Stripping Voltammetry in Unsupported Systems and Its Application in ZnO Suspensions, Acetonitrile Purification and Unsupported Lead Solutions
AuthorKARUNATHILAKE, NELUM MALA
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The focus of the dissertation is on electrochemical detection in the absence of excess electrolytes, so-called unsupported solution. This work uses anodic stripping voltammetry with a Hg ultramicroelectrode (Hg UME). The reduction potential of ZnO nanoparticles (NPs) is a function of size and the reduction of ZnO NPs in CH3CN follows the behavior predicted by Plieth: smaller NPs are thermodynamically easier to reduce. Stochastic collision studies explain the limitation of reduction of ZnO nanoparticles on Hg ultramicroelectrode and effect of migration plus diffusion in the presence of 1 mM tetrabutylammonium perchlorate acid (TBAP). Mobility and zeta potential characterize ZnO NPs transport to the UME. Electrolysis of NPs introduces ionic species and increases the migration rate allowing lower detection limits than in the presence of 1 mM TBAP. Smaller NPs become harder to reduce and require a larger potential window for the solvent. Also using a lower concentration of ZnO NPs make detection challenging due to the solvent background and other limitations. A part of the thesis describes the development of a purification method of acetonitrile (CH3CN), HPLC grade, which can be used in electrochemical studies involved in metal ions in the absence of electrolytes. The potential window of the purified CH3CN ranges from −2.8 V to +2.8 V vs. SCE without any faradaic current in the absence of supporting electrolytes. This potential window is larger than previously reported in the literature which ranges from −2.5 V to + 2.5 V vs. SCE in the presence of supporting electrolytes. In addition to electrochemical testing, CH3CN was analyzed by GC-MS and EDS of the dried residue on Si. Further, trace metals Cu2+, Pb2+, Cd2+ and Zn2+ in tap water were detected by anodic stripping voltammetry on Hg UME in the absence of electrolytes. Ionic lead (Pb) in tap water was quantified by electrochemical detection without altering existing chemical equilibria. The contribution of migration and diffusion in the reduction of aqueous Pb2+ on a Hg UME is discussed in detailed here.