Comparative study of synthesis of carbon quantum dots via different routes: Evaluating doping agents for enhanced photoluminescence emission

Fluorescent inks based on carbon quantum dots (CQDs) find versatile applications in both security and biotechnology sectors. They serve as a potent tool for anti-counterfeiting applications such as military documents, banknotes, valuable certificates, and checks. In this study, we embarked on the synthesis of CQDs through a one-step procedure employing citric acid, ethylene diamine, and aniline, in varying ratios, utilizing three distinct synthesis methods including hydrothermal, microwave-assisted, and simple heating techniques. Comprehensive characterization techniques, such as UV–Visible spectroscopy, Photoluminescence spectroscopy (PL), Energy Dispersive Spectroscopy (EDS), Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM), were employed to investigate the physicochemical properties of the synthesized carbon quantum dots. Among the various CQD samples synthesized in this study, the best one was selected as a functional dye for the formulation of fluorescent ink. The ink was subsequently applied to paper using inkjet printing techniques. To delve further into the interaction between the ink and paper substrate, water contact angle measurements were performed on both printed areas and unprinted paper. Notably, the results revealed a decrease in contact angle after printing, indicating enhanced ink penetration into the porous structure of the paper.