Boric Acid and In Situ Generated Boroxine Synergistically Functionalized Hyper-Cross-Linked Polymers with Tailored Microenvironments for Highly Selective CO2 Capture

Abstract

Boric acid groups, containing CO2-philic hydroxyl functionalities that exhibit strong affinity toward CO2 molecules, play a pivotal role in enhancing the selective CO2 adsorption and separation performance of microporous organic polymers. However, their electron-withdrawing character and existing synthetic limitations have hindered the straightforward incorporation of boric acid moieties into porous hyper-cross-linked polymer networks for efficient CO2 capture. Herein, a series of novel hyper-cross-linked polymers were synthesized via a one-pot Friedel–Crafts alkylation reaction employing boric acid derivatives as rigid and functional building units. The resulting polymers, which undergo incomplete cyclization conversion from boric acid groups to boroxine during the polymerization, exhibited hierarchical porosity, with a BET surface area of 1465 m2 g−1, a micropore area of 1410 m2 g−1, a CO2 uptake of 20.82 wt %, and a CH4 storage capacity of 2.67 wt % at 273.15 K and 1.00 bar. Benefiting from isolated boric acid groups, in situ generated boroxine functionalities, and well-developed micropores, the materials exhibited a remarkable CO2/N2 selectivity of 87.68 at 273.15 K under low-pressure conditions (<0.3 bar), as determined by Henry’s law initial slope analysis. Structural tuning of the boric-acid-based building blocks enabled fine control over porosity and CO2 adsorption capacity, highlighting the role of molecular design in optimizing gas separation performance. Complementary theoretical simulations elucidated charge density distributions and electrostatic potentials, providing insight into structure–adsorption correlations. This study broadens the scope of functional building blocks accessible for constructing hyper-cross-linked polymers and offers new design principles for high-performance porous materials in selective CO2 capture and separation.