Enhanced fluorescence of Zn-doped carbon quantum dots using zinc citrate chelate as precursor for fluorescent sensor applications

摘要

The Zn~(2+) doped Carbon Quantum Dots (Zn-CQDs) were synthesized with zinc citrate chelate as the precursor by a hydrothermal method. The evaluation results indicated that Zn~(2+) was successfully embedded in CQDs. Most of Zn~(2+) ions were combined with carboxyl groups on the surface of carbon dots to form Zn-O bonds and some Zn~(2+) ions were embedded in the interstice points of CQDs. The remaining Zn~(2+) were reduced to zinc atoms and adsorbed on the surface of CQDs. With the increase in Zn~(2+) concentration, the size of synthesized Zn-CQDs increased. When zinc ion concentration increased to 9%, the average size of Zn-CQDs grew up to 8 ran, but the size of undoped CQDs was just 1.5 nm. When Zn~(2+) concentration increased from 1% to 9%, the fluorescence intensity increased, while reaching above 9%, the fluorescence intensity showed a downward trend. When Zn~(2+) concentration was 7%, the fluorescence quantum yield of Zn-CQDs increased to 48%, but the fluorescence quantum yield of undoped CQDs was only 37%. With the increase in Zn~(2+) concentration, the PL spectrum of Zn-CQDs showed a red shift phenomenon. In addition, Zn-CQDs showed superior fluorescent sensing capability to Fe~(3+) and Hg~(2+), presenting greater fluorescence quenching effect on Fe~(3+) and Hg~(2+) than CA-CQDs. Therefore, Zn-CQDs demonstrated excellent fluorescence properties and can be applied in fluorescent sensor, biological imaging, optoelectronics, and catalysis fields.