Chemical Engineering

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This is the collection for the University of Waterloo's Department of Chemical Engineering.

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Browsing Chemical Engineering by Subject "2D materials"

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    Graphene Based Membranes for High Salinity, Produced Water Treatment by Pervaporation Separation
    (University of Waterloo, 2023-03-13) Almarzooqi, Khalfan
    Petroleum industries generate huge volumes of wastewater that is associated with oil and gas during extraction, known as produced water. It accounts for 98% of the amount extracted, and comprises diverse pollutants of salts, suspended solids, dissolved organic solutes, and dispersed oils; that require to be safely treated before being disposed to the environment, or reused for various beneficial applications. Nowadays, graphene-based membranes have shown potential as a membrane material due to their high performance and stability features. This research demonstrated the use of graphene oxide membranes supported on polyethersulfone films (GO/PES) for high salinity water, simulated produced water model (PWM), and PWM with simulated foulants treatment via the pervaporation separation technology. The membranes showed the highest water flux of 47.8 L m-2 h-1 for NaCl solutions in pervaporation testing operated at 60 oC, and salt and organic rejections of 99.9% and 56%, respectively. In addition, the membranes were tested for long-term pervaporation for 72 hours and showed a decline of 50–60% from the initial flux in the worst-case-scenario. Moreover, in-depth investigation of the Zn2+ crosslinker showed a hydrolysis reaction to Zn(OH)2, with the progress of the long-term pervaporation, in which much of it is being leached out. Consequently, since GO membranes are not stable in water, it remains challenging to be utilized in the industry. A more stable GO membrane in aqueous phase was proposed. The membrane’s stability was enhanced by divalent and trivalent metal cations of Zn2+ and Fe3+ crosslinkers, respectively, and partial reduction under vacuum. Two orders of fabrications were investigated of either crosslinking rGO (method I) or reducing M+–rGO (method II). The prepared membranes were examined for their characterization and performance. Fe3+–rGO prepared by method II showed the best organic solute rejection of 69%. Moreover, long-term pervaporation experiment was performed for 12 hours for Zn2+–rGO membranes, and revealed a drop in flux of 6% only, while Zn2+–GO membrane had a drop in flux of 24%. Additionally, the stability of the membranes was tested via an abrasion method using a rotary wheel abrader. The conducted experiments revealed that Fe3+–rGO membranes had the maximum mechanical integrity with an abrasion resistance of 95% compared to the initial control (non-reduced and non-crosslinked) GO/PES membrane.
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    Manipulating Exfoliated 2D Materials at the Air-Water Interface: Towards Large-area Coatings and Applications
    (University of Waterloo, 2023-09-26) Xu, Luzhu
    The aim of this thesis is to develop a versatile, large-area coating process for two-dimensional (2D) materials which preserves single-layer or exfoliated sheets and provides comprehensive investigation of the controlling factors for the deposition process. Compared to other approaches, traditional Langmuir film methods not only are economically suitable for transition to large-scale manufacturing but also permit retention of the exfoliated form and freedom of sheet rearrangements. However, challenges remain in existing Langmuir film-based traditional and continuous coating process: 1). Significant material loss due to water-miscible solvent; 2). External forces required for film densification and transfer. In this thesis, we expand upon my MASc work which focuses on the development of a solvent-spreading assisted Langmuir film method which enables large batch film transfer process or a continuous one for monolayer graphene-based materials. With the goal of applying the coating process for films in flexible, optoelectronic devices such as in solar cells, we refined the procedure for preparing spreading dispersion of exfoliated molybdenum disulfide (MoS2). During investigation of the chemical and colloidal stability of the precursor, chemically exfoliated MoS2 (ce-MoS2) dispersions in water, we found that ce-MoS2 degrades rapidly to form soluble molybdates under alkaline conditions and exposure to both light and air. Building upon this fundamental study, the modified spreading dispersion retains almost 100% of metallic MoS2 and contains ~40% increase in single-layer content. Then, we investigated the structure of the aggregates formed upon spreading each drop of the ink on the air-water interface. We observed cluster structure transitions from island-like domains to more linear networks in three different nanosheets as dispersion concentration is reduced. Regardless of assembly method, we found that cluster structure impacts the attainable density of transferred Langmuir films. Finally, since the spreading pressure of solvent provides the driving force for film assembly and transfer, we evaluated the spreading profiles of various combinations of organic solvents and their impacts on Langmuir film formation. We uncover that the formulation of mixing polar and water-immiscible solvents not only largely reduces the loss of materials into the subphase water but also induces a sharp increase in spreading pressure which facilities the formation of a solid film as well as further densification and transfer of the floating film to substrates in a R2R deposition system. We also develop a multi-dripper system to showcase the strategy of coating films with arbitrary widths. When conducting the R2R deposition, we unveil the importance of using wetting substrate to maximize the effectiveness from the spreading pressure for achieving continuous, uniform coatings. In the end, we attempt to utilize the Langmuir film of ce-MoS2 in the perovskite solar cell to demonstrate the potential use of our coating process.