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Study shows potential for light-activated material to turn CO2 into clean fuel

(Xinhua)    15:44, August 01, 2017

An international research team has developed a light-activated material that can chemically convert carbon dioxide (CO2) into carbon monoxide (CO) without generating unwanted byproducts.

When exposed to visible light, the material -- a "spongy" nickel organic crystalline structure -- converted CO2 exclusively into CO in a reaction chamber. The latter can be turned into liquid fuels, solvents and other useful products.

Published in the journal Science Advances, the achievement marks a significant step forward in developing technology that could help generate fuel and other energy-rich products using a solar-powered catalyst while mitigating levels of a potent greenhouse gas.

In chemistry, reduction refers to the gain of electrons in a reaction, while oxidation is when an atom loses electrons. Among examples of CO2 reduction is in photosynthesis, when plants transfer electrons from water to CO2 while creating carbohydrates and oxygen.

The reduction of CO2 needs catalysts to help break the molecule's stable bonds. Interest in devising catalysts for solar-powered reduction of CO2 to generate fuels has increased with the rapid consumption of fossil fuels over the past century and the desire for renewable energy.

While researchers have been keen on eliminating competing chemical reactions in the reduction of CO2, Haimei Zheng, staff scientist at Lawrence Berkeley National Laboratory, or Berkeley Lab, of the U.S. Department of Energy and co-corresponding author of the study, noted that "complete suppression of the competing hydrogen evolution during a photocatalytic CO2-to-CO conversion had not been achieved before our work."

The research was led by Berkeley Lab in Northern California and Nanyang Technological University (NTU) in Singapore.

At Berkeley Lab, Zheng and her colleagues dissolved nickel precursors in a solution of trimethylene glycol and exposed the solution to an unfocussed infrared laser, which set off a chain reaction in the solution as the metal absorbed the light. The reaction formed metal-organic composites that were then separated from the solution.

"When we changed the wavelength of the laser, we would get different composites," study co-lead author Kaiyang Niu, a materials scientist in Zheng's lab in the Materials Sciences Division, was quoted as explaining in a news release from Berkeley Lab. "That's how we determined that the reactions were light-activated rather than heat-activated."

At NTU, the new material was tested in a gas chamber filled with CO2, and the reaction products were measured at regular time intervals using gas chromatography and mass spectrometry techniques. Researchers there determined that in an hour at room temperature, 1 gram of the nickel-organic catalyst was able to produce 16,000 micromoles, or 400 milliliters of CO.

The reduction of CO2 by catalysts is not new, but other materials typically generate multiple chemicals in the process. The near-total production of CO with this material appeared to represent a new level of selectivity and control.

"We show a near 100 percent selectivity of CO production, with no detection of competing gas products like hydrogen or methane," said Zheng. "That's a big deal. In CO2 reduction, you want to come away with one product, not a mix of different things."

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