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Title:Development and physicochemical characterization of thin-film composite nanofiltration membranes with covalent organic framework active layers
Author(s):Valentino, Lauren
Director of Research:Mariñas, Benito J.
Doctoral Committee Chair(s):Mariñas, Benito J.
Doctoral Committee Member(s):Dichtel, William R; Espinosa Marzal, Rosa M.; Cusick, Roland
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Covalent organic framework (COF)
Abstract:The global demand for water is increasing due to unprecedented population growth, accelerated urbanization, economic development, and climate change. With water demand outpacing supply, intensifying periodic water shortages are driving the development of creative solutions to address this global challenge. These include sustainable and efficient management of traditional water resources, conservation strategies, and the incorporation of alternative water sources including seawater and wastewater effluents. Although more sustainable, these alternative water sources are complex and result in new challenges for providing a safe and reliable supply of drinking water. In comparison to conventional water treatment methods, pressure-driven membrane technologies are advantageous because they offer an effective single-step process for removing pathogens along with organic and inorganic contaminants. Despite their advantages, technical advances, and the development of novel membrane materials in recent decades, the relatively high cost of energy required for membrane processes and operational problems associated with membrane fouling and fouling control strategies have restricted a more widespread implementation of nanofiltration (NF) and reverse osmosis (RO) technologies. In addition, the similar polyamide (PA) chemistry used for most commercially available NF and RO membranes limits the water permeability and solute selectivity that could be achieved. In contrast, covalent organic frameworks (COFs) are an emerging class of materials that offer exceptional opportunities to overcome these challenges. COFs are constructed from modular building blocks to form crystalline, permanently porous materials. Employing two-dimensional (2D) COF active layers in the thin-film composite (TFC) membrane structure should provide selective layers with uniform pores that can be tailored at the molecular level. This molecular-level design allows for control of the pore structure and chemical functionality unlike the empirically optimized PA active layers that currently dominate the membrane technology sector. Furthermore, the ultrathin nature, uniform nanometer-size pores, strength, and durability of 2D COF active layers should provide a desirable combination of high selectivity and water permeability. For the first time, this work demonstrates the capability and potential of using COFs as TFC membrane active layers for water purification applications. Initially, NF active layers of polyimine COF were synthesized via the interfacial polymerization (IP) of terephthalaldehyde and tris(4-aminophenyl)benzene monomers on top of a polyethersulfone (PES) ultrafiltration membrane support. Rutherford backscattering spectrometry and Fourier transform infrared spectroscopy analyses confirmed the presence of an imine-linked film that was reproducibly formed with a thickness of ~10 nm. The rejection efficiencies of the COF NF membrane for a model organic compound, Rhodamine-WT, and a background electrolyte, NaCl, were higher than those of the PES support without the COF film. However, this preliminary work also demonstrated the need for COF NF membranes with smaller active layer pores and alternative support materials. This motivated the investigation of another COF monomer, triformylbenzene, to modulate the pore size and polyacrylonitrile (PAN) as a solvent-resistance support. Although the performance was not optimal in terms of water permeability and solute rejection, the first generation of COF membranes developed in this work represents a new paradigm for membrane development in which the active layer structure is pre-determined and highly controllable.
Issue Date:2017-09-12
Rights Information:Copyright 2017 Lauren Valentino
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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