Enhancing the Adsorption Sites of NH₂‑MIL-125 via a Copper Modification Strategy for Improved CO₂ Capture and CO₂/N₂ Separation

In contrast, the use of Cu(NO₃)₂ and CuSO₄ as the precursor significantly compromised the capture capacity of CO₂, indicating that the copper precursor plays a critical role in determining the pore environment and accessible adsorption sites. Further analysis using different contents of CuCl₂ was conducted, and theoretical calculations reveal that the Cu ion is anchored to the −NH₂ groups while preserving the microporous framework and the specific surface area of CuC-NH₂-MIL-125 was further increased.

The Cu²⁺ coordination modifies the electronic environment of neighboring amino groups, which collectively enhance the material’s affinity for CO₂. These findings highlight the decisive role of copper precursor selection in governing the CO₂ capture performance of Cu-modified NH₂-MIL-125 and identify CuCl₂ derived CuC-NH₂-MIL-125 as a promising adsorbent for practical CO₂/N₂ separation.