Two-Dimensional Designer Nanochannels for Controllable Ion Transport in Graphene Oxide Nanomembranes with Tunable Sheet Dimensions.

Graphene is a distinct two-dimensional (2D) material that provides a wide range of opportunities for membrane applications owing to its ultimate thinness, flexibility, chemical stability, and mechanical strength. In particular, chemically functionalized graphene oxide (GO) sheets containing amine and carboxylic acid groups facilitate solution-based processing and the formation of various internal structures depending on their properties such as the lateral dimension, defect density, and number of stacked layers. In this study, we designed and fabricated a multilayered GO membrane via the layer-by-layer assembly of two oppositely charged GO nanosheets and investigated the effects of the (1) lateral dimension of the GO nanosheet and (2) membrane thickness of the 2D nanochannels of the GO membrane on the ion permeation behavior. The correlations between the structural parameters of the GO membranes and ion diffusion kinetics were evaluated using the Nielsen model. The functional groups were selectively ionized by exposure to pH-adjusted water, which creates positive or negative net charges, resulting in an ion-selective permeability. The unique properties of the GO nanosheets play important roles in determining the trade-off between the membrane permeability and selectivity, leading to new applications of GO nanosheets as functional membranes.