Highly Selective SO₂ Capture by Triazine-Functionalized Triphenylamine-Based Nanoporous Organic Polymers

The emissions of sulfur dioxide (SO 2 ) from combustion exhaust gases pose significant risks to public health and the environment due to their harmful effects. Therefore, the development of highly efficient adsorbent polymers capable of capturing SO 2 with high capacity and selectivity has emerged as a critical challenge in recent years. However, existing polymers often exhibit poor SO 2 /CO 2 and SO 2 /N 2 selectivity. Herein, we report two triazine-functionalized triphenylamine-based nanoporous organic polymers (ANOP-6 and ANOP-7) that demonstrate both good SO 2 uptake and high SO 2 /CO 2 and SO 2 /N 2 selectivity. These polymers were synthesized through cost-effective Friedel–Crafts reactions using cyanuric chloride, 3,6-diphenylaminecarbazole, and 2,2′,7,7′-tetrakis(diphenylamino)-9,9′-spirobifluorene. The resultant ANOPs are composed of triazine and triphenylamine units and feature an ultramicroporous structure. Remarkably, ANOPs exhibit impressive adsorption capacities for SO 2, with uptakes of approximately 3.31–3.72 mmol·g –1 at 0.1 bar, increasing to 9.52–9.94 mmol·g –1 at 1 bar. The static adsorption isotherms effectively illustrate the ability of ANOPs to separate SO 2 from SO 2 /CO 2 and SO 2 /N 2 mixtures. At 298 K and 1 bar, ANOP-6 shows outstanding selectivity toward SO 2 /CO 2 (248) and SO 2 /N 2 (13146), surpassing all previously reported triazine-based nanoporous organic polymers. Additionally, dynamic breakthrough tests demonstrate the superior separation properties of ANOPs for SO 2 from an SO 2 /CO 2 /N 2 mixture. ANOPs exhibit a breakthrough time of 73.1 min·g –1 and a saturated SO 2 capacity of 0.53 mmol·g –1 . These results highlight the exceptional adsorption properties of ANOPs for SO 2, indicating their promising potential for the highly efficient capture of SO 2 from flue gas.