Nanofibers for heavy metal ion adsorption: Correlating surface properties to adsorption performance, and strategies for ion selectivity and recovery

The bioaccumulation of heavy metals and their biomagnification throughout the food chain raises a concern for both the environment and human health. When compared to other water treatment techniques, adsorption offers opportunities for high yields of heavy metal ion capture without secondary pollution, in a sustainable process and at low to moderate operational and capital costs. Among adsorbent choices, nanomaterials were shown to yield outstanding capacities from their enhanced reactivity, with nanofiber adsorbents attracting interest for their stability in water, practicability and customizable surface properties. This review examines the application of nanofiber materials as adsorbents for the removal of heavy metal ions in aqueous solutions. The correlations between physical properties, test conditions, and ion removal performance of the adsorbent materials are here investigated, to provide guidance on the design of nanofiber adsorbents. The performance of nanofiber adsorbents was benchmarked to that of bulk and other nanostructured materials with varying compositions. Finally, ion removal strategy and routes to recycle nanofiber adsorbents are discussed towards the development of a circular economy in metal extraction and reuse.