Greenhouse gases impact climate change, where the rising levels of CO2 are acidifying aqueous resources. Mitigation strategies by direct CO2 capture and storage through mineralization provides a viable pathway to address global challenges. However, there are open questions regarding mechanistic pathways when finding new materials for CO2 mineralization. Both liquid and solid interfaces adsorb CO2 at different rates to convert to carbonate minerals. Efficient CO2 capture requires a fundamental understanding of the surface chemical and physical processes for adsorption. Iron is one of the most prevalent elements comprising soils, dust, and minerals. In the presence of ions in aqueous solutions, iron is known to undergo spontaneous redox reactions and corrosion. Measuring surface transformations of iron mineralization involves complex interfaces, where the presence of ions, organic matter, and gases are present simultaneously under dynamic surface oxidation. Direct capture of atmospheric CO2 was measured at the air/electrolyte/iron interface using in situ polarized modulated infrared reflection absorption spectroscopy (PM-IRRAS) to track the rate of carbonate formation on iron surfaces. We find a connection between iron surface corrosion, solution pH, and mineralization, where the cation in the electrolyte influences the rate of carbonate film growth and the film identity at the interface. The rates of surface carbonation on iron interfaces using different chloride electrolytes with alkali and alkaline cations, Ca2+, Mg2+, Fe2+, Na+, K+, NH4+, H+, Li+, are compared and discussed. Here we show by promoting iron with alkali and alkaline cations, the initial stages of direct CO2 adsorption can be tuned by understanding the rate of carbonation. ATR-FTIR spectroscopy is use to identify vibrational signatures of carbonates uniquely grown at the interface, while in the submerged region, the same heterogeneous mixture of iron hydroxycarbonate and lepidocrocite is grown. These results link the surface chemistry with the physical changes, measured using in situ liquid atomic force microscopy (AFM) to determine the apparent rate of corrosion and ex situ AFM to verify the mineral morphology. These reactions at complex liquid and solid interfaces provide insight into the initial stages of efficient CO2 capture at interfaces for mineralization and sequestration.

Direct CO2 capture at the air/electrolyte/iron interface: Specific cation effects

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ACS Fall 2022

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