Spatially limited growth of ultrathin BiVO4/BiOCl heterostructures in molten salt as effective nitrogen photofixation photocatalyst

The efficient construction of semiconductor heterostructures with high crystallinity, small dimensions, and effective electron-hole pair separation is crucial for developing high-performance photocatalysts. In this study, we successfully fabricate a novel heterostructure composed of highly crystalline BiOCl ultrathin nanosheets (∼5 nm) and BiVO₄ nanodots (5–8 nm) via a facile one-step molten salt synthesis (MSS) strategy. Based on Eyring’s significant structure model, we propose a spatially limited growth process and a corresponding structural model in molten salt. Nanosheet-like vacancies formed in the molten salt act as barriers for spatially confined growth and serve as chemically reactive sites. We identify a band alignment with a valence band offset of ∼0.7 eV between BiVO₄ and BiOCl. Combined with theoretical calculations, we demonstrate that charge separation and injection efficiency are significantly enhanced due to improved charge transfer. As a result, the photocatalytic nitrogen fixation activity under visible-light irradiation is markedly improved (187.5 μmol·L⁻¹·h⁻¹·g⁻¹), which is approximately 7.5 times higher than that of pure BiVO₄. Moreover, this novel method can be extended to grow other two-dimensional materials.