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  • Smart polymer composite materials for water processing

    Ranwen Ou

    M. Eng. (Chemical)

    Thesis submitted in fulfilment of the requirements for the degree of

    Doctor of Philosophy

    Supervisors:

    Prof. Huanting Wang

    Prof. George P. Simon

    Department of Chemical Engineering

    Monash University

    May 2017

  • i

    Smart polymer composite materials for water processing

    Copyright Notices

    Notice 1

    Under the Copyright Act 1968, this thesis must be used only under the normal conditions of

    scholarly fair dealing. In particular no results or conclusions should be extracted from it, nor

    should it be copied or closely paraphrased in whole or in part without written consent of the

    author. Proper written acknowledgement should be made for any assistance obtained from this

    thesis.

    Notice 2

    I certify that I have made all reasonable efforts to secure copyright permissions for third-party

    content included in this thesis and have not knowingly added copyright content to my work

    without the owners permission.

    Ranwen Ou

    May 2017

  • ii

    Declaration

    This thesis contains no material which has been accepted for the award of any other degree

    or diploma at any university or equivalent institution and that, to the best of my knowledge

    and belief, this thesis contains no material previously published or written by another

    person, except where due reference is made in the text of the thesis.

    Ranwen Ou

    May 2017

  • iii

    Acknowledgements

    My deep gratitude goes first to my supervisors, Professor Huanting Wang and Professor

    George P. Simon, for their expert guidance, continuous support, encouragement and

    understanding through my Ph.D. study that benefits me much in the completion and success

    of this study, as well as my future career.

    Secondly, I would like to thank our group members for the encouragement, suggestion,

    comments and discussion on my research and their companionship during my study. They are

    Dr Jing Wei, Dr. Huacheng Zhang, Dr Yi Feng, Dr. Kha Tu, Dr Xiaocheng Lin, Dr Seungju

    Kim, Dr Ze-Xian Low, Dr Soo Kwan Leong, Dr. Ezzatollah Shamsaei, Dr. Jue Hou, Dr. Xiao

    Xie, Li Wan, Xiaofang Chen, Yan Liang, Yaoxin Hu, Kang Liu, Chen Zhao, Nhi Sa Nguyen,

    Jeffery Chan, Xingya Li, Jun Lu, Yuqi Wang and Zahra Abbasi. Thanks to my friends,

    especially Qianqian Shi and Zheng Ma, for their encouragement, support and companion.

    Thank you for the support of the staff in Department of Chemical Engineering, especially

    Kim Phu, Lilyanne, Price, and Jill Crisfield.

    Thank you for Monash University and Faculty of Engineering to cover the tuition fee and

    living expense of my Ph.D study. Thank you for the support of Baosteel-Australia Research

    and Development Center and the Australian Research Council.

    Thank you for the technical assistance with the use of electron microscopes of the staff of

    Monash Centre for Electron Microscopy (MCEM), especially Dr. Xiya Fang.

    Importantly, thank you so much for the unconditional support and love from my beloved

    family, including my parents, Huazhang Ou and Jieying Qian, and my younger brother,

    Qingwu Ou. Finally, I would like to express a big thank you for my beloved husband and my

    best friend, Hao Wu, for his endless encouragement, suggestion, care, and love.

    Ranwen Ou

    Monash University

    May 2017

  • iv

    Abstract

    Increasing population and improper industrialization practices have led to detrimental surface

    and underground water contamination at an unprecedented rate. Therefore, more effective,

    lower-cost, robust methods to purify water are urgently needed, without further stressing the

    environment or endangering human health by the treatment itself. Stimuli-responsive materials,

    which can respond to environmental conditions, have recently attracted much attention in water

    treatment. In this thesis, three types of responsive material for water processing are developed:

    responsive separation membrane, responsive forward osmosis draw agent, and responsive

    adsorbent.

    Recently, stimuli-responsive surfaces with switchable superwettability have attracted

    growing interest for controlled oil-water separation. The fabrication of such smart membranes

    with good mechanical properties, excellent recycling properties, and the ability to separate oil-

    water emulsions productively and inexpensively is highly desirable. In this thesis, a robust,

    thermo-responsive polymer membrane is produced by the combination of thermoplastic

    polyurethane (TPU) microfibre web and poly (N-isopropyl acrylamide) (PNIPAM). The TPU-

    PNIPAM membrane possesses switchable superhydrophilicity and superhydrophobicity as the

    temperature of membrane changes from 25 to 45 C. The composite membrane is able to

    separate a 1 wt. % oil-in-water emulsion and 1 wt. % water-in-oil emulsion at 25 and 45 C,

    respectively, with a high separation efficiency of 99.26 %. Furthermore, the composite

    membranes show excellent mechanical properties, and they are highly flexible and

    mechanically tough.

    The feasibility of using stimuli responsive polymer hydrogels as draw agent in the forward

    osmosis (FO) desalination was recently demonstrated by our group for the first time. The

    swelling pressure of hydrogel, the effective contact area between FO membrane and hydrogel,

    and the water transport through the draw agent are key factors affecting water flux. In this study,

    hydrophilic microfibre and hydrophobic microfibre are blended with hydrogel to prepare

    composite monoliths, respectively, and the relevant FO performance and improvement

    mechanism are studied. The incorporation of both hydrophilic and hydrophobic microfibres

    results in enhanced FO water flux of hydrogel monolith. Whilst the addition of hydrophilic

    microfibres is good for dewatering, the hydrophobic microfibre does reduce the dewatering

    flux. The 1st hour FO water flux and dewatering flux of hydrophilic TPU microfibre- poly

    (sodium acrylate) (PSA) monolith are 1.81 and 3.51 L m-2 h-1, respectively, twice of those for

  • v

    PSA particles. The water flux of PSA hydrophobic polyester microfibre composite (PSA

    PET) reaches 5.0 LMH in the first 10 mins, twice as high as the relevant pure hydrogel alone.

    Conversely, the dewatering flux of PSA-PET decreases to half of those of pure hydrogel. The

    kinetic swelling studies show that the use of monolithic hydrogels and the addition of

    hydrophilic microfibres enhance water diffusion through the draw agent and sustain high

    swelling pressure, resulting in improved FO performance. On the other hand, the combination

    of hydrophilic ionic hydrogel and hydrophobic PET microfibre produced pores in the

    composite hydrogel because of different wettability, with an additional relaxation force

    preserved in the composites because of the compressed pressure applied during the preparation.

    Thus, the porous structure improves the water diffusion, while the compressed pressure

    enhances the polymer chain relaxation rate.

    The introduction of responsive ability potentially advances MOFs more flexible for

    fundamental studies and other applications, such as controllable adsorption and separation,

    energy storage and clean energy, sensing, catalysis. Ion adsorption is of great environmental,

    technological, and biological importance, and it has been widely applied in separation,

    purification, catalysis, food processing, and pharmaceutical industry. Here, an amphoteric

    MOF-based ion adsorbent has been designed for stimuli-responsive ion sorption, especially for

    monovalent ions, by integrating weak acid groups with base groups. This is achieved by post-

    synthesis modification of MIL-121 via in situ polymerization of tertiary amine monomer

    introduced in the porous framework. The equilibrium NaCl adsorption capacity of the

    amphoteric MOF is 0.92 meq/g, which occupies 77 % of ion adsorption sites, demonstrating

    the efficiency of amphoteric MOF ion adsorbent. The adsorbed salt can be recovered and the

    MOF-based ion adsorbent can be regenerated with excellent cycle performance. Except for

    NaCl, the amphoteric MIL-121 is also able to adsorb other monovalent and divalent cations.

    This study indicates that the introduction of stimuli responsiveness advances the water

    treatment process to a controllable or smarter era, aiming at developing a more convenient,

    efficient, energy-saving, and environmental friendly water processing system.

    This study indicates that the introduction of stimuli responsiveness advances the water

    treatment process to a controllable or smarter era, aiming at developing a more convenient,

    efficient, energy-saving, and environmental friendly water processing system.

  • vi

    List of Publications

    Journal Publications:

    [1] Ranwen Ou, Jing Wei, Lei Jiang, George P. Simon, and Huanting Wang, Robust

    thermoresponsive polymer composite membrane with switchable superhydrophilicity and

    superhydrophobicity for efficient oil-water separation. Environ. Sci. Technol. 2016, 50, 906-

    914

    [2] Ranwen Ou, Huacheng Zhang, George P. Simon, Huanting Wang, Microfibre-polymer

    hydrogel monolith as forward osmosis draw agent. J. Membr. Sci. 2016

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