I'm trying to produce silver nanoparticles using plant extract, but I didn't observe the expected peak in the UV-Vis spectrum between 380-420 nm, where silver nanoparticles typically appear. After centrifugation, I obtained pellets suspected to contain AgNPs. Based on the provided UV-Vis spectrum, can it be inferred that AgNPs have indeed formed? Where might the AgNP peak be located, and is it possible that it's shifted outside the usual range?
Additionally, both my extract and the silver nanoparticles have a pH of 4-5. I'm curious about how I can adjust the conditions to make them more alkaline and optimize my "green" synthesis.
I would greatly appreciate any insights or advice on these questions. Thank you in advance for your help.
Michelle Darmawan
Judging by the UV spectra, you do not have silver nanoparticles. The spectrum is that of silver nitrate and extract. However, extract molecules can coat the nanoparticles and block electromagnetic absorption of light. Therefore, it is advisable to do X-ray diffraction of your sample.
"silver nanoparticles have a pH of 4-5". You spelled this phrase incorrectly. It was necessary to write “The dispersed system of possible silver nanoparticles has pH = 4-5.” Create pH with KOH. See articles
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Michelle Darmawan Seems you may have no reducing agent in your plant extract or you're not reducing under alkaline conditions. Normally the silver diammine complex is used for reduction as there is more control here. The alkaline conditions are produced by ammoniacal solutions. Further information in this webinar (free registration required):
Silver colloids and invisible ink
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W150902SilverColloidInvisibleInk.html
Note that the silver on the surface of your (nano)particles is in the +1 oxidation state. That is, Ag+ not Ag0. Easily shown by ESCA/XPS. This silver ion is the active bactericide not silver metal.
thanks to others' insights you have to consider that extracts driven by natural sources might contain unwanted materials in themselves the reason for that shift might be that but not that much shift!!!! I have experienced the same thing for the reduction of copper via plant extracts consider purification on top of that as Yuri Mirgorod said UV is not a proper way to judge since extracts might have different behaviors they might coat the surface of the desired particle
Thank you for your explanation sir Yuri Mirgorod Alan F Rawle Sina Sheidaei Since the quantity of my extract is four times the volume of AgNO3, it could potentially coat the AgNP absorption. Therefore, should I just focus on observing existing color changes to determine the optimum conditions for this synthesis? (I am optimizing the plant extract and AgNO3 concentration)
Michelle Darmawan
By changing the concentration of the extract you should get an absorption band in the visible part of the spectrum. It indicates the interaction of electromagnetic radiation with plasmons of silver nanoparticles.
Thank you very much for the advice sir Yuri Mirgorod
If you don't mind, may I ask again? Which color indicates that AgNPs are synthesized optimally? Is the closer to dark gray brown (D&E) a good color or does it indicate aggregation of AgNP particles?
Michelle Darmawan
I repeat. Your extract may contain dye molecules containing chromophreic functional groups. They may mask plasmonic uptake. Therefore, in addition to color changes, the particle size in different test tubes is determined by the XRD, DLS, and TEM methods. A change in color is not definitive proof that silver nanoparticles have been produced in the extract. If the reducing agent was hydrazine hydrate, then a color change may be evidence of the production of nanoparticles.
Thank you for your feedback again, sir Yuri Mirgorod . I have carried out characterization using DLS, and the results indicate polydisperse particles with a z-average of around 500 nm and a polydispersity index (PI) of 0.600. The distribution shows two peaks with means at 150 nm and 1300 nm.
Based on these results, can it be confirmed that AgNPs have been formed?
Michelle Darmawan
Nanoparticles are produced to exploit their size effect (plasmon resonance, paramagnetic properties...). At sizes larger than 100 nm, size effects disappear. DLS measures the hydrodynamic radius of the entire particle with an adsorbed layer of extract molecules. Therefore, a ХRD is needed that will determine the solid part of the nanoparticle.
Please make your plant extract alkaline first (pH~10). Then add dilute silver nitrate solution to this plant extract. If you want to synthesize AgNPs at room temperature, then you can use more alkali. Before taking UV spectra you have to wash the particles properly to remove excess plant extract and alkali.
Thank you for your answer, Sir Yuri Mirgorod and Sir M. Ahasanur Rabbi. I will try to carry out the suggestions you have given.