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 (78-220x 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. Nanoscale zero-valent iron (nFe0) materials have a long history in groundwater pollution remediation but conventional nFe0 has intrinsic shortcomings. Here the authors develop a lattice-sulfur-impregnated nFe0 that enables efficient and selective heavy metal removal and long-term metal encapsulation.