School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
Proc Natl Acad Sci U S A. 2012 Jul 17;109(29):11552-7. doi: 10.1073/pnas.1203818109. Epub 2012 Jul 2.
Photoreduction of P(2)W(18)O(62), S(2)Mo(18)O(62), and S(2)W(18)O(62) polyoxometalate anions (POMs) and oxidation of water occurs when water-ionic liquid and water-diethylether interfaces are irradiated with white light (275-750 nm) or sunlight. The ionic liquids (ILs) employed were aprotic ([Bmim]X; Bmim = (1-butyl-3-methylimidazolium, X = BF(4), PF(6)) and protic (DEAS = diethanolamine hydrogen sulphate; DEAP = diethanolamine hydrogen phosphate). Photochemical formation of reduced POMs at both thermodynamically stable and unstable water-IL interfaces led to their initial diffusion into the aqueous phase and subsequent extraction into the IL phase. The mass transport was monitored visually by color change and by steady-state voltammetry at microelectrodes placed near the interface and in the bulk solution phases. However, no diffusion into the organic phase was observed when P(2)W(18)O(62) was photo-reduced at the water-diethylether interface. In all cases, water acted as the electron donor to give the overall process: 4POM + 2H(2)O + hν → 4POM(-) + 4H(+) + O(2). However, more highly reduced POM species are likely to be generated as intermediates. The rate of diffusion of photo-generated POM(-) was dependent on the initial concentration of oxidized POM and the viscosity of the IL (or mixed phase system produced in cases in which the interface is thermodynamically unstable). In the water-DEAS system, the evolution of dioxygen was monitored in situ in the aqueous phase by using a Clark-type oxygen sensor. Differences in the structures of bulk and interfacial water are implicated in the activation of water. An analogous series of reactions occurred upon irradiation of solid POM salts in the presence of water vapor.
当用水-离子液体和水-二乙醚界面在白光（275-750nm）或阳光下照射时，P(2)W(18)O(62)、S(2)Mo(18)O(62)和S(2)W(18)O(62)多金属氧酸盐阴离子（POMs）的光还原和水的氧化会发生。所使用的离子液体（ILs）是质子惰性的([Bmim]X；Bmim=(1-丁基-3-甲基咪唑鎓，X=BF(4)、PF(6)))和质子亲核的(DEAS=二乙醇胺硫酸氢盐；DEAP=二乙醇胺磷酸盐)。在热力学稳定和不稳定的水-IL 界面处，光化学形成还原的 POMs 导致它们最初扩散到水相，并随后萃取到 IL 相中。通过在界面附近和在本体溶液相中放置的微电极进行的颜色变化和稳态伏安法来监测质量传输。然而，当P(2)W(18)O(62)在水-二乙醚界面处被光还原时，没有观察到扩散到有机相。在所有情况下，水作为电子供体作用，给出了整个过程：4POM+2H(2)O+hν→4POM(-)+4H(+)+O(2)。然而，可能会产生更高还原的 POM 物种作为中间体。光生成的 POM(-)的扩散速率取决于氧化的 POM 的初始浓度和 IL 的粘度（或在界面热力学不稳定的情况下产生的混合相系统）。在水-DEAS 系统中，通过使用克拉克型氧传感器在水相中原位监测氧气的演化。在水的活化中，暗示了体相和界面相水的结构差异。在存在水蒸气的情况下，照射固体 POM 盐时发生了类似的一系列反应。
