N-methyldiethanolamine (MDEA) as an effective CO2 absorbent for direct air capture (DAC) in cement-based materials

The escalating release of CO2 into the atmosphere has turned the matter of global warming into a pressing issue. Therefore, direct air capture (DAC - capturing CO2 from the environment) using buildings and infrastructure made of cement-based materials as "synthetic trees" could be an effective approach, given the growing urbanization trend. This study proposed a new technique to use N-methyldiethanolamine (MDEA) in cement-based materials to sequestrate CO2 from the environment. It has significant potential and flexibility compared to existing CO2 capture technologies, particularly given the limitations of CO2 mineralization in cement-based materials with slow kinetics. Furthermore, this study examined the resulting microstructural changes and reaction mechanisms of each hydrated phase, such as Ca(OH)2, calcium-silicate-hydrate (C-S-H), and hydrated cement, due to the addition of MDEA after carbonation. The study also investigated the effect of different percentages of amine on the carbonation of Ca(OH)2 under accelerated conditions, followed by the natural carbonation of cement paste coarse particles. The results showed that a 10% MDEA of water volume is optimal for CO2 capture in cement-based materials. Beyond this percentage, MDEA loss on the surface of solid particles was observed by thermogravimetric analysis (TGA). The study also examined the changes in microstructure, chemical environment, pH, and calcite formation in the cement paste samples with one side exposed to accelerated carbonation. MDEA increased calcite formation by 1.5–2 times compared to the samples that did not contain MDEA. Additionally, aragonite and calcite were formed when MDEA was present, whereas the samples without MDEA only formed calcite.