Water-assisted SO₂ capture in pyridine-functionalized COFs

Covalent organic frameworks (COFs) have emerged as promising materials for gas separation and purification due to their high porosity, structural tunability and chemical stability. However, the practical application of COFs in SO₂ capture is hindered by severe performance loss under humid conditions. To address this challenge, we develop a water-assisted adsorption strategy by incorporating pyridine groups into chemically robust COFs. Two COFs, TpBpy and TpTtp, exhibit high adsorption capacities and cycling stability. Notably, TpTtp exhibits a SO₂ uptake of 0.75 mmol g^-1 under dry simulated flue gas (2500 ppm SO₂, 15% CO₂ in N₂), which increases by 36% to 1.02 mmol g^-1 at 50% relative humidity. Mechanistic analysis confirms that water promotes SO₂ binding through synergistic interactions with pyridine sites. These results demonstrate the potential of COFs for deep desulfurization in humid flue gas streams.