Carbon dioxide turned into fuel using light

Xiao Zhang, a graduate student in Liu's lab, synthesised rhodium nanocubes that were the optimal size for absorbing near-ultraviolet light.

By: PTI | Washington | Updated: February 25, 2017 2:36 pm
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Scientists have developed tiny nanoparticles that help convert carbon dioxide into methane -a key building block for many types of fuels – using only ultraviolet light as an energy source. Having found a catalyst that can do this important chemistry using ultraviolet light, researchers at Duke University in the US hope to develop a version that would run on natural sunlight, a potential boon to alternative energy.

Chemists have long sought an efficient, light-driven catalyst to power this reaction, which could help reduce the growing levels of carbon dioxide in our atmosphere by converting it into methane. Not only are the rhodium nanoparticles made more efficient when illuminated by light, they have the advantage of strongly favouring the formation of methane rather than an equal mix of methane and undesirable side-products like carbon monoxide.

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This strong “selectivity” of the light-driven catalysis may also extend to other important chemical reactions, the researchers said. “The fact that you can use light to influence a specific reaction pathway is very exciting. This discovery will really advance the understanding of catalysis,” said Jie Liu, professor of chemistry at Duke University. Despite being one of the rarest elements on Earth, rhodium plays a surprisingly important role in our everyday lives.

Small amounts of the silvery grey metal are used to speed up or “catalyse” a number of key industrial processes, including those that make drugs, detergents and nitrogen fertilizer, and they even play a major role breaking down toxic pollutants in the catalytic converters of our cars. Rhodium accelerates these reactions with an added boost of energy, which usually comes in the form of heat because it is easily produced and absorbed.

However, high temperatures also cause problems, like shortened catalyst lifetimes and the unwanted synthesis of undesired products. “Effectively, plasmonic metal nanoparticles act like little antennas that absorb visible or ultraviolet light very efficiently and can do a number of things like generate strong electric fields,” said Henry Everitt, from Duke.

Xiao Zhang, a graduate student in Liu’s lab, synthesised rhodium nanocubes that were the optimal size for absorbing near-ultraviolet light. He then placed small amounts of the charcoal-colored nanoparticles into a reaction chamber and passed mixtures of carbon dioxide and hydrogen through the powdery material. When Zhang heated the nanoparticles to 300 degrees Celsius, the reaction generated an equal mix of methane and carbon monoxide, a poisonous gas.

When he turned off the heat and instead illuminated them with a high-powered ultraviolet LED lamp, Zhang was not only surprised to find that carbon dioxide and hydrogen reacted at room temperature, but that the reaction almost exclusively produced methane. The research was published in the journal Nature Communications.

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