Electrochemical Studies of Colloidal ZnO

The dissertation here in describes efforts towards the development of electrochemical methods to determine the free energy of formation of semiconductor nanoparticles (SCNP). This method is based on determining the electrochemical reduction potential of metal ions that compose the NP. This method allows fundamental thermodynamic properties to be correlated with size and shape of semiconductor nanostructures. The research was done using zinc oxide (ZnO) NPs and the reduction potential of ZnO NPs was determined by reducing Zn2+ in ZnO NPs at a Hg ultramicroelectrode. ZnO NPs of diameters ranging from ~11 nm to ~77 nm were synthesized and their reduction potentials, surface free energies and average surface tension were estimated. As a reference system to ZnO NPs, electrochemical reduction of Zn2+ was studied using different Zn2+ precursors in non-aqueous and aqueous media on Hg, C, fluorine doped SnO2 (FTO) and Pt electrodes. According to the results, Zn(Ac)2 shows a two-step electron transfer process in CH3CN on Hg, C and FTO and the most reproducible CVs were obtained on FTO. Furthermore, the observation of two steps in Zn2+ reduction in CH3CN led to the testing of the postulate of the existence of a Zn+ intermediate species.Moreover, observation of the formation of NPs during the study of the existence of Zn+ intermediate species led to the electrochemical synthesis of possible Zn based particles via electrochemical reduction of Zn(Ac)2 on FTO in CH3CN. By changing the reduction time and concentration of reacting species it was possible to obtain stable particles with different luminescence properties