Our Idea<\/h4>\n\n\n\n
A carbon-negative building material that locks away CO2<\/sub>\u00a0permanently\u00a0and\u00a0turns it into valuable materials, which can be used to manufacture concrete, cement, plaster and paint.<\/strong><\/p>\n\n\n\n The method transforms CO2<\/sub> into valuable, carbon-negative building materials using seawater and electricity, offering a scalable solution to reduce emissions and create sustainable construction materials.<\/strong><\/p>\n\n\n\n Professor Alessandro Rotta Loria, Professor Jeffrey Lopez, Postdoctoral fellow Nishu Devi, PhD students Xiaohui Gong and Daiki Shoji, Former graduate student Amy Wagner<\/strong><\/p>\n\n\n\n Using seawater, electricity, and carbon dioxide (CO2<\/sub>), Northwestern Engineering scientists have developed a new carbon-negative building material.<\/strong><\/p>\n\n\n\n As Earth\u2019s climate continues to warm, researchers around the globe are exploring ways to capture CO2<\/sub>\u00a0from the air and store it deep underground. While this approach has multiple climate benefits, it does not maximize the value of the enormous amounts of atmospheric CO2<\/sub>.<\/strong><\/p>\n\n\n\n Now, Northwestern\u2019s new strategy addresses this challenge by locking away CO2<\/sub> permanently and turning it into valuable materials, which can be used to manufacture concrete, cement, plaster and paint. The process to generate the carbon-negative materials also releases hydrogen gas \u2014 a clean fuel with various applications, including transportation. <\/p>\n\n\n The\u00a0study was published March 19<\/a>\u00a0in the journal\u00a0Advanced Sustainable Systems<\/em>.<\/strong><\/p>\n\n\n\n \u201cWe have developed a new approach that allows us to use seawater to create carbon-negative construction materials,\u201d said Northwestern\u2019s\u00a0Alessandro Rotta Loria<\/a>, who led the study. <\/strong>\u201cCement, concrete, paint, and plasters are customarily composed of or derived from calcium- and magnesium-based minerals, which are often sourced from aggregates \u2013 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 \u2014 not by digging into the Earth but by harnessing electricity and CO2<\/sub>\u00a0to grow sand-like materials in seawater.\u201d<\/p>\n<\/blockquote>\n\n\n\n Rotta Loria is the Louis Berger Associate Professor of Civil and Environmental Engineering at Northwestern\u2019s McCormick School of Engineering. Jeffrey Lopez<\/a>, an assistant professor of chemical and biological engineering at McCormick, served as a key coauthor on the study. Co-advised by Rotta Loria and Lopez, other Northwestern contributors include Nishu Devi, a postdoctoral fellow and lead author; Xiaohui Gong and Daiki Shoji, PhD students; and Amy Wagner, former graduate student. The study also benefited from the contributions of key representatives from the Global R&D department of Cemex, a global building materials company dedicated to sustainable construction. This work is part of a broader collaboration between Northwestern and Cemex.<\/p>\n\n\n\n The new study builds on previous work from Rotta Loria\u2019s lab to store CO2<\/sub> long term in concrete<\/a> and to electrify seawater to cement<\/a> marine soils. Now, he leverages insights from those two projects by injecting CO2<\/sub> while applying electricity to seawater in the lab.<\/p>\n\n\n\n \u201cOur research group tries to harness electricity to innovate construction and industrial processes,\u201d Rotta Loria<\/strong> said. \u201cWe also like to use seawater because it\u2019s a naturally abundant resource. It\u2019s not scarce like fresh water.\u201d<\/p>\n<\/blockquote>\n\n\n\n To generate the carbon-negative material, the researchers started by inserting electrodes into seawater and applying an electric current. The low electrical current split water molecules into hydrogen gas and hydroxide ions. While leaving the electric current on, the researchers bubbled CO2<\/sub> gas through seawater. This process changed the chemical composition of the water, increasing the concentration of bicarbonate ions.<\/p>\n\n\n Finally, the hydroxide ions and bicarbonate ions reacted with other dissolved ions, such as calcium and magnesium, that occur naturally in seawater. The reaction produced solid minerals, including calcium carbonate and magnesium hydroxide. Calcium carbonate directly acts as a carbon sink, while magnesium hydroxide sequesters carbon through further interactions with CO2<\/sub>.<\/p>\n\n\n\n Rotta Loria likens the process to the technique coral and mollusks use to form their shells, which harnesses metabolic energy to convert dissolved ions into calcium carbonate. But, instead of metabolic energy, the researchers applied electrical energy to initiate the process and boosted mineralization with the injection of CO2<\/sub>.<\/p>\n\n\n\n \u201cThe appeal of such an approach is the attention that is being given to the ecosystem and using science to harness the elements in the contemporary environment to develop valuable products for several industries and preserve resources,\u201d said Davide Zampini, vice president of global R&D at Cemex<\/strong>.<\/p>\n<\/blockquote>\n\n\n Through experimentation, the researchers made two significant discoveries. Not only could they grow these minerals into sand, but they also were able to change the composition of these materials by controlling experimental factors, including the voltage and current of electricity, the flow rate, timing and duration of CO2<\/sub> injection, and the flow rate, timing and duration of seawater recirculation in the reactor.<\/p>\n\n\n\n Depending on the conditions, the resulting substances are flakier and more porous or denser and harder \u2014 but always primarily composed of calcium carbonate and\/or magnesium hydroxide. Researchers can grow the materials around an electrode or directly in solution.<\/p>\n\n\n\n \u201cWe showed that when we generate these materials, we can fully control their properties, such as the chemical composition, size, shape, and porosity,\u201d Rotta Loria<\/strong> said. \u201cThat gives us some flexibility to develop materials suited to different applications.\u201d<\/p>\n<\/blockquote>\n\n\n\n These materials could be used in concrete as a substitute for sand and\/or gravel \u2014 a crucial ingredient that accounts for 60-70 percent of this ubiquitous building material. Or they could be used to manufacture cement, plaster and paint \u2014 all essential finishes in the built environment.<\/p>\n\n\n\n Depending on the ratio of minerals, the material can hold over half its weight in CO2<\/sub>. With a composition of half calcium carbonate and half magnesium hydroxide, for example, 1 metric ton of the material has the capacity to store over one-half a metric ton of CO2<\/sub>. Rotta Loria also says the material \u2014 if used to replace sand or powder \u2014 would not weaken the strength of concrete or cement.<\/p>\n\n\n\n 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. Alessandro Rotta Loria<\/p>\n\n\n\n Rotta Loria envisions industry could apply the technique in highly scalable, modular reactors \u2014 not directly into the ocean \u2014 to avoid disturbing ecosystems and sea life.<\/p>\n\n\n\nWhy It Matters<\/h4>\n\n\n\n
Our Team<\/h4>\n\n\n\n
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Seashell-inspired science<\/h3>\n\n\n\n
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Dual discoveries<\/h3>\n\n\n\n
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Storing carbon in structures<\/h3>\n\n\n\n
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