Even Incorporation of Nitrogen into Fe Nanoparticles as Crystalline FeN for Efficient and Selective Trichloroethylene Degradation.

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