Carbon Dot-Laponite Hybrid Nanocomposites as Selective Turn-Off Sensors for Hg2+ Detection and Photoluminescence Quenching Mechanism

Motivated by the importance of Hg2+ detection in water due to its harmful effect on the environment and human health, we investigated a recently developed nanocomposite based on carbon dots (CDs) and LAPONITE as an optical chemical sensor using photoluminescence emission. While several studies have reported the Hg2+ detection using CDs' photoluminescence emission, there is a lack of in-depth investigation into the quenching mechanisms involved in turn-off sensors. In this study, we propose a Stern-Volmer analysis at three different temperatures (288, 298, and 303 K). The results indicated selectivity for Hg2+ over that of the other evaluated metal. The optimum detection range for Hg2+ was found to be 1-40 mu M, with limits of detection and quantification of 2.5 and 8.3 mu M, respectively. Using the Stern-Volmer models, we found that static quenching dominates over collisional quenching, possibly due to the complexation between nanocomposite's carboxylate groups and Hg2+. Additionally, the modified Stern-Volmer model, which accounts for the fractional accessibility of the fluorophores by the quenchers, suggests that some parts of the sensor are inaccessible to the quencher.