Facile synthesis of amine hybrid silica aerogel globule via wet casting assisted self-catalysed sol-gel process for CO₂ capture including direct air capture

Amine hybrid silica aerogel globule (AHSAG) for CO₂ capture including direct air capture (DAC) was firstly synthesized via wet casting assisted self-catalyzed sol-gel process. AHSAG has abundant interpenetrating macropores, which favors diffusion of CO₂ into internal amine sites and can enhance CO₂ adsorption kinetics and capacity. The optimal CO₂ adsorption capacity of AHSAG with dry 100% and 400 ppm CO₂ are 3.82 (30 °C) and 1.86 mmol/g (55 °C), respectively. Corresponding amine efficiencies are 0.478 and 0.233. The effect of temperature on CO₂ adsorption capacity is attributed to simultaneous enhancement of mass transfer kinetics and adsorption thermodynamics. The highest CO₂ adsorption rate of AHSAG is achieved at 70 and 55 °C with 100% and 400 ppm CO₂, respectively. The trend of CO₂ adsorption rate with temperature is attributed to the synergistic effect of diffusion kinetics and desorption. Based on experimental CO₂ adsorption kinetics, adsorption mechanism in 400 ppm CO₂ was estimated with different diffusion models. Both film diffusion resistance and intraparticle diffusion resistance are involved in CO₂ capture of AHSAG from air under given condition to control the overall adsorption process. Three kinetics models were used to fit the experimental data of AHSAG for DAC, and the Avrami model showed the best fitting within the whole adsorption period. Comparing with its state-of-the-art counterparts, AHSAG offers significant advantages for practical DAC, such as high adsorption capacity and amine efficiency, fast adsorption kinetics, and excellent cyclic stability.