Effect of synthesis methods on the acetone sensing behaviour of fluorescent carbon dots

Abstract Carbon dots (CDs) are an emerging family of nanostructures due to their unique optical properties, high chemical stability, biocompatibility, and low toxicity, they have been able to attract a lot of attention and cause significant changes in various scientific fields. In this study, the green synthesis of stable CDs by hydrothermal and pyrolysis methods (H-CDs and P-CDs) is performed from Nigella sativa seeds as a natural precursor. Using these methods, the formation and the surface passivation of the CDs are done simultaneously, resulting in the intrinsic fluorescence emission. The as-prepared CDs are characterised by UV–vis spectroscopy, fluorescence spectroscopy, elemental analysis, dynamic light scattering, Fourier transform infrared spectroscopy, and transmission electron microscopy, from which their structural information and property are interpreted. The fluorescence intensity graph of H-CDs and P-CDs, with excitation wavelengths in 360 nm, shows the highest emissions at 430 and 410 nm, respectively. Particle size distribution was obtained at about 4 nm. The fluorescent quantum yield (QY) of H-CDs and P-CDs was measured to be 7% and 2%, respectively. The synthesised CDs showed good photoluminescence (PL) responses to acetone solution. Acetone had a different effect on the PL properties of CDs obtained from pyrolysis and hydrothermal methods so that in P-CDs, it increased the intensity of PL, and in H-CDs; it decreased the intensity of PL.