Nemoto Junichi, Harada Chihiro, Takei Yoshihito, Katakura Naoto, Kaneko Masao
Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, 310-8512, Japan.
Photochem Photobiol Sci. 2007 Jan;6(1):77-82. doi: 10.1039/b611894a. Epub 2006 Nov 24.
Visible light decomposition of aqueous NH3 to N2 was investigated using a photocatalyst aqueous solution based on molecular photoelectron relay systems of either sensitizer (tris(2,2'-bipyridine)ruthenium(II), (Ru(bpy)3(2+))/potassium peroxodisulfate(K(2)S(2)O(8)) or Ru(bpy)3(2+)/methylviologen dichloride(MV2+)/O2, capable of using visible light instead of UV-driven semiconductors such as TiO2. It was confirmed by using an in situ visible absorption spectral change under irradiation that the Ru(II) complex is oxidized to the Ru(III) complex by K(2)S(2)O(8), and that the Ru(III) complex formed is stable without NH3, while the added NH3 was oxidized by the Ru(III) complex to produce the Ru(II) complex. In the presence of 1 mM NH3 aqueous solution, the Ru(III) complex was the predominant species under the photostationary state, but in the presence of 100 mM NH3, Ru(II) predominated. Gas-chromatographic analysis of the gaseous phase in the presence of 8.1 M NH3 showed that the photochemical oxidation of ammonia yielded N2. It was also demonstrated by using the in situ visible absorption spectrum under irradiation of the NH3 (1 M)/Ru(bpy)3(2+) (0.1 mM)/MV2+ (10 mM) system under Ar that MV+* is accumulated, showing that NH3 works as an electron donor for MV+* accumulation with simultaneous formation of the oxidized product of ammonia ((NH3)ox) without producing N2. It was suggested that the reduced product (MV+) and the oxidized product ((NH3)ox) are in a kind of dynamic equilibrium prohibiting further oxidation of (NH3)ox by Ru(bpy)3(3+) to N2. In the O2 atmosphere, the oxidation of MV+ to MV2+ takes place to accumulate Ru(III) complex, so that (NH3)ox was further oxidized to N2. The high activity of IrO2 as a cocatalyst in this system was demonstrated.
使用基于敏化剂（三（2,2'-联吡啶）钌（II），（Ru（bpy）3（2+））/过二硫酸钾（K（2）S（2）O（8））或Ru（bpy）3（2+）/二氯甲基紫精（MV2+）/O2的分子光电子中继系统的光催化剂水溶液，研究了可见光将水溶液中的NH3分解为N2的过程，该系统能够使用可见光而非紫外线驱动的半导体（如TiO2）。通过辐照下的原位可见吸收光谱变化证实，Ru（II）配合物被K（2）S（2）O（8）氧化为Ru（III）配合物，并且形成的Ru（III）配合物在没有NH3的情况下是稳定的，而添加的NH3被Ru（III）配合物氧化以产生Ru（II）配合物。在1 mM NH3水溶液存在下，Ru（III）配合物是光稳态下的主要物种，但在100 mM NH3存在下，Ru（II）占主导。对8.1 M NH3存在下气相的气相色谱分析表明，氨的光化学氧化产生了N2。通过在Ar气氛下对NH3（1 M）/Ru（bpy）3（2+）（0.1 mM）/MV2+（10 mM）系统进行辐照下的原位可见吸收光谱也证明，MV+*得以积累，这表明NH3作为电子供体用于MV+积累，同时形成氨的氧化产物（（NH3）ox），而不产生N2。有人提出，还原产物（MV+）和氧化产物（（NH3）ox）处于一种动态平衡，阻止（NH3）ox被Ru（bpy）3（3+）进一步氧化为N2。在O2气氛中，MV+*被氧化为MV2+以积累Ru（III）配合物，从而使（NH3）ox进一步氧化为N2。证明了IrO2作为该系统中助催化剂具有高活性。
