Can sunlight convert emissions into useful materials?

Chemical engineers in California are developing an environmentally friendly way to upcycle carbon dioxide emissions into polymers and other materials, with some help from a high school student researcher – and the sun.

Shaama Sharada calls carbon dioxide, or the worst offender of global warming, a very stable, a “very happy molecule.” She aims to change that.

She and a team of researchers at the USC Viterbi School of Engineering are seeking to break CO2 apart and convert the greenhouse gas into useful materials like fuels or consumer products ranging from pharmaceuticals to polymers.

Typically, this process requires a tremendous amount of energy. However, in the first computational study of its kind, Sharada and her team enlisted a more sustainable ally: the sun.

How to excite organic molecules

Specifically, they demonstrated that ultraviolet (UV) light could be very effective in exciting an organic molecule, oligophenylene. Upon exposure to UV, oligophenylene becomes a negatively charged “anion,” readily transferring electrons to the nearest molecule, such as CO2 – thereby making the CO2 reactive and able to be reduced and converted into things like plastics, drugs or even furniture, explains a statement.

“CO2 is notoriously hard to reduce, which is why it lives for decades in the atmosphere,” Sharada said. “But this negatively charged anion is capable of reducing even something as stable as CO2, which is why it’s promising and why we are studying it.”

Since the start of the industrial age, humans have increased atmospheric CO2 by 45%, through the burning of fossil fuels and other emissions. As a result, average global temperatures are now two degrees Celsius warmer than the pre-industrial era. Thanks to greenhouse gases like CO2, the heat from the sun is remaining trapped in our atmosphere, warming our planet.

Carbon-based versus metal-based chemicals

Many research teams are looking at methods to convert CO2 that has been captured from emissions into fuels or carbon-based feedstocks for consumer products ranging from pharmaceuticals to polymers.

“Most other ways to do this involve using metal-based chemicals, and those metals are rare earth metals,” said Sharada. “They can be expensive, they are hard to find and they can potentially be toxic.”

Sharada said the alternative is to use carbon-based organic catalysts for carrying out this light-assisted conversion. However, this method presents challenges of its own, which the research team aims to address. The team uses quantum chemistry simulations to understand how electrons move between the catalyst and CO2 to identify the most viable catalysts for this reaction.

The first study of its kind

Sharada said the work was the first computational study of its kind, in that researchers had not previously examined the underlying mechanism of moving an electron from an organic molecule like oligophenylene to CO2. The team found that they can carry out systematic modifications to the oligophenylene catalyst, by adding groups of atoms that impart specific properties when bonded to molecules, that tend to push electrons towards the center of the catalyst, to speed up the reaction.

Sharada said that the team is now exploring catalyst design strategies that not only lead to high reaction rates but also allow for the molecule to be excited by visible light, using both quantum chemistry and genetic algorithms.

Image credit: Pixabay

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