Green synthesis of carbon quantum dots from lignite coal and the application in Fe³⁺ detection

Carbon quantum dots (CQDs) had attracted much attention due to their unique structures and excellent properties. Their green preparation was one of the research frontiers. However, most of the CQDs were prepared by strong acid oxidation, the way of which was not friendly to the environment. In this study, CQDs were prepared by green ozone oxidation of lignite coal, which is abundant and inexpensive. The CQDs were well dispersed, the size distribution of the obtained CQDs centralized from 2 to 4 nm with the average diameter of about 2.8 nm. In addition, the as-prepared CQDs containing rich oxygen functional groups exhibited good water-solubility and optical properties with yield reached 35%. The CQDs showed a highly sensitive and selective quenching effect to Fe³⁺ with desirable anti-interference performance. Moreover, the fluorescence intensity of CQDs had a good linear response to the Fe³⁺ concentration ranging from 10 to 150 μmol/L with the detection limit of 0.26 μmol/L. This green and facile synthesis method had the prospect of large-scale preparation of CQDs.