Facilitating Gas Accessibility via Macropore Engineering in Amine-Loaded Silica Particles for Enhanced CO₂ Adsorption Performance

The urgent need to mitigate climate change has spurred the development of efficient adsorbents for CO2 capture. Porous solid sorbents, especially those incorporating amine-modified porous silica materials, offer a promising alternative due to their superior selectivity and reversibility. However, the existing research has focused on developing mesoporous silica for CO2 adsorption applications, often overlooking the role of macropores. One critical challenge with mesoporous silica is the restriction in the loading amount of amine due to low pore volume, which is followed by reduction of the CO2 capture capacity due to pore blocking and a decrease in surface area at high amine concentration. Macroporous silica particles offer promising advantages over mesopores in CO2 adsorption performance, including improved mass transfer kinetics and enhanced accessibility of CO2 to amine sites. Therefore, the CO2 adsorption capacity of porous silica materials may not have reached its full potential, and the influence of macropore sizes ranging from 60 to 400 nm has yet to be fully explored. This research, for the first time, aims to address current limitations in CO2 capture methodologies by engineering controllable porous silica particles with various macropore sizes utilizing a spray process followed by tetraethylenepentamine (TEPA) modification. Results indicate that increasing TEPA concentration up to 70 wt % enhanced the CO2 adsorption capacity of the particles. The absorption performance was maximized in macroporous silica with a poly(methyl methacrylate) (PMMA) template size of 291 nm (6.08 mmol CO2/g of absorbent). Generally, larger macropore size facilitates CO2 diffusion within the particles, preventing the formation of inactive TEPA sites and reducing the CO2 diffusion resistance. This study not only highlights the relationship between the macroporous structure, TEPA modification, and CO2 adsorption capacity but also provides valuable insights for advancing carbon capture and storage (CCS) technologies, emphasizing the potential of macroporous silica to overcome the inherent limitations of its mesoporous counterpart.