Functionalisation of Graphite Surfaces with Varying Concentrations of Nitric Acid and Aqua Regia, and their Effect on the Deposition of Gold Nanoparticles By Daniel J. Wotton MPhil Thesis Department of Chemistry Cardiff University October 2017 1 | P a g e Abstract The surface science of graphite surfaces for real world applications currently is poorly understood but shows promise in certain chemical industries such as acetylene hydrochlorination and thiosulfate leaching of preg-robbing ores. In this work the role of oxygen functional groups on the surface of HOPG introduced through acid treatment with nitric acid, aqua regia and sulfuric acid has been explored to determine how these functionalities influence the deposition of gold nanoparticles. Previous work by Cardiff University has determined that acid treatment with 0.5 moldm-3 nitric acid introduces hydroxyl groups onto the surface determined by selective derivatization. Heating of these surfaces creates ketones and ethers and that these differences in functionality change how gold is deposited on the surface. HAuCl4 treatment of HNO3 activated HOPG resulted in very little gold deposition on the surface when using low concentrations of nitric acid or no nitric acid. At nitric acid concentrations of 1.0M or higher there is a large increase in the quantities of gold on the surface. Higher concentrations showed an increase in the ratio of Au(III) to Au(0) deposited. In aqua regia treated surfaces higher concentrations resulted in more ketone present on the surface as determined by selective derivatization. This effected gold deposition by showing a large increase in Au(0) deposited at these higher aqua regia concentrations. Sulfuric acid activated samples showed sulfur being incorporated into the HOPG samples. Dilute concentrations of sulfuric acid were required to deposit large amounts of gold and all gold deposited was in the form of Au(0). The results and conclusions derived from them give insight into the effect of acid washing with different acids and their effect on the subsequent loading of the active gold ion. 2 | P a g e Acknowledgements I would like to thank my supervisor Philip Davies as well as David Morgan for their continuous support and guidance throughout the course of this research. Philip Davies for always being available and David Morgan for his assistance in obtaining XPS results. I would also like to thank my friends Vaughn Roberts, Alice Josephine Schmitz and Emir Bouleghlimat for their support over this course. 3 | P a g e Contents 1. Introduction .................................................................................................................................... 8 1.1 Surface Science and Heterogeneous Catalysis........................................................................ 8 1.1.1 Activation Energy of Catalysed Reactions ..................................................................... 11 1.2 Catalysis at Surfaces .............................................................................................................. 12 1.3 Catalysis by Gold ................................................................................................................... 13 1.4 The Physical and Chemical Properties of Gold ..................................................................... 14 1.5 Physical Properties and Characterisation of Small Gold Particles ........................................ 14 1.6 Acetylene Hydrochlorination ................................................................................................ 16 1.7 Acetylene Hydrochlorination Using Mercury Catalysts ........................................................ 17 1.8 Studies of the Activities of Metal Chlorides as Catalysts for Acetylene Hydrochlorination . 18 1.9 Acid Washing of HOPG and its Effect on the Deposition of Au Metal Nanoparticles ........... 22 1.10 Atomic Force Microscopy (AFM) ........................................................................................... 24 1.11 Introduction to AFM Theory ................................................................................................. 24 1.12 AFM Scanning Modes ........................................................................................................... 25 1.12.1 Contact Mode ............................................................................................................... 25 1.12.2 Non-contact Mode ........................................................................................................ 26 1.12.3 Tapping Mode ............................................................................................................... 27 1.13 AFM Images........................................................................................................................... 27 1.13.1 Surface Topography ...................................................................................................... 27 1.13.2 Deflection Images ......................................................................................................... 28 1.14 X-ray Photoelectron Spectroscopy (XPS) .............................................................................. 29 1.15 Introduction to XPS Theory ................................................................................................... 29 1.15.1 Photoelectric Effect ....................................................................................................... 30 1.15.2 Electron Mean Free Path .............................................................................................. 31 1.15.3 Koopmans’ Theorem ..................................................................................................... 32 1.15.4 XPS Instrument .............................................................................................................. 32 1.16 Initial and Final State Effects on XPS Spectra ........................................................................ 34 4 | P a g e 1.16.1 Chemical Environment, Oxidation States and Chemical Bonds .................................... 34 1.16.2 Surface Charging ........................................................................................................... 34 1.16.3 Spin-Orbit Coupling ....................................................................................................... 35 1.17 XPS – Quantitative Analyses ................................................................................................. 36 1.17.1 Determining Surface Concentration of Adsorbed Species............................................ 36 1.18 Selective Derivatization for Determination of Oxygen Functionalities ................................ 37 2 Experimental ................................................................................................................................. 39 2.1 Graphite Samples .................................................................................................................. 39 2.2 Nitric Acid, Aqua Regia, Sulphuric Acid, Chloroauric Acid & Mixed Solutions ...................... 39 2.3 UPW Treatment for Creating References ............................................................................. 40 2.4 Nitric Acid Treatment ............................................................................................................ 40 2.5 Gold Treatment ..................................................................................................................... 40 2.6 Gold in Acid Treatment ......................................................................................................... 40 2.7 Selective Derivatization of Oxygen Functionalities ............................................................... 40 3 Results and Discussion .................................................................................................................. 42 3.1 Clean HOPG Treated with UPW ............................................................................................ 42 3.2 HNO3 Treatment on HOPG .................................................................................................... 44 3.2.1 0.25M HNO3 Treated HOPG .......................................................................................... 45 3.2.2 0.5M HNO3 Treated HOPG ............................................................................................ 46 3.2.3 1.0M HNO3 Treated HOPG ............................................................................................ 47 3.2.4 2.0M HNO3 Treated HOPG ............................................................................................ 48 3.2.5 5.0M HNO3 Treated HOPG ............................................................................................ 49 -6 -3 3.3 HAuCl4 (2x10 moldm ) Treatment of HNO3 Treated HOPG ............................................... 52 -6 3.3.1 Clean HOPG Treated with UPW before Treatment with HAuCl4 (2x10 M) .................. 53 -6 3.3.2 HNO3 (0.25M) – HAuCl4 (2x10 M) ................................................................................ 54 -6 3.3.3 HNO3 (0.5M) – HAuCl4 (2x10 M) .................................................................................. 55 -6 3.3.4 HNO3 (1.0M) – HAuCl4 (2x10 M) .................................................................................. 55 -6 3.3.5 HNO3 (2.0M) – HAuCl4 (2x10 M) .................................................................................. 56 5 | P a g e -6 3.3.6 HNO3 (5.0M) – HAuCl4