The reduced forms of quinones (Q •−/2− ) are well-known for their binding affinities toward electrophiles. The ability to modify and add substituents onto quinones to alter their electronic and steric properties allows the optimization of their structures for the highest interactions with electrophiles. Three reduced naphthoquinones with different methyl substitutions of their quinone ring were investigated for their suitability as electrocatalysts for CO 2 capture and conversion. In the aprotic organic solvent acetonitrile and in the absence of dissolved molecular oxygen, the quinones can be reduced in consecutive one-electron steps to form first the monoanion radicals (Q •− ) and then at more negative potentials the dianions (Q 2− ). When CO 2 (g) is purged into the solution, the two one-electron reduction processes merge into one two-electron chemically reversible reduction process at the same potential as the first one-electron reduction process observed in an Ar(g) atmosphere. It is proposed that a complex is formed between the reduced quinone and nCO 2 molecules, [Q(CO 2 ) n ] 2− , that allows the dianion to be formed at a lower energy (voltage) compared to under an Ar(g) atmosphere. The binding is completely chemically reversible so that purging the solutions of [Q(CO 2 ) n ] 2− with Ar(g) results in the carboxylated complex dissociating according to two major pathways. Pathway (A) involves the generation of Q 2− (or Q •− ) and CO 2 (g), while pathway (B) results in the negative charge transferring to the CO 2 molecules to form the carboxyl radical anion, CO 2•− , and the neutral Q.

An intelligent drug release system that is triggered into action upon sensing the motion of swarmer P. mirabilis is introduced. The rational design of the drug release system focuses on a pNIPAAm-co-pAEMA copolymer that prevents drug leakage in a tobramycin-loaded mesoporous silica particle by covering its surface via electrostatic attraction. The copolymer chains are also conjugated to peptide ligands YVLWKRKRKFCFI-NH2 that display affinity to Gram-negative bacteria. When swarmer P. mirabilis cells approach and come in contact with the particle, the copolymer-YVLWKRKRKFCFI-NH2 binds to the lipopolysaccharides on the outer membrane of motile P. mirabilis and are stripped off the particle surface when the cells move away; hence releasing tobramycin into the swarmer colony and inhibiting its expansion. The release mechanism is termed Motion-Induced Mechanical Stripping (MIMS). For swarmer B. subtilis, the removal of copolymers from particle surfaces via MIMS is not apparent due to poor adherence between bacteria and copolymer-YVLWKRKRKFCFI-NH2 system.

Within the field of electrografting with aryldiazonium cations, there are various methods available to graft a monolayer of organic groups onto electrode surfaces. One of these relies on the presence of steric groups or constraints on the aryldiazonium cation itself, which prevent multilayers from being formed by blocking access of the free aryl carbons on the grafted layer to the diazonium cations. Here, we investigate the nature of the layer formed from the electrochemical reduction of bulky 2,3,5,6‐tetramethylaniline monodiazonium cations on glassy carbon (GC) electrodes, to form 2,3,5,6‐tetramethylaniline‐modified GC (GC−TMA), which was subsequently characterized by atomic force microscopy scratching, cyclic voltammetry, electrochemical impedance spectroscopy, and X‐ray photoelectron spectroscopy. Despite the bulky structure of the TMA group, GC−TMA was found to exhibit sparse multilayers, owing to the ability of the precursor to undergo its own electropolymerization under the experimental conditions used.

The electrochemical properties of polymerized aniline (PANI) and polymerized melamine (PMEL) that were electrochemical copolymerized (PANIMEL) on a glassy carbon electrode (GCE) that had been coated with functionalized multiwalled carbon nanotubes (fMWCNT) to form a PANIMEL/fMWCNT/GCE film electrode were studied, with an aim toward electrochemical energy storage (EES). A number of factors, such as the choice of working electrode, electrolyte, switching potential, applied scan rate, and type of fMWCNTs, were initially investigated and evaluated during the individual electrochemical polymerization of aniline and melamine via successive potential cycling. The electrochemical copolymerisation of aniline and melamine was then studied with an ideal monomeric ratio of 1:3 that gave an optimal ratio of the voltammetric peak current heights with distinguishable redox peak potentials. Variable scan rate cyclic voltammetry (CV) of the electrosynthesized copolymer film electrode confirmed the dominance of the surface-confined electron transfer process at the electrode.The electrochemical stability of the copolymer film electrode was also assessed and revealed a limited cyclability of the daughter polymeric melamine, which was hypothesized to be due to an excessive nitrogen content combined with a low porosity that led to a poor ion intercalation-deintercalation mechanism.Electrochemical impedance spectroscopy (EIS) was performed to evaluate the electrochemical performance of the copolymerized film electrode with other control electrodes. The corresponding EIS results suggested that the copolymerized film electrode was electrochemically superior to the PMEL/fMWCNT/GCE film electrode but was inferior to the PANI/fMWCNT/GCE film electrode.

The chemical modification of electrode surfaces with organic molecules is an important reaction in electrochemistry. Of the multiple methods which exist for this purpose, aryldiazonium cation reduction is widely considered to be the most popular, due to the high stability of the grafted layer on the surface, as well as the relative ease of the modification procedure.One key disadvantage of grafting by diazonium chemistry is the inherent tendency of the grafted film to bear multilayers of organic molecules, which is not desired in most applications requiring modified electrodes. The side reactions forming these polymeric multilayers are known to occur at vacant, unsubstituted carbons on the aryl ring of the grafted layer. In the first of two broad parts of this thesis, studies were carried out on a glassy carbon (GC) electrode modified with bulky 2,3,5,6-tetramethylaniline (TMA) groups (i.e. GC-TMA), using the precursor to the diazonium salt, 2,3,5,6-tetramethyl-p-phenylenediamine (TMPD).Chapter 2 focuses on the formation of GC-TMA and its extensive characterization using electrochemical and spectroscopic techniques, with the aim of addressing the above problem of multilayer formation since TMPD bears a fully substituted aryl ring, thus preventing the multilayer-forming side reactions due to steric hindrance. The results show that sparse multilayers of TMA groups were observed on GC-TMA instead of the expected monolayer, with an investigation of the possible reasons for the unexpected formation of TMA multilayers.Chapter 3 then explores the same modified electrode further through additional coupling experiments performed on GC-TMA. Various small molecules were conjugated onto the TMA layer of GC-TMA with the intent of ascertaining the feasibility of such coupling, especially given the presence of outward-protruding methyl groups on each TMA moiety. Among these molecules were single-walled carbon nanotubes (SWCNTs), which allowed for Chapter 2Electrografting of sterically bulky tetramethylaniline groups on glassy carbon electrodes by aryldiazonium chemistry: reasons for the formation of multilayers ..

Activated carbon cloths (ACCs) were chemically modified with anthraquinone (AQ) groups and the resulting AQ‐modified ACCs were characterized and tested for their potential use in supercapacitors. At modest scan rates and current densities, AQ‐modified ACCs were found to store and release less charge than unmodified ACCs, under conditions where equivalent series resistance (ESR) is not minimized.