Modulator Mediated Functionalization (MoFu) of MOF-808 as a Platform Tool to Create High-Performance Mixed-Matrix Membranes.

Modulator mediated functionalization (MoFu) is introduced as a new and versatile platform tool to improve the separation performance of MOF-based membranes, exemplified here by the creation of mixed-matrix membranes (MMMs) with enhanced CO2 separation efficiency. The unique structure of MOF-808 allows incorporation of CO2-philic modulators in the MOF framework during a one-pot synthesis procedure in water, thus creating a straightforward way to functionalize both MOF and corresponding MMM. As a proof of concept, a series of fluorinated carboxylic acids (trifluoroacetic acid (TFA), pentafluoropropionic acid (PFPA) and heptafluorobutyric acid (HFBA)) and non-fluorinated alkyl carboxylic acids (acetic acid (AA), propionic acid (PA) and butyric acid (BA)) were used as modulator during MOF-808 synthesis. Two of the best MMMs prepared with 30 wt% MOF-TFA (100% increase in CO2/CH4 separation factor, 350% increase in CO2 permeability) and 10 wt% MOF-PFPA (140% increase in CO2/CH4 separation factor, 100% increase in CO2 permeability) scored very close to or even crossed the 2008 and 2018 upperbound limits for CO2/CH4. Due to its facile functionalization (and its subsequent excellent performance), MOF-808 is proposed as an alternative for widely used UiO-66, which is, from a functionalization point-of-view and despite its widespread use, a rather limited MOF.