Coupled nitrate-to-ammonia reduction and persulfate production for ciprofloxacin removal via Cu2O/Cu nanorod and BDD electrodes

Abstract

Electrocatalytic nitrate reduction (NO₃RR) processes that use actual aqueous nitrate pollution as a feedstock for ammonia production have two chief challenges for realization: (i), conversions are limited to neutral conditions and (ii) electrocatalysts are unable to drive nitride protonation while inhibiting hydrogen evolution. Herein, a facile electrodeposition method was applied to prepare Cu₂O/Cu nanorods on copper support, which exhibited an ammonia production rate of 454.1 μmol h^-1 cm^-2 and Faraday efficiency of 96.8 % at -0.9 V versus a reversible hydrogen electrode in neutral medium. Through application of a boron doped diamond electrode in anodic bath, persulfate production of 310.2 μmol h^-1 cm^-2 (18.2 % improvement in Faraday efficiency) afforded simultaneous degradation of a nitrogen-containing contaminant (ciprofloxacin). The high electron density of Cu sites on Cu₂O/Cu inhibited competing hydrogen evolution and accelerated nitrate transformation. Generation of oxidative radicals (SO₄^•- and •OH) on boron doped diamond electrode in sulfate electrolyte showed the possibility for simultaneous degradation of organic pollutants.

Keywords: Coupling reaction system; Electrocatalysis; Neutral medium; Nitrate-to-Ammonia; Persulfate production.