Ayşe Nur Şahin, Ahmet Altındal, Zeynep Güven Özdemir
Abstract This study presents comparative investigation of the QCM-based sensing performance of hydrothermally synthesized 2-D CuS and SnS 2 nanostructures toward divalent metal ions (Co 2+ , Ni 2+ , Zn 2+ , Cu 2+ , and Mg 2+ ) in aqueous media, offering new insights into their sensing behavior. Unlike previous studies mainly focused on single-material adsorption or electrochemical sensing approaches, the present work systematically compares the QCM sensing behavior of CuS and SnS 2 nanosheets toward multiple divalent metal ions under identical aqueous sensing conditions and provides a physicochemical interpretation of the adsorption-driven sensing mechanism. After the structural and morphological characterizations by XRD, FE-SEM, and TEM techniques, thin film of the sensing unit was deposited on Quartz Crystal Microbalance (QCM) transducers. XRD results showed that CuS in covellite phase and SnS 2 in Berndtite − 2T phase were successfully synthesized. FE-SEM and TEM results revealed that CuS nanostructures have an average thickness of approximately 31 nm and lateral dimensions of around 146 nm, while SnS 2 exhibits a thickness of about 38 nm with lateral dimensions of approximately 140 nm. QCM results showed that the maximum sensitivity was observed for Mg 2+ ions with CuS- and SnS 2 -based sensors. On the other hand, limit of detection (LoD) calculations showed that CuS-based sensors seem to be more suitable for detecting low concentrations of Mg 2+ ions, with the LoD value of 0.72 ppm, while SnS 2 -based sensors seem to be more suitable for detecting very low concentrations of Co 2+ ions. In addition, UV–Vis absorption analysis revealed noticeable spectral shifts after ion adsorption, indicating changes in the electronic environment of S 2− active sites and supporting the occurrence of ion–surface interactions. The adsorption isotherms of the DMIs from aqueous solutions onto CuS and SnS 2 were modelled using Langmuir, Freundlich, Temkin, and Jovanovic isotherm models. Regression analysis showed that the number of sulfur atoms and the acidity of the analyte ions have a strong effect on the DMIs adsorption isotherm.