A dual-mode pH sensor film based on the pyrene-based Zr-MOF self-destruction with fluorescence turn-on effect

Rapid detection of on-the-spot water sample pH has become an urgent problem to resolve, and developing a method with the characters of fast, convenient and low-cost is significant. In this study, an amino functionalized pyrene-based Zr-MOF (NU-1000-NH2) was synthesized by solvent-assisted ligand incorporation (SALI) method, in which the Zr6 metal cluster, fluorescent pyrene-based H4TBAPy and p-aminobenzoic acid were acted as node, linker and modulator, respectively. The as-synthesized NU-1000-NH2 possessed the pH-dependent fluorescence enhancement property at 450 nm emission under alkaline condition, thus a convenient fluorescence "turn-on" pH sensor was fabricated. Upon introduction of OH–, the carboxylate groups in NU-1000-NH2 could react with it, and the deprotonation and gradual collapse of the NU-1000-NH2 crystal were occurred, resulting in the release of the fluorescent H4TBAPy ligand and fluorescence enhancement. Moreover, to solve the difficulties of on-the-spot pH detection, the solid-phase pH film sensor was successfully constructed by embedding the NU-1000-NH2 particles into the polyvinyl alcohol (PVA), combining with the RGB model and smartphone detector. The proposed fluorescent MOF-based pH sensor with dual-mode detection is expected to achieve on-the-spot pH monitoring in the field of environmental monitoring.