A pyrocatechol violet-titanium alkoxide complex for HF sensing: Study on the complex structure and application

• PV-TALH complex dye was prepared with specific sensitivity to HF.
• Colorimetric detection of hydrofluoric acid vapor was achieved using the complex dye.
• Structure and cleavage of the complex dye was verified through the NMR analyses.

We prepared a pyrocatechol violet-titanium (IV) bis(ammonium lactato)dihydroxide (PV-TALH) complex that can be used as a colorimetric HF sensing dye. The titanium alkoxide, titanium (IV) bis(ammonium lactato)dihydroxide (TALH), easily formed a complex with pyrocatechol violet (PV) dye, which dissociated when exposed to HF and led to visible color change from dark blue to light yellow. The PV-TALH complex showed outstanding selectivity for HF over other acids. To elucidate the HF sensing mechanism, structural changes in the PV-TALH complex were investigated through nuclear magnetic resonance (NMR) and LC-mass spectroscopy for the first time. The NMR spectroscopy study revealed that PV catechol moiety associated with Ti of TALH to form a complex while changing the coordination of lactate ligand from bidentate to monodentate. When the complex is exposed to HF, fluoride ion cleaved the complex due to high affinity of fluoride to titanium. Further protonation of PV dye and dissociation of the lactate ligands from TALH occurred by the acidity. The PV-TALH complex allow to prepare HF sensing dye without complicate chemical synthesis or additional modification. Finally, as a practical application of the PV-TALH complex dye, the naked-eye detection of hydrofluoric acid vapor using a PV-TALH hydrogel was demonstrated.

The pyrocatechol violet-titanium (IV) bis(ammonium lactato)dihydroxide complex functioned as a HF sensing dye whose structural changes before and after exposure to HF were fully analyzed through NMR spectroscopy.Figure optionsDownload as PowerPoint slide