The sample of CuO mesoporous nanosheets (CuO-MNS) was prepared by a facile method of the reaction between NaOH and copper ammonia complex formed from CuSO4 and ammonia aqueous solutions at 25 degrees C. CuO-MNS shows greatly effective photothermocatalytic activity and excellent durability for the catalytic oxidation of CO (poisonous air pollutant) under the full solar spectrum illumination from a Xe lamp. Compared to commercial nonporous CuO and TiO2 (P25), the photothermocatalytic activity of CuO-MNS under the Xe lamp illumination is enhanced by 19.8 and 88.7 times, respectively. Under the UV-vis-IR illumination with the same light intensity, the photothermocatalytic activity of CuO-MNS is 331 times higher than its conventional photocatalytic activity. Impressively, CuO-MNS also demonstrates effective photothermocatalytic activity even under the lambda > 830 nm infrared illumination. It is discovered that the greatly effective photothermocatalytic activity of CuO-MNS is attributed to effective solar-light-driven (SLD) thermocatalytic CO oxidation. The significantly enhanced photothermocatalytic activity of CuO-MNS as compared to the commercial nonporous CuO is attributed to the tremendously higher thermocatalytic activity of the former than the later. The results of CO-TPR, Raman, and density functional theory (DFT) calculations reveal that the formation of mesopores in CuO-MNS significantly improves the lattice oxygen activity of CuO, thus significantly enhancing thermocatalytic activity of CuO. Very interestingly, a novel photoactivation, completely unlike the well-known photocatalysis of photocatalytic semiconductors such as TiO2, is discovered to considerably promote the SLD thermocatalytic CO oxidation on CuO-MNS. By combining the experimental evidence of CO-TPR and O-2-TPO in the dark and under the Xe lamp illumination as well as the theoretical evidence by the DFT calculations in the ground state and excited state, we reveal the origin of the novel photoactivation: the Xe lamp illumination considerably promotes the re-oxidation of the pre-reduced CuO-MNS, thus considerably enhancing the catalytic activity of CuO-MNS.