Plasma-treated polyethylene-based organic solvent forward osmosis membrane toward high flux and selectivity

Abstract

Recently, significant efforts have been dedicated to design materials for superior permeation efficiency in organic solvent forward osmosis (OSFO) membranes. However, creating low-cost materials with high selective permeability for OSFO remains a challenge. This study focuses on selecting support materials to minimize mass transfer resistance for organic solvent by utilizing a commercial porous polyethylene (PE) membrane. Prior to forming a dense polyamide (PA) layer through interfacial polycondensation, plasma technology was employed to hydrophilically modify both sides of the membrane at varying intensities. The optimized plasma parameters for the upper surface was 40 W/7 s aiming to achieve moderate hydrophilicity and minimal surface etching for the synthesize of defect-free PA layer, while that for the lower surface was 90 W/180 s aiming to achieve superhydrophilic matrix and enlarged pore size. Owing to the ultra-low membrane thickness of 7 μm, polar modification was effectively achieved throughout the entire membrane interior. The OSFO performance shows that the prepared PE/PA composite membranes exhibit exceptional ethanol flux of 5.45 LMH with a minimal reverse LiCl flux level of 0.44 gMH and a remarkably high tetracycline retention rate of 99.86 %. When oriented toward the drawing solution with its PA layer facing outward, ethanol flux even reaches 7.64 LMH. Long-term stability tests indicate that polar groups introduced by plasma treatment provide lasting promotion in organic solvent transport process.