Nanoscale zero-valent iron (nZVI) encapsulated within tubular nitride carbon for highly selective and stable electrocatalytic denitrification

Abstract

Nanoscale zero-valent iron (nZVI) encapsulated within tubular nitride carbon for highly selective and stable electrocatalytic denitrification. • Tubular NC encapsulated nZVI regulated selective NO 3 − reduction to N 2 . • N 2 selectivity reached 98% with rapid NO 3 − removal in eutrophic water. • Hydrophilic NC with high surface area and porosity promoted NO 3 − adsorption. • Electrons and [H] rejuvenated Fe(III) to Fe (II) for sustained NO 3 − reduction. • Tubular NC layer protected active Fe for high stability and acid-base tolerance. Denitrification of nitrate (NO 3 − ) to dinitrogen (N 2 ) is of fundamental importance in water pollution control and environmental remediation. Conventional catalytic denitrification requires the use of expensive and often toxic metal such as Pd and Cu. Nitrate also can be rapidly reduced by environment-friendly nanoscale Zero-Valent Iron (nZVI), unfortunately the end product is mostly ammonia. Herein, nZVI is reconstructed with nitrogen-doping, dispersed and encapsulated within a tubular nitride carbon (nZVI@NC) as an electrocatalyst, regulating the multi-electron transfer reaction. The tubular iron structure is about 400–450 nm in length, has a diameter around 70–100 nm and wall thicknesses about 20–25 nm, surface area at 1445 m 2 /g. The nZVI@NC exhibits high nitrate removal efficiency (92%) and N 2 selectivity (97%), and maintains consistent performance in the pH range of 5–11. With nitrate selectively adsorbing on the highly porous and hydrophilic NC layer, the N-O bond is efficiently cleaved by gaining electrons from nZVI and activated hydrogen [H] to produce benign N 2 . Meanwhile, the intermediate product NH 4 + can be oxidized to N 2 by the HClO generated on the anode. This study points to promising prospects of modified nZVI for applications in denitrification and environmental remediation.