Green synthesis of mango ginger (Curcuma amada) derived fluorescent carbon dots—a potent label-free probe for hexavalent chromium sensing in water

Carbon dots from bio-resources recently received significant impact due to ease of availability, low cost, and simple equipment requirements. In this work, a highly fluorescent carbon dots derived from agro-bio-based precursor, mango ginger rhizomes were developed through a straightforward, low-cost, rapid, economical, and one-step microwave method, without using any chemical reagents or any expensive instruments. The prepared carbon dots exhibited excitation-dependent fluorescence with excitation and emission maxima at 360 and 442 nm, respectively. On account of the excellent photoluminescent property of the system prepared, it is executed as an outstanding hexavalent chromium sensor by fluorescence quenching. Extensive usages of this metal in different fields are unfavorable and cause pollution to the ecological system, and thus sensing of hexavalent chromium in an environmental sample, especially in water resources are highly demandable. The system possesses higher selectivity and sensitivity toward chromium with a limit of detection of 84 nM (4.367 ppb) and a linear relationship between the concentration of chromium and fluorescence intensity maintained from 0 to 33.33 µM. The mechanism was studied using different methods and finally attributed to the inner filter effect. Hereby value addition has been given to the agro-based precursor through an environmentally benign method and is successfully employed as a hexavalent chromium sensor in real water samples with recovery from 95.07 to 102.70%.