Size effect of graphene oxide sheets on enantioseparation performances in membrane separation

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Recently, graphene oxide (GO)-based membranes have been demonstrated to be a potential candidate for gas purification and liquid separation techniques owing to their large surface area, tunable interactive sites, and adjustable interlayer spacing. Notably, GO-based membranes functionalized with chiral selectors have been demonstrated to possess high enantiomer permeability and impressive permeation selectivity toward enantiomeric target guests. However, the influence of the GO sheet size on the separation performance remains unclear. Here, we investigated the effect of the lateral size on the enantioseparation performances by modifying a chiral selector onto GO flakes with different sizes, considering that GO membranes possess an inherently high throughput character. In this work, three GO sheets with mean lateral sizes (~60, 650 and 4100 nm) were prepared, hereafter defined as GO1, GO2, and GO3, respectively. Then, a chemical modification of GO1, GO2 and GO3 with a chiral selector, L-Phenylalanine (L-Phe), yielded the corresponding L-Phe grafted GO sheets, L-Phe-GO1, L-Phe-GO2 and L-Phe-GO3. Finally, L-Phe-GO1, L-Phe-GO2 and L-Phe-GO3 membranes derived from a simple vacuum filtration method were employed to separate D-/L-phenylalanine. Results show that the L-Phe-GO3 based membrane allows for a remarkable chiral separation capacity, having a greatest enantioselectivity among three L-Phe-GO membranes with different lateral GO sizes. Our findings illustrate that the sheet size of GOs plays a dominant role in the enantioselectivity of membrane separation.