Hierarchically porous pip2-Mg₂(dobpdc)/sodium alginate composite aerogel for high efficiency CO₂ capture

Polyamine-functionalized metal-organic frameworks (MOFs) facilitate the coordination between CO₂ and amine-modified metal sites through chemical adsorption, exhibiting excellent CO₂ selectivity and enhanced capture capacity. However, the limited recyclability and structural instability of MOF powders still hinder their practical application. To address this challenge, we have stably synthesized an efficient pip2 (pip2 = 1-(2-aminoethyl) piperidine)-Mg₂(dobpdc) (dobpdc = 4,4'-biphenyldicarboxylic acid)/sodium alginate (SA) composite aerogel via a coagulation-induced method. The resulting hybrid aerogel system features a layered porous architecture. This optimized structural configuration promotes the rapid transport of CO₂ molecules while ensuring full exposure of the adsorption sites through interconnected channels, thereby synergistically enhancing both mass transfer efficiency and the accessibility of active sites. Furthermore, the micropores and mesopores within the pip2-Mg₂(dobpdc)/SA composite strengthen the interaction between CO₂ and the adsorbent, enabling rapid mass transfer through the mesoporous network. The hierarchical porous structure synergistically accelerates CO₂ diffusion through SA macropores while confining gas molecules within micropores for strong interactions, achieving a CO₂ adsorption capacity of 4.064 mmol/g, when the ratio of CO₂ to N₂ is 10:90, the selectivity value reaches 59.12, indicating a significant potential for selective CO₂ capture. In-situ DRIFTS analysis reveals that pip2-Mg₂(dobpdc)/SA captures CO₂ through an efficient mechanism: initially, CO₂ is introduced into the voids of the material and concurrently reacts with surface amino groups to form carbamate species, thereby enabling a synergistic adsorption mechanism that integrates both chemical and physical effects. This study contributes to the advancement of design and fabrication strategies for layered porous CO₂ adsorbents.