Atomic-level unveiling secondary recrystallization enabled micro- and macroscopic polarization enhancement for piezo-photocatalytic oxygen activation

Piezoelectric semiconductors bear the bifunctional photocatalysis and piezocatalysis, while the absent or weak internal charge driving force severely restricts its catalytic activity. Developing polarization strategy is desirable, and particularly understanding its mechanism from a microscopic perspective remains scanty. Herein, we report a secondary recrystallization approach to achieving the simultaneous micro- and macroscopic polarization enhancement on Bi₂WO₆ nanosheets for boosting piezo-photocatalytic oxygen activation, and unravel the mechanism at an atom-level. The secondary recrystallization process not only results in a strengthened distortion of [WO₆] octahedra with distortion index enhancement by ～ 20% for a single octahedron, but also enables lateral crystal growth of nanosheets along the ab plane (av. 50 to 180 nm), which separately allows the rise in dipole moment of unit cell (e.g., 1.63 D increase along a axis) and the stacking of the distorted [WO₆] octahedron to accumulate the unit cell dipole, collectively contributing to the considerably strengthened spontaneous polarization and piezoelectricity. Besides, exposure of large-area {001} front facet enables more efficient capture and conversion of stress into piezo-potential. Therefore, the well-recrystallized Bi₂WO₆ nanosheets exhibit considerably promoted piezo-photocatalytic reactive oxygen species generation, given the decreased specific surface area. This work presents a feasible methodology to regulate inside-out polarization for guiding carriers transfer behavior, and may advance the solid understanding on the intrinsic mechanism.