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

The emissions of sulfur dioxide (SO₂) 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 SO₂ with high capacity and selectivity has emerged as a critical challenge in recent years. However, existing polymers often exhibit poor SO₂/CO₂ and SO₂/N₂ selectivity. Herein, we report two triazine-functionalized triphenylamine-based nanoporous organic polymers (ANOP-6 and ANOP-7) that demonstrate both good SO₂ uptake and high SO₂/CO₂ and SO₂/N₂ 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 SO₂, 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 SO₂ from SO₂/CO₂ and SO₂/N₂ mixtures. At 298 K and 1 bar, ANOP-6 shows outstanding selectivity toward SO₂/CO₂ (248) and SO₂/N₂ (13146), surpassing all previously reported triazine-based nanoporous organic polymers. Additionally, dynamic breakthrough tests demonstrate the superior separation properties of ANOPs for SO₂ from an SO₂/CO₂/N₂ mixture. ANOPs exhibit a breakthrough time of 73.1 min·g^-1 and a saturated SO₂ capacity of 0.53 mmol·g^-1. These results highlight the exceptional adsorption properties of ANOPs for SO₂, indicating their promising potential for the highly efficient capture of SO₂ from flue gas.