Nanoflowers of octahedral layered birnessite (OL-NF) were synthesized and characterized with a variety of techniques. Remarkably, OL-NF exhibits a catalytic activity with a high efficiency for CO oxidation under irradiation of the full solar spectrum, visible-infrared, or infrared light. This highly efficient catalytic activity under solar-light irradiation originates from solar-light-driven thermocatalysis related to the efficient photothermal conversion and thermocatalytic activity of OL-NF. A conceptually novel photoactivation effect is found to significantly improve the activity of the lattice oxygen of OL-NF, thus considerably increasing the thermocatalytic activity of OL-NF.