GCRIS

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Preparation, Characterization of Enzyme Immobilized Membranes and Modeling Og Their Performances
(Izmir Institute of Technology, 2010) Yürekli, Yılmaz; Alsoy Altınkaya, Sacide
The objective of this thesis study is to prepare active and stable urease (URE) immobilized membranes for the efficient removal of urea and to predict the performances of these membranes under pressure. Two commercially available ultrafiltration membranes namely Poly (acrylonitrile-co-sodium methallyl sulfonate) copolymer (AN69) and polyethyleneimine (PEI) deposited AN69 membranes (AN69-PEI) were used as supporting materials on which urease is immobilized by means of physical adsorption using layer-by-layer self assembly method or chemical attachment using N-ethyl-N.-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and Nhydroxysuccinimide (NHS) coupling agents as a zero crosslinker. During physical immobilization (pH 7.4), the effect of polyelectrolyte type on the activity of immobilized urease was compared between PEI and chitosan (CHI) cationic polyelectrolytes where urease was located either on top of the polyelectrolyte layer (AN69-PEI-URE or AN69-CHI-URE) or between two polyelectrolyte layers in a sandwiched form (AN69-PEI-URE-PEI or AN69-CHI-URE-CHI). The results reveal that the amount of urease immobilized on AN69 membranes are similar and slightly higher than the amount adsorbed on the activated AN69 surface by chemical attachment (AN69-C-URE). The maximum reaction rate was observed with AN69-PEI-URE membrane while the maximum retained activity during storage time was determined with AN69-C-URE membrane. Under dynamic conditions, the hydraulic permeabilities of the commercial and urease immobilized membranes were found similar and the highest urea conversion was achieved with the AN69-PEI-URE-PEI membrane. At the end of 450 minutes of filtration under pressure, the catalytic activity of AN69-C-URE membrane was completely preserved. The mathematical model developed can correlate the experimental filtration data quite well.
Gas Permeation Through Sol-Gel Derived Alumina and Silica Based Membranes
(Izmir Institute of Technology, 2009) Topuz, Berna; Çiftçioğlu, Muhsin
The scope of this thesis is to design defect-free microporous and mesoporous ceramic membranes having micro-engineered pore network that would contribute to the enhancement of pore control abilities as well as the thermal stability.In this study, mono-dispersed silica sols having well-defined silica spheres ranging in size from 5 to 700 nm were prepared through sol-gel methods and thin membrane layers were consolidated on either y-alumina support or unsupported form.The packing of 5 nm silica spheres resulted in micropores of 0.87 nm in 400 oC treatedmembranes with the porosity of 0.32 which are in well aggrement with the porosity level of random loose packing. Silica spheres with varying concentration and size were incorporated into polymeric network to complement the percolative structure of sphere packing with interpenetrated polymeric silica network in order to design well-defined thermally stable transport pathway. Low shrinkage value was obtained for sphere incorporated system providing the high thermal stability by affecting the thermally induced microcrack formation as well as the structural relaxation during consolidation.The resulting hybrid structure enabled the detailed transport properties that support to be able to control the pore structure but N2/CO2 separation properties are needed to be improved.Stable polymeric alumina sols having particle sizes smaller than 2 nm could be obtained when the hydrolysis conditions were accurately controlled. The mixture of prepared polymeric silica and alumina sols in mullite compositions (3:2) provided to the crystallization of mullite with homogeneously mixed stable oxide network upon heat treatment at 775 oC.
Investigation of Effects of Microstructural and Surface Properties of Ultrafiltration/ Nanofiltration Ceramic Membranes on Their Performance
(Izmir Institute of Technology, 2009) Erdem, İlker; Çiftçioğlu, Muhsin
The ceramic membranes with their superior chemical, thermal, mechanical and microbiological properties and long service lives are gaining importance in pressure driven filtration processes. The diverse requirements of different applications enforce preparation of tailor-made ceramic membranes with specific characteristics. This dissertation focused on the preparation and characterization and filtration performance of asymmetric multilayer ceramic membranes. Support is the layer responsible for mechanical stability while top layer is mainly responsible for separation and intermediate layer is balancing the microstructural difference between these two layers. The permeability of alumina support could be increased over 100 L / m2 h by 15% starch addition. The intermediate layer was prepared by coating fine alumina or zirconia powders and / or colloidal sols with thicknesses between 0.2-70 .. The top layer was formed from pure or mix of zirconia or titania polymeric sols with average particle sizes in the range of 3 . 50 nm with a thickness smaller than 1.. The physicochemical properties of these mixed oxides were modified by changing the composition and calcination temperature enabling preparation of top layers with varying Donnan exclusion capacities. The membranes prepared could reject sugar, PEG 1000 and PEG 4000 up to 10, 60 and 19%, respectively, that which can be increased via further optimization of parameters in coating / heat treatment processes.

Phd Degree / Doktora

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