Chemically Modified Electrodes: A Supramolecular Assembly Approach

Abstract

The main objective of this dissertation is to design and study new superamolecular assemblies for membrane separation, sensing and catalysis applications. Three types of supramolecular assemblies will be addressed including ruthenium directed molecular assembly, polythiooxometalate encapsulated hydroquinone assembly and layer by layer assembly of gold nanoparticle and cobalt monosubstituted wells-dowson compound. The synthesis, characterization and related applications of these systems will be discussed in detail. Chapter 1 presents the comprehensive literature review on Supramolecular Assembly. Detailed information will be provided in terms of the fundamentals and recent advances in transition metal-directed tetrameric assembly and polyoxometalate based superamolecular assemblies. The latter is further addressed as wheel/sphere shaped polyoxometalate assembly and layer by layer (LbL) assembly. Chapter 2 provides a detailed discussion of Ruthenium based metallocycles linked by bipyridine spacers (pyrazine(PZ), 4,4’-bipyridine(BP), 4,4'-Azodipyridine(AZP), 4,4'-(1,3-butadiyne-1,4-diyl)bis-Pyridine(DPB) and 3,6-di-4-pyridinyl-1,2,4,5-Tetrazine(dipyTz). These metallocycles will be fully characterized using UV-Vis, Raman, NMR and electrochemistry. The equilibrium of square species and triangle species for DPB and dipyTz linked metallocycles will be studied using 1H NMR at different concentrations. Diffusion NMR and potential step experiment will also be employed to study the size of these metallocycles based on the measured diffusion coefficients. The use of BP tetramer as building unit for extended three dimensional frameworks will also be discussed. Chapter 3 presents the application of ruthenium molecular squares for membrane separation. Permeation tests will be discussed in both solution phase and gas phase. For solution phase permeation test, glassy carbon electrode covered with molecular square film will be examined in redox probes (Ru(NH3)63+, Co(bpy)33+) containing solution. Based on the amount of each probe that can permeate through the membrane, the separation capability of the film will be evaluated. For gas phase permeation test, the assessment will be performed with a home built glass cell connected to Gas Chromatography analyzer. The factors that constitute for the separation such as size and affinity effect will also be discussed. Chapter 4 presents the study of host-guest chemistry of polythiooxometalate encapsulated hydroquinone complex. The complex is designed in the way that weak interactions are expected between the POM backbone and encapsulated hydroquinone. Such a system can be used for sensor development. The complex will be fully characterized using single crystal x-ray diffraction, elemental analysis and Raman spectroscopy. The host guest interactions in solution will be studied by NMR and electrochemistry. Chapter 5 provides a detailed study of LbL assembly formed on glassy carbon substrate using PDDA stabilized Au nanoparticles and polyoxometalates (Cobalt monosubstituted wells Dawson) for oxygen reduction catalysis. The LbL assembly will be characterized using UV-Vis and electrochemistry. The influence of film thickness (number of layers) and polyoxometalate (transition metal substitution) on the kinetics of the ORR will be discussed. Also the specific activity towards oxygen reduction of this system will be calculated. The value will be compared to the published values to address the catalysis efficiency of the system. Chapter 6 is a brief summary of this research.