Study Explores Ways to Use Sunlight to Turn Emissions into Beneficial Materials

According to Shaama Sharada, a WISE Gabilan Assistant Professor from the University of Southern California (USC), carbon dioxide (CO₂), which is said to be the worst offender of global warming, is a very stable, “very happy molecule.”

She is now aiming to change that. Sharada and a research group from the Viterbi School of Engineering at USC are working toward splitting the CO₂ gas and changing the greenhouse gas into beneficial materials, such as fuels or consumer products spanning from polymers to pharmaceuticals.

The study was recently published in The Journal of Physical Chemistry A.

Normally, this process would need a huge amount of energy. But in a first-of-its-kind computational study, Sharada and her group enlisted the Sun as a more sustainable option.

The team particularly showed that ultraviolet (UV) light could be highly effective in stimulating oligophenylene, a kind of organic molecule. When exposed to UV light, this molecule turns into a negatively charged “anion” and instantly shifts electrons to the closest molecule, like CO₂—thus making the CO₂ reactive and capable of being reduced and turned into many different things, such as drugs, plastics, or even furniture.

CO₂ is notoriously hard to reduce, which is why it lives for decades in the atmosphere. 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.

Shaama Sharada, WISE Gabilan Assistant Professor, Viterbi School of Engineering, University of Southern California

An Urgent Need, a Promising Approach

CO₂ levels in the Earth’s atmosphere are growing rapidly. This is one of the most pressing issues that should be addressed by mankind to prevent a climate disaster.

Since the advent of the industrial era, humans have contributed to atmospheric CO₂ by increasing it as much as 45%, by burning fossil fuels and through other emissions. Consequently, in comparison to the pre-industrial era, average global temperatures are currently warmer by 2 °C. On account of greenhouse gases like CO₂, the Sun’s heat continues to remain trapped in the atmosphere, thus warming the Earth.

The researchers from the Mork Family Department of Chemical Engineering and Materials Science were headed by third year PhD student Kareesa Kron, under the guidance of Sharada.

Samantha J. Gomez from Francisco Bravo Medical Magnet High School has co-authored the study. She has also been a part of the USC Young Researchers Program, which allows high school students from underrepresented regions to participate in STEM research.

Several research groups are exploring ways to transform CO₂, which has been trapped from emissions, into carbon-based feedstocks or fuels for consumer products spanning from polymers to pharmaceuticals.

The procedure generally involves the use of either electricity or heat, together with a catalyst to accelerate the conversion of CO₂ into products. But a number of these approaches are usually energy-intensive, which is not practical for a process aiming to minimize environmental effects.

Using solar energy instead to stimulate the catalyst molecule is a feasible option because it is both sustainable and energy-efficient.

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

Shaama Sharada, WISE Gabilan Assistant Professor, Viterbi School of Engineering, University of Southern California

According to Sharada, one option is to employ carbon-based organic catalysts for performing this light-aided conversion. But this technique poses its own challenges, which the researchers are aiming to address. The group employs quantum chemistry simulations to comprehend how electrons travel between CO₂ and the catalyst to spot the most practical catalysts for this reaction.

Sharada added that the work was the first-of-its-kind computational study, in that the team had formerly not analyzed the fundamental mechanism of shifting an electron from an organic molecule, such as oligophenylene, to CO₂ gas.

The researchers learned that the oligophenylene catalyst can be systematically altered by incorporating groups of atoms that impart certain characteristics when attached to molecules that, in turn, tend to move electrons toward the core of the catalyst, to accelerate the reaction.

In spite of the difficulties, Sharada is enthusiastic about the opportunities for her research group.

“One of those challenges is that, yes, they can harness radiation, but very little of it is in the visible region, where you can shine light on it in order for the reaction to occur,” added Sharada. “Typically, you need a UV lamp to make it happen.”

The team is currently investigating catalyst design strategies that not only pave the way to high reaction rates but also enable the molecule to be stimulated by visible light, using genetic algorithms as well as quantum chemistry, added Sharada.

The Youngest Researcher

For high school student Gomez, this article is the first co-authored publication in a renowned peer-reviewed journal.

Gomez was a senior at the Bravo Medical Magnet school when she participated in the USC Young Researchers Program over the summer, and worked in Sharada’s laboratory. She was directly trained and mentored in simulations and theory by Kron. According to Sharada, Gomez’s contributions were so tremendous that the team decided to grant her authorship on the article.

According to Gomez, she was happy to have had the opportunity to work on a significant study that contributes to environmental sustainability. She added that during this study, she mainly carried out computational research, computing which kinds of structures were able to considerably decrease CO₂.

Traditionally we are shown that research comes from labs where you have to wear lab coats and work with hazardous chemicals. I enjoyed that every day I was always learning new things about research that I didn’t know could be done simply through computer programs.

Samantha J. Gomez, Study Co-Author and High School Student, Francisco Bravo Medical Magnet High School

“The first-hand experience that I gained was simply the best that I could’ve asked for, since it allowed me to explore my interest in the chemical engineering field and see how there are many ways that life-saving research can be achieved,” Gomez concluded.

Journal Reference:

Kron, K. J., et al. (2020) Computational Analysis of Electron Transfer Kinetics for CO₂ Reduction with Organic Photoredox Catalysts. The Journal of Physical Chemistry A. doi.org/10.1021/acs.jpca.0c03065.