UV-Visible-Infrared Light Driven Thermocatalysis for Environmental Purification on Ramsdellite MnO2 Hollow Spheres Considerably Promoted by a Novel Photoactivation.

Novel ramsdellite MnO2 hollow spheres consisting of closely stacked nanosheets (R-MnO2-HS) were synthesized by a facile method. The R-MnO2-HS sample was characterized with SEM, XRD, TEM, BET, XPS, diffusive reflectance UV-vis-IR absorption, etc. Remarkably, R-MnO2-HS exhibits highly efficient catalytic activity for the purification of benzene (a carcinogenic air pollutant) under the full solar spectrum or visible-infrared irradiation, even under the infrared irradiation. Its catalytic activity (initial CO2 production rate) under the full solar spectrum irradiation is as high as 210.5 times higher than TiO2(P25), a well-known benchmark photocatalyst for environmental cleanup. The excellent catalytic activity of R-MnO2-HS is ascribed to its efficient thermocatalytic activity and its efficient photothermal conversion in the whole solar spectrum region, resulting in high efficient solar light driven thermocatalysis. Very interestingly, a novel photoactivation, which is completely different from the well-known photoactivation induced by photoexcited electrons and holes on TiO2, considerably enhances the solar light driven thermocatalysis. By use of CO temperature-programmed reduction (CO-TPR) under solar light irradiation and in the dark together with density function theory (DFT) calculations, the origin of the novel photoactivation was revealed: The lattice oxygen activity plays a crucial role in the thermocatalysis on MnO2. The solar light irradiation significantly promotes the lattice oxygen activity of R-MnO2-HS, consequently resulting in a considerable enhancement in the thermocatalytic activity.