Functionalized 3D Covalent Organic Frameworks for High-Performance CO₂ Capture and Separation over N₂

Covalent organic frameworks (COFs) are emerging adsorbent materials for CO₂ capture and separation due to their tunable pore size, periodic permutation, and chemical thermal stability. Herein, four functionalized 3D COF-300s (COF-300-X, X = –SO₃H, –NO₂, –OH, and –NH₂) for CO₂ adsorption and separation are studied by using density functional theory and grand canonical Monte Carlo simulation. The results show that four functionalized COF-300s could create a feasible environment for CO₂ adsorption with high accessible surface area, suitable pore size, and high porosity. The CO₂ adsorption capacity in COF-300s could be significantly improved by functionalization. In comparison, the best performing COF-300-SO₃H shows a superior CO₂ adsorption capacity of 6.23 mmol g⁻¹ and a high CO₂/N₂ selectivity of 393 at 298 K and 100 kPa. The adsorption heat and interaction analyses demonstrate that the CO₂ affinity in COF-300s is enhanced by the introduction of polar functional groups, which renders great CO₂ adsorption and separation performances. The gas distribution shows that the adsorption sites are concentrated near the functional groups and the distribution of CO₂ in COF-300-SO₃H has a characteristic of multilayer adsorptions. This work highlights COF-300-SO₃H as an outperforming adsorbent candidate for CO₂ capture and separation.