Preparation of a positively charged NF membrane by evaporation deposition and the reaction of enPEI on the surface of the C-PES/PES blend UF membrane

A positive surface thin-film composite membrane was prepared via evaporation deposition and the reaction of polyethyleneimine (PEI) with the carboxyl groups on the surface of a carboxylated polysulfone (C-PES)/PES UF blend membrane. UF blend membranes with different C-PES/PES ratios were prepared and PEI solution was deposited on them, with subsequent cross-linking using glutaraldehyde. The optimal C-PES/PES ratio was used on the supporting UF blend membrane, with optimal crosslinking time using glutaraldehyde to obtain a significant rejection of salt and organic molecules rejection, while retaining the water flux at a reasonable level. The preparation of a UF blend membrane with a negative surface charge based on the C-PES/PES ratio and its interaction with PEI solutions with different concentrations for deposition and reaction was the key point in obtaining a membrane with the appropriate rejection of divalent cation and organic solutes. The effects of the membrane surface charge on the rejection of different salts and organic solutes were evaluated at different pressures to understand the rejection mechanism of the prepared NF membranes.