Green preparation of carbon dots with different surface states simultaneously at room temperature and their sensing applications

It is a considerable challenge to develop environmental friendly, low-cost methodology for green preparation of carbon dots (CDs). Herein, CDs with different surface states are prepared using o-phenylenediamine (o-PD) and hydroquinone (HQ) as precursors via oxidation/polymerization and Schiff base reaction at room temperature without additional oxidizing agents. Two CDs products (YCDs and GCDs) are obtained after separation with silica gel column chromatography based on their polarity differences. The different surface states endow these two CDs with different properties. The rich NO2 and OH groups on the surface of YCDs contribute to a narrow band gap, resulting in the red-shifted photoluminescence (PL) emission of this CDs product, making it a sensitive probe for the detection of toxic pollutant p-nitrophenol (p-NP) attributed to the inner filter effect, along with a detection limit of 0.08 μmol/L. GCDs are characterized with abundant surficial NH2 groups, and can be used as a potential probe to detect H2O content in D2O, giving a detection limit of 0.17 vol%.