Metal organic framework (MOF) functionalized membranes have garnered significant attention in separation processes due to the MOF's tunable properties. There is increased attention to utilizing polycrystalline MOF membranes because it holds the potential to minimize the permselectivity tradeoff often seen in conventional polymeric membranes. The method of making the MOF selective layer membrane may utilize pre-made MOFs which often leads to uncontrollability of the MOF particles, leading to defects. In-situ growth of MOFs is a promising alternative in solving the uncontrollability because it utilizes bottom-up approach growth and self-assembly of the MOF crystals, leading to the formation of a defect-free or minimally defective MOF layer. In a previous study, we reported the synthesis of 2D ZIF-L MOF grown on a polydopamine (PDA) support layer by horizontally dipping method on a commercial PES UF membrane. The MOF formation on PDA coated membrane at different timescales (30 min–48 h) and their corresponding water permeability and Methyl Orange (MO) dye rejection was reported. This study investigates the effect of MOF synthesis orientation—precisely, the vertical and horizontal positioning of the membrane within the MOF precursor solution—on the formation of ZIF-L layer (MOF-Film) and its subsequent impact on membrane performance, particularly permselectivity. The PDA supported membrane was dipped vertically in the ZIF-L precursor solution for 24 h – 48 h at room temperature with and without stirring to also investigate the effect of stirring on the MOF layer. The vertical dipping method changed the organization of ZIF-L growth, which was attributed to the preferential growth described by Van Der Drift model. In the absence of stirring, the ZIF-L crystals were partially organized, whereas upon introducing stirring, the ZIF-L crystals were formed in a completely organized manner. The water permeability and MO dyes rejections were investigated at different synthesis timescales and compared for the partially organized and completely organized membranes. The Blank PES UF showed water permeance of ~ 23 LMH/Bar, and the permeance decreased to ~13 LMH/Bar upon 1 h PDA coating due to increased transport resistance exerted by the PDA layer. Both the Blank, and the 1 h PDA coated PES showed ~10% rejection for the MO dye. 48 h ZIF-L (horizontal) on PDA showed water permeability of ~ LMH/Bar with 40% rejection of MO dye. The 48 h functionalized partially oriented ZIF-L Membrane showed almost 20 µm thick ZIF-L layer with water permeance of ~3 LMH/Bar with MO rejection of 60%. The completely organized ZIF-L membranes at 24 h timescale showed a ZIF-L thickness of ~7 µm with water permeance of ~10 LMH/Bar. The MO rejection showed >90% for 1 h. The completely organized ZIF-L membrane was found to be the best-case scenario among the non-organized, partially organized, and completely organized membranes in terms of the permselectivity.
