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Artificial Photosynthesis Holds Promise Of Cleaner, Greener Environment

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A system of artificial photosynthesis can collect carbon dioxide before it escapes into our atmosphere as a greenhouse gas and convert it to useful products including drugs and alternative fuels, researchers say.

The breakthrough technology is a hybrid of semiconducting nanowires and bacteria that can take in carbon dioxide and use solar energy to convert it into pharmaceutical drugs, biodegradable plastics or liquid fuels.

The U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California, Berkeley, developed the system.

The hybrid system mimics natural photosynthesis, the process used by plants to take energy from sunlight and synthesize carbohydrates out of water and carbon dioxide.

In the hybrid system, however, the CO2 and water are used to synthesize acetate, a basic building block for biosynthesis, the researchers explain.

"We believe our system is a revolutionary leap forward in the field of artificial photosynthesis," says study leader Peidong Yang, a chemist at the Berkeley Lab. "Our system has the potential to fundamentally change the chemical and oil industry in that we can produce chemicals and fuels in a totally renewable way, rather than extracting them from deep below the ground."

In the system, an "artificial forest" of silicon and titanium oxide nanowires in light-capturing arrays are seeded with bacterial populations, creating a solar-powered environmental-friendly chemistry factory that can use sequestered CO2 as its fuel source, the researchers report in the journal Nano Letters.

The bacteria is Sporomusa ovate, chosen for its excellent catalyst capabilities, they said.

"S. ovata is a great carbon dioxide catalyst as it makes acetate, a versatile chemical intermediate that can be used to manufacture a diverse array of useful chemicals," says chemist and biosynthesis expert Michelle Chang, who holds appointments at both the Berkeley Lab and UC Berkeley.

Technologies are being developed to capture and store carbon dioxide before it adds to the growing problem of the warming atmosphere, but that storage presents its own environmental problems, the Berkeley scientists note.

Their artificial photosynthesis system would be one way to put that stored CO2 to work, using it to synthesize a number of "targeted, value-added chemical products," says Christopher Chang, an expert in catalysts used in carbon-neutral energy conversions.

Any system for artificial photosynthesis must meet a dual challenge of light-capture efficiency levels and sufficient catalytic activity, the researchers point out.

Their nanowire array/bacteria hybrid system is capable of converting solar energy at an efficiency of around 0.38 percent under simulated sunlight, around the same level as that of a natural leaf, they say, while showing an impressive ability to generate the desired chemical molecules.

"We are currently working on our second-generation system which has a solar-to-chemical conversion efficiency of 3 percent," Yang says. "Once we can reach a conversion efficiency of 10 percent in a cost-effective manner, the technology should be commercially viable."

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