Ionic Liquid-Reduced Graphene Oxide Membrane with Enhanced Stability for Water Purification

Abstract

There has been a growing interest in water purification by graphene oxide (GO) laminate membranes due to their exceptional hydrophilicity, high throughput, and extraordinary separation performance originating from their two-dimensional and well-defined nanostructure. However, the swelling and stability in an aqueous environment are areas of concern for the GO laminate membranes. Here, a novel methylimidazolium ionic liquid-reduced GO (mimG)-assembled GO laminate membrane (mimG–GO) with remarkable stability was fabricated by a vacuum-assisted strategy for water purification. Methylimidazolium-based ionic liquid-reduced graphene oxide (mimG) was prepared by a facile nucleophilic ring-opening mechanism. Fabricated membranes were thoroughly characterized for stability, structural, permeance, and rejection properties in an aqueous environment. A combination of cationic mimG and GO nanosheets improves membrane stability in the aqueous environment via cation−π interactions and creates nanofluidic channels for facile water transport while yielding significant enhancement in the salt and dye separation performance. The pore size and the number of nanofluidic channels were precisely controlled via material deposition and laminate thickness to remove salts from water. The mimG–GO laminate membrane containing 72.2 mg m–2 deposition showed a permeance of 14.9 LMH bar–1, 50% higher than 9.7 LMH bar–1 of the neat GO laminate membrane, in addition to an increase in Na2SO4 salt rejection from 46.6 to 77.4%, overcoming the flux-rejection trade-off. The mimG–GO laminate membrane also rejected various anionic dyes (i.e., 99.9% for direct red 80 (DR 80), 96.8% for reactive black 5 (RB 5), and 91.4% for methyl orange (MO)). The mimG–GO laminate membrane containing 361.0 mg m–2 deposition showed the highest rejection for Na2SO4 (92.1%) and 99.9% rejection for DR 80, 99.0% rejection for RB 5, and 98.1% rejection for MO dyes keeping a flux of 2.6 LMH bar–1. Partial reduction and covalent grafting of ionic liquid moieties on GO helped to enhance the cation−π interaction between GO laminates, which showed enhanced stability, frictionless water transport, with high salt and dye rejection. Moreover, a simultaneous improvement in water permeance and solute rejection reveals the great potential of ionic liquid-functionalized GO laminate membranes for water-based applications.

Functionalization of graphene oxide with an ionic liquid (1‐butyl‐3‐methylimidazolium acetate): Preparation of epoxy‐based coating on carbon steel for anticorrosive applications

“…In Figure 2d, The C 1s XPS spectra of FGO revealed carbon components CC, CN, CO and NCO at 284.5, 285.5, 286.7, and 288.8 eV respectively 12,21 . Specifically, the existence of the NCO bond corresponding to the amide nitrogen suggested that amide bonds were established between carboxylic acid groups of GO and the amino group of IL 22,23 . The presence of CN bond illustrates the grafting of ionic liquid with graphene sheets via ring opening reaction 13,24 .…”

“…12,21 Specifically, the existence of the N C O bond corresponding to the amide nitrogen suggested that amide bonds were established between carboxylic acid groups of GO and the amino group of IL. 22,23 The presence of C N bond illustrates the grafting of ionic liquid with graphene sheets via ring opening reaction. 13,24 Additionally, the C/O intensity ratio (Figure 2e) was used to represent the reduction degree of GO.…”

Ionic liquids membranes for liquid separation: status and challenges

“…59 Similarly, Zambare and coworkers fabricated a composite membrane using the methylimidazolium ionic liquid for water purification. 140 In such work, the graphene oxide (GO) was also introduced as the carrier of IL, and the mimG-GO membrane was obtained. The combination of mimG and GO nanosheets has a synergistic effect that improves membrane stability through cation–π interactions and creates nanofluidic channels, thus enabling easy water transport.…”

Al3+ Modification of Graphene Oxide Membranes: Effect of Al Source

“…Previous work has shown that the GO membrane aqueous stability can be enhanced by incorporating molecular species such as ionic liquids into the membrane structure [17][18][19]. While ionic liquids can promote membrane stability through cation-π interactions, the molecular species must first be covalently attached to the graphene oxide sheet surfaces [17].…”

“…Previous work has shown that the GO membrane aqueous stability can be enhanced by incorporating molecular species such as ionic liquids into the membrane structure [17][18][19]. While ionic liquids can promote membrane stability through cation-π interactions, the molecular species must first be covalently attached to the graphene oxide sheet surfaces [17]. Metal ions (e.g., Na + , Ca 2+ , Mg 2+ , Fe 3+ , or Al 3+ ) can improve membrane stability Membranes 2022, 12, 1237 2 of 17 when simply incorporated into the membrane structure, with greatest stability enhancements observed with trivalent cations [6,8,11,[20][21][22][23][24].…”