The stability of graphene oxide (GO) membranes in a sodium sulfate aqueous solution is reported. The mechanism for the stability was interpreted with the assistance of molecular dynamic (MD) simulations as follows: GO disperses uniformly in water because it is hydrated. However, the hydration of GO is weakened when Na2SO4 is present because the Na+ and SO42 ions are preferentially hydrated over GO. Thus the movement of GO in the Na2SO4 solution becomes restricted and it is difficult for the GO in a GO membrane to uniformly disperse in a Na2SO4 solution even with ultrasonic treatment. (C) 2013 Elsevier B.V. All rights reserved.