High flux polyamide thin film composite forward osmosis membranes prepared from porous substrates made of polysulfone and polyethersulfone blends

• High flux TFC FO membranes were made from polyamide on PSf/PES blend supports.
• The ratio of PSf/PES affected the porous structure and top skin section thickness.
• The initial roughness from the substrate was amplified in the interfacial copolymerization process.

High water flux polyamide thin film composite (TFC) forward osmosis (FO) membranes with porous supporting substrate layers made from polysulfone (PSf) and polyethersulfone (PES) blends of varied PSf/PES ratio were prepared. The impact of PSf/PES ratio on the porous structure of the supporting substrates and resulting properties of TFC-FO membranes formed were investigated. There were three distinguished sections observed in the cross-sections of the substrates, a top dense skin section, a central porous section, and a bottom open section according to SEM images. With the joint favoring effects from maximum open bottom section percentage in the cross-section and maximum surface roughness, membrane samples made from substrates with a PSf/PES ratio of 2/3 exhibit a highest water flux of 27.6 L/m2 h for 2 M NaCl draw solution from a de-ionized water feed solution. And their water flux reached 12.7 L/m2 h under PRO mode and 10.6 L/m2 h under FO mode from an ocean seawater feed solution containing 3.5 wt.% of NaCl. This high flux is related to the existence of heavily populated cone shaped protrusions observed on the surfaces of formed TFC-FO membranes, resulting from amplification in initial surface roughness of the porous substrate during the active layer forming interfacial co-polymerization process.