Fabrication and Applications of Nanoporous Alumina Membranes

  • Kah Peng Lee

Student thesis: Doctoral ThesisPhD

Abstract

The performance of membranes in various processes is largely dependent ontheir morphological properties. Thus, membrane structure has been continuouslyoptimised for different applications. Anodic alumina membranes (AAMs) exhibitself-ordered pore structure and the pore size can be tuned in the sub-micrometrerange. The aim of this PhD project is to propose and develop AAMs for theapplications of membrane filtration and emulsification with potential for scale-up.In the project, the AAMs were initially fabricated in flat sheet form to optimise theprocess parameters to obtain membranes with a high quality of pore structure.The membrane pore diameter can be readily controlled by the anodizationvoltage. While AAMs are normally symmetric, by manipulating the anodizationvoltage, asymmetric AAMs consists of stem pores and active pores have beensuccessfully made. After that, the flat AAMs with symmetric and homogeneousstructure were used as a platform to study for surface modification and fluidtransport in nano-channels. The surface chemistry and wettability of themembranes has been altered by grafting of silane molecules and carbon coatingby chemical vapour deposition. Fluid flow measurement through pristine AAMswith pore diameter in the 20 nm to 100 nm range shows flow enhancement effect,experimentally for the first time, can occur in hydrophilic materials.Subsequently, tubular AAMs were fabricated using aluminium alloy tubes, to beassessed for ultrafiltration and membrane emulsification processes. The porestructure of the tubular AAMs was analogous to flat membranes. Despite thereduced pore circularity and hexagonal arrangement originated from thepresence of impurities in the starting materials, the narrow pore size distributionwas not compromised. In a selectivity-permeability analysis, the asymmetrictubular AAMs outperformed most of the commercial ceramic membranes buttheir flux was very low when compared to polymeric membranes. A bovine serumalbumin filtration test showed that complete pore blocking-cake filtration modelcan be used to describe the fouling behaviour. Finally, symmetric tubularmembranes were used to study dead-end and cross-flow emulsificationprocesses. The resulting emulsions show low polydispersity. Using a membranewith 25 nm average pore diameter, the obtained average droplet size was as lowas 120 nm during a cross-flow emulsification. This is by far the smallest achievedaverage droplet size by cross-flow membrane emulsification.
Date of Award31 Aug 2013
LanguageEnglish
Awarding Institution
  • University of Bath
SupervisorDavide Mattia (Supervisor) & Thomas Arnot (Supervisor)

Keywords

  • membranes
  • flow enhancement
  • Ultrafiltration
  • emulsification
  • ceramic

Cite this

Fabrication and Applications of Nanoporous Alumina Membranes
Lee, K. P. (Author). 31 Aug 2013

Student thesis: Doctoral ThesisPhD