Synthesis and photocatalytic properties of metastable β-Bi2O3 stabilized by surface-coordination effects

A metastable semiconductor, beta-Bi2O3, was successfully synthesized with the precursor Bi2O2CO3 in this study, which showed much higher photocatalytic activity in the photooxidation of isopropyl alcohol (IPA) than thermally stable alpha-Bi2O3. The prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HRTEM). Based on the previous study, a surface CO32- coordination effect was proposed to understand the formation mechanism of beta-Bi2O3 at room temperature. This speculation was supported by the surface chemical states' differences between alpha- and beta-Bi2O3, which were studied using Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric-differential thermal analysis (TG-DTA). Meanwhile, the energy band structures of alpha- and beta-Bi2O3 were measured with an ultraviolet-visible diffuse reflection spectroscope (UV-vis DRS) and a valence band X-ray photoelectron spectroscope (VB-XPS); the electronic structures were calculated using the plane-wave density functional theory (DFT) with the CASTEP program package. At last, the photo-induced charge separation efficiency and photocarriers' lifetime of alpha-Bi2O3 and beta-Bi2O3 were studied by steady state and dynamic photoluminescence (PL). Based on the results, the higher photocatalytic activity of beta-Bi2O3 than that of alpha-Bi2O3 was attributed to its higher visible light harvesting ability, the formation of O-2(-center dot) with strong oxide ability, higher charge separation efficiency, and larger surface area.