pi-Conjugated polyaniline nanofiber networks are an attractive material platform for reversible and selective capture and release of toxic heavy metal ions from water. The nanofiber geometry facilitates fastsorption kinetics, sulfur functionalization of the backbone for improved adsorption, and electrochemical control of the oxidation (charge) state for reversible triggered sorption/desorption of metal ions. These active materials also function as sensors in that the sorption of mercury ions can be detected by analysis of cyclic voltammograms. Calculations of binding energies between polyaniline and metal ions using molecular dynamics and density functional theory support the electrochemically controlled reversible sorption/desorption mechanism. These redox-active materials for removing He2+ from water create an attractive system that combines efficiency, capacity, selectivity, and reusability.