Electrochemical investigations of monolayer-protected gold clusters and functionalized nanoparticles using novel and atypical methodology.

摘要

Chapter One presents an overview of monolayer-protected Au clusters (MPCs) and their basic electronic and chemical properties. Also, recent applications of functionalized nanoparticles through either de novo synthesis or place-exchange reactions are discussed.; Chapter Two presents MPCs that have been prepared with mixed monolayers of alkanethiolates and alkanethiolates terminally w-functionalized with phenothiazine.; Chapter Three presents MPCs that have been prepared with mixed monolayers of alkanethiolates and mercaptopyridines. The mixed monolayer MPCs can contain as many as 22 pyridines/MPC.; Chapter Four presents MPCs that have been prepared with mixed monolayers of ω-functionalized alkanethiolates and n-alkanethiolates.; Chapter Five presents a computer simulation program that was developed to create simulated profiles of electrochemical responses of MPC samples that are based solely on the number of cores in a particular sample. The potential spacing of observed quantized double-layer charging (QDL) peaks observed in differential pulse voltammetry (DPV) of MPCs varies with capacitance.; Chapter Six presents experiments that probe the dynamics of the modified Brust synthesis of MPC samples that are smaller and more monodisperse in core population than in the conventional synthesis.; Chapter Seven presents MPC samples that are stable in solution for at least three weeks, with only small differences after six months.; Chapter Eight points out two methodological approaches to improving the information content in electrochemical observations of size-dependent (quantized) double layer charging (QDL) of solutions of metal nanoparticles. These methods are the use of reduced solution temperatures and of working electrodes bearing self-assembled monolayers (SAMs). Using cyclic (CV) and differential pulse voltammetry (DPV) measurements of annealed C6-MPCs, we find: (a) a sharply increased ability to resolve single electron charging events, (b) evidence that the nanoparticle double layer capacitance increases with decreasing temperature (278 to 203 K), and (c) currents that can be attributed to adsorption of nanoparticles onto the electrode surface, at temperatures below 223 K. The change in double layer capacity is roughly consistent with the expected temperature dependence of diffuse layer capacitance (Gouy-Chapman). The second useful methodology relies on the favorable background capacitance currents at SAM-covered working electrodes, which for solubility-fractionated C6-MPCs and mixed monolayer variants produced enhanced signal/noise in DPV and CV observations. Finally, the general concept of peak capacity in electrochemical voltammetry is outlined. About 50% of the theoretical peak capacity is observed in low temperature QDL voltammetry.