Piezoelectricity Induced by Na-Doping in NiFe ₂ O ₄ Nanoparticles for Piezocatalytic Dye Degradation

Nickel ferrite (NiFe2O4, NFO), a spinel-type ferrite, is inherently nonpiezoelectric due to its centrosymmetric crystal structure. In this study, we report the successful induction of piezoelectricity in NFO nanoparticles via sodium doping using a hydrothermal synthesis approach. The emergence of piezoelectricity in Na-doped NFO (Na-NFO) is confirmed by piezoresponse force microscopy. Leveraging this induced piezoelectricity, the Na-NFO exhibits significant piezocatalytic degradation of the model organic pollutant malachite green (MG) under mechanical stimulation in the absence of light. Comprehensive characterization, including analyses of crystal structure, surface morphology, surface electronic states, and optical and magnetic properties, was performed to elucidate the relationship between material properties and piezocatalytic activity. Comparative studies demonstrate no piezocatalytic performance in commercial undoped NFO, highlighting the critical role of sodium doping. This work presents an effective strategy for engineering spinel-based piezocatalysts and advances the development of sustainable technologies for environmental remediation.