Mechanistic Study of Rhodamine B Piezocatalytic Decomposition Using Poly(vinylidene Difluoride) and Related Polymers

Membranes of poly(vinylidene difluoride) (PVDF) and relatedpolymersare used as piezoelectric materials to decompose rhodamine B (RhB)under low power sonication. The change in the visible spectrum ofRhB allows determination of the rate constants for different polymercompositions and membrane thicknesses. The results indicate that thepiezoelectric field generated by mechanical deformation of the polymerscatalyzes the scission of the C-N bond in RhB. When PVDF isdoped with transition-metal nitrates to increase the fraction of thepiezoelectric beta-phase, the rate constants increase, but theanalysis is complicated by concurrent adsorption of RhB onto the membrane.A mechanism consistent with the observed data is proposed where thepiezocatalytic effect of the membrane is to heterolytically cleavethe C-N bond followed by formation of a C-Cl bond onthe new xanthene ring.