Study on structure and seperation properties of polysulfone membranes using ionic liquids as new structure-controlled additives

Introducing ionic liquids as new structure-controlled additives, Polysulfone (PSf) membranes were prepared by the wet-phase-inversion using 1-(n-Octyl)-3-Methyl limidazolium Hexfluorophosphate [C8mim][PF6] or 1-hexadecyl-3-methylimidazolium thiocyanate [C16mim][SCN] into the casting solution (PSF/NMP). Scanning electron microscope was utilized to visualize cross-sections and surfaces of the membranes to gain more better understanding the influence of different ionic liquids on the structure and seperation properties of the membrane. With increase of concentration of ionic liquid [C16mim][SCN] in casting solutions, the structures of the membranes changed from asymmetric finger pores to the spongy-finger-macrovoid structure of the pores. However, With increase of concentration of ionic liquid [C8mim][PF6] in casting solutions, the structures of the membranes changed from asymmetric finger pores, lengthened macroporous pores, to the close macrovoid pores. Fininally, permeation properties of the membranes was investigated. The result indicated that at the 4:76 ratio of [C16mim][SCN]/NMP, the retention rate and solution flux of the prepared membrane are 97.1% for PEG10000 and 48.7 L· h-1· m-2. At the 4:76 ratio of [C8mim][PF6]/NMP in the polymer solution, the retention rate of the membrane is 92.3% for PEG10000 and solution flux is 33.7 L· h-1· m-2. Meanwhile, the two ionic liquids were used as plasticizers, according the thermal properties of the membranes.