Dionysios Raptis

Per‐ and polyfluoroalkyl substances (PFAS) are emerging as bioaccumulative and toxic water pollutants, posing a large threat to human and aquatic organisms. This threat is aggravated by their extreme persistence to common degradation methods. Adsorption is regarded as the most conventional method to treat these contaminants, however, existing sorbents present considerable limitations on performance. The development of more efficient PFAS adsorbents is therefore of urgent need. The class of metal‐organic frameworks (MOFs) can hold great promise for these purposes, featuring porous materials with high tailoring potential. Herein, a series of functionalized Zr‐MOFs have been designed with boosted capacities for the adsorption of short‐ and long‐chain perfluorinated carboxylic acids of environmental interest. The approach relies on chemistry‐based concepts to introduce targeted post‐synthetic modifications that promote PFAS···MOF interactions, specifically through coordinative bonding and hydrophobic effects. In particular, the framework TFA‐MOF‐808 (TFA = trifluoroacetic acid) displays the highest capture capacities reported for MOF materials in this pollutant class. Mechanistic studies, assisted by advanced synchrotron characterization techniques and theoretical calculations, support a ligand exchange process occurring during the adsorption phenomena. The results demonstrate the potential of this design approach in developing advanced PFAS sorbents with optimal performance.

In the present work, we used DFT in order to study the interaction of SO₂ with 41 strategically functionalized benzenes that can be incorporated in MOF linkers. The interaction energy of phenyl phosphonic acid (–PO₃H₂) with SO₂ was determined to be the strongest (−10.1 kcal/mol), which is about 2.5 times greater than the binding energy with unfunctionalized benzene (−4.1 kcal/mol). To better understand the nature of SO₂ interactions with functionalized benzenes, electron redistribution density maps of the relevant complexes with SO₂ were created. In addition, three of the top performing functional groups were selected (–PO₃H₂, –CNH₂NOH, –OSO₃H) to modify the IRMOF-8 organic linker and calculate its SO₂ adsorption capacity with Grand Canonical Monte Carlo (GCMC) simulations. Our results showed a great increase in the absolute volumetric uptake at low pressures, indicating that the suggested functionalization technique can be used to enhance the SO₂ uptake capability not only in MOFs but in a variety of porous materials.

The interaction strength of nitrogen dioxide (NO₂) with a set of 43 functionalized benzene molecules was investigated by performing density functional theory (DFT) calculations. The functional groups under study were strategically selected as potential modifications of the organic linker of existing metal–organic frameworks (MOFs) in order to enhance their uptake of NO₂ molecules. Among the functional groups considered, the highest interaction energy with NO₂ (5.4 kcal/mol) was found for phenyl hydrogen sulfate (-OSO₃H) at the RI-DSD-BLYP/def2-TZVPP level of theory—an interaction almost three times larger than the corresponding binding energy for non-functionalized benzene (2.0 kcal/mol). The groups with the strongest NO₂ interactions (-OSO₃H, -PO₃H₂, -OPO₃H₂) were selected for functionalizing the linker of IRMOF-8 and investigating the trend in their NO₂ uptake capacities with grand canonical Monte Carlo (GCMC) simulations at ambient temperature for a wide pressure range. The predicted isotherms show a profound enhancement of the NO₂ uptake with the introduction of the strongly-binding functional groups in the framework, rendering them promising modification candidates for improving the NO₂ uptake performance not only in MOFs but also in various other porous materials.