A dual-functional metal phosphate for high proton conduction and selective luminescence turn-on sensing of Co2+ ions

Abstract

In this work, {[Zn(H₂PIPZ)](H₂O)}_n was synthesized by self-assembly of an N,N′-piperazinebis(methylenephosphonic acid) [H₄PIPZ] ligand and zinc chloride under hydrothermal conditions. The Zn²⁺ ion is four-coordinated by oxygen atoms from four different H₂PIPZ²⁻ ligands to form a tetrahedral configuration. The Zn²⁺ tetrahedral units are further connected by a phosphate group of the H₂PIPZ²⁻ ligand to form a 3D structure. AC analysis shows that the proton conductivity of compound 1 is excellent and by introducing 1 into PVA to make composite membranes, the proton conductivity of composite membrane 1@PVA-10 (10% wt) reached 2.78 × 10⁻⁴ S cm⁻¹ at 98% RH and 353 K, which is approximately ten times higher than that of 1. In addition, compound 1 has excellent selectivity and sensitivity to cobalt ions in water due to turn on fluorescence. The detection limit is 1.0 × 10⁻⁸ M. In contrast, the Fe³⁺ ion has a turn off fluorescence effect on 1 and the detection limit is 1.0 × 10⁻⁶ M.