An Investigation into the Colloidal Stability of Silver Nanoparticles Produced in Ethanol Micro-Jets

The preparation of nanoparticles in liquids is a challenging task. To immerse metal atoms into liquids, chemical reduction methods are typically employed. Whilst such methods are able to produce a wide range of nanoparticles, the technique is restricted by the need for soluble starting materials, and they often produce excess chemical waste. The novel, and globally unique method of sputtering atoms into a liquid jet, developed by the University of Leicester, allows the even dispersion of any metal / semi-metal atoms into any liquid in a clean and controlled environment, thus clearly overcoming these restrictions. This project’s aim was to determine how the concentration of water present in an ethanol solution affected the colloidal stability of the silver nanoparticles that formed in the liquid jet solution. By modifying the experimental set-up, the purity of the samples was improved by an order of magnitude, allowing water to be reintroduced in a controlled manner. Through ultra-violet and visible light spectroscopic analysis of a range of samples produced under various conditions, it was concluded that water fundamentally affects the reactions that occur, and the nanoparticles that form. The results from this investigation show that in the absence of water, silver nanoparticles, produced by sputtering silver onto a liquid ethanol jet, undergo an avalanche-type reaction, which causes the clusters to lose their stability in solution, exhibited by the disappearance of the surface plasmon feature from their UV-Vis spectra over time. In contrast, in the presence of water, the nanoparticles are apparently more stable, and in particular retain their plasmon resonance for prolonged periods. This is a result that may be of great interest for the practical use of metal nanoparticles produced in solution, particularly for plasmonic applications