Development of the nano devices with photo-hydrogen-evolving abilities

人们越来越认识到，石油、煤炭和天然气等化石燃料的储量是有限的，向可再生能源过渡是必要和紧迫的。鉴于全球变暖和空气污染等全球性和区域性的环境问题，人们普遍认为氢将成为石油的重要补充，尽管基本的实际问题仍有待解决。尽管以H_2和1/2O_2为基础的燃料电池汽车的技术进步很快，但是产生和储存氢气的方法还没有完全建立起来。在这种情况下，将水电化学分解成H_2和1/2O_2被认为是产生氢的备选方法之一，其中风力发电站或太阳能电池被认为是电力来源。然而，在这种系统中投入的能源的能源回报仍然不符合实际使用的标准。另一方面，众所周知，用蒸汽处理甲烷会产生氢气，这也会导致温室气体（CO_2）作为副产品的排放。而且，这个过程需要能量来产生蒸汽。因此，由于水和太阳光丰富，且无CO_2排放，促进水分解为H_2和1/2O_2的光催化体系的研究受到了广泛的关注。在这方面，我们关注了一个众所周知的光系统，该系统由EDTA、三（2,2 ' -联吡啶）钌（II）、甲基紫素和析氢催化剂组成，其中特定的Pt（II）配合物作为催化剂。此外，人们还不断努力开发由光敏化的钌（II）中心和铂(II)-催化剂中心组成的光-析氢分子器件。各种异质核Ru(II)Pt（II）或Ru(II)_2Pt(II)_2配合物被制备和评价。然而，我们长期以来一直无法证明这种分子装置的实用性。我们最近成功地制备了第一个基于Ru(II)Pt（II）的分子装置，该装置可以有效地催化可见光诱导的edta还原水为分子氢。已经证实，观察到的h_2演化活性不是由于任何光分解产物。在本研究中，为了阐明影响Ru(II)Pt（II）基分子器件光催化活性的重要因素，制备了其他几个结构类似物，并对它们的光- h_2演化活性进行了评价。结果表明，在氩气环境下，在EDTA存在下的氙灯照射下，具有肽链的器件会产生H_2。另一方面，具有两个或两个以上光敏钌（II）中心的化合物对H_2的光化学生成无效，这可能是由于分子内能量传递猝灭过程的增强。少

There is an increasing understanding that the reserves of fossil fuels, such as oil, coal, and natural gas, are limited and the transition to renewable energies is necessary and urgent. In view of the global and regional environmental issues such as global warming and air pollution, it is generally considered that hydrogen would become an important supplement to oil, even though basic practical problems still need a solution. In spite of the rapid technological advance in the development of fuel-cell cars based on H_2 and 1/2O_2, the means of generating and storing hydrogen gas has not been well established as yet. In this context, the electrochemical decomposition of water into H_2 and 1/2O_2 is regarded as one of the candidates as a method of generating hydrogen, where wind power stations or solar batteries are considered as the source of electricity. Nevertheless, the energy return on energy invested in such systems still does not meet the criteria for the practical use. On the othe … More r hand, hydrogen is also known to be generated upon the treatment of methane with steam, which also leads to the emission of greenhouse gas (CO_2) as a byproduct. Moreover, this process requires the energy to produce the steam. Consequently, great attention has been paid to the studies on the photocatalytic systems promoting the solar-light-induced splitting of water into H_2 and 1/2O_2 because water and sunlight are abundant and such systems are free of the CO_2, emission.In this regard, we have focused on a well-known photosystem consisting of EDTA, tris(2,2′-bipyridine)ruthenium(II), methylviologen, and hydrogen-evolving catalysts, where particular Pt(II) complexes serve as the catalysts. Further, continuous efforts have also been made to develop the photo-hydrogen-evolving molecular devices consisting of photosensitizing rnthenium(II) centers and platinum(II)-catalyst centers. Various heteronuclear Ru(II)Pt(II) or Ru(II)_2Pt(II)_2 complexes have been prepared and evaluated. However we have long been unable to demonstrate the usefulness of such molecular devices. We recently succeeded in the preparation of the first Ru(II)Pt(II)-based molecular device which effectively catalyzes visible-light-induced EDTA-reduction of water into molecular hydrogen. It has been confirmed that the observed H_2-evolving activity is not due to any photodecomposition products.In the present study, to clarify the important factors which govern the photocatalytic activity of the Ru(II)Pt(II)-based molecular device, several other structural analogs have been prepared and their photo-H_2-evolving activities have been evaluated. As a result, the devices with peptide-linkage are found to evolve H_2 upon Xe-lamp irradiation in the presence of EDTA under Ar atmosphere. On the other hand, the compounds having two or more photosensitizing ruthenium(II) centers are found to be ineffective towards the photochemical H_2 generation, presumably due to the enhancement in intramolecular energy-transfer quenching processes. Less