It is crucial nowadays to predict
in a fast and simple manner physical-chemical
behaviors like, the size-dependent optical properties of gold nanospheres
(Au NSs). The idea behind this experiment is trying to replace (as
much as possible) robust and expensive microscopy techniques with
UV–vis spectrophotometry and friendly simulations. Students
chemically synthesized ∼4 and ∼15 nm diameter NSs and
grew larger ones to ∼32, ∼50, and ∼70 nm diameter
using the previously obtained ∼15 nm as seeds. They characterized
them via UV–vis spectroscopy to ultimately compare the spectra
with user-friendly software including MiePlot, , and the Amendola algorithm
(Wolfram Mathematica). For Au NSs ≤25 nm diam., the experimental
UV–vis spectra fitted very well with the Amendola algorithm
to determine the size. For Au NSs >25 nm diam., the experiment
exhibited
larger Au NSs than expected as noticed by the systematic red shift
of the plasmon band with respect to the simulated one. A SEM image
confirmed larger Au NSs; therefore, students were challenged to determine
the source of discrepancy between experimental and simulated UV–vis
spectra, which was later attributed to the aging of the Au NSs seeds.
This experiment demonstrates an easy way to accurately determine the
nanoparticle size while exploring and solving potential issues that
students may face during the chemical synthesis and simulations.
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