Graphene oxide nanocomposite membrane cooperatively cross-linked by monomer and polymer overcoming the trade-off between flux and rejection in forward osmosis

Abstract

A forward osmosis membrane consisting of graphene oxide (GO) nanosheets cooperatively cross-linked by ethylenediamine (EDA) molecule and poly(acrylic acid) (PAA) polymer chain is proposed. Desirable GO-based nanocomposite membrane must satisfy the conflicting requirements of high water flux and salt rejection simultaneously, which is yet to be achieved. In this study, the GO/EDA/PAA nanocomposite structure demonstrates that good water flux (52 LMH) and salt rejection (97%) can be achieved simultaneously by cooperatively employing the short monomer molecule EDA and the long PAA polymer chain within the channel region of the GO nanocomposite membrane structure. It is suggested that the membrane-wide network of hydrogen bonds between the GO nanosheets and the PAA chains aligned parallel to them is supplemented by anchoring carbon-nitrogen covalent bonds between GO and EDA molecules to form the nanocomposite structure. The nanocomposite structure resulting from the configurations of EDA molecules and PAA chains within the channel region provide an optimal condition for blocking hydrated salt ions while allowing the flow of water molecules. Also, it functions as a reinforcement of the membrane structure for the improved structural integrity.