Determination of gold nanoparticles sizes from their plasmon resonance within the optical spectrum.

Abstract

Nanoparticles have exciting properties that can be tailored by altering their size, density and shape. One such property is the localized surface plasmon resonance that is gaining interest in the application of dye sensitized solar cells. In this work, a study was carried to establish the right sizes of gold nanoparticles that give optimum localized surface plasmon resonance. The gold nanoparticles were prepared using reduction process where the hydrogen tetrachloroaurate acid was used as the base gold salt and reduced by sodium citrate prepared at different molarity ranging from 0.015 to 0.035 mol/L. The process took approximately 18 minutes and the colour changed from pale-yellow to wine-red. The absorbance of resulting gold nanoparticles was determined using UV Vis spectrophotometer within the range of 300 nm to 800 nm. The LSPR peaks were found to occur within 518 nm to 520 nm and from a Gaussian fit, the FWHM ranged from 45.5 to 51.0 nm. The absorption peaks had a narrow range of 14 nm over the range of molarity of sodium citrate. High molarity concetration of 0.35 mol/L produced a small particle with a diameter of 17 nm while low concentration of 0.015 mol/L produced a size of 26 nm. The small sized gold nanoparticles were found to exhibit multiple resonances attributed to interactions between electrons in sp- and d- bands of the nanoparticle.