Carbon quantum dots derived by direct carbonization of carbonaceous microcrystals in mesophase pitch

Aggregation of the central aromatic ring system of asphaltene molecules due to π-π interaction can lead to the formation of carbon quantum dots (CQDs). However, to date, such a roadmap has not been demonstrated. Here, we present a simple approach to the synthesis of CQDs by direct carbonization of dispersed carbonaceous microcrystals in mesophase pitch. The size of the as-prepared CQDs is modulated by adjusting the nucleation temperature for mesophase formation. Due to the oxygen-free character, the CQDs exhibit excitation-independent fluorescent behavior with a quantum yield up to 87%. The CQDs were successfully applied to fluorescent detection of Fe³⁺ ions with good specificity and sensitivity. Our results not only provide a scalable production of CQDs at low cost, but also give valuable clues to understand the solidification of asphaltene at nanoscale.