Adsorption Removal of Trace SO 2 from Wet Flue Gas Using a Functionalized Zr-MOF

The efficient removal of trace sulfur dioxide (SO 2 ) from wet flue gas remains a critical challenge for porous adsorbents. In particular, high humidity imposes stricter requirements on the robustness of the framework and selective adsorption, degrading sorbent materials and SO 2 capture performance under realistic conditions. Herein, we report a zirconium metal–organic framework (Zr-MOF), BUT-196 (BUT = Beijing University of Technology), isoreticular to UiO-68, constructed from a carbazole-containing dicarboxylate ligand, 4,4′-(5,11-dihydroindolo[3,2- b ]carbazole-6,12-diyl)dibenzoic acid, and 12-connected Zr 6 cluster. Featuring a robust fcu network with a tailored pore environment, BUT-196 exhibits steep low-pressure SO 2 uptake at ambient temperature. Postsynthetic modification of the carbazole NH site with bromoacetic acid introduces carboxylic acid groups without disrupting the framework integrity, yielding BUT-196-COOH. Notably, BUT-196-COOH achieves a dramatically enhanced SO 2 adsorption capacity under humid conditions. Breakthrough experiments revealed that, at 90% relative humidity, the SO 2 breakthrough time increases from ∼800 to ∼2300 min g –1, both for single-component SO 2 and simulated quadruple flue gas mixtures. Further, BUT-196-COOH maintains excellent selectivity and stable cyclic performance. This study highlights that rational pore functionalization can transform high humidity from a competing factor into a cooperative contributor for trace SO 2 capture within a robust framework, offering a viable strategy to MOF sorbent design for wet flue gas desulfurization.