Preparation of colorimetric hydrogel beads for hydrofluoric acid detection

Colorimetric HF-sensitive hydrogel beads were prepared using alginate hydrogel as a host matrix and a pyrocatechol violet (PV)-titanium(IV) bis(ammonium lactato)dihydroxide (TALH) complex as a HF-sensing dye. The PV-TALH complex dye was released into a HF solution from the host matrices and turned the transparent HF solution yellow. From the results of control experiments, this yellow color was exclusively observed when the beads were exposed to HF. The color change allowed the detection of HF with the naked eye. Optimal conditions for the preparation of the HF-sensitive hydrogel were determined with consideration of the swelling behavior of the alginate hydrogel beads.