Mechanistic studies on the beta-resorcylic acid mediated carbon dots for the pH-induced fluorescence switch and sensing application

Abstract

Carbon dots (CDs) responsive to external stimuli that cause changes in their optical properties are in high demand. Herein, we present a microwave synthesis of highly fluorescent CDs derived for the first time from beta-resorcylic acid (henceforth referred as R-CDs) in sulfuric acid (H2SO4) medium. Interestingly, the as-synthesized R-CDs showed tunable optical properties with three distinguishable colors (green/blue/blue-violet) depending on pH under UV irradiation. Spectral analyses and mechanistic studies revealed that the fluorescence switch is due to the deprotonation of the oxygenous surface functionalities in the R-CDs. The pH-dependent color switchability was tested in a number of cycles under UV light by adding 0.1 (M) HCl and NaOH. Although several mechanisms involving the complex photoluminescence of CDs have been reported, we propose here that the photoluminescence behavior of the CDs can be tuned by deprotonation of the oxygenous surface functionalities. Moreover, these R-CDs can be used as a potential visual indicator of three different pH ranges, and as highly selective and sensitive sensing medium for Fe3+ ions. The limit of detection was calculated to be 0.43 mu M.