水体中常见无机阳离子对TiO_2薄膜光催化还原Cr(Ⅵ)的影响

Effects of inorganic cations on photocatalytic reduction of chromium(Ⅵ) over TiO_2 thin films

选择了6种水体中常见的阳离子(Na+、Mg2+、Ca2+、Al3+、Cu2+、Ni2+),分别考查了其对TiO2薄膜光催化还原Cr(Ⅵ)的影响;从光吸收、无机离子本身的性质对光生电子的捕获及传递等讨论了上述离子影响TiO2薄膜光催化还原Cr(Ⅵ)的反应速率的原因。结果表明:由于其不能捕获光生电子,Na+、Mg2+、Ca2+本身对TiO2薄膜光催化还原Cr(Ⅵ)的反应速率影响不大;Al3+吸引电子能力较强,成为光生电子和Cr(Ⅵ)之间的桥梁,促进了Cr(Ⅵ)的还原;浓度为1 mmmol/L时,Cu2+显著地促进了Cr(Ⅵ)的光催化还原,其主要原因是Cu2+捕获光生电子的能力很强,起到了催化剂的作用,而浓度大于10 mmol/L时,Cu2+形成单质Cu以及对紫外光的吸收都使促进作用降低;Ni2+未充满的d轨道具有获得并传递光生电子的能力,也促进了Cr(Ⅵ)的还原;在浓度同为1mmol/L时,对Cr(Ⅵ)光催化还原的促进作用依次为:Cu2+>Al3+>Ni2+>Na+、Ca2+、Mg2+。

The effects of six inorganic anions（Na^＋,Mg^2＋,Ca^2＋,Al^3＋,Cu^2＋,Ni^2＋） which are commonly present in water and wastewater on the photocatalytic activity of TiO2 thin films for the photocatalytic reduction of chromium（Ⅵ） were investigated.They were observed from two respects：UV-vis absorption by inorganic cations,and photogenerated electrons trapping and subsequent transferring to chromium（Ⅵ） by the inorganic cations.The results indicated that Na^＋,Ca^2＋ and Mg^2＋ had almost no effects on rate of photocatalytic reduction of Cr（Ⅵ） because themselves were highest oxidation state and couldn＇t capture photogenerated electrons.Al^3＋ enhanced the rate due to its high charge,so that the photogenerated electrons were attracted and then transfer to Cr（Ⅵ）.1 mmol/L Cu^2＋ were found to significantly accelerate the photocatalytic reduction of Cr（Ⅵ）,which attribute to Cu^2＋ could easily capture photogenerated electrons and played a catalyst role;however,the acceleration reduced when the concentration of Cu^2＋ came to 10 mmol/L owing to on the one hand a portion Cu^2＋ was converted to Cu,on the other hand the part of ultraviolet radiation to the TiO2 surface was absorbed by Cu^2＋.Based on the same mechanism with Cu^2＋,Ni^2＋ promoted the reduction of Cr（Ⅵ）,too.The promotion for the photocatalytic reduction of Cr（Ⅵ） was in the order of Cu^2＋〉Al^3＋〉Ni^2＋〉Na^＋,Ca^2＋,Mg^2＋,at the concentration of these inorganic anions was 1 mmol/L.