Synthesis and characterization of thin film nanocomposite forward osmosis membrane for water desalination process
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Date
2014
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Publisher
Universiti Teknologi Malaysia
Abstract
In this study, two types of novel thin film nanocomposite (TFN) membranes were synthesized by either coating a typical polyamide (PA) film over the surface of substrate made of polysulfone (PSf)–titanium dioxide (TiO2) or embedding amino functionalization titanate nanotubes (NH2-TNTs) into PA thin layer formed over a typical PSf substrate. Both membranes were aimed to reduce membrane fouling and/or internal concentration polarization (ICP) during forward osmosis (FO) applications. In the first stage of this study, both hydrophilicity and porosity of the substrate were increased upon addition of TiO2 nanoparticles. In comparison with a typical thin film composite (TFC) and commercial cellulose triacetate (CTA) membranes (i.e. HTI-NW and HTI-ES), the prepared TFN membranes (i.e. TFN (NMP)0.5 and TFN (DMF/NMP)0.6) always demonstrated much higher FO water flux without showing a significant increase in reverse solute flux when tested under the same conditions. When tested at two different membrane orientations (FO and pressure retarded osmosis (PRO) mode), it was found that the water flux of the TFN membrane was 120% and 85-95% higher than that of the commercial membrane and typical TFC membrane, respectively. The increase in water permeability was attributed to the decrease in structural parameter, due to the formation of finger-like structure, connecting the top and bottom layer of the substrate and reducing the tortuosity. This increased the mass transfer coefficient (km) of the substrate, resulting in decreased ICP. Although solvent composition played a role in altering substrate structure, the performance of TFN(DMF/NMP) membrane prepared from substrate made of different solvent composition was not much different. In the PRO mode, bovine serum albumin (BSA) removal in the presence of calcium (Ca2+), confirmed that TFN FO membrane could significantly mitigate the fouling tendency compared with the TFC FO membrane. Results showed that BSA and Ca2+ ion fouling in TFN FO was almost reversible, with more than 92% of permeate flux was recovered after a simple water rinse without using any chemical agents. In the second stage of this study, the self-synthesized TNTs which calcinated at 300 °C were first modified by [1-(2-amino-ethyl)-3-aminopropyl] trimethoxysilane (AATES) to produce NH2-TNTs before being used in preparing TFN membrane. The reaction between NH2- TNTs and PA of TFN occurred during interfacial polymerization, creating a covalent bonding between nanotubes and PA layer of TFN membrane, which further improved membrane separation properties. The TFN membrane (designated as TFN0.05) was reported to have two times higher water flux than the control TFC membrane without significant different in terms of salt rejection. In addition, in FO mode, TFN0.05 membrane was also found to have much better anti-fouling tendency against BSA in comparison to the control TFC membrane and achieving close to 100% flux recovery during FO application. As a conclusion, it was found that both microporous substrate and PA skin layer of composite membrane could be modified using hydrophilic nanomaterials, improving not only membrane permeability/selectivity but also its anti-fouling property.
Description
Thesis (PhD. (Chemical Engineering))
Keywords
Saline water conversion—Research, Membranes (Technology)—Permeability, Osmosis