Department of Chemistry, University of Toronto, Toronto, Ontario, Canada.
Environ Sci Technol. 2011 Dec 1;45(23):10004-12. doi: 10.1021/es202263q. Epub 2011 Nov 4.
We have used a novel photochemical Knudsen cell reactor to investigate the uptake and phototransformation of some atmospherically important trace organics on TiO(2) and TiO(2)-SiO(2) mixed films. Illumination of TiO(2) films led to an enhanced uptake of isopropanol and n-propanol and the concurrent production of gas-phase acetone and propionaldehyde, respectively, with high efficiency. Acetone production from isopropanol on illuminated TiO(2) films displayed a significant enhancement in the presence of cosorbed AgNO(3) or KNO(3). Uptake of cyclohexene by TiO(2) films required the presence of both nitrate anion and light. The wavelength and substrate (TiO(2) vs SiO(2)) dependence of the nitrate-induced enhancement in uptake indicates that it was not caused by direct photolysis of nitrate anion. We propose a 2-fold role for nitrate anion in the present experiments: first, as an electron trapping agent that activates the TiO(2) surface toward photooxidation; second, as suggested by our results for cyclohexene, as a source of reactive nitrate radical at the TiO(2) surface. These observations suggest that mineral dust containing photoactive components may catalyze the transformation of photochemically inactive organic compounds into species that absorb in the actinic region.
我们使用了一种新颖的光化学克努森细胞反应器来研究一些在大气中重要的痕量有机物在 TiO(2) 和 TiO(2)-SiO(2) 混合薄膜上的吸收和光转化。TiO(2) 薄膜的光照导致异丙醇和正丙醇的吸收增强，分别生成气相丙酮和丙醛，效率很高。在吸附的 AgNO(3) 或 KNO(3) 的存在下，光照 TiO(2) 薄膜上的异丙醇产生的丙酮显示出显著的增强。TiO(2) 薄膜对环己烯的吸收需要硝酸盐阴离子和光的存在。硝酸盐诱导吸收增强的波长和底物（TiO(2) 与 SiO(2)）依赖性表明，这不是由硝酸盐阴离子的直接光解引起的。我们在本实验中提出了硝酸盐阴离子的双重作用：首先，作为电子捕获剂，使 TiO(2) 表面对光氧化活化；其次，正如我们对环己烯的结果所表明的，作为 TiO(2) 表面活性硝酸盐自由基的来源。这些观察结果表明，含有光活性成分的矿物尘埃可能催化光化学惰性有机化合物转化为在光化区域吸收的物质。
