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An investigation into photocatalysts mainly focuses on inorganic powders, and their fixation, recycle, and repair in an open and flowing environment remains a problem. Herein, the photocatalytic property of polyvinylidene fluoride (PVDF) is utilized to solve this problem. It can be facilely recycled and repaired because of the form of membrane, and porous structure ensures its sufficient contact with pollutants. In addition, its photocatalytic activity can be effectively modified by compositing TiO2 nanopowder, which performs better photocatalytic activity than equivalent content TiO2 powder, originated from the enhanced separation efficiency of electron and hole resulting from the extra driving force maybe generated by PVDF's ferroelectric spontaneous polarization and heterojunction structure, which reduces the recombination of charge carriers. In addition, the pore structure with large density and small size provides more reaction area for the composite structure, which also benefits for the enhancement of photocatalytic activities. Tight combination between PVDF and TiO2 guarantees the stable activity of the composites under flowing environment, and so PVDF/TiO2 composite can sustain its initial photocatalytic activity after at least 10 times cycles. More importantly, when the membrane is damaged, it can be easily repaired by the cost of a small quantity of solvent and can maintain its initial photocatalytic activity. This work would promote the understanding of physical mechanisms of enhanced photocatalytic activities, and recycle and repair properties in PVDF‐xTiO2 composites. [ABSTRACT FROM AUTHOR]

Defect engineering plays an important role in property modification for piezoelectric materials. In this work, we pay much attention to the effect of Nb nonstoichiometry on structure and properties of typical 0.95(K0.45Na0.55)Nb1+xO3–0.05Bi0.5Na0.5HfO3 ceramics. Large piezoelectric constant (d33 ~ 425 pC/N and d33∗ ~482 pm/V) together with high Curie temperature (TC ~ 315°C) have been achieved in the ceramics with excess Nb content (x = 0.01). However, the ceramics with deficient Nb element have seriously suppressed cryogenic εr‐T curves and deteriorated electrical properties. Multi‐scale characterizations including phase structure, microstructure, defect structure and domain structure have been adopted to explain the corresponding phenomenon. Defect complex VNb″″′-VO·· caused by deficient Nb induces clamped domain wall motion, leading to blocked polarization vector and poor electrical properties. On the contrary, the enhanced properties for the ceramics with excess Nb are attributed to easier domain switching due to the suppressed vacancies. We believe that defect engineering, for example nonstoichiometry, cannot only modulate electrical properties but also help us to understand some fundamental and critical problems about KNN‐based ceramics. [ABSTRACT FROM AUTHOR]