Graphene oxide on porous polyurethane substrates : synthesis, deposition, and characterisation

Abstract

Graphene oxide (GO) is a chemically functionalised, two-dimensional nanomaterial with broad applicability in areas such as water purification, sensing, coating and membrane fabrication. Its abundant oxygen-containing functional groups enable strong interactions with various polymers, making it a suitable candidate for forming multifunctional hybrid materials. Traditional GO synthesis methods involve corrosive acids, strong oxidising agents, and elevated temperatures, which pose safety risks due to the release of toxic fumes and the potential of forming explosive by-products. This doctoral study proposes a simplified, room temperature method using only concentrated H2SO4 and KMnO4, eliminating the need for heating and reducing hazardous emissions. Characterisation confirmed the effective oxidation and exfoliation of graphite with an average lateral flake size of 15.06 ± 1.87 μm and 87 layers, into GO sheets with resultant lateral sheet size of 10.22 ± 0.62 μm and ~ 10 layers. X-ray Photoelectron Spectroscopy (XPS) analysis showed that in-house synthesised GO had a comparable oxygen content and functional group distribution to commercial GO, with epoxy (C–O) as the dominant group. X-ray induced Auger spectroscopy revealed a reduction in sp2-hybridised carbon from 80.21% in graphite to 45.52% in GO, confirming effective oxidation. The second phase of this study focused on the deposition of the synthesised GO on the top surface of a modified porous polyurethane (PU) support. Due to the inherent chemical inertness of PU, surface modification was carried out using chromic acid etching followed by polydopamine (PDA) deposition at a fixed concentration and varied deposition times (6, 12, and 24 hours). Characterisation showed that chromic acid altered the PU surface both physically and chemically, increasing hydrophilicity. PDA further modified the surface, introducing functional groups such as COOH/N-C=O, C-O-C=O, and C=O, thus enhanced the compatibility with GO. GO was then deposited at two concentrations (1 g/L and 10 g/L) and three different deposition times (6, 12, and 24 hours). Only the higher concentration resulted in uniform coverage. Characterisation confirmed the successful chemical anchoring of GO to the PDA-modified PU, facilitated by reactions between the oxygen functionalities in GO (acid anhydride and epoxy groups) and the amine groups in the PDA layer.