Onsite naked-eye detection and quantification of Cu(ii) ions in drinking water using N-doped carbon nanodots

Abstract

Carbon nanodots (CNDs), benefitted by an array of fine features, have emerged as exemplary members among the various carbon forms in the nanoregime. This study unveils the potential of N-doped CNDs for visual detection and quantification of trace Cu(II) ions in water. Green synthesis was adopted, and the system was characterised using Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) Raman spectroscopy, Fourier transform infrared (FT-IR), UV-visible absorbance, and fluorimetric spectral analysis. Dual-emissive CNDs of average size of 2.8 nm with an N-doped carbon core and associated carboxyl, amino, hydroxyl, and carbonyl functional groups were identified. Naked-eye detection of Cu(II) ions was effortlessly achieved, as evidenced by a distinct colour change in the solution, with a lower limit of detection of 20 μM, which is a highly significant value in the context of the permissible amount of copper in drinking water. Further, lower detection was achieved via fluorimetric sensing. The detection method was also successfully extended to a solid-state sensor strip, which is desirable for practical onsite applications. An in-depth analysis supported by microscopic and spectral characterisation supported the formation of copper hydroxynitrate as the basis of the detection strategy.