Highly controllable CO2 capture performance under varied humidity conditions by finely tuned metal and organic ligand compositions of DMOF adsorbents

Excessive CO₂ emissions significantly contribute to global warming, promoting the advancement of carbon capture and storage (CCS) technologies. Metal-organic frameworks (MOFs) are promising candidates for selective CO₂ adsorption; however, their effectiveness is often compromised in humid environments, such as flue gas streams. To overcome this limitation, this study synthesizes six isostructural DABCO-pillared MOFs (DMOFs) by finely tuning metal nodes (from Zn to Ni) and integrating methyl (-CH₃) functional groups on the organic ligand to enhance CO₂ adsorption performance, especially under humid conditions. Single gas adsorption isotherms reveal that the Ni-TM DMOF achieves the highest CO₂ adsorption capacity of 5.0 mmol g⁻¹ and maintains 100 % regenerability after five cycles. Binary CO₂/N₂ dynamic breakthrough experiments further demonstrate that the Ni-TM DMOF excels in both CO₂ uptake and CO₂/N₂ separation performance under both dry and humid conditions (80 % relative humidity). Mechanistic insights from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations elucidate the molecular interactions between CO₂ and the DMOF structure, revealing that CO₂ adsorption predominantly occurs via physisorption, enhanced by C-H·O interaction from the -CH₃ groups. This work provides a strategic approach for enhancing the stability and efficiency of MOFs in industrial CO₂ sequestration applications.