A team of researchers has discovered how to efficiently turn carbon dioxide into carbon monoxide using visible light. The discovery opens the doors for scientists to explore what organism is out there – or could be created – to chemically break down the greenhouse gas into a useful form. The results are reported in the Journal of the American Chemical Society.

Researchers succeeded in using an enzyme-modified titanium oxide to get carbon dioxide's electrons excited and willing to jump to the enzyme, which then catalyzes the reduction of carbon dioxide to carbon monoxide. A photosensitizer that binds to the titanium allows the use of visible light for the process. The enzyme is more robust than other catalysts, willing to facilitate the conversion again and again. The trick: It can't come near oxygen.

"By using this enzyme, you put it into a solution that contains titanium dioxide in the presence of a photosensitizer," said University of Michigan biochemist Steve Ragsdale. "We looked for a way that seems like nature's way of doing it, which is more efficient."

Not only do the findings demonstrate that an abundant compound can be converted into a commercially useful compound with considerably less energy input than current methods, it also is a method not so different from what organisms regularly do.

"This is a first step in showing it's possible, and imagine microbes doing something similar," Ragsdale said. "I don't know of any organism that uses light energy to activate carbon dioxide and reduce it to carbon monoxide, but I can imagine either finding an organism that can do it, or genetically engineering one to channel light energy to coax it to do that."

The direct product – carbon monoxide – is a desirable chemical that can be used in other processes to produce electricity or hydrogen. Carbon monoxide also has significant fuel value and readily can be converted by known catalysts into hydrocarbons or into methanol for use as a liquid fuel. Although carbon monoxide serves as a source of energy and biomass for microbes, it is toxic for animals and this risk needs to be managed when it is generated or used in chemical reactions.

Citation: Woolerton et al., 'Efficient and clean photo-reduction of CO2 to CO by enzyme-modified TiO2 nanoparticles using visible light', J. Am. Chem. Soc., 2010, 132 (7), 2132–2133; doi: 10.1021/ja910091z