Post‐Synthetic Modification of Dibromomethane Knitted Hyper‐Cross‐Linked Polymers With Sulfonic and Nitro Groups for Enhanced CO ₂ Capture and Selectivity

Efficient and selective CO 2 capture represents a crucial technological challenge for carbon emission mitigation in post‐combustion processes. This study demonstrates a dual‐strategy approach combining high surface area engineering with post‐synthetic functionalization (sulfonation and nitration) that breaks the traditional trade‐off between adsorption capacity and selectivity in porous polymers for CO 2 capture, thereby simultaneously enhancing CO 2 adsorption capacity and CO 2 /N 2 selectivity. We synthesized a hyper‐cross‐linked polymer (HCP‐TPB) using triphenylbenzene (TPB) as a rigid building block and dibromomethane as a cross‐linker, achieving exceptional textural properties (BET surface area: 2738 m 2 g −1 ) and CO 2 uptake (21.3 wt% at 273 K). Through post‐synthetic sulfonation and nitration, the polymer framework was deliberately engineered to deliver three notable performance improvements: (1) increased CO 2 capacity to 23.7 wt% for HCP‐TPB‐SO 3 H and 23.3 wt% for HCP‐TPB‐NO 2 at 273 K, (despite reduced surface area (1796 and 1564 m 2 g −1 ) respectively); (2) enhanced CO 2 /N 2 selectivity (from 16 for the pristine HCP‐TPB to 32 and 42 for HCP‐TPB‐SO 3 H and HCP‐TPB‐NO 2 at 273 K), and (3) improved Ideal Adsorption Solution Theory (IAST)‐predicted selectivity (14→22→35) for 15:85 CO 2 /N 2 mixtures at 298 K. These results establish an effective structure‐property relationship between sulfonic and nitro functionalities and gas separation performance.