Even Incorporation of Nitrogen into Fe0 Nanoparticles as Crystalline Fe4N for Efficient and Selective Trichloroethylene Degradation.

Surface modification of microscale Fe powder with nitrogen has emerged recently to improve the reactivity of Fe0 for dechlorination. However, it is unclear how an even incorporation of a crystalline iron nitride phase into Fe0 nanoparticles affects their physicochemical properties and performance, or if Fe0 nanoparticles with a varied nitridation degree will act differently. Here, we synthesized nitridated Fe0 nanoparticles with an even distribution of N via a sol-gel and pyrolysis method. Nitridation expanded the Fe0 lattice and provided the Fe4N species, making the materials more hydrophobic and accelerating the electron transfer, compared to un-nitridated Fe0. These properties well explain their reactivity and selectivity toward trichloroethylene (TCE). The TCE degradation rate by nitridated Fe0 (up to 4.8 × 10-2 L m-2 h-1) was much higher (up to 27-fold) than that by un-nitridated Fe0, depending on the nitridation degree. The materials maintained a high electron efficiency (87-95%) due to the greatly suppressed water reactivity (109-127 times lower than un-nitridated Fe0). Acetylene was accumulated as the major product of TCE dechlorination via β-elimination. These findings suggest that the nitridation of Fe0 nanoparticles can change the materials' physicochemical properties, providing high reactivity and selectivity toward chlorinated contaminants for in situ groundwater remediation.