Synthesis of cationic carbon quantum dot-based dual emission fluorescence sensor for detecting perrhenate anions in aqueous solutions

Abstract

This study developed a carbon quantum dot to selectively detect perrhenate anions, which was used as a surrogate for the radioactive pertechnetate anion, in aqueous solutions. A blue emission carbon dot (B-CD) was prepared using a simple microwave technique, whereas a dual-emission carbon dot (D-CD) was prepared using 1,3,6-trinitropyrene. When the concentration of the perrhenate anion was increased, both B-CD and D-CD exhibited a decrease in fluorescence brightness owing to the inner filter effect; however, no changes were observed in terms of color. Therefore, cationic D-CDs (C-CDs) were synthesized by introducing quaternary ammonium functional groups on the surface of D-CD to enhance the binding characteristics with the perrhenate anion. At an excitation wavelength of 350 nm, both B-CD and D-CD failed to exhibit a decrease in fluorescence brightness; however, the change in color and reduced brightness of fluorescence were observed in C-CD because of the perrhenate anion. The change in fluorescence color can be attributed to the difference in the intensity reduction in dual-emission wavelength regions. Furthermore, C-CD exhibited linear correlations for perrhenate anion concentrations of up to 1 mM, and the limits of detection were 87 and 208 μM at excitation wavelengths of 254 and 350 nm, respectively. Additionally, the results indicate that C-CD can be used as a sensor to detect perrhenate anions despite the presence of excess chloride anions. This fluorescence change can be attributed to the photoinduced electron transfer mechanism caused by the electrostatic interactions between the cationic surface functional groups of C-CD and perrhenate anions.