Facile synthesis of nitrogen-doped carbon dots from COOH-functional ionic liquid and their sensing application in selective detection of free chlorine

Heteroatom doped carbon dots (CDs) possess many unique properties and have attracted increasing attention. The precursor is vital for the preparation of highly fluorescent heteroatom doped CDs. Herein, 1, 3-bis(carboxymethyl)imidazolium chloride ([Im(AH)2]Cl, a COOH-functional ionic liquid) and aminoethylethanolamine (AEEA) were firstly used as precursors to prepare nitrogen-doped carbon dots (N-CDs) by a simple one-step pyrolysis approach. The effects of reaction time, temperature, and mass ratio of precursors on the quantum yield (QY) of N-CDs were investigated. The prepared N-CDs are spherical morphology with an average diameter of 2.4 nm, and have blue fluorescence with a QY of 23.2% and excitation-dependent emission behavior. They also possess good water solubility and fluorescent stability. In addition, based on the obtained N-CDs, a sensing method of free chlorine detection in acidic water system was introduced. The proposed method has good sensitivity and selectivity to free chlorine, and exhibits a nice linear response in the concentration range from 0.2 to 22 μM with a detection limit of 0.15 μM. Furthermore, this sensing method was successfully applied to detect free chlorine of tap water with satisfactory recovery (97%–103%), suggesting it has the potential application in water quality monitoring.