Diamines cross-linked graphene oxide free-standing membranes for ion dialysis separation

Design and tuning of the permeation channels of graphene oxide (GO) membranes are crucial for separation. Herein, GO membranes were covalently cross-linked by a series of diamines utilizing two cross-linking methods (carboxyl activation/amidation, catalytic amidation) for the first time. The effects of cross-linking parameters (temperature, diamines concentration, diamines molecular structure) on the elastic modulus, contact angle, swelling degree and ion dialysis separation of GO membranes were systematically studied, It was found that the carboxyl activation/amidation cross-linking method does not favor the fabrication of free-standing GO membranes. In the catalytic amidation cross-linking, with the increase in chain length of aliphatic diamines, the elastic modulus and the contact angle with water generally increase, while the swelling degree in water decreases. The cross-linked GO membranes display higher fluxes and K+/Mg2+ separation factor than those of the pristine membrane. The p-phenylenediamine (PPD) cross-linked membranes shows excellent elastic modulus (10.5402 GPa) and high K+/Mg2+ selectivity factor (7.15) along with low swelling degree due to its rigid structure, demonstrating its great potential in ion dialysis separation. (C) 2016 Elsevier B.V. All rights reserved.