| Summary: | To realize simple and intelligent electrochemical ammonia (NH<sub>3</sub>) 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 (Cu<sub>2</sub>O) thin film. The colloidal CuNPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, whereas the fabricated Cu<sub>2</sub>O/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 Cu<sub>2</sub>O/GCE showed the crystalline nature of the thermally converted Cu<sub>2</sub>O thin film, whereas XPS demonstrated that the thin film formed on the surface of GCE was primarily composed of Cu<sub>2</sub>O. The SEM images of Cu<sub>2</sub>O/GCE revealed Cu<sub>2</sub>O crystals with hexapod morphology. The EIS study exhibited substantially higher charger transfer activity of Cu<sub>2</sub>O/GCE compared to bare GCE. The drop coating of ammonia (NH<sub>3</sub>) solution onto Cu<sub>2</sub>O/GCE enabled the fabricated electrode to be utilized as an electrochemical sensor for NH<sub>3</sub> detection in water. The cyclic voltammetric (CV) behavior of NH<sub>3</sub>/Cu<sub>2</sub>O/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 NH<sub>3</sub>/Cu<sub>2</sub>O/GCE displayed high selectivity for the detection of NH<sub>3</sub> in the presence of various coexisting cations and anions in 0.1 M pH 7 phosphate buffer. The recovery of NH<sub>3</sub> in the drinking water sample varied from 98.2% to 99.1%.
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