Three-dimensional architecture constructed by graphene oxide nanosheets - polymer composite for high-flux forward osmosis membranes
Forward osmosis (FO) membrane technology holds profound potential for addressing global challenges in sustainable water and energy supply. Developing FO membranes of three-dimensional (3D) architecture with interconnected channels in support layers remains exceedingly desirable and challenging for breaking the intrinsic internal concentration polarization (ICP) bottleneck on FO water flux. For the first time, a novel 3D interconnected porous architecture is constructed by graphene oxide (GO) nanosheets - polymer composite via a facile and economic phase-inversion approach, and as-synthesized GO-polymer 3D architecture is successfully used as the support layer of FO membrane. This GO-polymer 3D architecture provides shortcut pathways for water molecules to readily pass through, which minimizes support layer tortuosity to 1.55 ± 0.13 (among the best value in literature). The minimization of tortuosity significantly reduces support layer structural parameter and thereby effectively mitigates ICP. As a result, FO water flux (JW) of membrane with GO-polymer 3D architecture reaches 18.3 ± 1.5 L m-2 h-1 (salt rejection: 94.8 ± 1.2%), which is 73% higher than the JW of membrane with conventional 1D architecture and 280% times higher than the JW of commercial HTI CTA FO membrane under the same operating conditions. More importantly, the mechanism for forming this 3D architecture is carefully revealed by developing a new theory i.e. “GO-induced phase inversion” of architecture transformation process. Through systematic study for 2D GO nanosheets and traditional 0D/1D nanomaterials as membrane building blocks, the unique role of GO’s 2D structure characteristics in forming this 3D membrane architecture is unveiled. This study opens a new door for 2D nanomaterials to construct 3D architecture for developing high performance membranes.