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

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. SO2 capture demands sorbents that exhibit high capacity, precise molecular recognition, and robust tolerance under extreme conditions. Here, the authors report a sp2 carbon-conjugated covalent organic framework engineered with densely aligned and ordered pyridazine groups for efficient SO2 capture.