NH3热还原处理TiO2的结构与光催化活性研究

研究了NH3气氛热还原处理两种TiO2光催化剂的形态(ATiO2,BTiO2)及其活性,400和500℃处理2 h的催化剂均显示黄色,而600℃以上处理则显示深灰色．以XRD、UV-Vis分析了NH3处理TiO2的结构,XRD表明ATiO2催化剂以锐钛矿和金红石混合晶型存在,而BTiO2只有锐钛矿型．UV-Vis结果发现NH3处理的两种TiO2在可见光区域都有很强的吸收．以甲基橙和苯酚研究了紫外光和太阳光下的光催化活性,结果表明NH3处理对两种不同制备方法的TiO2光催化活性影响存在显著差异,ATiO2随氨热处理温度提高活性降低,甲基橙50 min脱色率由400℃样品的100％逐步降到700℃样品的37％;而BTiO2随处理温度提高活性增加,甲基橙50 min脱色率由400℃样品的29％逐步提高到700℃样品的88％．在可见光下,ATiO2的活性与紫外光下规律相似,而BTiO2除了500℃样品外几乎都没有活性．最后对经过NH3处理的与未经处理的BTiO2活性进行了比较,发现NH3处理导致BTiO2光催化活性显著降低．

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.