Monitoring WAD Cyanide Concentration in River Waters with a Glassy Carbon Electrode Modified with 9,10-Phenanthroquinone

Heavy metal-containing industrial effluent streams from electroplating and metalworking industries represent a major environmental issue. They contain metal cyanide complexes ([Ni(CN)4]2- and [Cu(CN)3]2-) referred to as weak acid dissociable cyanide (CN-WAD), which require continuous in situ monitoring. In this scenario, a glassy carbon (GC) electrode superficially decorated with 9,10-phenanthroquinone (FNQ) is manufactured and employed for the simultaneous electrochemical monitoring of cyanide WAD complexes. The interaction between GC and FNQ was characterized by Raman and electrochemical impedance spectroscopies, cyclic voltammetry, and chronocoulometry. The electrochemical evaluation was conducted by differential pulse voltammetry (DPV) and CV. The GC/FNQ electrochemical sensor simultaneously detected cyanide complexes with an average linear range of 9.09 - 92.8 μmol L-1, and a detection limit of 1.47 ± 0.11 μmol L-1 and 1.2 ± 0.6 μmol L-1 for [Ni(CN)4]2- and [Cu(CN)3]2-, respectively. The sensor demonstrated remarkable selectivity in the presence of multiple interfering species with a percentage variation range of 89.2-109.4%. Moreover, a computational DFT study provided valuable insights into the electrode/electrolyte interface. Finally, the developed sensor was applied for the electrochemical detection of WAD cyanide in river water samples.