Composition and Structure Evolution of Bi2O3 Coatings as Efficient Photocatalysts

To overcome the recovery disadvantages of Bi2O3 photocatalyst in the form of powder, Bi2O3 photocatalyst coatings were developed via a ball milling, followed by the calcination method. The composition and structure evolution rules of the as-synthesized samples were analyzed based on XRD (X-ray powder diffraction) patterns and SEM (scanning electron microscope) observations. XPS (X-ray photoelectron spectroscopy) and UV-Vis (Ultraviolet-visible) spectra were also employed to characterize the samples. The results showed that monoclinic Bi2O3 coatings were obtained after sintering Bi coatings at 673 or 773 K for 2 h, while calcination at a higher temperature and for a longer time resulted in monoclinic and triclinic mixed-phase Bi2O3 coatings. Bi2O3 coatings with a radial growth structure assembled by nanosheets could be realized at a lower temperature lasting for a longer time, while sintering at a higher temperature with relatively short oxidation time led to tangential growth structure. Photodegradation of malachite green solution under simulated solar irradiation for 180 min showed that the largest degradation efficiency of 91.49% was achieved over the photocatalyst coatings calcined at 873 K for 5 h. Additionally, the degradation efficiency was maintained above 80% even after three cycles.