MOF-derived bimetallic coordination polymer@cobalt-aluminum layered double hydroxide for highly selective CO₂...

Selective capture of CO₂ is one of the most effective strategies for combating the greenhouse effect. In this study, we report the synthesis of a novel adsorbent-an amine-based cobalt-aluminum layered hydroxide with a hafnium/titanium metal coordination polymer (denoted as Co-Al-LDH@Hf/Ti-MCP-AS)-through the derivatization of metal-organic frameworks (MOFs) for selective CO₂ adsorption and separation. Co-Al-LDH@Hf/Ti-MCP-AS achieved the maximum CO₂ adsorption capacity of 2.57 mmol g^-1 at 25 °C and 0.1 MPa. The adsorption behavior followed the pseudo-second-order kinetics and Freundlich isotherm models, indicating that chemisorption occurs on a non-homogeneous surface. Co-Al-LDH@Hf/Ti-MCP-AS also exhibited selective CO₂ adsorption in CO₂/N₂ and excellent stability over six adsorption-desorption cycles. An in-depth analysis of the adsorption mechanism through X-ray photoelectron spectroscopy and density-functional theory and frontier molecular orbital calculations revealed that adsorption occurs through acid-base interactions between amine functional groups and CO₂ and that the tertiary amines (N3) have the highest affinity toward CO₂. Our study provides a novel strategy for designing high-performance adsorbents for CO₂ adsorption and separation.