Influence of citric acid on the optical properties of folic acid-derived amorphous carbon nanoparticles and detection of triethylamine

Carbon nanoparticles (CNPs) with unique photoluminescence properties have promising potential for detecting volatile organic compounds. In this work, employing folic acid as the carbon source and citric acid as the surface modifier, blue fluorescent CNPs were synthesized using a simple and inexpensive hydrothermal method. These CNPs feature an amorphous carbon structure and present a reduced size of 24 nm and an increased presence of carbonyl groups on their surface owing to the incorporation of citric acid, demonstrating enhanced surface defect states and exhibiting excitation-dependent fluorescence behavior. The citric acid-assisted composite CNPs exhibit excellent optical selectivity towards triethylamine (TEA), with a particularly optical response, enhancing at low concentrations and quenching at high concentrations. The synergistic effect of electron transfer results in high sensitivity and a low detection limit of 0.28 µM. The synthesized CNPs serve as fluorescent probes for TEA in an aqueous medium. The detection mechanism of citric acid-assisted CNPs is explored in detail.