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Precisely controlling pore size of porous materials is of great importance for chiral separation, but a great challenge in practical applications. In contrast, the molecular dynamics (MD) simulation can be quite a convenient way to determine the effect of the pore dimension on the chiral resolution performances and thus to define the optimal pore size. In this work, inner-wall functionalised carbon nanotubes (CNTs) were used as porous materials and D- and L-phenylalanine were selected as chiral probes. The enantioseparation behaviour was investigated via varying the pore diameter of CNTs, controlling the grafting amount of chiral selectors and tuning the spacer length. Results show that varying the pore size has a significant effect on the enantioselectivity. Additionally, the effect of the introduction of varying the grafting ratio and tuning the spacer length on the chiral separation performance was also examined in this work. It was found that varying the grafting ratio, especially the spacer length between substrates and selectors, could also be one of the most effective alternatives to improving enantioselectivity. Our findings can provide a guidance for the practical applications in the chiral separation. [ABSTRACT FROM AUTHOR]

At present, the separation of racemates is still a great challenge due to their similarity in chemical structures and physicochemical properties. Here, we proposed a new strategy to improve the enantioseparation performances of graphene oxide (GO) based membranes via controlling the degree of functionalization (DF) of GO by the aid of an epoxide ring-opening reaction with a carboxyl-terminated ionic liquid (IL-COOH) as a spacer, followed by an amidation reaction of the l-glutamic acid (GO-IL-Glu) as chiral selectors. Results show that: i) these membranes are superior in the enantioselectivity and 1–3 orders of magnitude higher in the flux than traditional chiral separation membranes; ii) compared with l-glutamic acid modified GO membranes and their complex membranes with polypeptides in our previous work, they afford a ca. 40–80% increase in enantioselectivities and an order of magnitude increase in fluxes. Herein, IL-COOH groups can not only serve as a spacer, which is propitious to expanding the interlayer spacing of GO-IL-Glu nanosheets, thereby achieving high throughput of enantiomers, but also function as an active site to improve the grafting amount of chiral selectors (l-Glu), helpful for enhancing enantioselectivities. In particular, the flux is not compromised by the improved enantioselectivity in such membranes; on the contrary, it has an order of magnitude increase. Our findings suggest that the strategy used in this work, i.e., combining more chiral selectors with a wider interlayer spacing, could provide new opportunities for simultaneously facilitating high-flux and high-selectivity and a potential application in a great many enantio- and bio-separations. Image 1 • GO-IL-Glu membranes were used in chiral separations. • GO-IL-Glu membranes were a 1–3 orders of magnitude higher in the flux. • GO-IL-Glu membranes exhibited a high selectivity (the maximum exceeds 3.83). • IL-COOH serve not only as a spacer, but also as an active site to enhance separation performances. • The degree of functionalization (DF) of GO was controlled via manipulating the reaction temperature. [ABSTRACT FROM AUTHOR]

The primary aim of this investigation was to achieve chiral separations via fabricating graphene oxide (GO) based membranes with high separation performances, derived from incorporating a chiral selector ( L -Glutamic acid) into GO flakes, based on considerations of GO membranes having the inherently high throughput nature. The GO membrane was fabricated via a simple vacuum filtration method, in which L -Glutamic acid not only provided the stacked GO nanosheets with the necessary stability to overcome their inherent dispensability in water environment but also finely tuned spacing of the GO nanosheets and the resulting performance. The corresponding membrane structure together with GO and amino acid modified GO nanosheets was systematically characterized by SEM, TEM, AFM, XPS, XRD, FT-IR and so on. Finally, enantioseparation performances of amino acid modified GO membranes toward 3, 4-Dihydroxy-D, L -phenylalanine were detected. Results show that such membranes exhibit extraordinary chiral resolution properties, which are 1−2 orders of magnitude higher in the flux and greater in selectivity, compared to common chiral separation membranes. Our findings demonstrate that the modified GO membranes might provide another general approach to simultaneously facilitate high-flux and high-selectivity for a host of enantio- and bio-separations. [ABSTRACT FROM AUTHOR]