Ultraviolet light could be a powerful new source of green fuel | Science

A gallium nitride nanowire forest uses the energy of light to convert methanol to ethanol.

Sheng Chu / McGill University

By Robert F. Service

Methanol – a colorless liquid that can be made from agricultural waste – has long been touted as an environmentally friendly alternative to fossil fuels. But it is toxic and has only half the energy that the same volume of gasoline. According to researchers, they have created a potentially inexpensive way to use sunlight to convert methanol into ethanol, a more popular alternative fuel that is less harmful and more energy intensive.

Zhongmin Liu, a chemist at the Dalian Chemical Physics Institute in China, says Zhongmin Liu, who did not participate in the research. If the process can be optimized and scaled, it says, "It has the potential to change the world."

The idea of ​​converting methanol to ethanol is not new. Companies already have a trio of chemical processes that do it. But these require the addition of heat, pressure and toxic additives, such as carbon monoxide. Companies can also directly produce ethanol by fermenting corn kernels or sugar cane. But to cultivate these crops, you need precious lands that could otherwise feed. Researchers and companies have also found ways to convert agricultural waste into ethanol. Until now, however, these have proved too expensive to be competitive.

Chao-Jun Li, a chemist at McGill University in Montreal, Canada, thought that there might be a better way. In 2014, his colleagues and he showed that a tiny forest of nanowires made from gallium nitride (GaN) semiconductor could play a catalytic role in the conversion of methane to benzene, a basic chemical used to make dozens of other industrial compounds such as plastics, solvents and adhesives. Catalysts are compounds that cause other chemicals to react but are not used in the workplace themselves. As a result, they can do their work again and again. In this case, the nanowires have rearranged the chemical bonds between the carbon atoms, which is also necessary to convert methanol into ethanol. McGill researchers have therefore decided to see if GaN nanowires could use their magic with methanol.

The researchers developed and tested several compositions of different nanowires. As they report online last week in the newspaper Chem, they discovered that a long, thin, magnesium-enriched GaN nanowire forest works better at absorbing ultraviolet (UV) radiation and uses this energy to convert methanol to ethanol. The team discovered that the UV rays absorbed more negatively charged nanowire surfaces than their nuclei. The charge pulls a molecule of water from an individual molecule of methanol located on the surface of a nanowire, leaving behind a reactive compound called methylcarbene. As the water molecule floats, the carbene reacts with a neighboring methanol molecule to produce ethanol.

Liu notes that the process is only a proof of concept. The conversion of methanol into ethanol requires ultraviolet rays, which are just a small ray of sunshine reaching the Earth. For the process to be economical, he adds, it may be necessary to refine the nanowires to make them work with visible light, which has less energy than UV light, but which is much more abundant in the rays. of the sun.

In addition to producing ethanol, the nanowire catalyst can also generate other valuable hydrocarbons, such as 1-propanol, an alcohol used in pharmaceutical manufacturing, from methanol, Li note. The capacity raises the hope of customizing nanowires to convert low value base chemicals into a higher value product line, using only light.

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