Ultra-sensitive and stable N-doped carbon dots for selective detection of uranium through electron transfer induced UO2+(V) sensing mechanism

Abstract

Unintended leakage of toxic and radioactive uranyl ion (UO22+) ions poses high harmful to human health and environment, hence its monitoring and detection is of utmost significance. Here, we developed a mild synthetic route to prepare stable N-doped carbon nanodots (CDs) with special hydrophilicity functional groups and graphitic N by polymerization and carbonization of novel norfloxacin precursor with nitrogen heterocyclic structure. The morphology, chemical structure, fluorescent properties, sensing competition and selectivity behaviors of CDs-UO22+ were systematically analyzed. Controllable experiments including low and high concentration CDs-UO22+ and another type of carbon dots (TEA-CDs) with low graphitic N amount using triethanolamine (TEA) precursor without nitrogen heterocyclic structure were designed, which further confirmed the effective coordination and interaction mechanism between CDs and UO22+ that graphitic N in CDs induced the formation UO2+(V) by electron transfer. It is very suitable for on-site and real-time monitoring of UO22+ with an ultra-fast response time (∼20 s) and low detection limit of 20.38 nM (4.7 μg L−1), which is lower than the permissible limits (30 μg L−1) defined by the United States Environmental Protection Agency (EPA). More importantly, different form the liquid sensor, solid sensors (printed test strip and hydrogel) were also successfully employed to monitor UO22+ targets quickly, broadening the potential application for the advanced image encryptions.