(Hf)PCN-224(Co) as an efficient ppm-level sensor for toxic SO2

Herein, we report the first experimental investigation, supported with theoretical calculations, of a porphyrin-based metal organic framework (PMOF) to address the difficult challenge of SO 2 detection and sensing. Specifically, the highly porous hafnium cobalt-porphyrin tetracarboxylate named (Hf)PCN-224(Co) was used as probe material. (Hf)PCN-224(Co) demonstrated a moderate SO 2 sorption of 1.0 mmol g −1 at 0.1 bar and 298 K, and a limit of detection of 175.5 ppm, obtained by photoluminescent experiments. Furthermore, clear, different emission responses are observed for (Hf)PCN-224(Co) after the exposure to CO 2 and water vapor, compared to SO 2 . Remarkably, (Hf)PCN-224(Co) shows crystalline retention after exposure to SO 2 at low concentrations ( i.e. , 0.1 bar). The use of Hf 4+ , as well as microwave-assisted solvothermal synthesis, lead to crystalline defects in the form of missing linkers, providing additional Hf(IV) open metal sites, able to interact with SO 2 molecules. Based on UV–Vis and X-ray photoelectron spectroscopies, we suggest ligand to metal charge transfer as primal emission mechanisms, and the coordination of SO 2 with Hf 6 (OH) 8 coordinatively unsaturated clusters as the most plausible origin for the emission response in SO 2 detection/sensing. The tendency of this behavior is verified from the density functional theory calculations. SO 2 molecules’ interaction with (Hf)PCN-224(Co), which shows crystallographic defects in the form of missing linkers, as well as fluorescence emission spectra of activated (Hf)PCN-224(Co) and (Hf)PCN-224(Co) exposed to SO 2 at 0.1 bar. • First study of a porphyrin-based MOF for SO 2 detection/sensing. • (Hf)PCN-224(Co) shows chemical stability after the exposure to SO 2 at low concentrations ( i.e. , 0.1 bar). • Good detection selectively of SO 2 against CO 2 and water vapor in solid-state. • Detection and sensing of SO 2 in solution-state with a limit of detection (LOD) of (175.5 ppm). • Competitive LOD compared to previously reported MOFs.