In this research work, following the efforts for providing fresh water for humans, a novel nanocomposite membrane was prepared. In this regard, potassium cation was added to co-polymerized graphene oxide (GO) to tune the interlayer spacing of the GO nanosheets. The prepared membranes were characterized by X-ray diffraction, contact angle measurement, Atomic Force Microscopy (AFM), and Field emission scanning electron microscopy (FE-SEM) equipped with Energy-dispersive X-ray spectroscopy (EDX). The XRD patterns confirmed that by adding potassium chloride (KCl) to GO containing membranes, interlayer spacing was optimized and led to presence of interlayer spacing in the range of 4-6 angstrom and 7.80 angstrom which are highly active in rejection of salt ions. To evaluate the desalination performance of the prepared nanocomposite membranes, forward osmosis (FO) process was considered. The results showed that although the membrane showed acceptable permeability, the salt rejection activity was enhanced considerably. The potassium cation containing membrane exhibited reverse salt rejection of 2.03 which was 6.31 in absence of it. This can be attributed to effect of potassium cations in optimizing and modifying interlayer spacing along with repulsion of Na+ due to charge similarity with K+. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.