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 μM, with limits of detection and quantification of 2.5 and 8.3 μM, 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.