PHOTOACTIVATION OF SILVER LOADED ON TITANIUM(IV) OXIDE FOR ROOM-TEMPERATURE DECOMPOSITION OF OZONE

Dark and photoinduced decomposition of ozone (O3, approximately 80 ppm ) in air over silver (Ag) or silver(I) oxide (Ag2O) loaded onto commer cially available titanium(IV) oxide (TiO2) powder was studied using a flow-type reactor (1.5 dm3 min-1) at room temperature. The relatively lower catalytic activity of bare TiO2 in the dark was significantly im proved by the loading of Ag or Ag2O via photodeposition or precipitati on from an alkaline solution respectively. The enhanced activity was a ttributed to the thermal reaction with O3 to yield silver(II) oxide (A gO). Therefore, in the dark, the catalytic activity decreased graduall y with the formation of AgO, as was indicated by the simultaneous blea ching of the catalyst surface. During prolonged dark reaction, the tot al molar amount of O3 decomposed over TiO2-Ag2O catalyst was much larg er than that estimated on the assumption of a stoichiometric equimolar reaction of O3 with Ag2O to yield AgO, suggesting the slow thermal de composition of AgO at room temperature. Photoirradiation of the deacti vated AgO catalyst recovered the activity via regeneration of purple-g rey Ag deposits. The recovered high activity was kept almost constant by photoirradiation. The mechanism of these O3 decomposition processes is discussed.