Responsive Polymer-Based pH Sensors and Environmental Remediation Technologies

  • Author / Creator
    Ahiabu, Andrews
  • My Ph.D. research involved the generation of stimuli responsive poly(N-isopropylacrylamide) (pNIPAm)-based microgels and the modification of their chemistry to generate a series of pH responsive microgel-based optical devices (etalons). The pH responsivity of the synthesized microgels was used also for drug delivery applications by taking advantage of the different ionizable groups that can be incorporated during the microgel synthesis. pH responsive microgels were used also as sorbents for environmental remediation applications, i.e., to remove heavy metal ions from solution. The porous nature and versatility of microgels made them possible to be incorporated into other remediation technologies. Specifically, they have been used to stabilize zero valent iron, which suffers aggregation in the remediation process. In Chapter 1, I present a brief introduction of stimuli responsive polymers and hydrogels, with emphasis on their structure and swelling theories. Chapter 2 focuses on the synthesis of a library of pH responsive microgels using different ionizable groups and the evaluation of their response to solution pH changes. The response kinetics to solution pH for a series of pH responsive microgels differing only in their alkyl pendant groups was investigated in Chapter 3. The longer alkyl group chains yielded the fastest response rate, with nearly a 1000 fold increase in response rate when compared to the shortest alkyl chain microgel. The knowledge obtained from pH responsive microgels in Chapter 2 was implemented in drug delivery applications in Chapter 4. Two ionizable groups of opposite charges at different pH regimes were used to load and release model drugs in a controlled manner through the aggregation (drug loading) and disaggregation (drug releasing) of the microgels controlled by solution pH. In Chapter 5, the microgels were used as sorbents for the remediation of heavy metal ions, such as Cd2+ and Pb2+. The role that crosslinking density, type and composition of the microgels, played in remediating these ions was presented. An attempt to expand the remediating capability of these microgels to other recalcitrant contaminants such as selenium, which is a metalloid, failed. However, the microgels played a significant role in dispersing zero valent iron (ZVI), which is an emerging technology capable of remediating many contaminants, ranging from halogenated organic compounds to heavy metals and metalloids. However, its propensity to aggregate limits its use. In Chapter 6, I present the enhanced ability to remove Se with microgel stabilized ZVI as compared to either N2 purged or pristine ZVI. In Chapter 7, conclusions and future suggestions are presented for further directions to the work presented.

  • Subjects / Keywords
  • Graduation date
    Spring 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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