Development of multi-layered gradient ceramic membrane

Abstract

Ceramic membranes are the permselective barriers usually made from ceramic materials such as Al2O3, TiO2, ZrO2, SiO2 and zeolites. Layer thickness, pore size and amount of porosity are the key elements that govern the fabrication of ceramic membranes. The aim of this research is to explore the development of ceramic based multilayer membrane of porous structure with gradient porosity for potential filtration and purification applications. Disc shaped macro-porous alumina support was fabricated by powder metallurgy technique with α-alumina particle size of 0.3 µm and compacting pressure of 620 MPa followed by sintering at 1400°C for 2h. An average pore size of 0.25 µm with 50% porosity and thickness of 2mm were obtained as determined by scanning electron microscopy and mercury porosimetry technique. Further research was carried out for the preparation of meso- and micro-porous layers which were deposited on top of the macro-porous α-alumina support. The intermediate meso-porous TiO2 layer was deposited on top of α-Al2O3 support using sol-gel dip coating technique followed by drying and heat treatment. The average pore size obtained was approximately 0.08µm with porosity of 30% and thickness of approximately 1 µm. The micro-porous zeolite A (LTA) layer was synthesized on the deposited meso-porous TiO2 layer, after being subjected to UV irradiation. The intermediate meso-porous layer of titania was applied to bridge the pore size gap between the α-alumina support and micro-porous LTA zeolite layer (possessing sub-nanometer pore size), thus forming a multi-layered ceramic membrane with a porosity gradient. The pre-treatment of mesoporous titania layer with UV photons played a major role to improve the surface hydrophilicity of the substrate. In-situ aging microwave heating synthesis method was utilized to synthesize LTA zeolite layer. During the synthesis, the effect of such parameters, like in-situ aging time and synthesis time, on the formation of LTA zeolite layer was investigated. Crystals of 1-3 µm were grown on the substrate surface yielding a continuous and dense layer of LTA zeolite. The measured thickness of the formed zeolite layer was 2-3 µm. The developed multilayer membrane with graded (macro-, meso- and micro) porous structure will have the potential to allow selective passage of a particular species (solvents such as water molecules), while other species i.e, solutes (such as heavy metals, hydrated ions) are retained partially or completely during filtration/purification/desalination process. The next phase of this project is to evaluate the filtration performance of these developed membranes using dedicated flow test cell.