Studies on the Exfoliation, Reassembly and Applications of Layered Materials
Open Access
- Author:
- Henderson, Camden Neil
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 11, 2013
- Committee Members:
- Thomas E Mallouk, Dissertation Advisor/Co-Advisor
David Lawrence Allara, Committee Member
Raymond Edward Schaak, Committee Member
Clive A Randall, Committee Member - Keywords:
- Layered Perovskites
Perchlorate Rememdiation
Tungsten Disulfide Exfoliation
Proton Conductivity - Abstract:
- This work investigates three research problems around a central theme of the chemistry of layered inorganic oxides. The first theme includes the exfoliation and reassembly of layered perovskites as well as the intercalation/exfoliation of graphite-like layered materials. The second concerns the design of anion-exchanging clay/ polymer composites for use in environmental remediation. The third theme investigates the ionic/electronic conductivity of layered perovskites. The results of the experiments as well as their possible applications are described in detail within each chapter. Chapter two describes research performed on the exfoliation and reassembly of layered perovskites. The reassembly (with in-plane registry) of exfoliated sheets was of particular interest. Multiple layered perovskites were synthesized and ion exchanged. While most of these materials did not exfoliate to a significant degree, it was observed that there are specific criteria required for sheets exfoliate and even more stringent requirements for reassembly. It was also observed that even with materials that exfoliate and restack completely, a mixture of sheets from two distinct compounds do not reassemble together. An interesting trend was observed in which the degree to which a material exfoliates is correlated to the acidity of the interlayer protons. Chapter three describes a study of anion-exchanging clay/polymer composites designed as materials for the sequestration of environmentally hazardous anions such as perchlorate and pertechnetate. Exfoliated synthetic fluoromica was reassembled with cationic polymers to produce composites, which selectively bind perchlorate in solutions that contain both perchlorate and chloride. The focus of this chapter is the binding isotherms observed for numerous composite systems. Most of the composites exhibited cooperative binding, while one conformed to a Langmuirian isotherm. Experiments detailing the use of these composites as hosts for catalytic particles are also discussed in this chapter. Chapter four focuses on the exfoliation of layered materials with uncharged sheets, such as tungsten disulfide and hexagonal boron nitride. Combining the methods in recent reports of the intercalation of phosphoric acid into hexagonal boron nitride with reports of solution based exfoliation of layered materials, an increase in the yield of exfoliated flakes was observed. There is a significant increase in the number of thin flakes obtained using acid-assisted exfoliation as compared to experiments without the acid. Interestingly, a small degree of exfoliation is observed by stirring the solids with ethylphosphonic acid in isopropyl alcohol solution. Chapters five and six are discussions on the conductivity of several layered perovskites. Chapter four focuses on the layered perovskite HLa2Ti2TaO10 and related phases formed by A-site substitution in the H(1+x)Sr(x)La(2-x)Ti2TaO10 series. Chapter five is a detailed study of the electronic/ionic conductivity of HCa2Nb3O10. Each material was found to be primarily an electronic conductor under reducing atmospheres, as opposed to an ionic (proton) conductor.