Single-layered GO/LDH hybrid nanoporous membranes with improved stability for salt and organic molecules rejection

Abstract

Graphene oxide (GO) has been intensively adopted as the building block of separation membranes due to its excellent mechanical strength and atomic scale interlayer spacing. However, the practical application of GO nanosheet-based membranes are limited by the swelling and disintegration of GO membranes in water owing to hydration and electrostatic repulsion. In this work, we firstly fabricated a type of layered double hydroxide (LDH) nanosheets, Co(OH)2 nanosheets, by in-situ growth on the surface of GO nanosheets, followed by coating such GO/Co(OH)2 hybrid nanosheets on a microporous substrate through vacuum suction to form a single-layered GO/Co(OH)2 hybrid thin membrane. The electrostatic and coordination interactions between GO and Co(OH)2 nanosheets are found to stabilize the GO/Co(OH)2 hybrid membrane in water, and the hybrid membrane shows good resistance to shear force in a pressurized crossflow nanofiltration system with crossflow speed as high as 0.5 m s−1. With permeation flux up to 17.0 L m−2 h−1, >91% rejection to inorganic salts like Na2SO4 and >98% rejection to various organic dyes (transmembrane pressure: 6 bar, crossflow speed: 0.27 m s−1), the hybrid membrane also survives the challenges of different pH environments, elevated transmembrane pressure and a 60 h continuous crossflow test. Such significantly improved stability from pure GO membranes is expected to enable the 2D nanomaterial based membranes for practical filtration applications in the water industry.