Abstract
M.Sc.(Nanoscience)
Abstract:
This work describes the fabrication of novel nanosilver/carbon nanotube polyamide thin-film composite (TFN) membranes by the interfacial polymerization of a thin polyamide layer containing nanosilver (nAg) particles over a polyethersulfone (PES) support containing either oxidised carbon nanotubes (CNTs) or nitrogen-doped carbon nanotubes (N-CNTs).
Firstly, the CNTs and N-CNTs were prepared using a conventional floating catalyst chemical vapour deposition (FCCVD) method followed by acid treatment to achieve surface functionalisation or oxidation. The structure and surface functionalisation of CNTs and N-CNTs was studied using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy. N-CNTs were found to possess a typical bamboo-structure within their internal walls that is distinct from the hollow tubular morphology associated with undoped CNTs. The negatively charged surface functional groups such as –COOH, –OH and –C=O identified from FT-IR spectra of CNTs are essential for promoting hydrophilicity of the CNTs and to act as reactive sites for chemical bonding with PES support. The CNTs used in this work were of the multi-walled type.
Moreover, the influence of the presence of oxidized CNTs or N-CNTs in the PES support membrane was studied. CNTs or N-CNTs (at dosages of 0.1 – 1.0 wt.%) were incorporated into the PES matrix via a phase inversion method to form CNT/PES or N-CNT/PES blend membranes. The PES blends were characterised using FT-IR spectroscopy, scanning electron microscopy (SEM) and contact angle analysis. An improvement in surface hydrophilicity upon the inclusion of CNTs in the PES blends was achieved (contact angle measurements). Furthermore, the presence of CNTs and N-CNTs at 0.1 wt.% dosage led to a reduction in macrovoids formed in the membrane sub-layer. However, at 1.0 wt.% loading the sub-layer structure became denser. The surfaces of PES blends were found to be more porous than bare PES membrane. This could be attributed to the increase in viscosity of the solution at high CNT dosages thus leading a delayed liquid mixing-demixing rate. Water permeation flux increased from 62.99 L/m2.h for bare PES supports to 80.21 L/m2.h for 0.1 CNT/PES and 100.80 L/m2.h for 0.1 N-CNT/PES membranes, at a working pressure of 80 Psi. The heightened permeability of PES blends obtained was congruent to their enhanced hydrophilicities. At high CNT or N-CNT loading (1.0 wt.%), pure water flux of PES blends decreased due to the dense structure formed. Flux decline patterns of PES and PES blend supports obtained from fouling studies were conducted using humic acid as a model natural organic matter foulant. The data revealed that whilst the patterns were similar, that of bare PES support was sharper due to its highly hydrophobic nature...