ECO SPECIAL.......... Solar powered device to clean greenhouse gases

Solar powered device to clean greenhouse gases   Researchers have developed an artificial photosynthetic system to convert carbon dioxide into useful products like plastics, pharmaceuticals and liquid fuels using solar power A potentially game-changing breakthrough in artificial photosynthesis has been achieved with the develop ment of a system that can capture carbon dioxide emissions before they are vented into the atmosphere and then, powered by solar energy, convert that carbon dioxide  into valuable chemical products, including biodegradable plastics, pharmaceutical drugs and even liquid fuels. Scientists with the US Department of Energy'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 synthesizes  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,“ says Peidong Yang, one of the leaders of this 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.“ The research appears in the journal Nano Letters. The more carbon dioxide that is released into the atmosphere the warmer the atmosphere becomes. The artificial photosynthetic technique developed by the researchers solves the storage problem by putting the cap tured carbon dioxide to good use. “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,“ says Chris Chang, an expert in catalysts for energy conversions. “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.“ HOW IT WORKS By combining biocompatible lightcapturing nanowire arrays with select bacteria, the new system offers a winwin situation for the environment: solar-powered green chemistry using sequestered carbon dioxide. “Our system represents an emerging alliance between the fields of materials sciences and biology, where oppor tunities to make new functional devices can mix and match components of each discipline,“ says Michelle Chang, an expert in biosynthesis. “For example, the morphology of the nanowire array protects the bacteria like Easter eggs buried in tall grass so that these usually-oxygen sensitive organisms can survive in environmental carbon-dioxide sources such as flue gases.“ 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. “Our artificial forest is similar to the chloroplasts in green plants,“ Yang says. “When sunlight is absorbed, photo-excited electron whole pairs are generated in the silicon and titanium oxide nanowires, which absorb different regions of the solar spectrum. The photogenerated electrons in the silicon will be passed onto bacteria for the CO2 reduction while the photo-generated holes in the titanium oxide split water molecules to make oxygen.“ Once the forest of nanowire arrays is established, it is populated with microbial populations that produce enzymes known to selectively catalyze the reduction of carbon dioxide. For this study, the 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. “We are currently working on our second generation system which has a solar-to-chemical conversion efficiency of three per cent,“ Yang says. “Once we can reach a conversion efficiency of 10 per cent in a cost effective manner, the technology should be commercially viable.“

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