Fundamental Understanding of Ultrathin, Highly Stable Self-Assembled Liquid Crystalline Graphene Oxide Membranes Leading to Precise Molecular Sieving through Non-equilibrium Molecular Dynamics

Pathan, S and Islam, SS and Sen Gupta, R and Maity, B and Reddy, PR and Mandal, S and Anki Reddy, K and Bose, S (2023) Fundamental Understanding of Ultrathin, Highly Stable Self-Assembled Liquid Crystalline Graphene Oxide Membranes Leading to Precise Molecular Sieving through Non-equilibrium Molecular Dynamics. In: ACS Nano, 17 (8). pp. 7272-7284.

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Abstract

Self-assembled graphene oxide lyotropic liquid crystal (GO LLC) structures are mostly formed in aqueous medium; however, most GO derivatives are water insoluble, so processing GO LLCs in water poses a practical limitation. The use of polar aprotic solvent (like dimethyl sulfoxide) for the formation of GO LLC structures would be interesting, because it would allow incorporating additives, like photoinitiators or cross-linkers, or blending with polymers that are insoluble in water, which hence would expand its scope. The well-balanced electrostatic interaction between DMSO and GO can promote and stabilize the GO nanosheets’ alignment even at lower concentrations. With this in mind, herein we report mechanically robust, chlorine-tolerant, self-assembled nanostructured GO membranes for precise molecular sieving. Small-angle X-ray scattering and polarized optical microscopy confirmed the alignment of the modified GO nanosheets in polar aprotic solvent, and the LLC structure was effectively preserved even after cross-linking under UV light. We found that the modified GO membranes exhibited considerably improved salt rejection for monovalent ions (99%) and water flux (120 LMH) as compared to the shear-aligned GO membrane, which is well supported by forward osmosis simulation studies. Additionally, our simulation studies indicated that water molecules traveled a longer path while permeating through the GO membrane compared to the GO LLC membrane. Consequently, salt ions permeate slowly across the GO LLC membrane, yielding higher salt rejection than the GO membrane. This begins to suggest strong electrostatic repulsion with the salt ions, causing higher salt rejection in the GO LLC membrane. We foresee that the ordered cross-linked GO sheets contributed to excellent mechanical stability under a high-pressure, cross-flow, chlorine environment. Overall, these membranes are easily scalable, exhibit good mechanical stability, and represent a breakthrough for the potential use of polymerized GO LLC membranes in practical water remediation applications. © 2023 American Chemical Society.

Item Type:	Journal Article
Publication:	ACS Nano
Publisher:	American Chemical Society
Additional Information:	The copyright for this article belongs to American Chemical Society.
Keywords:	Additives; Blending; Dimethyl sulfoxide; Electrostatics; Graphene; Ions; Liquid crystals; Mechanical stability; Membranes; Molecular dynamics; Molecules; Nanosheets; X ray scattering, Graphene oxide membrane; Graphene oxides; Interlayer nanostructure; Liquid crystal structures; Lyotropic liquid crystal; Molecular separation; Molecular sieving; Oxide membrane; Salt rejections; UV cross-link membrane, Self assembly
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	19 May 2023 09:42
Last Modified:	19 May 2023 09:42
URI:	https://eprints.iisc.ac.in/id/eprint/81570

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