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

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.