Revisiting the BaBiO₃ semiconductor photocatalyst: synthesis, characterization, electronic structure, and...

This article revisits the properties of BaBiO₃ examined extensively in the last two decades because of its electronic properties as a superconductor and as a semiconductor photocatalyst. Solid-state syntheses of this bismuthate have often involved BaCO₃ as the barium source, which may lead to the formation of BaBiO₃/BaCO₃ heterostructures that could have an impact on the electronic properties and, more importantly, on the photocatalytic activity of this bismuthate. Accordingly, we synthesized BaBiO₃ by a solid-state route to avoid the use of a carbonate; it was characterized by XRD, SEM, and EDX, while elemental mapping characterized the composition and the morphology of the crystalline BaBiO₃ and its thin films with respect to structure, optoelectronic, and photocatalytic properties. XPS, periodic DFT calculations, and electrochemical impedance spectroscopy ascertained the electronic and electrical properties, while Raman and DRS spectroscopies assessed the relevant optical properties. The photocatalytic activity was determined via the degradation of phenol in aqueous media. Although some results accorded with earlier studies, the newer electronic structural data on this bismuthate, together with the photocatalytic experiments carried out in the presence of selective radical trapping agents, led to elucidating some of the mechanistic details of the photocatalytic processes that previous views of the BaBiO₃ band structure failed to address or clarify. Analytical refinement of the XRD data inferred the as-synthesized BaBiO₃ adopted the C_2/m symmetry rather than the I_2/m structure reported earlier, while Tauc plots from DRS spectra yielded a bandgap of 2.05 eV versus the range of 1.1-2.25 eV reported by others; the corresponding flatband potentials were 1.61 eV (E_VB) and - 0.44 eV (E_CB). The photocatalytic activity of BaBiO₃ was somewhat greater than that of the well-known Evonik P25 TiO₂ photocatalyst under comparable experimental conditions.