Porosity Engineering and Functionalization of Hyper-Cross-Linked Polymers for Highly Selective CO₂ Adsorption

Selective carbon dioxide (CO₂) capture from industrial processes is vital for reducing emissions associated with fossil fuel combustion. Achieving both high CO₂ adsorption capacity and excellent CO₂/N₂ selectivity, however, remains a significant challenge. In this study, a novel strategy is introduced that integrates porosity engineering using various cross-linkers-dimethoxymethane (F), p-dichloroxylene (D), and dibromomethane (B)-with post-synthetic modifications to incorporate nitro (─NO₂) and amino (─NH₂) functional groups into the polymer matrix. Nitration of hyper-cross-linked polymer based on dimethoxymethane (HCP-F) yields HCP-F-NO₂, which, upon reduction, produces the amine-functionalized framework HCP-F-NH₂. Both HCP-F-NO₂ and HCP-F-NH₂ demonstrate relatively high CO₂ uptake. Despite its lower surface area (784 m² g⁻¹) compared to HCP-F-NO₂ (1066 m² g⁻¹), HCP-F-NH₂ exhibits superior CO₂/N₂ selectivity of 100, compared to 70 for HCP-F-NO₂. Furthermore, ideal adsorbed solution theory (IAST) selectivity calculations at 298 K and 1 bar for 15:85 CO₂/N₂ confirm enhanced CO₂/N₂ selectivity after post-synthetic modification, with HCP-F-NH₂ reaching the highest value (64), breakthrough experiments at 298 K with 3 mL min^-1 flow rate validate increased CO₂ retention, while regeneration tests confirm structural stability and recyclability, reinforcing the potential of functionalized HCPs for CO₂ capture applications.