Structure-interface function relationships in piezoactive PVDF/BaFe12O19 membranes enabling ultrasound-and magnetically driven catalytic degradation

Porous Poly(vinylidene fluoride)/BaFe 12 O 19 (PVDF/BAF) composite membranes with different BaFe 12 O 19 (BAF) loadings were fabricated via a non-solvent/thermally induced phase separation (NIPS-TIPS) approach and systematically investigated in photo-, piezo-, piezophotocatalytic, and magnetically induced piezocatalytic degradation of methylene blue. Structural, phase, and surface analyses performed by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray photoelectron spectroscopy (XPS) revealed the formation of a developed interfacial region and stabilization of the electroactive (β + γ) phase of PVDF upon incorporation of BAF, while preserving the phase integrity and chemical stability of the f BAF component within the polymer matrix. It was experimentally established that under ultrasonic activation the piezocatalytic mechanism dominates, providing a high dye degradation efficiency (up to ~95-96%), with the maximum performance already achieved at a low filler loading (2 wt.%). Using selective scavenger tests and a fluorescent terephthalic acid probe (TA-probe) method, hydroxyl radicals (·OH) were identified as the primary reactive species governing the piezocatalytic oxidation mechanism; the apparent steady-state ·OH concentration was estimated to be on the order of 10 -14 –10 -15 M. The results obtained by both independent approaches are in good agreement and confirm the radical oxidative nature of the process. Magnetically induced piezocatalysis was demonstrated for the first time in PVDF/BAF membrane composites without direct mechanical contact and without optical excitation. Under an alternating magnetic field, the catalytic activity increases monotonically with increasing ferrimagnetic phase content, reaching ~81% degradation after 240 min for the membrane containing 10 wt.% BAF. This behavior is attributed to magnetostriction-induced local deformations of BAF particles and their efficient transfer to the piezoactive polymer matrix. Piezoelectric response measurements using a piezoelectric nanogenerator (PENG) revealed a non-monotonic dependence of the output voltage amplitude on composition and showed a maximum piezopotential for the PVDF/BAF2 membrane (~1.3–1.4 V), which directly correlates with its highest piezocatalytic activity. Overall, the results experimentally demonstrate the key role of interfacial interactions, morphology, and mechanical compliance in controlling the efficiency of piezo- and magnetically induced catalytic processes and identify PVDF/BAF membranes as a promising platform for energy-efficient water treatment systems activated by remote physical fields.