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Introducing piezoelectric materials with the built-in electric field caused by mechanical force has been confirmed as an effective strategy to boost the separation efficiency of photoexcited charge carriers that determines the photocatalytic performance. In this study, we introduced Bi4Ti3O12 with superior piezoelectric properties into BiVO4–Bi4V2O10 materials to synthesize a 2D Bi4Ti3O12–BiVO4–Bi4V2O10 photocatalyst via a facile hydrothermal method. Compared with bare BiVO4, the Bi4Ti3O12–BiVO4–Bi4V2O10 piezo-photocatalytic activity towards Cr(VI) removal and oxygen evolution is boosted remarkably under both illumination and ultrasound treatments. The promoted photocatalytic activity can be ascribed to the accelerated photoexcited carrier separation efficiency driven by the polarization electric field and the synergy effect in the heterostructure. This work provides a simple and sustainable strategy for the design and development of piezo-photocatalysts with high photoredox activity capacity. [ABSTRACT FROM AUTHOR]

Li1.6Mn1.6O4 is a representative ion sieve material that is used to recover lithium from salt brines and bitterns owing to its high lithium ion adsorption capacity reaching 11.9–44 mg g−1. However, manganese dissolution during acid treatment hinders the industrial application of the material. For investigating the mechanism of manganese dissolution, the precursor Li1.6Mn1.6O4 and ion sieve H1.6Mn1.6O4 were prepared and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), chemical content analyses, diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). The results of XRD, SEM, and FT-IR showed that the bulk phase of Li1.6Mn1.6O4 retained the spinel structure, whereas the lattice diminished during acid treatment. The results of chemical content analyses showed that the bulk phase of Li1.6Mn1.6O4 contained a few trivalent manganese atoms and that the mean valence of manganese in the material increased during acid treatment. DRIFTS and XPS exhibited that the surface of Li1.6Mn1.6O4 was mostly full of tetravalent manganese and retained the spinel structure during acid treatment. In the proposed mechanism of manganese dissolution, an electron of trivalent manganese in the bulk phase transfers to the surface and is captured by tetravalent manganese within the acidic environment. Then, tetravalent manganese is converted to bivalent manganese after acquiring sufficient electrons, and dissolution occurs simultaneously. [ABSTRACT FROM AUTHOR]