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.