Abstract:
Nanoparticles have exciting properties that can be tailored by altering their size, density, and
shape. A number of important properties of the nanoparticles have been investigated for
various applications. One such property that is strongly affected by nanoparticle size is localised
surface plasmon resonance (LSPR). The resonance from metal nanoparticles has been used in
dye-sensitised solar cells to improve their performance. In this work, the dependence of
plasmonic properties on nanoparticle sizes is shown. The gold nanoparticles were prepared
using a reduction process where hydrogen tetrachloroaurate acid was used as the base gold salt
and reduced by sodium citrate at different molarities ranging from 0.015 to 0.035 mol/L. The
method produces monodispersed nanoparticles whose sizes are sensitive to the concentration
of chemicals used and the completeness of the reduction process. The process took
approximately 18 minutes, and the colour changed from pale yellow to wine-red. The
absorbance of the resulting gold nanoparticles was determined using a 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. A
high molarity concentration of 0.035 mol/L produced a small particle with a diameter of 17.04
nm, while a low concentration of 0.015 mol/L produced a size of 26.55 nm. The interaction of
electrons in the specific orbitals, sp- and d-, of nanoparticles exhibited pronounced multiple
resonances with the reduction of nanoparticle sizes.
