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Nanotubes Fill Key Role in Artificial Photosynthesis

Carbon nanotubes may be the key in overcoming a challenging roadblock for scientists trying to create artificial photosynthesis.

Thanks to their unique ability to store multiple electrons, nanotubes may be able to provide enough electrons for the energy-intensive chemical reactions required by photosynthesis, such as synthesizing carbohydrates. Until now, scientists have not been able to create a system to contribute the sufficient energy.

The researchers, led by Xian-Fu Zhang at the Hebei Normal University of Science and Technology in Qinhuangdao, China,  have discovered that carbon nanotubes can receive and store multiple electrons at a time - specifically, one electron for every 32 carbon atoms in the carbon nanotube. This amounts to quite a few electrons for even a short nanotube (and more electrons for longer nanotubes). Currently, other known systems can only receive and store one electron at a time.

The nanotube's multiple electrons could be used in a chemical reaction where hydrogen reacts with carbon dioxide to synthesize carbohydrates. In photosynthesis, carbohydrates are used to store energy.

While it's an innovative discovery, nanotubes can only account for half the solution to this challenge - at the receiving end. Scientists are still looking for a small molecule that can act as an electron donor, which would need to absorb visible light and subsequently give off multiple electrons to the nanotubes.

One kind of molecule, called phthalocyanines, can release a single electron when it absorbs light. As a test, the researchers bonded several of these donor molecules to a nanotube, creating a complete multiple-electron system that was activated by visible light.

Because in photosynthesis, energy from sunlight is used to break down water into oxygen and hydrogen, artificially recreating the process could have several relevant applications. It could provide a method to efficiently produce hydrogen, which could be used as clean fuel for vehicles. It could also be used to counter global warming by taking carbon dioxide out of the atmosphere.

The study is published in ChemPhysChem (DOI: 10.1002/cphc.200800191).

 via: New Scientist