Mild Alkaline-Enhanced depolymerization of Long-Flame coal for the synthesis of Coal-Derived fluorescent carbon dots with application as probes.

[Display omitted] • Fluorescence carbon dots were directly prepared by alkaline hydrothermal method from low-rank coals. • Carbon dots had an average size of 1.36 nm with graphitic structure and fewer functional groups. • Carbon dots exhibit high emission intensity at both long and low excitation wavelengths. • Low fluorescence emission is caused by quantum size effects while the long one is resulted from functional groups. • The carbon dots shows excellent trace detection of Fe3+ or Cu2+ ion with detection limit of ∼ 0.04 μM. The intricate composition and structural of low-rank coal have hindered its broad utilization in the field of material science. The study utilized an alkaline hydrothermal method to enhance the depolymerization of long-flame coal and achieve the purification of fluorescent carbon dots for the first time, which were then being employed for the trace detection of Cu2+ or Fe3+ ions. The carbon extraction efficiency reached 58 %, with the carbon dots averaging size of 1.36 ± 0.42 nm, the sp2 hybridized structure of the carbon dots indicated successfully purification under alkaline conditions. After reduction with sodium borohydride, defects in the core region of the carbon dots were repaired, and the C = O functional groups were transformed into O–H groups, leading to an increase in fluorescence intensity. At a concentration of 0.25 g/L of carbon dots, demonstrated high emission intensity at both long and low emission wavelengths, which can be used as LED luminescent material. Furthermore, the application of these carbon dots in detecting heavy metal ions (Cu2+, Fe3+) in aqueous solutions was explored, showing as low as detection limit of ∼ 0.04 μM. This study achieved higher depolymerization of coal and purification of fluorescent carbon dots for use in probe-based detection, providing fresh perspectives on the high-value utilization of low-rank coal. [ABSTRACT FROM AUTHOR]