SO2 presents a threat to human health, industrial processes, and the environment. Metal-organic frameworks (MOFs) have been shown to be promising candidates for SO2 adsorption due to their large surface area and structural tunability. However, the efficiency, selectivity, and cyclability of SO2 capture present challenges that no group of MOFs has yet satisfied. Here, we report a series of N-modified MOFs synthesized with ligands containing different N sites. The introduced N sites with lone pair electrons will enhance the SO2 capacities for these MOFs at various degrees due to the different levels of binding strength between N sites and adsorbed SO2 molecules. Powder X-ray diffraction results confirm that N-modified MOFs possess the same topology and show strong chemical stability to SO2. SO2 adsorption from a stream of 0.1% SO2 in balance N2 was measured using a home-built breakthrough system. The results showed that except for UiO-66-NO2, all the other N-modified UiO-66 MOFs presented higher SO2 loadings. For example, UiO-66-2,5-PDC (pyridine-modified UiO-66) adsorbed 0.997 mmol/g of SO2, a loading six times higher than that of pristine UiO-66 (0.13 mmol/g). This talk will present SO2 adsorption results for this family MOFs, and the mechanism governing the adsorption process will be explored through in-situ infrared spectroscopy (in-situ IR) and X-ray photoelectron spectroscopy (XPS) experiments. The results suggest that the introduced N sites can act as favorable adsorption sites for SO2. Additional density functional theory (DFT) simulation reveals which type of N sites exhibit the best SO2 adsorption behavior. Overall, this study provides insights into establishing basic rules for the design of MOFs with N-containing functional groups for SO2 adsorption.

Systematic study of MOFs containing different N-sites for sulfur acid gas adsorption

ACS Spring 2022

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