Lower Rim-Modified Calix[4]arene–Bentonite Hybrid System as a Green, Reversible, and Selective Colorimetric Sensor for Hg²⁺ Recognition

A new quinaldine-functionalized calix[4]­arene receptor (QHQC) was synthesized, characterized, and analyzed for its selective sensing properties toward Hg²⁺ ions, and the binding event with characteristic color change can be followed by the naked eye. The sensing process is reversible, and the detection limit for Hg²⁺ ions is 2.95 × 10^–6 M. A colorimetric solid state Hg²⁺ sensor was fabricated by intercalating this receptor molecule into the bentonite galleries via the ion-exchange method. This organic–inorganic hybrid sensor shows properties analogous to the receptor molecule and effectively detects Hg²⁺ ions rapidly with visual color change. The solid state Hg²⁺ sensor is economically affordable, environmentally benign, portable, reversible, and reusable