Characterization and application of fluorescent carbon NANODOTS from dragon fruit peel as probes for detection of metal ions

In this work, we demonstrate the production of highly fluorescent carbon nanodots (C-dots) from dragon fruit peel using carbonization method. The as-prepared C-dots have been characterized and applied as probes to detect zinc (Zn²⁺) ions. The characterization of the as-produced C-dots was conducted through the measurement of their absorption (Abs), photoluminescence (PL), and FTIR spectra before and after synthesis with Zn²⁺ ions, X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) image. The Abs spectrum of these C-dots demonstrated two Abs peaks at 250 and 292 nm corresponding with π → π* and n → π* transitions, respectively. The appearance of these two Abs peaks confirmed the formation of the C-dots from dragon fruit peel in ethanol solution. By using an excitation wavelength of 350 nm, the PL peak at 434 nm corresponds to the blue emission color of typical C-dots. Thus, the FTIR spectrum strongly displayed OH and CO bonds as hydroxyl and carbonyl groups on the surface of the C-dots, respectively. The characterization of XRD patterns and TEM image displayed an amorphous state and dispersed spherical shape of C-dots, respectively. Fortunately, the PL intensity of these C-dots quenched after coordination with Zn²⁺ ions with the enhancement of the concentration of Zn²⁺ ions. The quenching of the PL intensity of these C-dots through Zn²⁺ chelation demonstrated their sensing system up to the detecting limit of 3.2 μM.