Selective Nitrate Reduction to Dinitrogen by Electrocatalysis on Nanoscale Iron Encapsulated in Mesoporous Carbon

Excessive nutrients (N and P) are among the most concerned pollutants in surface and ground waters. Herein, we report nanoscale zero-valent iron supported on ordered mesoporous carbon (nZVI@OMC) for electrocatalytic reduction of nitrate (NO₃^–) to nitrogen gas (N₂). This material has a maximum removal capacity of 315 mg N/g Fe and nitrogen selectivity up to 74%. The Fe–C nanocomposite is prepared via a postsynthetic modification including carbon surface oxidation, in-situammonia prehydrolysis of iron precursor and hydrogen reduction. The synthesized materials have large surface areas (660–830 m²/g) and small iron nanoparticles (3–9 nm) uniformly dispersed in the carbon mesochannels. The iron loading can be adjusted in the range of 0–45%. Results demonstrate that the reaction reactivity of electrocatalysis can be fine-tuned by manipulating iron nanoparticle size, degree of crystallization, as well as porous structure. Meanwhile, the small, uniform, and stable iron nanoparticle promotes fast hydrogen generation for rapid cleavage of the N–O bond. Furthermore, this material can maintain its high performance over repetitive experimental cycles. Results suggest a new approach for fast and eco-friendly nitrate reduction and a novel nZVI application.