Morphological and structural aspects in PVDF/CoFe2O4 membranes and their influence on piezocatalytic activity

Abstract

This study explores the structural, morphological, optical, dielectric, piezoelectric, and piezocatalytic properties of polyvinylidene fluoride (PVDF) composite membranes incorporating cobalt ferrite (CoFe2O4, CFO) nanoparticles at 25 and 35 wt% loadings. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the retention of electroactive β- and γ-phases, with the PVDF matrix maintaining approximately 50% crystallinity. Morphological analysis demonstrated reduced porosity, increased surface roughness (Rq increased from 155 to 442 nm for PVDF/CFO10), and nanoparticle aggregation with higher CFO content. Optical studies revealed a significant reduction in reflectance and increased absorption due to CFO incorporation. Piezoelectric force microscopy (PFM) confirmed enhanced local electromechanical response, with a 20% increase in active piezoresponse areas under an external magnetic field. Dielectric analysis demonstrated frequency-dependent permittivity changes, with a notable increase in ε′ under mechanical load. The piezoelectric coefficient d₃₃ increased from 3.5 pC/N in pure PVDF to 9.1 pC/N for PVDF/CFO10. Under ultrasonic excitation, PVDF/CFO10 achieved 84% methylene blue degradation, attributed to cavitation centers formed by surface-exposed CFO nanoparticles. Piezoelectric nanogenerators (PENGs) based on PVDF/CFO10 generated a maximum open-circuit voltage of 17.6 V under vertical compression and ±2 V under ultrasonic stimulation. These findings highlight the multifunctionality of PVDF/CFO composites for energy harvesting, dielectric applications, and environmental remediation. Highlights: Cobalt ferrite CoFe2O4 (CFO) nanoparticles improve polyvinylidene fluoride (PVDF) piezocatalysis, achieving 84% methylene blue degradation. Approximately 10% CFO content enhances membrane surface activity and cavitation effects. PVDF/CFO composites retain approximately 50% crystallinity with β- and γ-phase stability The piezoelectric coefficient d₃₃ increased from 3.5 pC/N (PVDF) to 9.1 pC/N (PVDF/CFO10). ±2 and 17.6 V output voltage achieved under ultrasonic excitation and under mechanical compression in PVDF/CFO10 membranes. Composite membranes offer dual functionality for energy and environmental uses.