Facet-dependent photocatalytic NO conversion pathways predetermined by adsorption activation patterns

Abstract

Photocatalysts with different exposed facets generally exhibit different physicochemical properties, but the underlying mechanism has not been revealed. In this study, we synthesized nanoflake-assembled flower-like Bi₂O₂CO₃ and homodisperse nanoflakes Bi₂O₂CO₃ with exposed {110} and {001} facets (110-BOC and 001-BOC), respectively, to probe the activation and reaction mechanism of facet-dependent reactants. The results showed that Bi₂O₂CO₃ with exposed {001} facets exhibited superior photocatalytic activity for photocatalytic abatement of NO in the air in comparison with 110-BOC. According to the combined results of ESR spectra and DFT calculation, the superior photocatalytic activity of 001-BOC stemmed from its enhanced capability to activate the reactants (O₂ and H₂O), which facilitated the formation of reactive radicals to participate in the photocatalytic NO oxidation. Most significantly, the time-dependent in situ DRIFTS spectra and DFT simulation results reveal that the adsorption activation of pollutants and desorption mechanisms of products were different for 110-BOC and 001-BOC in photocatalytic NO oxidation. Due to the differences in the atomic arrangement on the {110} and {001} facets, 001-BOC enabled the transformation of NO into NO⁻ or cis-N₂O₂²⁻ during adsorption activation, while 110-BOC induces the adsorption activation of NO into NO⁺ or N₂O₃. The {001} facet of Bi₂O₂CO₃ could promote the oxidation of intermediates to final products (NO₃⁻) and enhance NO₃⁻ desorption. These different adsorption activation patterns on {110} and {001} facets essentially predetermined the facet-dependent conversion pathways of photocatalytic NO oxidation on different facets. The findings of this work would have critical implications for the understanding of the facet-dependent reaction mechanism and the design of novel efficient catalysts.