Tuning Pore Chemistry in Dioxin-Linked Porous Organic Polymers for Enhanced High-Pressure CO2 Uptake

Precise tuning of pore chemistry in three-dimensional porous organic polymers (3D-POPs) is critical for high-performance gas (CO2)-separation. Here, we demonstrate the impact of functional groups on the dioxine-linked 3D-tPOPs bearing a tetraphenylene core, synthesized under solvothermal conditions using NaCl as a template, on the high-pressure CO2 uptake. The post-synthetic amidoxime functionalization of 3D-tPOPs, involving the reaction of pendant nitrile moieties with hydroxylamine hydrochloride, has been shown to precisely tailor pore chemistry without altering the network structure. Whereas the incorporation of the amidoxime moieties, 3D-tPOP-AO, enables higher heteroatom content, a critical factor to enhance CO2 affinity at low pressures, strong hydrogen bonding interactions between amidoxime units limit framework flexibility, thus leading to a significant decrease in the high-pressure gas uptake. 3D-tPOPs showed a high CO2 uptake capacity of 57.4 wt% at 33 bar and 270 K; after modification, CO2 uptake decreased to 19.4 wt% at 273 K and 34 bar. Similarly, CH₄ uptake capacity also decreased from 14.0 wt% at 116 bar and 270 K to 3.8 wt% at 75 bar and 273 K. These findings highlight the critical role of the interactions between functional groups and pore chemistry to form robust adsorbents with high CO₂ uptake performance at high pressures.