Mechanism of Photocatalytic CO₂ Reduction by Bismuth-Based Perovskite Nanocrystals at the Gas-Solid Interface

We report here a series of nontoxic and stable bismuth-based perovskite nanocrystals (PeNCs) with applications for photocatalytic reduction of carbon dioxide to methane and carbon monoxide. Three bismuth-based PeNCs of general chemical formulas A₃Bi₂I₉, in which cation A⁺ = Rb⁺ or Cs⁺ or CH₃NH₃ ⁺ (MA⁺), were synthesized with a novel ultrasonication top-down method. PeNC of Cs₃Bi₂I₉ had the best photocatalytic activity for the reduction of CO₂ at the gas-solid interface with formation yields 14.9 μmol g^-1 of methane and 77.6 μmol g^-1 of CO, representing a much more effective catalyst than TiO₂ (P25) under the same experimental conditions. The products of the photocatalytic reactions were analyzed using a gas chromatograph coupled with a mass spectrometer. According to electron paramagnetic resonance and diffuse-reflectance infrared spectra, we propose a reaction mechanism for photoreduction of CO₂ via Bi-based PeNC photocatalysts to form CO, CH₄, and other possible side products.