A highly efficient, rapid, room temperature synthesis method for coal-based water-soluble fluorescent carbon dots and its use in Fe³⁺ ion detection

We report a method for the of coal-based fluorescent carbon dots (CDs) at room temperature using a mixture of hydrogen peroxide (H₂O₂) and formic acid (HCOOH) as the oxidant instead of concentrated HNO₃ or H₂SO₄. The CDs have an excitation dependent behavior with a high quantum yield (QY) of approximately 7.2%. The CDs are water soluble and have excellent photo-stability, good resistance to salt solutions, and are insensitive to pH in a range of 2.0-12.0. The CDs were used as a very sensitive probe for the turn-off sensing of Fe³⁺ ion with a detection limit as low as 600 nmol/L and a detection range from 2 to 100 μmol/L. This work provides a way for the high value-added utilization of coal.