The Cu doped ramsdellite MnO2 nanosheet samples with different Cu/Mn molar ratio were prepared by a facile hydrothermal redox reaction among Cu(NO3)(2), Mn(NO3)(2), and KMnO4 at 60 degrees C. They were characterized by ICP-OES, XRD, TEM, SEM, N-2 adsorption, XPS, UV-vis-IR absorption, etc. The Cu doped ramsdellite MnO2 nanosheet samples demonstrate highly efficient photothermocatalytic activity and very good catalytic stability for the catalytic purification of CO as one of poisonous air pollutants under the full solar spectrum infrared irradiation. Compared to the pure ramsdellite MnO2 nanosheet sample and TiO2(P25), the photothermocatalytic activity of the optimum Cu doped ramsdellite MnO2 nanosheet sample under the full solar spectrum irradiation is enhanced by 2.3, 281.7 times, respectively. The Cu doped ramsdellite MnO2 nanosheet sample also demonstrates highly efficient catalytic activity even under the lambda > 830 nm infrared irradiation. The highly efficient catalytic activity of the Cu doped ramsdellite MnO2 nanosheet sample derives from efficient solar-light-driven thermocatalysis because of its strong absorption across the entire full solar spectrum and high thermocatalytic activity. The Cu doping considerably enhances the lattice oxygen activity of ramsdellite MnO2, thus promoting its thermocatalytic activity. A novel photoactivation, completely unlike the well-known photocatalysis on photocatalytic semiconductors such as TiO2, is discovered to further enhance the solar-light-driven thermocatalytic activity. We combine the experimental evidence of CO-TPR and DFT calculation to reveal the origin of the novel photo activation: the irradiation considerably enhances the lattice oxygen activity of the Cu doped ramsdellite MnO2 nanosheets, thus accelerating their solar-light-driven thermocatalytic activity.