Flexo-photocatalysis in centrosymmetric semiconductors

The separation of photogenerated electron–hole pairs is vitally important for photocatalysis, which can be effectively promoted by polarization field. However, it only manifests in piezoelectric/pyroelectric/ferroelectric materials that have a non-centrosymmetric structure. Here, we demonstrate that the polarization enhanced photocatalysis (with wide spectra from ultraviolet (UV) light to visible light) can be achieved in centrosymmetric semiconductors, such as δ-MnO2 and TiO2 nanosheets integrated nanoflowers, by using the strain-gradient-induced flexoelectric polarization that is always overlooked in polarization-enhanced catalysis. Under ultrasonic and illumination excitation, the organic pollutants (methylene blue (MB), etc.) can be effectively degraded within 30 min with excellent stability and repeatability. Compared with photocatalysis, the flexo-photocatalytic performance of above centrosymmetric semiconductors is substantially increased by 85%. Moreover, the factors related to flexo-photocatalysis such as material morphology, mechanical stimuli source, and adsorption are explored to deeply understand the mechanism of flexo-photocatalysis. This work opens up a way for high-performance photocatalysis in centrosymmetric semiconductors.