Synthesis of Eco-Friendly Sustainable Carbon Dots: A Fluorescent Probe for Chromium VI Ions in Aquatic Environment

Owing to its high toxicity and water solubility, chromium (VI) poses severe risks to biological systems through aquatic environments. Therefore, it is important to develop new, sustainable, and efficient detection techniques for Cr⁶⁺ ions. In this study, blue-emitting carbon dots (DL-CDs) were synthesized from biomass via a direct heating method using Dalbergia latifolia leaves as the carbon source. Upon excitation at 380 nm, the DL-CDs exhibit strong blue fluorescence emission at 435 nm. The synthesized DL-CDs possess an average particle size of approximately 5.5 nm and are rich in surface functional groups such as carbonyl, hydroxyl, and carboxyl groups. The DL-CDs demonstrate high selectivity and sensitivity toward Cr⁶⁺ ions, with a detection limit of 0.80 µg/mL. A clear linear relationship was observed between fluorescence intensity and Cr⁶⁺ concentration over the range of 0–30 µg/mL, accompanied by consistent fluorescence quenching. Fluorescence lifetime measurements revealed that the quenching mechanism is primarily due to ground-state complex formation. The developed DL-CDs-based fluorescent probe is cost-effective, highly sensitive, and selective, and it performs well in the detection of Cr⁶⁺ ions in real water samples with good accuracy. Additionally, the residual carbon material was further activated and successfully utilized for the adsorption of various pollutants.