Artificial photosynthesis method turns waste CO2 into fuels

In a breakthrough in artificial photosynthesis, researchers have developed a new system that uses sunlight to convert waste carbon dioxide into valuable chemical products such as biodegradable plastics, pharmaceuticals, and even liquid fuels.
Scientists with the US Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have created a hybrid system of semiconducting nanowires and bacteria that mimics the natural photosynthetic process by which plants use the energy in sunlight to synthesise carbohydrates from carbon dioxide and water.
However, this new artificial photosynthetic system synthesises the combination of carbon dioxide and water into acetate, the most common building block today for biosynthesis.

"We believe our system is a revolutionary leap forward in the field of artificial photosynthesis," said Peidong Yang, a chemist with Berkeley Lab's Materials Sciences Division and one of the leaders of the study.
"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," Yang said.
"In natural photosynthesis, leaves harvest solar energy and carbon dioxide is reduced and combined with water for the synthesis of molecular products that form biomass," said Christopher Chang, who holds joint appointments with Berkeley Lab and UC Berkeley.

"In our system, nanowires harvest solar energy and deliver electrons to bacteria, where carbon dioxide is reduced and combined with water for the synthesis of a variety of targeted, value-added chemical products," Chang said.

By combining biocompatible light-capturing nanowire arrays with select bacterial populations, the new artificial photosynthesis system offers a win/win situation for the environment: solar-powered green chemistry using sequestered carbon dioxide, researchers said.
The system starts with an 'artificial forest' of nanowire heterostructures, consisting of silicon and titanium oxide nanowires, developed earlier by Yang and his research group.
Once the forest of nanowire arrays is established, it is populated with microbial populations that produce enzymes known to selectively catalyse the reduction of carbon dioxide.

In the study published in the journal Nano Letters, the Berkeley team used Sporomusa ovata, an anaerobic bacterium that readily accepts electrons directly from the surrounding environment and uses them to reduce carbon dioxide.
Once the carbon dioxide has been reduced by S ovata to acetate (or some other biosynthetic intermediate), genetically engineered E coli are used to synthesise targeted chemical products.
The team achieved a solar energy conversion efficiency of up to 0.38 per cent for about 200 hours under simulated sunlight, which is about the same as that of a leaf.