Understanding the Adsorption of PFOA on MIL-101(Cr)-Based Anionic-Exchange Metal–Organic Frameworks: Comparing DFT Calculations with Aqueous Sorption Experiments

To examine the effects of different functionalization methods on adsorption behavior, anionic-exchange MIL-101­(Cr) metal–organic frameworks (MOFs) were synthesized using preassembled modification (PAM) and postsynthetic modification (PSM) methods. Perfluorooctanoic acid (PFOA) adsorption results indicated that the maximum PFOA adsorption capacity was 1.19 and 1.89 mmol g^–1 for anionic-exchange MIL-101­(Cr) prepared by PAM and PSM, respectively. The sorption equilibrium was rapidly reached within 60 min. Our results indicated that PSM is a better modification technique for introducing functional groups onto MOFs for adsorptive removal because PAM places functional groups onto the aperture of the nanopore, which hinders the entrance of organic contaminants. Our experimental results and the results of complementary density functional theory calculations revealed that in addition to the anion-exchange mechanism, the major PFOA adsorption mechanism is a combination of Lewis acid/base complexation between PFOA and Cr­(III) and electrostatic interaction between PFOA and the protonated carboxyl groups of the bdc (terephthalic acid) linker

Photoreactivity of Metal–Organic Frameworks in Aqueous Solutions: Metal Dependence of Reactive Oxygen Species Production

Promising applications of metal–organic frameworks (MOFs) in various fields have raised concern over their environmental fate and safety upon inevitable discharge into aqueous environments. Currently, no information regarding the transformation processes of MOFs is available. Due to the presence of repetitive π-bond structure and semiconductive property, photochemical transformations are an important fate process that affects the performance of MOFs in practical applications. In the current study, the generation of reactive oxygen species (ROS) in isoreticular MIL-53s was studied. Scavengers were employed to probe the production of ¹O₂, O₂^•–, and •OH, respectively. In general, MIL-53­(Cr) and MIL-53­(Fe) are dominated by type I and II photosensitization reactions, respectively, and MIL-53­(Al) appears to be less photoreactive. The generation of ROS in MIL-53­(Fe) may be underestimated due to dismutation. Further investigation of MIL-53­(Fe) encapsulated diclofenac transformation revealed that diclofenac can be easily transformed by MIL-53­(Fe) generated ROS. However, the cytotoxicity results implied that the ROS generated from MIL-53s have little effect on the viability of the human hepatocyte (HepG2) cell line. These results suggest that the photogeneration of ROS by MOFs may be metal-node dependent, and the application of MIL-53s as drug carriers needs to be carefully considered due to their high photoreactivity