Simple and Intelligent Electrochemical Detection of Ammonia over Cuprous Oxide Thin Film Electrode

To realize simple and intelligent electrochemical ammonia (NH3) detection in water, highly dense colloidal copper nanoparticles (CuNPs) were prepared and subsequently deposited onto a glassy carbon electrode (GCE). The CuNPs/GCE was then placed in an oven at 60 °C to intelligently transform CuNPs into cuprous oxide (Cu2O) thin film. The colloidal CuNPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, whereas the fabricated Cu2O/GCE was subjected to Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The XRD of Cu2O/GCE showed the crystalline nature of the thermally converted Cu2O thin film, whereas XPS demonstrated that the thin film formed on the surface of GCE was primarily composed of Cu2O. The SEM images of Cu2O/GCE revealed Cu2O crystals with hexapod morphology. The EIS study exhibited substantially higher charger transfer activity of Cu2O/GCE compared to bare GCE. The drop coating of ammonia (NH3) solution onto Cu2O/GCE enabled the fabricated electrode to be utilized as an electrochemical sensor for NH3 detection in water. The cyclic voltammetric (CV) behavior of NH3/Cu2O/GCE was investigated in 0.1 M pH 7 phosphate buffer, which led to the formation of a copper-ammonia complex and revealed the nobility of the fabricated electrode. The square wave voltammetric (SWV) response was linear over the 10 µM and 1000 µM ranges with a detection limit of 6.23 µM and good reproducibility. The NH3/Cu2O/GCE displayed high selectivity for the detection of NH3 in the presence of various coexisting cations and anions in 0.1 M pH 7 phosphate buffer. The recovery of NH3 in the drinking water sample varied from 98.2% to 99.1%.