Mechanism of preferential adsorption of SO${}_2$ into two microporous paddle wheel frameworks M(bdc)(ted)0.5

Abstract

The selective adsorption of a corrosive gas, SO${}_2$, into two microporous pillared paddle-wheel frameworks M(bdc)(ted)0.5 [M = Ni, Zn; bdc = 1,4-benzenedicarboxylate; ted = triethylenediamine] is studied by volumetric adsorption measurements and a combination of in-situ infrared spectroscopy and ab initio density functional theory (DFT) calculations. The uptake of SO${}_2$ in M(bdc)(ted)0.5 at room temperature is quite significant, 9.97 mol/kg at 1.13 bar. The major adsorbed SO${}_2$ molecules contributing to the isotherm measurements are characterized by stretching bands at 1326 and 1144 cm${}^{-1}$. Theoretical calculations including van der Waals interactions (based on vdW-DF) suggest that two adsorption configurations are possible for these SO${}_2$ molecules. One geometry involves an SO${}_2$ molecule bonded through its sulfur atom to the oxygen atom of the paddle-wheel building unit and its two oxygen atoms to the C-H groups of the organic linkers by formation of hydrogen bonds. Such a configuration results in a distortion of the benzene rings, which is consistent with the experimentally observed shift of the ring deformation mode. In the other geometry, SO${}_2$ establishes hydrogen bonding with -CH${}_2$ group of the ted linker through its two oxygen atoms simultaneously. The vdW-DF-simulated frequency shifts of the SO${}_2$ stretching bands in these two configurations are similar and in good agreement with spectroscopically measured values of physisorbed SO${}_2$.In addition, the IR spectra reveal the presence of another minor species, characterized by stretching modes at 1242 and 1105 cm${}^{-1}$ and causing significant perturbations of MOFs vibrational modes (CH${}_x$ and carboxylate groups). This species is more strongly bound, requiring a higher temperature ($\sim$150 ${}^{\circ }$C) to remove it than for the main physisorbed species.

References in corpus (4)

• Stability and Hydrolyzation of Metal Organic Frameworks with Paddle-Wheel SBUs upon Hydration
• Tuning the Gate Opening Pressure of Metal Organic Frameworks (MOFs) for the Selective Separation of Hydro-carbons
• Diffusion of Small Molecules in Metal Organic Framework Materials
• Theoretical and experimental analysis of H2 binding in a prototype metal organic framework material

Cited by in corpus (5)

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• Ab-initio Study of the Electron Mobility in a Functionalized UiO-66 Metal Organic Framework