posted on 2024-02-08, 15:37authored byZiyang Li, Liangliang Lin, Jie Shen, Cheng-Dong Li, Kostya Ken Ostrikov
Green continuous synthesis of fluorescent carbon dots
(CDs) from
natural resources is a promising but challenging alternative to batch
processing. Herein, a microflow approach was used to prepare CDs from
a lemon juice precursor in one step. Through optimization of the reaction
conditions, CDs prepared at 160 °C and 30 min of residence time
were selected as a study model. Their structures, morphology, size,
chemical composition, and optical properties were comprehensively
analyzed. The results show small-sized fluorescent CDs with a high
quantum yield and narrow size distribution, which are composed of
a mixture of sp2- and sp3-hybridized carbon
atoms and functional groups. The CDs show excellent photoluminescence
properties and fluorescence stability at different pH values (pH:
5–11) and salt levels (KCl concentration: 0.25–4 M).
Relying on the high binding affinity toward Co2+ ions,
the microflow-synthesized CDs exhibited good selectivity and sensitivity
for Co2+ sensing, with a detection limit down to 318 nM.
The microflow approach was compared with existing techniques for the
synthesis of CDs to show its advantages. In addition, a plausible
Co2+-induced fluorescence quenching process and scale-up
strategy for CDs synthesis are discussed.