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，向可再生能源的过渡是必要和紧迫的。鉴于全球变暖、大气污染等全球性和地区性环境问题，人们普遍认为氢气将成为石油的重要补充，尽管基本的实际问题仍然需要解决。尽管以氢和1/2O_2为基础的燃料电池汽车的技术发展很快，但氢气的产生和储存手段尚未完全建立起来。在这种背景下，将水电化学分解为H_2和1/2O_2被认为是一种候选的制氢方法，其中风力发电站或太阳能电池被认为是电能的来源。然而，投入这类系统的能量回报仍然不符合实际使用的标准。在Othe…上另一方面，用蒸汽处理甲烷也会产生氢气，这也会导致作为副产品的温室气体(CO2)的排放。此外，这一过程需要产生蒸汽的能量。因此，由于水和阳光充足，且无CO_2排放，促进太阳光诱导水分解为H_2和1/2O_2的光催化体系的研究受到了极大的关注。在这方面，我们重点研究了由EDTA、三(2，2‘-联吡啶)Ru(II)、甲基紫精和析氢催化剂组成的光催化体系，其中特定的铂(II)络合物作为催化剂。此外，还不断努力开发由光敏化Rn(II)中心和铂(II)催化剂中心组成的光放氢分子器件。合成了多种Ru(II)、Pt(II)或Ru(II)_2Pt(II)_2异核配合物，并对其进行了表征。然而，长期以来，我们一直无法证明这种分子装置的有用性。我们最近成功地制备了第一个基于Ru(II)-Pt(II)的分子器件，它能有效地催化可见光诱导EDTA将水还原为分子氢。已经证实，观察到的析氢活性不是由于任何光分解产物。在本研究中，为了阐明控制Ru(II)-铂(II)分子器件的光催化活性的重要因素，我们还制备了其他几个结构类似物，并对它们的光催化放氢活性进行了评价。结果发现，在Ar气氛下，在EDTA存在下，具有多肽键的器件在Xe灯照射下放出H2。另一方面，具有两个或两个以上光敏Ru(II)中心的化合物对光化学H_2的产生无效，可能是由于分子内能量转移猝灭过程的增强。较少

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