High-pressure band-gap engineering and structural properties of van der Waals BiOCl nanosheets.

van der Waals BiOCl semiconductors have gained significant attention due to their excellent photochemical catalysis, low-cost and non-toxicity. However, their intrinsic wide band gap limits visible light utilization. This study explores high-pressure band-gap engineering, a "chemical clean" method, to optimize BiOCl's electronic structure. Utilizing high-pressure ultraviolet-visible (UV-vis) absorption spectra, Raman spectroscopy and XRD, we systematically investigate the effects of compression on band gap and crystal structure evolution of BiOCl. Our results demonstrate that pressure efficiently narrows the band gap from 3.44 eV to 2.81 eV within the pressure range of 0.4-44 GPa. The further Raman and XRD analyses reveal an isostructural phase transition, leading to a significant change in the compressibility of the lattice parameters and bonds from anisotropic to isotropic. These findings provide a potential pathway to tune the bandgap for enhancing the photocatalytic efficiency of BiOCl.