Modification of Glassy Carbon Electrodes with Diazonium Cation Terminated Films: "Sticky Surfaces"
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
This thesis described the modification of glassy carbon (GC) electrodes with aminophenyl (AP) films via in situ reduction of aminobenzene diazonium ions. The characterisation of the AP modified GC was conducted electrochemically by oxidation of the AP functionalities in acidic aqueous conditions. Ferricyanide and ruthenium hexamine redox probes were also used to investigate the blocking properties of the AP films. Before electrochemical oxidation of the AP functionalities, AP films were shown to have a nett positive charge at pH 7. After electrochemical oxidation in protic conditions, the film was either neutral or negatively charged. The preparation of diazonium cation terminated surface, which is termed 'sticky surface', by reaction of the AP modified electrodes with NaNO₂ in acidic condition, was investigated and the sticky surface was electrochemically characterised. More than one species was formed in the reaction of the AP film with NaNO₂. The reactions of sticky surface with aniline, citrate- and thiol-capped gold nanoparticles (Au-nps) were also studied. Spontaneous reaction of sticky surface with thiol-capped Au-nps had been achieved, and suggested that the reaction leads to the formation of Au–C bonds, via the loss of nitrogen. However, for the reaction of the sticky surface with citrate-capped Au-nps, it was unclear whether covalent bonding had been achieved. The reason for this was due to the possibility of an electrostatic interaction between the negatively charged citrate-capped Au-nps and the positively charged sticky surface. The stability of the sticky surface in acidic aqueous conditions was studied electrochemically and by reaction with thiol-capped Au-nps. It was found that the diazonium cations on the sticky surface are not stable over one hour in aqueous acidic conditions, or even in low temperature. The electro-catalytic activity of the thiol-capped Au-nps attached to the GC electrode via sticky surface towards the oxidation of ascorbic acid was briefly examined, and the surface was found to catalyse the oxidation reaction.