Transition of BiOCl nanosheet into cotton-like clusters for piezoelectric enhanced photocatalytic degradation of dye and photocatalytic hydrogen production

Photocatalysts offer sustainable treatment of water pollutants using light and they can be further piezoelectrically enhanced. As a highly efficient, stable, and environmentally friendly photocatalytic material, bismuth oxychloride (BiOCl) exhibits significant advantages in the degradation of rhodamine B, but its morphology can be easily affected by solvothermal synthesis. In this study, the solvent effects of ethylene glycol and water were compared in the presence of polyvinylpyrrolidone (PVP) through solvothermal and hydrothermal reactions, respectively. X-ray diffraction patterns, Fourier-transform infrared spectra, and X-ray photoelectron spectra confirmed the formation of BiOCl nanosheets with numerous oxygen-rich vacancies. Scanning electron microscopy and transmission electron microscopy images showed circular plate-like structures or spherical clusters with a diameter of approximately 1 μm when BiOCl was prepared using water or without the addition of PVP, respectively. The plate-like structure and the spherical clusters transformed into cotton-like spherical clusters assembled from ultra-thin nanosheets with diameters ranging from 20 to 50 nm after using ethylene glycol and PVP. UV–vis absorption spectra showed that BiOCl with a cotton-like spherical structure could achieve higher dye degradation efficiency than BiOCl with a plate-like or spherical structure. The piezoelectric-enhanced photodegradation rates of rhodamine B were significantly increased by about 22 times since the piezoelectric photocurrent intensities rose nearly three times and the generation of •O₂⁻ and •OH increased. The photocatalytic hydrogen production was improved by 55.3 % and sustained up to 4 cycles due to the conduction band reduction, as proven by the Mott-Schottky plot.