Modulator-Tuned Cu(II) Metal-Organic Frameworks for Cooperative Sulfur Dioxide Capture

Sulfur dioxide (SO₂), a typical industrial byproduct and hazardous pollutant, requires efficient capture for environmental protection and resource recovery. However, existing adsorbents face challenges such as unsatisfactory selectivity and performance degradation at elevated temperatures in complex flue gas environments. This study presents the judicious construction of isostructural metal-organic frameworks (MOFs) (Cu-L, Cu-L-FA, Cu-L-BA) using a pyrazine tetracarboxylate linker and copper ions, with formic/benzoic acid modulators retained to fine-tune adsorption performance. The resulting MOFs exhibit a rare 4,4-connected mfj topology. These isostructural Cu-L variants demonstrate substantial SO₂ uptake capacity and performance retention at relatively high temperatures. Notably, the formate-modulated variant (Cu-L-FA) achieves an SO₂ adsorption capacity of 4.5 mmol·g^-1 at 298 K and 1 bar, and retains 97% of its capacity at 313 K, significantly outperforming conventional physisorbents. Mechanistic studies reveal that the adsorption process is governed by reversible coordination to Cu(II) sites and multifaceted interactions with basic pyrazine nitrogen atoms. The incorporation of modulators not only optimizes the trade-off between adsorption and regeneration energy but also triggers SO₂-induced dynamic modulator-node interactions, leading to instant high SO₂ uptake at low pressures and enhanced cooperative adsorption. This work provides a novel strategy for designing SO₂ adsorbents with salient performance for flue gas desulfurization.