Triple-Interpenetrated Lanthanide-Organic Framework as Dual Wave Bands Self-Calibrated pH Luminescent Probe

pH value is a key
parameter in reflecting the health status, reaction
process, and water quality. The construction of highly sensitive pH
luminescent ratiometric is important but challenging. Herein we designed
and synthesized a unique triple-interpenetrated luminescent lanthanide-organic
framework {[Eu­(PPTA)0.5(NO3)­(DMF)2]·H2O}n(V104) based on an amphoteric ligand 4,4′,4′′,4′′′-(1,4-phenylenebis­(pyridine-4,2,6-triyl))­tetrabenzoic
acid (H4PPTA). Compound V104 possesses high
solvent and acid/alkaline stabilities. Luminescent investigations
reveal that V104 exhibits dual emission peaks at 390
and 480 nm, and these two peaks can separately detect OH– and H+ among various anions and cations. Importantly, V104 can serve as a self-calibrated pH ratiometric to quantitatively
detect pH value, and the sensitivity can reach 403.2% per pH for OH–, and 129.5% per pH for H+. Furthermore,
by encapsulating magnetic γ-Fe2O3 nanoparticles
in V104, the pH sensor can be readily separated from
the analyte by external magnet and recycled at least four times, suggesting
as-synthesized γ-Fe2O3@V104 has potential for monitoring pH fluctuations in water. To our knowledge,
this is the first self-calibrated ratiometric pH-sensor based on two
responsive wave bands which can separately detect OH– and H+.