Access Type

Open Access Embargo

Date of Award

1-1-2021

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Prof. Claudio N. Verani

Abstract

The work reported in this thesis focused on the use of redox-active metallosurfactants for current rectification and redox-innocent metallosurfactants for corrosion inhibition. These studies were done based on the hypothesis that redox-active metallosurfactnats can promote electron transport, while redox-innocent metallosurfactants can hinder electron transport. As such, new redox-active phenolate based iron(III), chromium(III), oxovanadium(IV) and redox-innocent gallium(III) and zinc(II) complexes were synthesized and characterized for the aforementioned applications. First, we studied the current rectification ability of a homobimetallic iron(III) hydrophobe with [N4O6] ligand environment. This complex displayed rectification with rectification ratio ranges from 2.6 to 9.8 between -2.0 and 2.0 V and 4.5 to 15.5 between -4.0 and 4.0 V. Solid state calculations suggested that SOMO energies are energetically compatible with electrode Fermi energy and electron transport can happen through that orbital. In this mechanism, metallosurfactant get reduced first. However, in this study, we did not see an enhancement in the rectification compared to monometallic iron(III) complexes due to only certain molecules directly in contact with the electrodes. In order to further modulate the Fermi/SOMO/HOMO gaps, we have synthesized and characterized chromium(III), and oxovanadium(IV) complexes with [N2O3]/ [N2O2] ligand environments. Devices were fabricated by sandwiching LB monolayers of each complex, and current-voltage (I-V) measurements were taken. All three complexes showed rectification, with the rectification ratio ranges from 3.08 to 17.22 between -2 to +2V. Solid state calculations displayed that HOMO energies are energetically comparable with electrode Fermi level for all three complexes. That suggested that electron transport can happen through HOMOs. In this mechanism, metallosurfactants get oxidized first. Similarly, the use of LB films in corrosion inhibition was investigated using redox-innocent gallium(III) and zinc(II) complexes. We studied the corrosion inhibition ability of these complexes on both iron and aluminum surfaces. Iron corrosion inhibition was investigated using SEM, ferroxyl staining, potentiodynamic polarization and impedance spectroscopy studies in both acidic and basic media. Both complexes acted best as inhibitors in saline medium, while in acidic medium, inhibition was present but less pronounced. Aluminum corrosion was studied using SEM, potentiodynamic polarization and impedance spectroscopy studies in the saline medium. Both complexes inhibited aluminum corrosion. However, zinc complexes exhibited superior inhibition compared to gallium during both iron and aluminium corrosion inhibition studied. These observations suggested that redox-innocent metallosurfactants can hinder electron transfer, and orderly physisorbed Langmuir-Blodgett film can act as a barrier against environmental influences. The work presented herein highlights the significance of modulating the Fermi-SOMO/HOMO and Fermi-LUMO energy gaps while developing current rectifiers and corrosion inhibitors.

Available for download on Friday, December 23, 2022

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