Atomically-precise gold and silver electrocatalysts for superior nitrate reduction and detection.

Abstract

This study investigates the electrocatalytic performance of chemically-synthesised gold and silver nanoclusters for nitrate reduction, with the intent of designing an accurate, sensitive and robust electrochemical nitrate sensing platform. An exhaustive literature survey has identified no prior reports which have used such compounds for this specific role, nor have any analogous studies performed such an extensive electrochemical testing nor treatment of experimental data. As such, the majority of findings and conclusions presented in this thesis are without precedent; they establish a rich and varied landscape for future work. Notably, all small gold clusters used in this work are found to be considerably active electrocatalysts for nitrate reduction, in direct contrast to conventional knowledge which has placed bulk gold in an inert status. The respective activity of individual carbon-supported gold-phosphine nanoclusters is also evaluated, and during the course of this thesis an interesting explanation will be offered to rationalise the trends observed, which are independent of size however are contingent on deeper, underlying physiochemical properties.

In Chapter 1, the reader will be introduced to fundamental concepts of electrochemical sensing and the electrochemical reduction of nitrate alongside the specific aims of this work, whilst in Chapter 2 physiochemical aspects of gold nanoclusters and their synthesis will be given. Chapter 3 will summarise current knowledge of the specific nanoclusters synthesised herein, while Chapter 4 will elaborate on their non-aqueous electrochemical behaviour where the first of many novel observations are made. Chapter 5 presents the results and discussion of the detailed investigation into the electrochemical behaviour of carbon-supported gold and silver nanomaterials. Chapter 6 presents a detailed kinetic perspective on the electrocatalytic performance of these catalysts towards the reduction of nitrate. This is concluded with a compelling, novel and logical argument on the nature of nitrate electroreduction at small gold clusters which has not yet been attempted in the scientific literature. Chapter 7 will briefly investigate the best-performing undecagold-based catalyst for the electrochemical sensing of nitrate in both artificial and authentic environmental matrices, followed by a brief conclusion to this work and avenues for future work are outlined. Finally, Chapter 8 provides a detailed description of experimental procedures and characterisation data.