Large-scale facilities that capture carbon dioxide from the air are already operating around the world. But the high-tech materials they use are expensive.
Researchers have now found that clay, one of the most abundant materials on Earth, could be a much simpler, cheaper way to for direct air capture of carbon dioxide. The results appear in The Journal of Physical Chemistry C.
While clay minerals have been studied before to trap carbon dioxide, most of the work has focused on carbon sequestration in geological reservoirs where clay is present. In these scenarios, carbon dioxide is injected deep underground under high temperature and pressure. “Our work is novel because it showed that carbon dioxide can be sorbed on clays under ambient and near-ambient conditions,” said Cliff Johnston, professor of agronomy and earth sciences at Purdue in an email.
Many direct air capture systems today rely on advanced porous materials such as metal-organic frameworks and clay-like zeolites to capture carbon. Pores give these materials a high surface area to hold the carbon dioxide.
Clay minerals such as bentonite and smectite also have a very high surface area: a tablespoon of clay has approximately the same surface area as an American football field. And these minerals are some of the most ubiquitous nanomaterials found on Earth.
Johnston and colleagues have found in the past that these clays can bind significant quantities of highly toxic contaminants. This was surprising because these types of clays are generally water-loving, or hydrophilic, while the contaminants are exceptionally water-repelling, or hydrophobic, he says. “These results showed that clay interlayers have both hydrophilic and hydrophobic properties that can be manipulated,” he says.
This led to the team’s work on carbon dioxide capture on clays. They found that molecules like carbon dioxide are drawn to the hydrophobic regions of clay, while water vapor tends to occupy the hydrophilic regions.
“We have shown that these materials can sorb significant quantities of carbon dioxide, comparable to other direct capture sorbents, in clay interlayers,” Johnston says. “The surface chemistry and ability to bind carbon dioxide can be manipulated through geochemical controls and changes in humidity and temperature.”
He says that the team now has a patent application in process, and are trying to implement the technology on a large scale.
Source: Cliff T. Johnston et al. Competitive Sorption of H2O and CO2 in Clay Mineral Interlayers. J. Phys. Chem. C, 2025.
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