Thiol-functionalized porous clay heterostructures (PCHs) deposited as thin films on carbon electrode: Towards mercury(II) sensing

Thiol-functionalized porous clay heterostructures (PCHs) have been prepared by intragallery assembly of mesoporous organosilica in natural smectite clay. The mesoporous framework was formed by surfactant-directed co-condensation of tetraethoxysilane (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS), at various MPTMS/TEOS ratios, in the interlayer region of the clay. After template removal, the resulting PCHs were characterized by large specific surface areas (400–800 m2 g−1) and pore volumes (0.3–0.6 mL g−1), with mesopore channels bearing a high number of accessible mercaptopropyl groups (0.4–3.0 mmol g−1). These functionalized mesoporous layered materials were deposited as thin films onto the surface of glassy carbon electrodes and applied to the voltammetric detection of Hg(II) subsequent to open-circuit accumulation. They displayed attractive features as the regular mesostructure offered a favorable environment for fast diffusion rates, resulting in great sensitivity, while the layered morphology ensured good mechanical stability. Various parameters have been optimized to get the highest current responses, such as the film composition and thickness, accumulation time, detection conditions, and concentration of the analyte. Linear calibration curves were obtained in the Hg(II) concentration ranges from 4 nM to 20 nM and 0.05 μM to 0.8 μM, respectively, for 20 min and 3 min accumulation. The detection limit calculated on the basis of a signal-to-noise ratio of 3 was 5 × 10−10 M (20 min).