Effects of Porogen PEG and Pore Structure of PVDF Substrates on the Permeability-Selectivity Trade-off of TFC-NF Membranes

Thin-film composite (TFC) nanofiltration (NF) has beenwidely utilizedto separate monovalent ions from multivalent ions in industrial wastewatertreatment. In this study, the pore properties of polyvinylidene fluoride(PVDF) substrates were adjusted by varying the content and molecularweights (MWs) of porogen polyethylene glycol (PEG). The TFC membranesfabricated on different substrates showed distinguishable permeanceand selectivity. The PVDF membranes with 2 kDa PEG of 0.5-3.0wt % and 20 kDa PEG of 0.2 wt % were fit for the substrates of theTFC NF membrane. These substrates are usually characterized by evenlydistributed surface pores with porosity of 7-12% and tiny finger-likepores of less than 15 & mu;m length. Such pore structures in thesubstrates are fit for the storage and migration of amine monomers,resulting in a defect-free PA layer. In a 6 h filtration of miningwastewater using an optimized TFC membrane, the permeance remainedaround 5 LMH/bar and the separation factor of SO4 (2-)/Cl- stayed over 13.39 with a maximum value over30. This study shed light on improving NF membrane performance bysimply adjusting the porogen in the substrate casting solution.