The influence of metallic Bi in BiVO₄ semiconductor for artificial photosynthesis

BiVO₄ is a non-titania inorganic photocatalyst recognized as an effective visible-light-driven semiconductor that has been shown to be effective for CO₂ reduction. However, some characteristics, such as a low separation rate of photogenerated electron-hole pairs and low mobility of electron-hole carriers, are still challenges to the widespread use of this semiconductor. In this paper, the influence of metallic Bi on the CO₂ photoreduction activity was evaluated for the BiVO₄ semiconductor. Bi–BiVO₄ catalysts were prepared by microwave heating at 240 °C, employing different reaction times and magnetic stirring regimes. Metallic Bi improved the catalytic activity of BiVO₄ for CO₂ reduction, enhancing the absorption of visible light and promoting internal photoemission of electrons in the metal-semiconductor interface, which improves the electron density in the surface of the catalyst. This resulted in an astonishing concentration of methanol; Bi–BiVO₄ prepared at 240 °C, for 5 min, and without magnetic stirring, produces around 5.0 mmol L⁻¹ g⁻¹_catalyst of methanol and 40 μmol L⁻¹ g⁻¹_catalyst of acetone after 240 min of reaction. The mechanism of charge transfer between the BiVO₄ and the metallic Bi is influenced by the size of the microsphere crystallites, moreover, the production of methanol increased as the Bi grain size decreased.