CONTROL THE SURFACE CHEMISTRY OF CARBON NANODOTS BY ENGINEERING THE PRECURSOR ACID/AMINE RATIO

Abstract

Controlling the surface functional groups of carbon nanodots is important to deploy carbon nanodots in various applications, such as visible-light photocatalysts, nanobiosensors, and multifunctional materials. In this study, we prepared a series of carbon nanodots by hydrothermal treatment mixtures of citric acid and ethylenediamine with different citric acid/ethylenediamine ratios. By using Fourier transform infrared, photoluminescent, and UV-Vis spectroscopies, it was demonstrated that the surface chemistry of carbon nanodot changed from carboxy-rich to amino-rich when the citric acid/ ethylenediamine ratio decreased. All carbon nanodots had a common absorption band at about 350 nm while their emission quantum yield varied from 2.5% to 63.0%. Theoretical calculations suggest that the energy levels of HOMO and LUMO of carboxy functionalized carbon nanodots were lower than those of amino-functionalized carbon nanodots while their bandgaps were similar. These research results provide important information for designing carbon nanodots for targeted applications.