Water- and pH-Stable Methylthio-Containing Metal-Organic Frameworks as Luminescent Sensors for Metal-Ion Detection

Currently, metal-organic frameworks (MOFs) with thiol functionalities are used as advanced robust materials to solve the problems of pollution and damage caused by metal ions in water. Herein, we report a framework assembled by reacting cadmium nitrate with a new ligand, 4-methylthiopyridine-2,6-dicarboxylic acid, which possesses methylthio and carboxyl functional groups. The resultant MOFs exhibit 5-c net, fnb-type, uninodal net topology with {3³·4·6⁴·7²} point symbols. The thiol-functionalized MOF features good thermal, water, and pH stabilities and luminescence emission at different temperatures. The methylthio-containing cadmium MOF (Cd-MOF) selectively detects the heavy-metal ions Cu²⁺, Hg²⁺, and Pb²⁺in water by luminescence quenching, with low limits of detection (LODs) of 22.60 × 10^-7, 11.07 × 10^-6, and 9.58 × 10^-6M, respectively. The highly selective response and performance of the Cd-MOF probe toward Cu²⁺, Hg²⁺, and Pb²⁺ions were determined by investigating the effects of other interfering ions and different pH values, and the reusability performance was evaluated.