Rational design of nitrogen-doped carbon quantum dots decorated g-C ₃ N ₄ nanosheets: a fluorescent chemosensor for the selective detection of bismuth ions and its application in real samples

Abstract In this work, nitrogen-doped carbon quantum dots (N-CQDs) decorated graphitic carbon nitride (g-C 3 N 4 ) nanocomposite (N-CQDs/g-C 3 N 4 ) has been synthesized through hydrothermal method. The resulting nanocomposite was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, elemental mapping, high-resolution transmission electron microscopy, elemental dispersive X-ray spectroscopy, and UV–vis analysis. Utilizing this nanocomposite, we developed a novel fluorescent probe for the selective detection of Bi 3+ ions. The presence of carbon and nitrogen groups in the nanocomposite enables Bi 3+ ion detection via a fluorescent ‘turn off–on’ process with a detection limit of 0.289 µM in a DMF:H 2 O (1:1) mixture. This nanoprobe demonstrates exceptional reusability as it can be chemically regenerated and employed for Bi 3+ ion detection for up to 10 cycles without any loss in fluorescence properties. Furthermore, it reaches equilibrium within 2 min of Bi 3+ ion addition and remains stable for over 10 min ensuring its reliability and stability. The efficacy of the N-CQDs/g-C 3 N 4 chemosensor was validated in real-world applications through the analysis of water samples from Kaveri and Siruvani Rivers (Tamil Nadu, India), delivering impressive recovery rates ranging from 87.4 to 90.1 % and 76.2 to 83.9 % respectively.