UV-Visible spectroscopy can be used as a characterization technique that provides information on whether the nanoparticle solution has destabilized over time. when particles aggregate and the conduction electrons near each particle surface become delocalized and are shared amongst neighbouring particles.When this occurs, the surface plasmon resonance shifts to lower energies, causing the absorption and scattering peaks to red-shift to longer wavelengths.(see attachment). this definition is from NANOCOMPOSIX https://nanocomposix.com/pages/gold-nanoparticles-optical-properties. question : thoes magnetite nanoparticles posses such behaivour also?
In recommendation to Mikelashvili Sir, the same trend is followed and observed for magnetite materials.
Hi,
thank you for your question. The Mie theory gives the relationship between the cross section of scattering, absorption and extinction and tell us that the absorption and scattering of light by a particle is dependent on size, shape, chemical composition, surrounding dielectric medium, coupling of colloids and adsorbed solutes. Iron oxide or magnetic nanofluids do have plasmonic properties, but they are not as strong as gold nanoparticles. This is because of the differences in electronic structures of the two materials. The free electron densities of the typical plasmonic metals (Au, Ag and Cu) are much lower compared to iron (see table http://230nsc1.phy-astr.gsu.edu/hbase/Tables/fermi.html ), and this means that lower energy is required to transition electrons from d to s2, and they absorb light in the visible spectrum. However, iron NPs can also exhibit LSPR but due to a larger electron density, this is not as distinct as for the noble metals. Easily explained, gold nanoparticles have a greater absorption coefficient at approx 520 nm due to the oscillation of the plasmonic electrons.
When you compare the graphs from magnetic nanofluids and plasmonic gold NPs, you can clearly see that the maximum peak wavelength is dramatically shifted in the latter compared to the former. While in the case for magnetic nanofluids, the wavelength is the same, indicating a larger portion of nanoparticles per volume. In the second graph you show, the NPs with dextran also has a shoulder that is red shifted, that would indicate that you have a population of partly aggregated NPs. However, have a look at http://ajp.asj-oa.am/816/1/03_Khordad.pdf
I hope this was helpful.
Best, Birgitte
Dear Birgitte,
thank you for such interesting information. For additional information in my picture black curve is bare magnetite nanoparticles, when uncovered they tend to agglomerate causing wider spectrum. the same concentration (gr/100ml) drives in big adsorption but narrower spectrum. we just use it as an indicator of monodispersity. see also realistic pic of that fluid, it is like a viskey :)
in general, magnetite nanoparticles do not exhibit strong plasmonic resonance.
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