Single-molecule quantification of photoredox activities and dynamics at the nanoscale on multi-faceted 2D materials

Abstract

Two-dimensional bismuth oxybromide (BiOBr) with multiple facets has been widely used in photocatalytic pollutant degradation and clean energy production. Herein, we used in situ single-molecule fluorescence microscopy to quantify structure-specific photoredox activities of facet-dependent BiOBr. The nanometric-mapping of photoredox reactions (resolution: 20 nm) clearly unveils the catalytic heterogeneity on {001} facet-dominant and {010} facet-dominant BiOBr, respectively (BiOBr-001 and BiOBr-010). The corners of BiOBr nanoplates exhibit the highest photoredox activities, followed by edges and basal planes, which are attributed to the unsaturated coordination sites in corners and edges. BiOBr-001 corners show the photoreduction and photo-oxidation activities of 108.0 ± 11.5 and 654.5 ± 83.2 s⁻¹ μm⁻², respectively, which are 1.2 and 3.4 times those of BiOBr-010 corners. Other structures of BiOBr-001 also exhibit superior reactivity to BiOBr-010. Such phenomena are ascribed to shorter charge transfer distance and the existence of high-index facets in BiOBr-001. Bulk activity evaluation further supports the single-molecule analysis. The investigation of temporal activity fluctuation reveals surface restructuring probably accounts for the activity enhancement at the nanoscale under practical reaction conditions. Hence, our study correlates the catalyst structure and reaction dynamics at nanometer resolution, which guides the performance improvement at both single-molecule and ensemble levels.