Chemical sensors based on nano-sized lanthanide-grafted periodic mesoporous organosilica hybrid materials

Abstract

In this work we introduce the use of nano-sized (50–70 nm) lanthanide-grafted periodic mesoporous organosilicas for both metal ion sensing and solvent sensing. For this study a PMO constructed from the N,N-bis(trimethoxysilylpropyl)-2,6-pyridine dicarboxamide linker and tetraethyl orthosilicate (at a 5 : 95 ratio) was employed. This material was grafted with Eu³⁺, Tb³⁺ or a mixture of Eu³⁺–Tb³⁺ chloride salts to obtain strongly emitting nano-sized luminescence materials. To further enhance the luminescence properties of the materials two different co-ligands were used – 1,10-phenanthroline (phen) and 5,5′-dimethyl-2,2′-dipyridyl (bpy). The luminescence properties of the developed series of hybrid materials were studied in detail in the solid-state and after dispersing in water. The materials were investigated for their use as ion sensors, with the Eu³⁺ and Tb³⁺ phen and bpy co-grafted materials showing selective “turn on” fluorescence for Pb²⁺ and Cr³⁺ ions (at a 10 ppm concentration of the ions). The Eu³⁺–Tb³⁺ co-grafted materials showed solvatochromism and could be used as a solvent sensor to distinguish between protic and aprotic solvents.