Study finds clay could solve global warming problem

Sandia National Laboratories bioengineer Susan Rempe (left) and chemical engineer Tuan Ho view an artistic representation of the chemical structure of clay. Their team is studying how clay can be used to capture carbon dioxide. (Credit: Craig Fritz)

Atmospheric levels of carbon dioxide—a gas that traps heat and contributes to climate change—are nearly double the levels before the Industrial Revolution, but make up only 0.0415% of the air we breathe.

This presents a challenge for researchers trying to design artificial trees or other methods of capturing carbon dioxide directly from the air. This problem is trying to solve a group of scientists led by Sandia National Laboratories.

Led by Sandia chemical engineer Tuan Ho, the team used powerful computer models combined with laboratory experiments to study how clay can absorb and store carbon dioxide.

The scientists shared their initial findings in a paper published earlier this week in Journal of Letters in Physical Chemistry.

“These fundamental discoveries have the potential to be captured from the air; that’s what we’re working on,” said Ho, the paper’s lead author. “Clay is really inexpensive and common in nature. This should allow us to significantly reduce the cost of direct carbon capture if this high-risk, high-reward project eventually leads to the technology.”

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Why capture carbon?

Carbon capture and sequestration is the process of capturing excess carbon dioxide from the Earth’s atmosphere and storing it deep underground to reduce the effects of climate change, such as more frequent severe storms, rising sea levels, increased droughts and wildfires. This carbon dioxide can be captured in fossil fuel power plants or other industrial facilities such as cement kilns, or directly from the air, which is more technologically difficult. Carbon capture and sequestration is widely considered to be one of the least controversial technologies being considered for climate intervention.

“We need cheap, environmentally friendly energy,” said Susan Rempe, Sandia bioengineer and senior project scientist. “We can live without producing so much carbon dioxide, but we cannot control what our neighbors do. Direct capture of carbon dioxide in the air is important to reduce the amount of carbon dioxide in the air and reduce the carbon dioxide emissions that our neighbors emit.”

Ho suggests that clay-based devices could be used as sponges to absorb carbon dioxide, and then the carbon dioxide could be “squeezed” out of the sponge and pumped deep underground. Or the clay can be used more as a filter to capture carbon dioxide from the storage air.

In addition to being cheap and widely available, clay is also stable and has a large surface area – it is made up of many microscopic particles, which in turn have cracks and crevices about a hundred thousand times smaller than the diameter of a human hair. These tiny cavities are called nanopores, Rempe says, and within these nanopores the chemical properties can change.

This is not the first time Rempe has been studying nanostructured materials to capture carbon dioxide. In fact, she is part of a team that has studied a biological catalyst to convert carbon dioxide to water-stable bicarbonate, developed a thin nanostructured membrane to protect the biological catalyst, and received a patent for its biologically inspired carbon trapping membrane. Of course, this membrane is not made from inexpensive clay and was originally intended to work in fossil fuel power plants or other industrial facilities, Rempe said.

“These are two complementary possible solutions to the same problem,” she said.

How to model the nanoscale?

Molecular dynamics is a kind of computer simulation that considers the movements and interactions of atoms and molecules at the nanoscale. By looking at these interactions, scientists can calculate how stable a molecule is in a particular environment, such as clay nanopores filled with water.

“Molecular modeling is a really powerful tool for studying interactions at the molecular level,” Ho said. “This allows us to fully understand what happens between carbon dioxide, water and clay, and the goal is to use this information to develop clay material for carbon capture applications.”

In this case, Ho’s molecular dynamics simulations showed that carbon dioxide can be much more stable in the nanopores of wet clay than in plain water, Ho said. This is because the atoms in water do not share their electrons evenly, making one end slightly positively charged and the other end slightly negatively charged. On the other hand, the atoms in carbon dioxide evenly distribute their electrons, and like oil mixed with water, carbon dioxide is more stable near similar molecules, such as the silicon-oxygen regions of clay, Rempe said.

Purdue University researchers led by Professor Cliff Johnston recently used experiments to confirm that water trapped in clay nanopores absorbs more carbon dioxide than ordinary water, Ho said.

Sandia PhD researcher Nabankur Dasgupta also found that within the oil-like regions of the nanopores, less energy is needed to convert carbon dioxide to carbonic acid, making the reaction more favorable than the same conversion in plain water, Ho said. He added that by making this transformation favorable and requiring less energy, ultimately the oil-like regions of the clay’s nanopores allow more carbon dioxide to be captured and stored more easily.

Abstract illustration: Understanding the formation of H2CO3 in water from CO2 is important for environmental and industrial processes. (CREDIT: ACS Publications)

“So far, this tells us that clay is a good material for capturing carbon dioxide and converting it into another molecule,” Rempe said. “And we understand why this is so that synthesis people and engineers can modify the material to improve it. Simulation can also guide experiments to test new hypotheses.”

Ho says the project’s next step will be to use simulations and molecular dynamics experiments to figure out how to get carbon dioxide back out of the nanopores. By the end of the three-year project, they plan to develop a concept for a clay-based direct carbon capture device.

The project is funded by the Sandia Laboratory Research and Development Program. The research was conducted in part at the Center for Integrated Nanotechnology, a Science Administration user facility operated for the Department of Energy by Sandia and Los Alamos National Laboratories.

For more science news, visit our New Discoveries section at The bright side of the news.

Note. Materials courtesy of the US Department of Energy/Sandia National Laboratories. Content can be edited for style and length.

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