The effect of carbonized zeolitic imidazolate framework-67 (ZIF-67) support on the reactivity and selectivity of bimetal-catalytic aqueous NO₃ ⁻ reduction

A metallic catalyst, Cobalt N-doped Carbon (Co@NC), was obtained from Zeolitic-Imidazolate Framework-67 (ZIF-67) for efficient aqueous nitrate (NO₃ ⁻) removal. This advanced catalyst indicated remarkable efficiency by generating valuable ammonium (NH₃/NH₄ ⁺) via an environmentally friendly production technique during the nitrate treatment. Among various metals (Cu, Pt, Pd, Sn, Ru, and Ni), 3.6%Pt–Co@NC exhibited an exceptional nitrate removal, demonstrating a complete removal of 60 mg/L NO₃ ⁻-N (265 mg/L NO₃ ⁻) in 30 min with the fastest removal kinetics (11.4 × 10⁻² min⁻¹) and 99.5% NH₄ ⁺ selectivity. The synergistic effect of bimetallic Pt–Co@NC led to 100% aqueous NO₃ ⁻ removal, outperforming the reactivity by bare ZIF-67 (3.67%). The XPS analysis illustrated Co's promotor role for NO₃ ⁻ reduction to less oxidized nitrogen species and Pt's hydrogenation role for further reduction to NH₄ ⁺. The durability test revealed a slight decrease in NO₃ ⁻ removal, which started from the third cycle (95%) and slowly proceeded to the sixth cycle (80.2%), while NH₄ ⁺ selectivity exceeded 82% with no notable Co or Pt leaching throughout seven consecutive cycles. This research shed light on the significance of the impregnated Pt metal and Co exposed on the Co@NC surface for the catalytic nitrate treatment, leading to a sustainable approach for the effective removal of nitrate and economical NH₄ ⁺ production.