Lattice-sulfur-impregnated zero-valent iron crystals for long-term metal encapsulation

Using nanoscale zero-valent iron (nFe⁰) materials for heavy metal removal is a viable approach for in situ groundwater pollution remediation. However, conventional nFe⁰ materials have indiscriminate reactivity towards various electron acceptors (for example, water) and just accumulate heavy metals onto the surface, which leads to poor selectivity and short longevity. Here we develop a lattice-sulfur-impregnated nFe⁰ (S-nFe⁰), achieving intraparticle sequestration of heavy metals enabled by a boosted Kirkendall-like effect. This metal-encapsulation approach outcompetes water for electrons and efficiently uses Fe-released spots, and the reacted S-nFe⁰ becomes inert to release metals (78–220× less than nFe⁰) in real groundwater matrices. The treated groundwater is estimated to meet drinking-water standards with a longevity of over 20–100 years. The synthesis of S-nFe⁰ has negligible environmental impacts according to Biwer–Heinzle environmental evaluation results. S-nFe⁰ also shows competitive production and operation costs for metal-contaminated groundwater remediation. Overall this work presents a strategy for achieving metal encapsulation in nFe⁰, which breaks the reactivity–selectivity–stability trade-offs of redox nanomaterials, providing a powerful tool to tackle groundwater pollution.