APPROACH TO DE-NOX-ING PHOTOCATALYSIS .2. EXCITED-STATE OF COPPER IONS SUPPORTED ON SILICA AND PHOTOCATALYTIC ACTIVITY FOR NO DECOMPOSITION

Cu2+ ions supported on SiO2 (Cu2+/SiO2) prepared by an ion-exchange method are reduced to Cu+ when Cu2+/SiO2 samples are evacuated at temperatures higher than 573 K. Reduced Cu2+ ions on SiO2 (Cu+/SiO2 catalyst) decomposes NO molecules photocatalytically and stoichiometrically into N2 and O2 at 275 K. The physicochemical and photochemical properties of copper ions anchored onto SiO2 have been investigated by means of ESR and dynamic photoluminescence spectroscopies, as well as the analysis of photoreaction products. These results indicate that the excited state of the copper ions (Cu+ species) plays a significant role in the photocatalytic decomposition of NO molecules and the photoreaction involves an electron transfer from the excited state of the Cu+ ion into an anti-bonding pi-orbital of NO molecule within the lifetime of its excited state. Thus, the present results obtained with the Cu+/SiO2 catalysts imply the possibility of their utilization as a potentially promising type of photocatalysts in gas-solid systems.