Effect of Ammonia Thermal Treatment on the Structure and Activity of Titanium Oxide Photocatalysts

Different titanium oxide powders （ATiO2, BTiO2） were pretreated in ammonia （NH3） gas at high temperatures. After the pretreatment, the color of the titanium oxide powders changed from white to yellow or gray depending on the pretreatment temperatures. Morphologies and structures of the treated titanium oxide powders were characterized by physical chemical methods. XRD measurements showed that the crystalline structures were mainly mixture of anatase and rutile for the ATiO2 but only anatase for the BTiO2, Stronger absorption of visible light was observed for both types of samples using UV-Vis diffuse reflectance spectra. X-ray photoelectron spectroscopy demonstrated that doped nitrogen existed on the surface TiO2 after ammonia gas pretreatment. The photocatalytic activities of the treated titanium oxide samples were evaluated via the photodegradation of methyl orange and phenol in aqueous suspensions. No obvious improvement in photocatalytic activity was achieved by ammonia pretreatment although it could enhance the absorption of light. Effects of treatment temperatures on photoactivities were complete different for ATiO2 and BTiO2 （i.e. higher treated temperatures yielded higher activities for BTiO2 but lower for ATiO2）. All samples yielded lower activity levels after ammonia pretreatment without regard to pretreatment temperature or the reaction light resource.