Sunlight Converts Greenhouse Gas into Useful Materials
Tue, April 20, 2021

Sunlight Converts Greenhouse Gas into Useful Materials


Greenhouse gases, like carbon dioxide (Co2) and methane, can be toxic at high concentrations and cause global warming. But a team of researchers from the University of Southern California Viterbi School of Engineering sought to break Co2 apart and convert it into useful materials, such as fuels and consumer products, ranging from polymers to pharmaceuticals.

The whole process of converting the greenhouse gas into useful materials, however, typically requires a tremendous amount of energy. So, the USC team considered a more sustainable option: the sunlight.

The electron transfer step from OPP to Co2

Shaama Mallikarjun Sharada from the Mork Family Department of Chemical Engineering and Materials Science and team demonstrated that the ultraviolet light can be effective in exciting an organic molecule oligo(p-phenylene) (OPP) radical anions to Co2. When they exposed it to UV light, the OPP becomes negatively charged anion – one that would be attracted to the anode in electrolysis. This also means that it is readily transferring electrons to the nearest molecule, like the Co2, and makes the colorless gas reactive. When it happens, it can then be reduced and be converted into things, such as drugs, furniture, and plastics.

Sharada went on to say that Co2 is notoriously difficult to reduce the reason why it stays in the atmosphere for decades. However, the negatively charged anion can reduce even something as stable as Co2 in the atmosphere.



How Co2 enters the atmosphere

According to the United States Environmental Protection Agency, gases that trap heat in the atmosphere are called greenhouse gases. Co2 enters the atmosphere through burning fossil fuels (oil, natural gas, and coal), trees, solid waste, and other biological materials. Co2 can also be a result of certain chemical reactions, like the manufacture of cement. There are different ways to remove carbon pollution from the sky, such as photosynthesis or when it is absorbed by plants as part of the biological carbon cycle.

Bio-energy with carbon capture and storage (BECCS) technology is also another option but the process is far more complicated than managing agricultural soils or planting trees. Carbon mineralization or enhanced weathering can also turn carbon from a gas into a solid but it naturally happens very slowly, such as hundreds of years, and scientists are still figuring out how they can speed up the carbon mineralization process.

For the USC team, they believe that the rapidly increasing concentration of Co2 in the planet’s atmosphere is an urgent issue that humanity must address to avoid a climate catastrophe. Beginning the industrial age, a period that encompasses changes in social and economic organization, people have increased the Co2 in the atmosphere by 45% through emissions. Because of this, we now have an average global temperature of two degrees Celsius warmer compared to the pre-industrial period.



The greenhouse effect

Greenhouse gases also keep the Earth warm by preventing heat from escaping. Supposedly, the solar energy that is absorbed in Earth’s surface should be radiated back into the atmosphere as heat and then back to space. This is why the USC team looked for methods to convert the greenhouse gas into carbon-based feedstocks for consumer products or into fuels.

They said that the process traditionally utilizes electricity or heat but since many of these procedures are energy-intensive, they believe it is also not ideal to reduce environmental impacts. So, the team used the sunlight instead as it is more sustainable and energy-efficient. The result of their experiments shows that the sun excites the catalyst module. In physics, excitation is the addition of a discrete amount of energy to a system that results in the alteration from the condition of the lowest energy to one of higher energy.



Sunshine duration

The mean monthly sunshine hours in Seoul, South Korea from 1961-1990 were as follows: January (163.2), February (165.1), March (204.0), April (205.3), May (227.1), June (190.2), July (121.2), August (149.6), September (179.6), October (204.3), November (150.9), December (147.3). This is according to UN Data.

Meanwhile, Sleepopolis ranks the world cities by average annual sunshine hours. In Asia, the top 5 cities with the most sunshine hours include Dubai (United Arab Emirates), Muscat (Oman), Tel Aviv (Israel), Abha (Saudi Arabia), and Baghdad (Iraq). In Africa, it includes Marsa Alam (Egypt), Dakhla Oasis (Egypt), Keethmanshoop (Namibia), Kharga (Egypt), and Khartoum (Sudan).

In Europe, the top 5 cities with the most sunshine per hour are Nicosia (Cyprus), Ierapetra (Greece), Valletta (Malta), Athens (Greece), and Marseille (France). Meanwhile, the top cities with the least sunshine hours in December are Dikson, Russia (0.0 hours of sunshine), Tórshavn, Faroe Islands (6.0 hours), Yakutsk, Russia (9.3), Iqaluit, Canada (12.6), and Moscow (14.0).

Although different parts of the Earth receive varying amounts of solar radiation, it makes sense why the USC researchers opted to use the sun’s energy in converting the greenhouse gas into fuel. Sure, there are other means to do that, such as using metal-based chemicals. Yet, they can be potentially toxic, hard to find, and can be expensive. With sunlight, though, it is more sustainable and energy-efficient. They also mentioned one of the challenges in their work is that although they can harness radiation in their region, very little of it is visible where they can shine a light on so that the reaction will happen. Typically, they would need a UV lamp to make the process work.

Sharada mentioned that their work is the first computational study of its kind. Previous studies have not examined the underlying mechanism of moving an electron from an organic molecule, such as the OPP to Co2. In their study, which also appeared in the Journal of Physical Chemistry, it was detailed that the team carried out systematic changes to the oligophenylene catalyst by adding groups of atoms that impart certain properties when they are bonded to molecules. By doing so, it tends to push the electrons towards the center of the catalyst. Thus, speeding the reaction.

NASA Technology Transfer Program also previously developed a new technology that can convert CO2 into fuel using solar-powered thin-film devices.

Sharada and the team’s research shows us that it is possible to combat global warming by converting Co2 to fuel with the help of solar energy.