Effect of different structure of membrane support on polyamide formation and its performance in reverse osmosis

Abstract

This work aims to investigate the polyamide (PA) morphology on polysulfone (PSf) membrane supports with different morphologies. It was achieved by systematically varying the N-Methyl-2-Pyrrolidone (NMP) and Dimethylformamide (DMF) solvent composition ratios in dope solution as adapted in Tiraferri et al. The PSf membrane support was firstly synthesized via phase separation technique. Next, the PA layer of the thin film composite (TFC) membrane was synthesized via consistent interfacial polymerization parameters on the PSf membrane support. The PA layer over the resulting array of membrane supports was investigated on their surface wettability, top and cross-sectional morphologies, and performances. Result shows that with more NMP content in the dope solution produces thin and dense sponge-like top skin layer with intense extended finger-like macrovoids sublayer. Meanwhile, more DMF content in the dope solution produces thicker and dense sponge-like morphology on the top skin with finger-like pores underneath. A layer of smaller and loosen ridge-and-valley PA structures is formed on the thicker and dense sponge-like morphology. TFC membrane over support made of NMP to DMF (40:60) was observed had the highest hydrophilicity with the lowest contact angle measurement of 61.9 ± 3.1°. It also performed the highest water permeability of 4.06 LMH/bar, moderate salt rejection of 95.65% with salt permeability of 1.9 gMH.