Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    PREPARATION OF POLYELECTROLYTE MEMBRANES EMBEDDED WITH ZEOLITE NANOPARTICLES FOR ENHANCED PERFORMANCE IN FORWARD OSMOSIS
    (2016) Kang, Yan; Mi, Baoxia; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Water scarcity is a global issue that has already affected every continent. Membrane technology is considered as one of the most promising candidates for resolving this worsening issue. Among all the membrane processes, the emerging forward osmosis (FO) membrane process is osmotically-driven and has unique advantages compared with other traditional pressure-driven membrane processes. One of the major challenges to advancing the FO membrane process is the lack of a suitable membrane. Polyelectrolyte thin film prepared via layer-by-layer (LbL) technique has demonstrated its excellent performance in many applications including electronics, optics, sensors, etc. Recent studies have revealed the potential of polyelectrolyte thin films in acting as the active separation layer of FO membranes, but significant efforts are still needed to improve the membrane performance and understand the transport mechanisms. This dissertation introduces a novel approach to prepare a zeolite-embedded polyelectrolyte composite membrane for enhanced FO performance. This membrane takes advantages of the versatile LbL process to unprecedentedly incorporate high loading of zeolite nanoparticles, which are anticipated to facilitate water transport due to the uniquely interconnected structure of zeolites. Major topics discussed in this dissertation include: (1) the synthesis and evaluation of the polyelectrolyte-zeolite composite FO membrane, (2) the examination of the fouling resistance to identify its technical limitations, (3) the demonstration of the membrane regenerability as an effective strategy for membrane fouling control, and (4) the investigation of crosslinking effects on the membrane performance to elucidate the transport mechanisms involved in the zeolite-embedded polyelectrolyte membranes. Comparative studies have been made between polyelectrolyte membranes with and without zeolite incorporation. The findings suggest that the zeolite-embedded membrane, although slightly more susceptible to silica scaling, has demonstrated enhanced water flux and separation capability, good resistance to organic fouling, and complete regenerability for fouling control. Additionally, the embedded zeolite nanoparticles are proved to be able to create fast pathways for water transport. Overall, this work provides a novel strategy to create zeolite-polymer composite membranes with enhanced separation performance and unique fouling mitigation properties.
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    Silane Cross-Linked Graphene Oxide Membrane Demonstrating Unique Transport Phenomena in Aqueous Phase Separation
    (2015) Zheng, Sunxiang; Mi, Baoxia; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Graphene oxide (GO) membranes are considered promising for water purification applications. We synthesized a novel GO membrane using inorganic silane as a cross linker. Briefly, a pH 3 GO solution was filtrated through polyethersulfone (PES) membrane supports by vacuum filtration. The GO layers deposited on the PES supports were subsequently soaked in a saturated sodium metasilicate solution for crosslinking and stabilization. As a final step, the readily stabilized GO membranes were transferred into a 10% H2SO4 solution for further stabilization. The GO membrane exhibits unique rejection properties to uncharged organic species (~ 85%) and ionic species (~6%). A high water flux of 39 L/m2/h and a reasonable back solute flux of 0.011 mol/m2/h were observed with 0.25M trisodium citrate dehydrate (TSC) as draw solution in forward osmosis (FO). The GO membrane also demonstrates some interesting Janus effects and enables directional water gating (by blocking the permeation in one direction while allowing the permeation in the other direction).