Enhanced Sunlight-Driven Reactive Species Generation via Polarization Field in Nanopiezoelectric Heterostructures

Although it is established that the force-induced electric polarization field of piezoelectric semiconductors can be used to tune the transfer rate of photoexcited charge carriers, there is still a lack of successful strategies to effectively improve the photocatalytic reactivity and solar-to-chemical conversion efficiency (SCC) of piezoelectric materials. Here, we are the first to prepare and study a kind of catalyst based on nanopiezoelectric heterostructures of LiNbO₃-type ZnTiO₃·TiO₂ and tetragonal BaTiO₃ with Pt or FeO nanoparticle modification (i.e., ZBTO-Pt or ZBTO-FeO) for reactive species generation. With respect to the production of ^•OH and ^•O₂^- radicals, higher amounts were observed in piezophotocatalysis relative to those for individual piezo- and photocatalysis. Benefiting from the charge transfer resistance decreases by the deposition of Pt and FeO, the amounts of ^•OH radicals formed on ZBTO-Pt and ZBTO-FeO were approximately 48 and 21% higher than that on isolated ZBTO during piezophotocatalysis, and for the amounts of ^•O₂^- radicals the enhancements were approximately 11 and 6%, respectively. Furthermore, the concentrations of H₂O₂ formed on ZBTO-Pt and ZBTO-FeO under piezophotocatalysis reached approximately 315 and 206 μM after 100 min of reaction (and was still increasing) corresponding to 0.10 and 0.06% SCCs, respectively, which were also much higher than the concentrations and SCCs observed for piezo- and photocatalysis. The enhancements of piezophotocatalytic activities with these piezoelectric materials were related to the mechanical strain exerted on ZBTO, which generated a larger electric polarization field than those on ZnTiO₃·TiO₂ and BaTiO₃ as analyzed by a finite element method. This high-intensity electric polarization field accelerated the separation and transportation of photoexcited charge carriers in the highly sunlight responsive nanopiezoelectric heterostructures based on ZBTO-Pt and ZBTO-FeO.