Year

2012

Degree Name

Doctor of Philosophy

Department

School of Chemistry

Abstract

This thesis explores the development of novel carbon nanotube membranes (buckypapers, BPs) incorporating antibiotic and macrocyclic ligands as dispersants. Membranes were obtained by vacuum filtration of dispersions containing the functional dispersants, or the surfactant Triton X-100 (Trix), and either single-walled carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs). The homogeneity and stability of SWNT dispersions was first evaluated using a combination of UV-vis- NIR spectrophotometry, optical microscopy and Raman spectroscopy.

Microanalytical data and energy dispersive X-ray spectra were obtained for the SWNT buckypapers, and provided evidence for retention of dispersant molecules within the structure of the membranes. The electrical conductivities of the SWNT membranes varied between 30 ± 20 and 220 ± 60 S cm-1, while goniometry revealed they all possessed hydrophilic surfaces (contact angle = 28 - 89°). The mechanical properties of SWNT buckypapers prepared using both macrocyclic ligands and antibiotics were shown to be comparable to that of a benchmark material prepared using SWNTs and Trix. Analysis of images obtained using scanning electron microscopy (SEM) showed that the surface morphology of the buckypapers was dependant on the identity of the dispersant, and the type of CNTs used to prepare the sample, with the average surface pore size varying between 7 ± 3 and 80 ± 20 nm. The surface area of SWNT buckypapers was determined through BET analysis of nitrogen adsorption-desorption isotherms, and found to vary between 30 ± 1 and 790 ± 4 m2 g-1. The length of sonication was shown to influence the porosity of SWNT buckypapers, which were also characterised using cyclic voltammetry and thermogravimetric analysis. The results of analysis by these methods revealed that the physical properties of the buckypapers membranes were highly dependent on their composition and the conditions used during their preparation.

The permeability towards water of selected SWNT and MWNT buckypapers was explored using a custom made dead-end filtration setup. The permeability of membranes prepared using SWNTs was found to be strongly dependant on the identity of the dispersant used to produce the buckypaper (25 – 2400 L m-2 h-1 bar-1), and in some cases rivalled that of commercial microfiltration membranes (1900 – 7000 L m-2 h-1 bar-1). Transport of water through SWNT membranes was found to occur much more rapidly than with MWNT buckypapers made using the same dispersant.

The ability of buckypapers containing SWNTs or MWNTs, and either Trix or the antibiotic ciprofloxacin, to filter aqueous suspensions containing the bacterium Escherichia coli (E. coli) was examined. Analysis of the filtrates obtained after these experiments revealed that MWNT buckypapers were more effective at removing the bacteria from solution, and that incorporation of ciprofloxacin resulted in near complete removal of E. coli by both types of membranes.

The ability of MWNT buckypapers to remove metal ions and a radionuclide from solution was also investigated. These buckypapers proved to be ineffective for recovery of cesium or strontium from acidic solution, however, significant quantities of molybdenum, present as the molybdate ion, MoO4 2- could be adsorbed. Experiments performed using molybdate containing the radioisotope 99Mo, showed that buckypapers became saturated with adsorbed molybdate after relatively short periods of time (c.a. 4 h). Furthermore, up to 2.6 mmol MoO4 2- g-1 could be recovered.

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