《自然—纳米技术》：利用病毒从水中分离出氢

据美国物理学家组织网4月12日(北京时间)报道，美国麻省理工学院的研究人员利用病毒将氢从水中分离出来，在将水变成氢燃料的漫漫征程中迈出了关键一步。相关研究发表在最新出版的《自然—纳米技术》（Nature Nanotechnology）杂志上。
麻省理工学院材料化学家安琪拉·贝尔彻领导的团队模拟植物利用太阳光分离水并制造化学燃料来促进自身生长的过程，对一个病毒进行了基因改造，同时将其作为生物支架，将一些纳米组件搭建在一起，最终把水分子分离成了氢原子和氧原子。

以往，研究人员使用太阳能电池板产生的电力来分离水分子，但麻省理工学院的研究人员直接使用太阳光来制取氢。贝尔彻表示，虽然他们的最终目的是从水中得到氢气，但将氧气从水中分离出来面临的技术挑战更大，于是该研究团队首先开始攻克这一难关。

贝尔彻团队将无毒的细菌病毒M13进行基因改造，让它吸附一个催化剂分子氧化铱和一个吸光物质锌卟啉，并同它们绑在一起，吸光物质源源不断地将阳光沿着病毒传递，于是该病毒就变成了类似电线的设备，能够高效地将氧从水分子中分离出来。

然而实验发现，一段时间后，该病毒“电线”会簇拥在一起，失去效力。于是，研究人员将它们变成凝胶状态封入一个胶囊内，这些病毒因此能够保持自己的状态，从而维持了其稳定性和有效性。

这种方法使产生氧气的效率提高了4倍，研究人员希望能够找到同样的以生物学为基础的系统来完成这个反应的另一半过程——分离氢气。目前，从水中分离的氢被分成质子和电子。研究人员正在进行第二步攻关，将这些质子和电子变成氢原子或者氢分子。该研究团队也希望找到更常见、更便宜的物质来做催化剂，替代昂贵而稀少的铱。

贝尔彻表示，她们将在两年内研制出能够自我支持并持久耐用的模型设备，实现将水分离成氢气和氧气。

CAMBRIDGE, Mass. — A team of MIT researchers has found a novel way to mimic the process by which plants use the power of sunlight to split water and make chemical fuel to power their growth. In this case, the team used a modified virus as a kind of biological scaffold that can assemble the nanoscale components needed to split a water molecule into hydrogen and oxygen atoms.

Splitting water is one way to solve the basic problem of solar energy: It’s only available when the sun shines. By using sunlight to make hydrogen from water, the hydrogen can then be stored and used at any time to generate electricity using a fuel cell, or to make liquid fuels (or be used directly) for cars and trucks.

Other researchers have made systems that use electricity, which can be provided by solar panels, to split water molecules, but the new biologically based system skips the intermediate steps and uses sunlight to power the reaction directly. The advance is described in a paper published on April 11 in Nature Nanotechnology.

The team, led by Angela Belcher, the Germeshausen Professor of Materials Science and Engineering and Biological Engineering, engineered a common, harmless bacterial virus called M13 so that it would attract and bind with molecules of a catalyst (the team used iridium oxide) and a biological pigment (zinc porphyrins). The viruses became wire-like devices that could very efficiently split the oxygen from water molecules.

Over time, however, the virus-wires would clump together and lose their effectiveness, so the researchers added an extra step: encapsulating them in a microgel matrix, so they maintained their uniform. arrangement and kept their stability and efficiency.

While hydrogen obtained from water is the gas that would be used as a fuel, the splitting of oxygen from water is the more technically challenging “half-reaction” in the process, Belcher explains, so her team focused on this part. Plants and cyanobacteria (also called blue-green algae), she says, “have evolved highly organized photosynthetic systems for the efficient oxidation of water.” Other researchers have tried to use the photosynthetic parts of plants directly for harnessing sunlight, but these materials can have structural stability issues.

Belcher decided that instead of borrowing plants’ components, she would borrow their methods. In plant cells, natural pigments are used to absorb sunlight, while catalysts then promote the water-splitting reaction. That’s the process Belcher and her team, including doctoral student Yoon Sung Nam, the lead author of the new paper, decided to imitate.

In the team’s system, the viruses simply act as a kind of scaffolding, causing the pigments and catalysts to line up with the right kind of spacing to trigger the water-splitting reaction. The role of the pigments is “to act as an antenna to capture the light,” Belcher explains, “and then transfer the energy down the length of the virus, like a wire. The virus is a very efficient harvester of light, with these porphyrins attached.

“We use components people have used before,” she adds, “but we use biology to organize them for us, so you get better efficiency.”

Using the virus to make the system assemble itself improves the efficiency of the oxygen production fourfold, Nam says. The researchers hope to find a similar biologically based system to perform. the other half of the process, the production of hydrogen. Currently, the hydrogen atoms from the water get split into their component protons and electrons; a second part of the system, now being developed, would combine these back into hydrogen atoms and molecules. The team is also working to find a more commonplace, less-expensive material for the catalyst, to replace the relatively rare and costly iridium used in this proof-of-concept study.

Thomas Mallouk, the DuPont Professor of Materials Chemistry and Physics at Pennsylvania State University, who was not involved in this work, says, “This is an extremely clever piece of work that addresses one of the most difficult problems in artificial photosynthesis, namely, the nanoscale organization of the components in order to control electron transfer rates.”

He adds: “There is a daunting combination of problems to be solved before this or any other artificial photosynthetic system could actually be useful for energy conversion.” To be cost-competitive with other approaches to solar power, he says, the system would need to be at least 10 times more efficient than natural photosynthesis, be able to repeat the reaction a billion times, and use less expensive materials. “This is unlikely to happen in the near future,” he says. “Nevertheless, the design idea illustrated in this paper could ultimately help with an important piece of the puzzle.”

Belcher will not even speculate about how long it might take to develop this into a commercial product, but she says that within two years she expects to have a prototype device that can carry out the whole process of splitting water into oxygen and hydrogen, using a self-sustaining and durable system.