Bio-Inspired Fabrication of Ultrafiltration Membranes Incorporating Polydopamine Functionalized Graphene Oxide Nanoparticles

Abstract

Graphene oxide (GO) and its based materials have gained a significant interest in the membrane functionalization sector in the recent years. Inspired by their unique and tunable properties, several GO-based nanomaterials have been investigated and utilized for various membranes in water treatment, purification and desalination sectors. In this dissertation, novel polysulfone (PSF) ultrafiltration membranes incorporating polydopamine-functionalized reduced graphene oxide nanoparticles (rGO-PDA) were fabricated and investigated. Starting from natural graphite, GO nanoparticles with high oxidation degree were synthesized using an improved Hummers' method. A GO functionalization based on the bio-inspired PDA was then conducted to produce rGO-PDA nanoparticles. The high-oxidation degree of graphite and the successful functionalization with PDA were confirmed using several analytical techniques including CHNSO elemental analysis, XPS, FTIR-UATR, Raman spectroscopy and XRD. Several bands have emerged in the FTIR spectra of rGO-PDA attributed to the amine groups of PDA confirming the successful functionalization of GO. Raman spectra and XRD patterns showed different crystalline structures and higher interlayer spacing of rGO-PDA. The change in elemental compositions was confirmed by XPS and CHNSO elemental analysis while the change in the morphological structure was confirmed by SEM and TEM analyses. The second part of the dissertation was on the embedding of the above mentioned nanoparticles in a membrane matrix. Pristine PSF, PSF/GO, and PSF/rGO PDA mixed matrix membranes (MMMs) were prepared by embedding GO and rGO PDA at concentrations from 0 to 0.15 wt% using the phase inversion technique. All membranes were analysed using FTIR-UATR, SEM, AFM, and contact angle. The cross-section SEM images showed better distribution of rGO-PDA nanoparticles in the pores and polymer wall whereas the pristine GO nanoparticles aggregate and partially block the pores. Thus, the flux increased with the embedding of rGO-PDA without affecting the rejection properties, while it decreased with the embedding of pristine GO. The highest pure water permeability (PWP) was obtained with PSF/rGO PDA-0.1 to be approximately twice that of the pristine PSF and PSF/GO-0.1. All membranes exhibited complete rejection of BSA and HA and showed almost similar rejection performance against different dyes. The flux recovery ratio of the pristine PSF after three fouling cycles (FRR3) against BSA and HA were recorded to be 57.8% and 70.7% respectively. FRR3 was enhanced by around 30% with PSF/rGO PDA composites. The MMMs prepared in this work are expected to have great potential on ultrafiltration and provide insights on developing other types of membranes embedding rGO-PDA with different materials and for different purposes