Highly selective charge-guided ion transport through a hybrid membrane consisting of anionic graphene oxide and cationic hydroxide nanosheet superlattice units

Abstract

The development of graphene-based functional membranes with the ability to effectively filter and separate molecules or ions in solutions based on a simple criterion (for example, the size or charge of solutes) is crucial for various engineering-relevant applications, ranging from wastewater purification and reuse to chemical refinement. Here, we report a hybrid membrane consisting of anionic graphene oxide (GO) and cationic Co-Al (or Mg-Al) layered double hydroxide (LDH) nanosheet (NS) superlattice units for high selectivity charge-guided ion transport. The hybrid membrane possesses a series of characteristics, including being easy to access, mechanically robust, freestanding, flexible and semitransparent as well as having a large area. The interlayer spacing of the hybrid membrane is insensitive to humidity variations, ensuring the structural stability in solution-based mass transport applications. The concentration gradient-driven ion transmembrane diffusion experiments show that the cations bearing various valences can be effectively separated strictly according to their charges, independent of the cationic and charge-balancing anionic species. The relative selectivity of the hybrid membranes toward monovalent and trivalent cations is as high as 30, which is not achievable by GO multilayer stacks, LDH-NS multilayer stacks or their bulk-stratified membranes, indicating that a synergistic effect originating from the molecular-level heteroassembly of GO and LDH-NS has a dominant role in the high-performance charge-guided ion filtration and separation processes. These excellent properties of GO/LDH-NS hybrid membranes make them promising candidates in diverse applications, ranging from wastewater treatment and reuse and chemical refinement to biomimetic selective ion transport.

Recent progress on exploring exceptionally high and anisotropic H+/OH− ion conduction in two-dimensional materials

“…To achieve this, two possible strategies are proposed here, both of which involve the fabrication of large-area lamellar membranes composed of overlapped and stacked 2D nanosheets through the well-established liquid-based membrane formation techniques ( e.g. vacuum-filtration, 57 , 58 drop-casting, 59 , 60 spin-coating, 61 , 62 dip-coating, 63 spraying, 64 layer-by-layer electrostatic assembly 65 , 66 and Langmuir–Blodgett 67 , 68 ), followed by exposing the fresh in-plane conduction channels through properly scrolling or stacking.…”

A novel nanofiltration membrane inspired by an asymmetric porous membrane for selective fractionation of monovalent anions in electrodialysis

“…Membrane technology, which has a high water recovery rate and is environmentally friendly, is a key process in water treatment. [1][2][3] Electrodialysis (ED) is a promising membrane process to recover high value substances from water streams. ED is operated with a series of alternating cation-exchange and anionexchange membranes arranged between a cathode and anode, 4 leading to the recovery of valuable substances from industrial wastewater and brackish water.…”

Preparation of freestanding graphene-based laminar membrane for clean-water intake via forward osmosis process

“…16,18,19 Therefore, to enhance their stability in aqueous systems, laminar GO membranes need to be modied by processes such as chemical cross-linking, [20][21][22] partial reduction 23,24 and intercalation. 25 As an emerging membrane technology, forward osmosis (FO) has attracted much attention because of its wonderful advantages over other traditional membrane separation techniques, including low energy consumption, 26 low membrane fouling [27][28][29] and low equipment requirement, and so on. Nevertheless, the application of FO technique still suffers from some problems, especially, internal concentration polarization (ICP), 26 which stems from the bilayer structure of FO membrane, thin selective layer and porous supporting layer.…”

“…23 Sun et al prepared a freestanding hybrid membrane consisting of anionic GO, cationic Co-Al (or Mg-Al) layered double hydroxide (LDH) that exhibited robust mechanical strength, and a highly selective charge-guided ion transport in concentration gradientdriven systems. 25 In this work, we report a facile strategy to prepare thin freestanding graphene-based laminar membrane through thermally-induced chemical cross-linking process, named as freestanding crosslinked GO (F-CGO) membranes. The sensitivity of water to the inter-laminar distance of the F-CGO membranes was evaluated by X-ray diffraction (XRD), and terahertz time-domain spectroscopy (THz-TDS).…”