水体中常见无机阴离子对TiO_2薄膜光催化还原Cr(Ⅵ)的影响

选择了5种水体中常见的阴离子(Cl~-,SO_4~(2-),HCO_3~-,NO_3~-以及HPO_4~(2-)/H_2P_4~-),分别考察了其对TiO_2薄膜光催化还原模拟Cr(Ⅵ)废水的影响.从上述离子的光吸收,对·OH的捕获作用以及与Cr(Ⅵ)的竞争吸附三个方面讨论了上述离子影响TiO_2薄膜光催化还原Cr(Ⅵ)速率的原因.结果表明,体系酸性越强,越有利于Cr(Ⅵ)的还原;在pH值约为6时,HCO_3~-,Cl~-和SO_4~(2-)对TiO_2薄膜光催化还原Cr(Ⅵ)具有促进作用,NO_3~-具有抑制作用,H_2PO_4~-/HPO_4~(2-)在低浓度时具有促进作用,而在高浓度时具有抑制作用.造成上述结果的主要原因是Cl~-,SO_4~(2-)和HCO_3~-具有较强的·OH捕获作用和在TiO_2表面较低的吸附能力;H_2PO_4~-/HPO_4~(2-)在TiO_2表面具有较强的吸附能力;NO_3~-对紫外光吸收作用降低了TiO_2表面的紫外光强度以及自身光化学反应产生了·OH.

EFFECTS OF INORGANIC ANIONS ON PHOTOCATALYTIC REDUCTION OF CHROMIUM (Ⅵ) OVER TiO_2 THIN FILMS

The effect of five inorganic anions (Cl~-,SO_4~(2-),HCO_3~-,NO_3~- and HPO_4~(2-)/HPO_4~(2-)) which are commonly present in water and wastewater on the photocatalytic activity of TiO_2 thin films for the photocatalytic reduction of Cr(Ⅵ) was investigated. On the following three aspects: UV-vis absorption by inorganic anions, ·OH scavenging by inorganic anions and adsorption of inorganic anions to the TiO_2 surface. The results indicated that, the reduction rate of Cr(Ⅵ)by photocatalytically-induced electrons was significantly higher in acidic solutions than in for alkaline solutions. HCO_3~- , Cl~- and SO~4~(2-) promoted the photocatalytic reduction of Cr(Ⅵ) at pH 6 due to their potentness of · OH scavenging and adsorption to the TiO_2 surface. H_2PO_4~-/HPO_4~(2-)enhanced the photocatalytic reduction of Cr (Ⅵ) at lower concentration but inhibited it at higher concentration mostly because of its strong adsorption to the TiO_2 surface. NO_3~- also inhibited the photocatalytic reduction of Cr(Ⅵ) , by the two mechanisms : firstly, · OH was produced under irradiated ultraviolet in the presence of NO_3~- , secondly, light intensity to the TiO_2surface was reduced because of adsorption by NO_3~-.