Kirkendall Effect Boosts Phosphorylated nZVI for Efficient Heavy Metal Wastewater Treatment.

Removal of non-biodegradable heavy metals has been the top priority in wastewater treatment and the development of green technologies remains a significant challenge. We demonstrate that phosphorylated nanoscale zero-valent iron (nZVI) is promising for removal of heavy metals (Ni , Cu , Cr , Hg ) via a boosted Kirkendall effect. Phosphorylation confines tensile hoop stress on the nZVI particles and "breaks" the structurally dense spherical nZVI to produce numerous radial nanocracks. Exemplified by Ni removal, the radial nanocracks favor the facile inward diffusion of Ni and the rapid outward transport of electrons and ferrous ions through the oxide shell for surface (Ni /electron) and boundary (Ni /Fe ) galvanic exchange. Accompanied by a pronounced hollowing phenomenon, phosphorylated nZVI can instantly reduce and immobilize Ni throughout the oxide shell with a high capacity (258 mg Ni g  Fe). For real electroplating factory wastewater treatment, this novel nZVI performs simultaneous Ni and Cu removal, producing effluent of stable quality that meets local discharge regulations.