Basicity regulated MgO aerogel with high adsorption capacity for medium-temperature CO2 capture

MgO-based adsorbents exhibit superior adsorption selectivity for acidic CO₂, positioning them as promising candidates for medium-temperature CO₂ capture. However, conventional porous MgO materials suffer from several limitations, including significant pore structural heterogeneity, insufficient strong basic sites, and sluggish adsorption kinetics. This study reports the synthesis of a high-capacity MgO aerogel adsorbent via an alkoxide sol-gel route. The physicochemical structure, carbonation adsorption behavior, thermodynamic equilibrium, and kinetic characteristics of the adsorbent were systematically investigated. The results demonstrate that the synthesized MgO aerogel features well-developed pores and enhanced basicity, characterized by a surface area of approximately 400 m²/g and a strong basic site density of 38.98 %. Hydroxyl groups dynamically coordinate with Mg²⁺ sites on the MgO surface during CO₂ adsorption, and monodentate carbonates progressively transform into bidentate and polydentate carbonate species with superior thermal stability. Thermodynamic modeling indicates that the equilibrium CO₂ partial pressure remains below 0.3 bar within the temperature range of 580–660 K. Adsorbents with increased exposure of strong basic O²⁻ sites exhibit higher adsorption equilibrium temperatures, achieving a saturated adsorption capacity of 6.8 mmol/g. Kinetic analysis under humidified conditions reveals a three-stage adsorption characteristic, where MgCO₃ crystal growth follows a three-dimensional volume nucleation model, and intraparticle diffusion is identified as the rate-limiting step in the adsorption process. The regenerability evaluation indicated that, compared with fresh samples, MgO aerogels retained no less than 80 % of the adsorption capacity after multiple regeneration cycles. This work provides mechanistic insights into the practical application of MgO aerogel in medium-temperature CO₂ capture fields.