Modulation of electric dipoles inside electrospun BaTiO3@TiO2 core-shell nanofibers for enhanced piezo-photocatalytic degradation of organic pollutants

Ferroelectric materials can generate a built-in electric field under strain, which can produce reactive oxygen species (ROS) for in-situ piezocatalysis via a series of redox reactions, or enhance photocatalytic activities through the separation of the photoinduced electron and hole pairs. In this study, the synergistic piezophototronic effect is enhanced by increasing the inner piezopotential of ferroelectric nanofibers in fibrous piezoelectric/oxide semiconductor heterostructures. Ferroelectric BaTiO3 nanofibers are fabricated by a sol-gel assisted electrospinning and subsequent annealing at 700 degrees C for 2 h, 4 h, and 6 h, respectively (denoted as BT2H, BT4H, and BT6H). Piezoelectric force microscopy results reveal that the necklace-like BT6H nanofibers demonstrate the highest local piezoelectric coefficient d(33) (42.7 pm V-1) than BT2H (26.3 pm V-1) and BT4H (37.8 pm V-1) nanofibers because BT6H nanofibers are composed of highly crystallized electric dipoles with single domain nanostructures. Additionally, BT6H@TiO2 core-shell nanofibers are synthesized by a wet-chemical coating of TiO2 on BT6H nanofibers. Under both ultrasound and UV light irradiations, BT6H@TiO2 core-shell nanofibers exhibit a high piezo-photocatalytic degradation rate constant of 6 x 10(-2) min(-1) because of the enhancement of the piezotronic effect by the high piezoelectricity of electric dipoles that promote the separation of the photoinduced electron and hole pairs. The enhancement of the synergistic piezo-phototronic effect is ascribed to the highly active reaction sites that are confined into the high specific surface area of the one-dimensional fibrous boundary of BT6H@TiO2 core-shell nanofibers, beneficial for the migration of the interfacial charge carriers. This study presents a simple approach to improve the piezo-photocatalysis through modulating the crystallization and the size of electric dipoles, providing an efficient pathway for underpinning the coupling mechanism between the enhancement of local ferro/piezoelectricity and piezo-phototronic effect.