Synthesis of Functionalized Carbon Quantum Dots as Fluorescent Probes for Detection of Cu2+

Polyethyleneimine functionalized carbon quantum dots (PEI-CQDs) were synthesized by one-step hydrothermal method using biomass tar as carbon precursor, which was produced in the reduction smelting process. Based on the selective fluorescence quenching effect between Cu 2+ and PEI-CQDs, the accurate and rapid detection of Cu 2+ was achieved. The results showed that as-prepared PEI-CQDs were spherical particles with uniform sizes, and the average particle size was 1.98 nm. Excellent dispersibility could be obtained in aqueous solution due to the hydrophilic functional groups (such as −COOH, −NH, −CN and C−O) on the surface of PEI-CQDs. The fluorescence quantum yield of CQDs increased from 11.3% to 27.3% after PEI functionalization. Cu 2+ could selectively interact with amino groups on the surface of PEI-CQDs by complexation, leading to the fluorescence quenching effect of PEI-CQDs. And the fluorescence quenching degree exhibited a linear relationship with the Cu 2+ concentration ranging from 0.08 μmol/L to 400 μmol/L with a detection limit of 80 nmol/L. As fluorescent probes, PEI-CQDs have good accuracy and repeatability in Cu 2+ detection, showing outstanding practical feasibility.