Dual functions of CO2 molecular activation and 4f levels as electron transport bridges in erbium single atom composite photocatalysts therefore enhancing visible-light photoactivities

Abstract

Only when the interfacial charge separation is enhanced and the CO₂ activation is improved, can the heterojunction nanocomposite photocatalyst be brought into full play for the CO₂ reduction reaction (CO₂RR). Here, Er³⁺ single atom composite photocatalysts were successfully constructed based on both the special role of Er³⁺ single atoms and the special advantages of the SrTiO₃:Er³⁺/g-C₃N₄ heterojunction in the field of photocatalysis for the first time. As we expected, the SrTiO₃:Er³⁺/g-C₃N₄ (22.35 and 16.90 μmol g⁻¹ h⁻¹ for CO and CH₄) exhibits about 5 times enhancement in visible-light photocatalytic activity compared to pure g-C₃N₄ (4.60 and 3.40 μmol g⁻¹ h⁻¹ for CO and CH₄). In particular, the photocatalytic performance of SrTiO₃:Er³⁺/g-C₃N₄ is more than three times higher than that of SrTiO₃/g-C₃N₄. From Er³⁺ fluorescence quenching measurements, photoelectrochemical studies, transient PL studies and DFT calculations, it is verified that a small fraction of surface doping of Er³⁺ formed Er single-atoms on SrTiO₃ building an energy transfer bridge between the interface of SrTiO₃ and g-C₃N₄, resulting in enhanced interfacial charge separation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) and adsorption energy calculations demonstrated that the exposed Er single-atoms outside the interface on SrTiO₃ preferentially activate the adsorbed CO₂, leading to the high photoactivity for the CO₂RR. A novel enhanced photocatalytic mechanism was proposed, in which Er single-atoms play dual roles of an energy transfer bridge and activating CO₂ to promote charge separation. This provides new insights and feasible routes to develop highly efficient photocatalytic materials by engineering rare-earth single-atom doping.