Synthesis and Characterisation of Core-shell Gold Nanoparticles

Technology developed at Victoria University of Wellington by Professor James H. Johnston and Dr Kerstin Lucas allows for the colouring of high quality wool fibres using spherical gold nanoparticles. Gold nanoparticles have interesting colours and optical properties due to surface plasmon resonance effects and, using this technology, a boutique range of colours can be imparted onto wool fibres. The colour of gold nanoparticles is determined by their size and shape, hence the colour range achievable using spherical nanoparticles is limited to those obtained by changing the particle diameter and degree of aggregation of these particles. This limitation can be overcome by using gold nanoparticles of different shapes in conjunction with other materials. This research details the synthesis and characterisation of gold nanoshells on spherical silica cores and their use for the colouring of wool. Silica cores were used in this research as they are reasonably chemically inert and so serve as a stable substrate for the gold shells. Silica spheres are also easily prepared in a manner that allows control over the final particle diameter. Several syntheses of these core-shell particles have been previously devised however they are not suitable for commercial use. Such syntheses involve many time-consuming steps, high temperatures or light-sensitive reagents. Synthetic methods set out in this research involve a novel in-situ seeding of gold nanoparticles for the growth of the shells eliminating the step of growing gold nanoparticles ex-situ commonly involved in other synthetic schemes. The need for light-sensitive reducing agents is eliminated by the use of other reductants such as sodium borohydride and hydroxylamine. All steps of the synthetic schemes are carried out at less than 100 °C. Several methods of synthesising core-shell particles are outlined in this research, which achieved varying degrees of success. Many syntheses investigated successfully produced core-shell particles but also left many silica spheres without the desired gold shell coating. This was not a problem for the proposed application of colouring wool. As silica is easily dispersed in water and does not have the same affinity to bind to wool as gold does, the silica spheres without gold shells simply wash off after colouring. This allowed the core-shell particles synthesised in this research to be successfully used to colour wool fibres and achieve a shade of purple not previously obtained using the earlier methodologies.