32. Nanofibers for Water Treatment

Water colorization has raised a worldwide health and environmental concern due to the impact of dyes on marine and river organisms. The volume of nonrecycled dyes discarded varies depending on the dye/fabric affinity, but is for instance estimated to reach up to 40% of the total dyeing volume for reactive dyeing of cellulose. In addition, the large majority of the dyeing facilities are remotely located and operating into emerging economies where water treatment processes are limited, further increasing pressure and damage on already pollution-stressed ecosystems. Dye pollutants cover a category of organic molecules with different molecular structures, hence biodegradability, yet their composition often includes multiple aromatic rings and trace heavy metals, as well as other toxic and potential carcinogen compounds such as azoic groups. Adsorption is a promising technique to limit the release of dyes and partially degraded dyes in the environment, while reversible adsorption offers the possibility to recycle wasted dyes for reuse, hence minimizing the pollution load. As opposed to other separation techniques, adsorption, typically performed with activated carbons, offers opportunities to combine low operation cost with high performance as well as fast kinetics of capture if custom-designed with the right choice of adsorbent structure and surface chemistry. Nanofibers possess a higher surface to volume ratio compared to commercial macro-adsorbents and a higher stability in water than other nanostructures such as nanoparticles. This chapter comprehensively reviews the performance of nanofiber materials against benchmark commercial and recognized adsorbents for basic, acid, direct, and reactive ionic dyes adsorption. The discussion further investigates the impact of fibers morphology and composition on their adsorption capacity and proposes routes toward rationale design of cost-effective nanofiber-based adsorbents.