Fabrication Techniques for Graphene Oxide-Based Molecular Separation Membranes: Towards Industrial Application

Abstract

Graphene oxide (GO) has been a prized material for fabricating separation membranes due to its immense potential and unique chemistry. Despite the academic focus on GO, the adoption of GO membranes in industry remains elusive. One of the challenges at hand for commercializing GO membranes lies with large-scale production techniques. Fortunately, emerging studies have acknowledged this issue, where many have aimed to deliver insights into scalable approaches showing potential to be employed in the commercial domain. The current review highlights eight physical methods for GO membrane fabrication. Based on batch-unit or continuous fabrication, we have further classified the techniques into five small-scale (vacuum filtration, pressure-assisted filtration, spin coating, dip coating, drop-casting) and three large-scale (spray coating, bar/doctor blade coating, slot die coating) approaches. The continuous nature of the large-scale approach implies that the GO membranes prepared by this method are less restricted by the equipment's dimensions but rather the availability of the material, whereas membranes yielded by small-scale methods are predominately limited by the size of the fabrication device. The current review aims to serve as an initial reference to provide a technical overview of preparing GO membranes. We further aim to shift the focus of the audience towards scalable processes and their prospect, which will facilitate the commercialization of GO membranes.

Keywords: fabrication methods; graphene oxide; membrane; scale-up; separation.

Figure 1

Widely adopted graphene oxide (GO) membrane fabrication methods; classified by scalability.

Figure 2

(a) GO nanoribbon (GONR)/GO composite membrane prepared by vacuum filtration [22]. Copyright 2019 American Chemistry Society; (b) GO layer deposition on wrinkled substrates for high water flux [23]. Copyright 2019 Elsevier; (c) nanoporous GO sheet membranes for nanofiltration application [24]. Copyright 2021 Elsevier.

Figure 3

(a) Comparative analysis of various filtration-based methods for GO membrane preparation [19]. Copyright 2015 Elsevier; (b) La³⁺ ion crosslinked small flake GO membranes for nanofiltration [14]. Copyright 2020 The American Association for the Advancement of Science; (c) high-stability GO layers by molecular bridging on ceramic tube type membranes [13]. Copyright 2020 John Wiley and Sons.

Figure 4

(a) Vacuum-assisted spin coating technique for highly aligned gas separation GO membranes [30]. Copyright 2016 American Chemical Society; (b) crosslinked polymer GO membranes for OSN application [31]. Copyright 2018 American Chemical Society.

Figure 5

(a) Alignment of GO sheets by shear force during the pulling process [33]. Copyright 2017 Royal Society of Chemistry; (b) GO-coated hollow fiber membranes enabled by ethylenediamine functional groups for nanofiltration [34]. Copyright 2020 American Chemical Society; (c) GO-coated metal mesh substrates for oil-water separation [35]. Copyright 2019 Elsevier.

Figure 6

Mechanisms for rGO layer deposition for drop-casting method [38]. Copyright 2014 Elsevier.

Figure 7

(a) Nonwrinkled GO membranes prepared by the spray-coating method [41]. Copyright 2018 Elsevier; (b) alternating charged GO sheet deposition for O₂ barrier films [42]. Copyright 2019 Nature Publishing Group.

Figure 8

(a) Scalable production of GO membranes enabled by nematic phase GO alignment [16]. Copyright 2016 Nature Publishing Group; (b) GONR hydrogel membrane fabrication for nanofiltration [17]. Copyright 2020 American Chemical Society; (c) crosslinked, freestanding GO membranes for ion rejection [47]. Copyright 2019 Royal Society of Chemistry.

Figure 9

Scalable production of GO membranes by slot-die coater [15]. Copyright 2020 Elsevier.