Conjugation-induced π-electron modulation in pyridazine-integrated covalent organic frameworks for SO₂ capture and upcycling.

Abstract

Sulfur dioxide (SO₂) capture is of critical importance for environmental protection and sustainable sulfur resource cycling. This process demands sorbents that exhibit high SO₂ capacity, precise molecular recognition, and robust tolerance under extreme conditions. Here, we report a sp² carbon-conjugated covalent organic framework engineered with densely aligned and ordered pyridazine groups (DpTb-COF). This design enables efficient SO₂ capture, achieving an ultrahigh capacity of 19.4 mmol/g (25 °C, 1.0 bar) and exhibiting precise selectivity gradients (SO₂/H₂S = 11.3, SO₂/COS = 13.1, SO₂/CO₂ = 55.3, SO₂/N₂ = 730.1, 0.1/0.9=v/v). Its exceptional stability is evidenced by negligible performance loss over 50 adsorption-desorption cycles. This enhanced performance is achieved by strategically anchoring pyridazine motifs into the highly conjugated DpTb-COF framework. Unlike their non-conjugated counterparts, DpTb-COF's planar conjugated structure promotes framework electron delocalization, which synergistically enhances SO₂ affinity via enriched π-electron density while weakening interaction with CO₂ due to reduced basicity. Furthermore, DpTb-COF exhibits remarkable resilience against humidity and corrosive conditions, maintaining its structural integrity and performance. The captured SO₂ can be efficiently transformed into cyclic sulfites over the Cu₁@DpTb-COF catalyst. This work thereby establishes a rational design strategy for high-performance multifunctional materials that enable both capture and upcycling of acid gases.