Electrochemical Studies of Colloidal Semiconducting Nanoparticles at Ultramicroelectrodes

Abstract

In this thesis we describe a method to detect the collisions of semiconducting nanoparticle colloids by photoelectrochemical (PEC) current events at ultamicroelectrodes (UMEs). As the reference system, we studied oxidation of methanol by the photogenerated holes in the anatase TiO2 NPs (nanoparticles) with and without sensitization. The stepwise behavior of the photocurrent observed at Pt UME denotes long-term interactions of NPs with the UME. NPs interacting with FTO (fluorine doped tin oxide) UME show current oscillations rather than discrete current step observed with Pt UME. Further, the collisions of dye-sensitized TiO2 NPs (DSNPs) at FTO show similar trend as in bare TiO2 NPs, the magnitude of these oscillations are comparatively larger than those of bare TiO2 NPs. The addition of iodide into the DSNP colloidal suspension did not result in increasing the size of the PEC current oscillations at FTO, as expected based on NPs film behavior. The electrochemical studies of iodide at FTO provide evidence of electrochemical generation of iodine atoms (I*) at FTO. Nitrone spin trapping agents, DMPO (5,5-Dimethyl-1-pyrroline N-oxide) and TMPO (3,3,5,5-Tetramethyl-1-pyrroline N-oxide) were used to investigate the formation of this unstable radical and in the electron paramagnetic resonance (EPR) spectrum the radical intermediates of DMPO and TMPO were observed. The GCMS (gas chromatography-mass spectrometry) analysis of the electrolyte after long term electrolysis of tetrabutyleammonium iodide (TBAI) in acetonitrile is consistent with the formation of I* during the electrolysis process of I- at FTO.