A new “on–off–on” g-C3N4 nanosheets fluorescent sensor for 5-Br-PADAP and Co2+ under acidic conditions

Abstract

Scientists are still working on developing a “turn-on” fluorescence sensor for Co²⁺, especially in acidic solutions. A novel “on–off–on” fluorescence sensor based on g-C₃N₄ nanosheets was designed and prepared in this paper. It was able to detect (2-(5-bromo-2-pyridylazo)-5(diethylamino)phenol (abbreviated to 5-Br-PADAP) and Co²⁺ quantitatively by quenching and restoring the fluorescence of the g-C₃N₄ nanosheet system, respectively. Also discussed are the effects of solvent, pH, order of addition, and interaction time of 5-Br-PADAP and Co²⁺, as well as the concentration range of the object on measurement. Furthermore, in acidic conditions, the sensor demonstrated good selectivity and sensitivity. In the solvent system EtOH : H₂O (v/v = 1 : 9, pH = 3), the fluorescence intensity had a good linear relationship with 5-Br-PADAP and Co²⁺ concentrations in the ranges of 0–15 μM and 0–10 μM, with low detection limits of 64 nM and 44 nM, respectively. Experiments and theoretical calculations were used to describe the interaction characteristics and sensing mechanism. It was eventually successful in detecting Co²⁺ in environmental samples.