Calcium hydroxide aerogels and xerogels toward CO2 fixation: through an epoxide-mediated sol-gel reaction

Calcium-based CO₂ sorbents have garnered attention due to the capability of CO₂ separation through a process based on carbonation-calcination reaction from flue gas. Ca-based materials with high porosity, allowing for CO₂ diffusion and tolerance for volume change upon carbonation, would be promising for carbon capture and storage (CCS) applications. The present study focused on developing Ca-based aerogels and xerogels prepared through a sol-gel reaction toward CCS application. Calcium hydroxide aerogels and xerogels, which transform into CaO at a high temperature, were prepared through the epoxide-mediated sol-gel reaction using propylene oxide (PO). Two types of carboxylic acids, poly acrylic acid (PAA) and malonic acid (MA), were employed to inhibit the extensive crystal growth of calcium hydroxide in the initial step of the alkalization reaction induced by PO, resulting in the formation of nanocrystalline aerogels and xerogels through supercritical and ambient drying, respectively. The present systematic study revealed that the obtained xerogels prepared with MA exhibit relatively high CO₂ fixation characteristics thanks to the unique card-house nanostructure allowing for the formation of high porosity.

Graphical Abstract