Synthesis and Characterization of Micro-Patterned Thin Film Composite (TFC) Membranes for Water Treatment

Thin film composite (TFC) membranes, mostly used in reverse osmosis and nanofiltration are critical for water treatment and provide clean and desalinated water to millions on daily basis. The two main limitations: fouling and low permeance of these membranes greatly affect their performance and sustainability. Several measures have been taken for membrane fouling mitigation including chemical, physical and hydrodynamic methods. Recently, patterned membranes have been evolved as an innovative tool for fouling mitigation. However, the synthesis procedure for patterned membranes has not been developed at a scale-up level. Lately, Prof. Vankelecom’s research group (KU Leuven) has introduced a non-solvent spray assisted phase inversion (s-NIPS) as an efficient synthesis procedure for patterned membranes. s-NIPS makes the use of a patterned casting knife combined with modified non-solvent spray assisted phase inversion process. It overcomes the limitations of previously used methods such as phase separation micromolding (PSμM) and imprinting lithography (IL) as phase separation induces from the pattern side and no reduction in pore size is observed. Previous studies for patterned TFC membranes have only managed to create a top selective layer above patterned UF supports with heights in the range of 160 nm to 5 μm which limits the potential advantages of such membranes. s-NIPS patterned supports can significantly enhance the intrinsic low permeance of such NF/RO membranes by producing UF supports with higher pattern heights up to 180 μm. Hence, in this study, a defect-free thin film polyamide layer was developed over s-NIPS micro-patterned supports through interfacial polymerization (IP). In order to achieve this, several parameters were explored including effect of monomer concentrations, effect of pattern height, removal of excess monomer solution from the valleys before IP, effect of UF polymer support and spin assisted layer by layer thin film deposition. It was found that the 1, 2 and 3 layered TFC membrane could give a maximum of ca. 85, 96 and 97 % MgSO4 retention respectively at enhanced permeance. Furthermore, 2 layered spin assisted IP with 2 wt% MPD and 0.1 wt% TMC concentration was found to be optimum for PSf500 supports (polysulfone supports prepared using casting knife with pattern height 500 μm) with 94% MgSO4 retention at the permeance of 1.66 LMH/bar.