New chemical structures show vastly improved carbon capture ability

Oregon State University researchers have synthesized new molecules able to quickly capture significant amounts of carbon dioxide from the air, an important tactic in climate change mitigation.

The study, which focused on titanium peroxides, builds on their earlier research into vanadium peroxides. The research is part of large-scale federal effort to innovate new methods and materials for direct air capture, or DAC(Link is external), of carbon dioxide, produced by the burning of fossil fuels.

Findings of the research, led by May Nyman and Karlie Bach of the OSU College of Science, were published today in Chemistry of Materials(Link is external).

In 2021 Nyman, the Terence Bradshaw Chemistry Professor in the College of Science, was chosen as the leader of one of nine direct air capture projects funded by the Department of Energy through an initial investment of $24 million. Her team is exploring how some transition metal complexes can react with air to remove carbon dioxide and convert it to a metal carbonate, similar to what is found in many naturally occurring minerals.

Transition metals are located near the center of the periodic table and their name arises from the transition of electrons from low energy to high energy states and back again, giving rise to distinctive colors.

Facilities(Link is external) that filter carbon dioxide from the air are still in their infancy. Technologies for mitigating carbon dioxide at the point of entry into the atmosphere, such as at power plants, are more mature. Both types of carbon capture will likely be needed if the Earth is to avoid the worst outcomes of climate change, the scientists say.

At present there are a combined 18 active direct air capture plants operating in the United States, Canada and Europe, with plans(Link is external) for an additional 130 around the globe. Challenges to direct air capture include big costs and high energy requirements compared to working with industrial exhausts. Additionally, the atmosphere’s concentration of carbon dioxide, four parts per million, is low, challenging the performance of carbon capture materials.

“We opted to look into titanium as it’s 100 times cheaper than vanadium, more abundant, more environmentally friendly and already well established in industrial uses,” said Bach, a graduate student in Nyman’s lab. “It also is right next to vanadium on the periodic table, so we hypothesized that the carbon capture behavior could be similar enough to vanadium to be effective.”

Bach, Nyman and the rest of the research team made several new tetraperoxo titanate structures – a titanium atom coordinated with four peroxide groups – that showed varying abilities to scrub carbon dioxide from the air. Tetraperoxo structures tend to be highly reactive because of the peroxide groups, which are potent oxidizing agents.

Related peroxotitanates have been studied for their potential uses in catalysis, environmental chemistry and materials science. However, the tetraperoxotitanates in this study had never been definitively synthesized; Bach was able to use inexpensive materials for high-yield chemical reactions.

“Our favorite carbon capture structure we discovered is potassium tetraperoxo titanate, which is extra unique because it turns out it is also a peroxosolvate,” Bach said. “That means that in addition to having the peroxide bonds to titanium, it also has hydrogen peroxide in the structure, which is what we believe makes it so reactive.”

The measured carbon capture capacity was about 8.5 millimoles carbon dioxide per gram of potassium tetraperoxo titanate – roughly double that of vanadium peroxide.

“Titanium is a cheaper, safer material with a significantly higher capacity.” - Karlie Bach

Named for the titans of Greek mythology, titanium is as strong as steel but much lighter. It’s non-toxic, does not easily corrode and is the ninth most abundant element in the Earth’s crust – found in rocks, soil, plants and even the human body in trace amounts.