges of using functional nanofibers for several representative environmental applications are reviewed.

Scanning electron micrographs of a solvent-extracted sheared polyethylene (PE) blend revealed, for the first time, an unexpected shish-kebab structure with multiple shish. The blend contained 2 wt % of crystallizing ultrahigh molecular weight polyethylene (UHMWPE) and 98 wt % of noncrystallizing PE matrix. The formation of multiple shish was attributed to the coil-stretch transition occurring in sections of UHMWPE chains. Synchrotron x-ray data provided clear evidence of the hypothesis that multiple shish originate from stretched chain sections and kebabs originate from coiled chain sections, following a diffusion-controlled crystallization process.

The major challenges in membrane technology for water filtration are the development of new materials (e.g. high durability, low cost and low environmental concerns) and new structures (e.g. directed water channels) that can produce high permeation flux (thus low energy input) while maintaining a high selectivity or rejection rate. This highlight discusses the utilization of ultra-fine cellulose nanofibers (UCN, diameter 5–10 nm), made by TEMPO/NaBr/NaClO oxidation of natural cellulose (e.g. wood pulp), in different nanofibrous composite formats that can meet this challenge for microfiltration (MF) and ultrafiltration (UF) applications. The unique features of ultra-fine cellulose nanofibers include small diameter, high surface-to-volume ratio, easy surface functionality, good mechanical properties and good chemical resistance. The electrospun nanofibrous scaffolds with fine pore size defined by the fiber diameter could be used to remove waterborne bacteria at two to three times higher flux when compared to that of commercial MF membranes (e.g., Millipore GS9035). When UCN were used as a functionalized adsorbent infused in the asymmetric two-layered non-woven fibrous format, the membranes exhibited a high ability to remove bacteria (by size exclusion) and viruses (by adsorption) simultaneously. When UCN were used as the barrier layer in an asymmetric three-layered non-woven fibrous format containing fibers of different diameters (from 5 nm to 20 µm), the membranes exhibited a two- to ten-fold increase in permeation flux over commercial membranes for ultrafiltration of oil and water emulsions (e.g., for purification of bilge water in ships or industrially produced water).