Date of Award

November 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Nidal Abu-Zahra

Committee Members

Benjamin Church, Marcia Silva, Xiaoli Ma, Steven Hardcastle

Abstract

Membrane filtration has become the focus of separation processes in different industries including water and waste water treatment. Synthetic asymmetric polymeric membranes are the most widely used membrane type for filtration technologies such as ultrafiltration, nanofiltration, and reverse osmosis due to better control of the pore forming mechanism, higher flexibility, lower cost, and ease of operation compered to inorganic membranes. Among the available polymers, polyethersulfones polymers (PES) demonstrate strong chemical and thermal stability, making them popular as basic materials for filtration and support materials for composite membranes. They are hydrophobic intrinsically and the application of such membranes is still limited by some challenges such as permeability and selectivity trade-off, and low resistance to fouling. Unique properties of nanomaterials including high reactivity, strong sorption, fast dissolution, and specific interaction with contaminants in water make them a great option for water/wastewater treatment. It is well known that the nanoparticles especially metal oxide nanoparticles have high adsorption capacities for heavy metal ions. Their extremely small size, however, brings forth some issues in utilizing nanomaterials. These issues include mass transport and pressure drop when applied in fixed bed or any other flow-through systems, difficulties in separation and reuse, and even possible risk to ecosystems and human health caused by a potential release into the environment.

Incorporation of nanoparticles such as titania (TiO2), alumina (Al2O3), silica (SiO2), silver and many others into PES membranes has been a recent trend in membrane research. This can influence structural and physicochemical properties of membranes (e.g. porosity, charge density, and mechanical stability) and introduce new functionalities, including heavy metal ions removal. Recently, modification of nanoparticles before incorporating into polymeric materials has attracted great interests. A common method to modify the nanoparticles is treating them with silane coupling agents; such as methacryloyloxy methylenemethyl diethoxysilane (MMDES), and 3-aminopropyltriethoxysilane (APTES). Silane coupling agents are used extensively in inorganic polymer composites such as mineral filled polymer composites. Choosing the appropriate silane group can alter the surface of an inorganic material from hydrophilic to hydrophobic and increase its affinity to functional groups of the polymer matrix [1, 2], and decrease the agglomeration of nanoparticles.

In this project, asymmetric ultrafiltration membranes were synthesized by phase inversion immersion precipitation method. The effect of main synthesizing parameters (casting temperature and polymer concentration in the casting solution) on the morphology and performance of the membranes were investigated in order to optimize the performance of the prepared membranes. Afterward, PES/Alumina nanocomposite membranes with optimized pore structure, mechanical and thermal stability, and permeability were synthesized. The performance of the nanocomposite membranes in removal of copper ions from water were also investigated. The prepared membranes were characterized using FTIR, XRD, FESEM, AFM, contact angle, viscosity measurement, BET, and BJH techniques. The performance of the membranes including solute rejection and water flux was also investigated.

Alumina nanoparticles were also modified by 3-aminopropyltriethoxysilane (APTES) and were used to fabricate novel nanocomposite PES membranes. The morphology and physio-chemical properties of the modified nanoparticles and membranes were investigated. The performance of the membranes was also examined in terms of Cu (II) ion removal from water as well as pure water flux measurements. Finally, the Speiger-Kachalsky-Kedem model was used to develop a novel model to analyze the separation mechanism and predict the rejection performance of the synthesized membranes. The model parameters were obtained from the Steric Hindrance model. The developed model was able to predict the copper ion rejection of the membranes by about 20% accuracy.

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