A New Highly Sensitive Optical Sensor Based on Congo-Red for the Determination of Thorium (IV) in Aqueous Solution

This essay explores the use of the sol–gel method based on the Congo-red reagent as an effective approach to create an optical sensor for the detection and tracking of Thorium (IV) (Th 4+ ). Upon exposure to a Th 4+ -containing solution, the sensor exhibits significant absorption signal change that linearly correlates with Th 4+ ion concentration across a wide range. It is capable of detecting Th 4+ ion in the linear dynamic range of 1.7 × 10 −8 to 1.1 × 10 −3 mol/L, with a detection limit of 5.3 × 10 −9 mol/L. This optode's exceptional porous network, created through the sol–gel technique, contributes to its commendable performance, reliable repeatability, improved sensitivity, swift response time, and discerning selectivity.