A Nanoselenium Sponge for Instantaneous Mercury Removal to Undetectable Levels

Selective removal of aqueous mercury to levels below 10 ng L⁻¹ or part per trillion remains an elusive goal for public health and environmental agencies. Here, it is shown that a low-cost nanocomposite sponge prepared by growing selenium (Se) nanomaterials on the surface and throughout the bulk of a polyurethane sponge exhibits a record breaking-mercury ion (Hg²⁺) removal rate, regardless of the pH. The exposure of aqueous solutions containing 10 mg L⁻¹–12 ng L⁻¹ Hg²⁺ to the sponge for a few seconds results in clean water with undetectable mercury levels (detection limit: 0.2 ng L⁻¹). Such performance is far below the acceptable limits in drinking water (2 µg L⁻¹), industrial effluents (0.2 µg L⁻¹), and the most stringent surface water quality standards (1.3 ng L⁻¹). The sponge shows a unique preference for Hg, does not retain water nutrients, and can significantly reduce the concentration of other heavy metal pollutants. Furthermore, the sponge shows no cytotoxic effect on human cells while exhibiting strong antimicrobial properties. The high affinity of Hg for Se results in irreversible sequestration and detoxification of mercury by the sponge, confirming the suitability for landfill disposal.