Smart multi-stimuli responsive magneto-piezoelectric composite material based on PVDF and BiFeO3 nanoparticles for catalysis and energy harvesting

Abstract

The development of hybrid magneto-piezoelectric composite materials with enhanced functional capabilities represents a relevant area of research. The integration of the functional properties of piezoactive nanomaterials and a ferroelectric polymer matrix creates novel solutions for applications in catalysis and electronics. This study proposes a new approach to creating two-phase polymer-inorganic composite films based on the piezoelectric polymer PVDF and the nanocrystalline multiferroic BiFeO₃ (BFO). Phase inversion using a non-solvent and thermal treatment combined with doctor blade technology enabled the formation of PVDF/BFO composites with an 86 % electroactive phase content. The variation in BFO concentration led to changes in morphology, increased magnetization, and improved mechanical and electromagnetic energy conversion characteristics. Photocatalytic and piezocatalytic experiments demonstrated methylene blue (MB) degradation efficiencies of 97 % (photocatalysis) and 79 % (piezocatalysis) for PVDF/BFO5, and 95 % (photocatalysis) and 83 % (piezocatalysis) for PVDF/BFO10, with reaction rate constants of 0.048 min⁻¹ and 0.035 min⁻¹, respectively. The absence of synergistic enhancement in combined photo- and piezocatalysis was attributed to charge compensation at the interface. The degradation mechanism of MB was confirmed using radical scavenger experiments and density functional theory (DFT) calculations, identifying hydroxyl radicals (^•OH) as the primary active species and elucidating key intermediate products, including hydroxylated and ring-opening derivatives. Mechanical energy harvesting characteristics were studied under various excitations applied to the piezoelectric nanogenerator (PENG), including rolling motion, compression, periodic vibrations, and ultrasonic (US) exposure. Under US, PENG tests revealed an increase in output voltage from 5.2 V (pure PVDF) to 7.6 V (PVDF/BFO5) and 9.9 V (PVDF/BFO10), corresponding to a 1.5–1.9-fold enhancement. Under vertical compression with a 4.4 N force, the peak output voltage of PVDF/BFO10 reached 24 V, with a corresponding power density of 12 μW/m² at an optimal load resistance of 10 MΩ. The ability to convert parasitic magnetic fields through magneto-mechanoelectric coupling was confirmed. When placed near the power cable of an electric kettle (2200 W), the PENG device generated an induced voltage, demonstrating its capability to harvest stray electromagnetic energy. The reduced conversion efficiency of BFO10 compared to BFO5 under magnetic field exposure is attributed to decreased membrane elasticity at high nanoparticle loadings, leading to lower deformation and reduced electrical power output. These findings highlight the potential of PVDF/BFO composites for applications in energy harvesting and catalysis, paving the way for the development of smart multifunctional materials.