Novel charged membranes were prepared with sulfonated poly(ether ether ketone) (SPEEK). Methylsulfonic acid was used as solvent to accommodate the very low degree of sulfonation of the SPEEK. Membranes were prepared by immersion phase inversion method, using coagulation baths of different composition and temperature. Low molecular weight and negatively charged dye molecules were used as model solutes to test the nanofiltration (NF) performance of the membranes. Higher than 93% rejection of the two dye molecules, Rose Bengal and Reactive Brilliant Red, was observed at normal operating temperature. A permeate flux as high as 497 L m2 h1 and higher than 90% of solute rejection at 80 degrees C was achieved in the NF of Reactive Brilliant Red aqueous solution, in contrast to a flux of 226 L m2 h1 and about 78% of solute rejection at the same temperature in the case of Rose Bengal solute. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013