Bismuth ferrite (BiFeO₃, BFO) submicron cubes and 3D BFO/graphene composite materials were synthesized by a simple hydrothermal process. The crystallization processes of the 3D BFO/graphene composites with different graphene oxide (GO) concentrations were studied for their visible light photocatalytic properties. Compared to the single BFO submicron cubes, 3D BFO/graphene composites have greatly improved photocatalytic activity. A high photocatalytic performance is obtained at a GO concentration of 3 mg/mL, with the degradation rate of methylene blue (MB) dye reaching up to 92% in 140 min. The enhancement of photocatalytic activity can be attributed to the large specific surface area and 3D architecture of 3D composites, which provide more transport paths to effectively improve the separation rate of photo-generated electrons and holes. Therefore, 3D BFO/graphene composites have a broad prospect of application in the field of photocatalysis.

Flexoelectricity is a novel kind of electromechanical coupling phenomenon that is prevalent in all solid dielectrics and usually of vital importance in nanostructures and soft materials. Although the fundamental theory of flexoelectric solids and related beam or plate theories were extensively studied in recent years, the coupling effect of flexoelectricity and piezoelectricity in piezoelectric nanostructures has not been completely clarified yet. In the present work, a geometrically nonlinear piezoelectric plate model is established with a focus on the coupling effect. The constitutive equations for piezoelectric plates are derived under both the electrically short-circuit and open-circuit conditions. It is found that due to the coupling between flexoelectricity and piezoelectricity, stretching-bending coupling stiffness arises in the homogeneous plate and its specific value relies on the applied electrical boundary conditions. The effects of the flexoelectric-piezoelectric coupling on the effective mechanical behavior and the electromechanical behavior of nanobeams and nanoplates are also discussed. The developed model and presented results are expected to benefit the design and analysis of piezoelectric and flexoelectric devices and systems.