Graphene-based membranes for gas separation and water purification applications

Abstract

This thesis explores the preparation of mixed matrix membranes (MMMs) containing a polymer matrix and chemically modified graphene oxide (GO) nanofillers. The resulting membranes were evaluated for gas separation and water treatment applications, and the role of the graphene-like nanofiller in the membrane performance was assessed. Membranes are industrially used for natural gas treatment, although their insufficient performance often prevents membrane technology from expanding its market. PIM-1 belongs to a new family of polymers (Polymer of intrinsic microporosity, PIMs) having high free volume and intrinsic microporosity, along with superior CO2/CH4 separation performance. However, it undergoes physical aging resulting in a decrease of free volume and therefore a reduction in its gas permeability. In this thesis, several GO-based materials have been incorporated to PIM-1 with the aim of hindering rearrangement of polymer chains and thus, preventing physical aging. In order to improve the compatibility with the polymer matrix (PIM-1), all graphene-like fillers (GO, Holey GO and ((3-aminopropyl)triethoxysilane)-functionalised GO (i.e. APTS-GO)) were chemically functionalised with PIM-1. MMMs containing (PIM-1)-functionalised APTS-GO nanofillers showed a drop in CO2 permeability of 310 Barrer after 150 days, which entails a great improvement in comparison to pure PIM-1 (CO2 permeability drop of 2908 Barrer after 150 days). For several decades, membranes have played an important role in numerous water treatment processes. Many polymers have been proposed as membrane materials, and in particular PES is commonly used for the fabrication of commercial ultrafiltration membrane systems. In this thesis, MMMs made of PES and APTS-GO were tested for water filtrations. The incorporation of APTS-GO along with pore-forming agents were able to boost the performance of the MMMs leading to an increase in the pure water flux (from 0.5 to 9.9 L m−2 h−1 bar−1) and enhanced rejection properties towards MgSO4 salts (from 18 to 51.6%) and dyes (from 40 to 96.5%). Consequently, the prepared MMMs lay on the nanofiltration (NF) range, whereas purely polymeric PES membranes belong to the ultrafiltration range (UF).

Date of Award	31 Dec 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stuart Holmes (Supervisor) & Patricia Gorgojo (Supervisor)