Facile synthesis of heteroatom-doped carbon dots: Structural insights, Solvatochromism and selective sensing of picric acid

Carbon dots, zero-dimensional carbon nanostructures with multicolour emission in various solvents, have garnered significant interest as a new category of luminescent nanomaterials due to their low production cost and facile synthesis. Herein, we propose a simple one-pot pyrolysis method that uses 4-bromo-1,2-phenylenediamine as the starting material to prepare carbon dots with bromine and nitrogen doping (Br, N-CDs). Several spectroscopic and microscopic techniques were employed to thoroughly characterise the resultant CDs. HR-TEM demonstrated that the particles were spherical with an average diameter of roughly 3 nm, while HR-SEM displayed a characteristic nano-roller comb morphology. Surface functional groups, such as carboxyl, hydroxyl and amine groups, were verified by IR and XPS analysis. The Br, N-CDs demonstrated excellent photostability and high solvent-dependent fluorescence. Interestingly, they exhibited high fluorescence quantum yield (QY) of up to 39% in acetone, exhibiting excitation-independent emission. Their fluorescent characteristics allowed for the sensitive finding of picric acid (PA) in aqueous solution via an inner filter effect-based fluorescence quenching mechanism. The limit of detection was found to be 50 nM, and an attractive linear retort was observed in the region of 0–1 μM. High selectivity for PA over other nitroaromatic compounds was shown by the fluorescence probe.