Three-Dimensional Nonconjugated Microporous Organic Polymers Based on Tröger’s Base: Integrating Physical Confinement and Chemisorption for Enhanced NO x Capture

Abstract

Abstract Nitrogen oxides (NOx) demand urgent capture—they can trigger self-catalytic decomposition in nitrocellulose, risking combustion or explosion under high temperature and humidity. To counteract this, rigid, nonplanar building blocks with aliphatic C–H units, contorted Tröger’s base (TB) units, are integrated into microporous organic polymers (MOPs), where micropores enable rapid physisorption, tertiary nitrogen sites allow stable chemisorption, and the aliphatic C–H units within these scaffolds restrict conjugation and donate electrons to benzene rings, further promoting continuous NOx adsorption. Among the polymers, triptycene-based TB (Trip-TB, 1011 m2 g–1, 3.36 mmol g–1) and tetraphenyladamantane-based TB (TAPA-TB, 826 m2 g–1, 3.32 mmol g–1) outperform the triphenylbenzene analog (TAPB-TB, 926 m2 g–1, 2.99 mmol g–1). With only 3 wt% Trip-TB, NOx release is reduced by 70.2 % in titration tests, and the methyl violet color-change time extends 3.15-fold. This enhancement is attributed to the conjugation-interrupting and electron-donating effects of the aliphatic cores to the benzene rings. Characterization and calculations further elucidate the adsorption mechanism. Collectively, these findings establish a cooperative physicochemical mechanism for efficient NOx capture and provide a rational blueprint for adsorbent design.