As global temperatures rise, researchers continue seeking efficient ways to remove CO2 from the atmosphere. While many efforts focus on burying the captured carbon underground, Northwestern's approach goes further by transforming CO2 into functional materials for use in cement, concrete, plaster, and paint. This innovative process not only locks away CO2 permanently but also yields hydrogen gas, a clean energy source suitable for applications such as transportation.
Details of this breakthrough are set to appear on March 19 in the journal Advanced Sustainable Systems.
"We have developed a new approach that allows us to use seawater to create carbon-negative construction materials," said Northwestern's Alessandro Rotta Loria, who led the study. "Cement, concrete, paint and plasters are customarily composed of or derived from calcium- and magnesium-based minerals, which are often sourced from aggregates -- what we call sand. Currently, sand is sourced through mining from mountains, riverbeds, coasts and the ocean floor. In collaboration with Cemex, we have devised an alternative approach to source sand - not by digging into the Earth but by harnessing electricity and CO2 to grow sand-like materials in seawater."
Rotta Loria, who holds the Louis Berger Assistant Professorship of Civil and Environmental Engineering at Northwestern's McCormick School of Engineering, collaborated with chemical and biological engineering assistant professor Jeffrey Lopez on the project. Additional contributors from Northwestern included lead author and postdoctoral fellow Nishu Devi, Ph.D. students Xiaohui Gong and Daiki Shoji, and former graduate student Amy Wagner. Cemex's Global R and D team, a partner in sustainable construction, also played a key role. The research stems from an ongoing collaboration between Cemex and Northwestern.
The method draws inspiration from marine life, particularly the formation of seashells. Previous studies by Rotta Loria's lab explored CO2 storage in concrete and the electrification of seawater to stabilize marine soils. Building on these findings, the current study utilizes CO2 and electricity to induce mineral growth in seawater.
"Our research group tries to harness electricity to innovate construction and industrial processes," Rotta Loria said. "We also like to use seawater because it's a naturally abundant resource. It's not scarce like fresh water."
To initiate mineral formation, researchers inserted electrodes into seawater and applied a low electric current, splitting water into hydrogen gas and hydroxide ions. Introducing CO2 gas into the mix increased the level of bicarbonate ions. These ions, in combination with naturally occurring calcium and magnesium in seawater, produced solid compounds such as calcium carbonate and magnesium hydroxide. While calcium carbonate directly traps CO2, magnesium hydroxide can store additional CO2 through further reactions.
The team likened this mechanism to how corals and mollusks build shells from dissolved ions, using metabolic energy. Here, electrical energy replaces biology, accelerating the mineralization process with CO2 injection.
Two key findings emerged from their experiments. First, the team successfully grew these minerals into sand-like substances. Second, they could fine-tune the material properties by adjusting experimental parameters such as voltage, current, CO2 flow rate, and seawater circulation. This allowed them to create materials ranging from porous flakes to hard, dense particles, all primarily composed of calcium carbonate or magnesium hydroxide.
"We showed that when we generate these materials, we can fully control their properties, such as the chemical composition, size, shape and porosity," Rotta Loria said. "That gives us some flexibility to develop materials suited to different applications."
These custom-grown materials can replace sand or gravel in concrete, which constitute 60-70% of the mixture, or be used in cement, plaster, and paint production.
Notably, these materials can store more than half their weight in CO2. For instance, a blend of 50% calcium carbonate and 50% magnesium hydroxide can absorb over 0.5 metric tons of CO2 per metric ton of material. Rotta Loria emphasized that substituting sand or powder with these substances would not compromise the strength of construction materials.
He proposed deploying the process in scalable, modular reactors along coastlines, rather than directly in the ocean, to avoid harming marine ecosystems. "This approach would enable full control of the chemistry of the water sources and water effluent, which would be reinjected into open seawater only after adequate treatment and environmental verifications," he said.
According to the World Economic Forum, the cement industry contributes 8% of global CO2 emissions, making it the fourth-largest emitter. Combined with concrete production, this number increases. Rotta Loria envisions reducing this impact by integrating CO2 into construction materials.
"We could create a circularity where we sequester CO2 right at the source," Rotta Loria said. "And, if the concrete and cement plants are located on shorelines, we could use the ocean right next to them to feed dedicated reactors where CO2 is transformed through clean electricity into materials that can be used for myriad applications in the construction industry. Then, those materials would truly become carbon sinks."
The study, "Electrodeposition of carbon-trapping minerals in seawater for variable electrochemical potentials and carbon dioxide injections," was supported by Cemex and Northwestern's McCormick School of Engineering.
Research Report:Electrodeposition of carbon-trapping minerals in seawater for variable electrochemical potentials and carbon dioxide injections
Related Links
Northwestern University
Space Technology News - Applications and Research
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
