A new fabrication approach for mixed matrix membrane fabricated with interstitially sealed MOF nanoparticles

Metal-organic framework-based mixed matrix membranes (MOF-MMMs) become increasingly attractive in several applications (e.g., water treatment and gas separation) due to the excellent functionality. However, they have several common problems such as unsatisfactory performance due to lower MOF loading and thicker coating layer. Herein, a new fabrication strategy was proposed and tested in this reported study: the selected MOF(s) is/are deposed on porous substrate(s) by filtration to form dense layers, while their interstices are simultaneously sealed by in-situ polymerization of monomers percolating through the MOF layer. This approach allows a high MOF loading and controlled thickness of MOF-MMM. Zeolitic imidazolate framework-8 (ZIF-8) was used as a model MOF along with two acrylic monomers, hydrophobic butyl methacrylate (BMA) and mildly hydrophilic glycidyl methacrylate (GMA), resulting in 42% ZIF-8 loading. The membranes demonstrated rejection of Congo Red dye up to 97% and 60% for ZIF-8/BMA and ZIF-8/GMA membranes, respectively, emphasizing the advantage of more hydrophobic and dense poly-BMA as a more efficient sealant compared to more open and porous poly-GMA. It is also found that optimization of MOF and monomer concentrations for MMM preparation is critical and could greatly improve both dye rejection and water permeance. The results demonstrate the potential of the new approach for controlled preparation of selective MOF MMMs for water treatment and other membrane processes.