Functionalised 2D Materials for Desalination and Ionic Permeation through 2D Material Membranes

Abstract

This thesis has three main focuses: the development and understanding of a simultaneous method for exfoliation and functionalisation of MoS2, the optimisation of organic dye functionalised MoS2 for membrane applications, and the study of ionic permeation through 2D material membranes. Laminar membranes of dye functionalised MoS2 have been shown to exhibit highly selective properties, while maintaining a high water flux and excellent mechanical stability. Such materials show great promise for desalination applications, contributing to a solution to global water scarcity; membranes are essential for industrial desalination and water treatment processes. However, functionalisation of MoS2 within the literature is highly time consuming, often defective, and almost always confined to a very small scale. This limits its capabilities significantly. Furthermore, while initial NaCl rejection results were extremely positive, the mechanism was poorly understood, and the fabrication method unoptimized for consistent, reproducible results. Here, we methodically optimise a fabrication procedure for large scale laminar membrane fabrication, and highlight areas of little understanding and of literature debate. A readily scalable, simultaneous electrochemical exfoliation and organic functionalisation of MoS2 is presented, with a phase engineering aspect to utilise the reactive, metallic 1T phase. The procedure is extended to multiple organic dyes, with varying structures, though confined thus far to cationic and neutral molecules. The scaling up of this method is optimised and characterised, to ensure modifications have no effect on the final product. The poorly understood mechanism of sacrificial 1T phase reaction and functionalisation is explored, focusing on methylene blue functionalised MoS2. An electrochemical investigation was carried out, utilising cyclic voltammetry and chronoamperometry alongside spectroscopic characterisation methods. It was determined that the nucleophilic 1T phase causes the spontaneous reduction of methylene blue on binding to the surface. Methods of large-scale organic MoS2 functionalisation were optimised to yield consistent NaCl rejection results when fabricating laminar membranes. Diffusive ionic permeation tests were carried out, consistently showing up to 97% NaCl rejection. Ionic permeation tests were further employed to probe the physical properties of a novel organic 2D interwoven polymer, determining that the material exhibited long range order and the ability to act as a net, with pores of a fixed size.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Krishna Persaud (Supervisor) & Robert Dryfe (Supervisor)