I am preparing AgNPs/PANI nanocomposite. I can see the brown yellow color of AgNPs during synthesis and the green-violet color of PANI (emeraldine) after precipitation with ethanol. I can also see a pure uniform silver metal after ethanol precipitation. I can detect the UV-Vis band for AgNPs in aqueous solution but I cannot detect a UV-Vis band for emeraldine either in ethanol or in water.
It may be due to the full surface coating on PANI with Ag NPs.
Did you checked with TEM?
You will find transmittance and reflectance from the UV-vis spectroscopy. I think if these two factors are much more, the absorbance peaks are minimal. If this will possible the composite you synthesis has wide applications e.g.skin protecting layer from sun burn.
Thank you Sunil Dutt. I have not performed the TEM yet but I'll do of course.
Dear Manal,
PANI is insoluble in water as well as in alcohols. Therefore, you can see only the band of plasmonic absorption band of Ag-NPS in these solvents. If you would like to see also the PANI bands, you must use other solvents such as NMP (to see the Q-band at about 630 nm) or DMSO in acidic environment in order to see the band of polarons at about 900 nm.
Best regards, Jiri V.
Dear Jiri
Thanks a lot for the valuable answer.
* Is there a solvent for all the oxidation products of aniline in addition to AgNPs?
* Since PANI is water insoluble, why I could not see the green-violet color clearly in the aqueous medium but I could see it after treatment with ethanol? Is it possible that the color of the AgNPs hindered the appearance of the green-violet PANI color. This could be explained in terms of the appearance of pure silver metallic disc after precipitation with ethanol.
* I'll try the solvents you mentions and record the bands starting from 1100 to 200 nm.
Thanks again and sorry for my many questions.
Dear Manal,
Ag-NPS form a sol in any solvent provided that they are stabilized by a layer of positive or negative ions adsorbed on their layers. Tpical Ag-NPS of dimensions around 10 nm show strong plasmonic extinction band around 400 nm and, upon aggregation induced by another adsorbate such as conjugated polymer this band shifts to above 500 nm or more far (see. for example Dammer et al., Phys.Chem.Chem.Phys. 2009, pp. 5455-5461, or Mat.Chem.Phys. 2009, Vol. 115(1), pp 352-360.
The color of your alcohol solution most probably originates from oligomeric side products formed in the PANI synthesis. You can extract them by the almost end-less repeated treatment with acetone.
Best regards, Jiri
If your product is a solid, I think it is better for your to use UV-Vis diffuse reflectance technique. Or some time the bands of both AgNPs and PANi are overlap on each other due to similar wavelength.
Dear Eldewik, I think that overlapping of bands of both material AgNPs and PANI are not possible. Because PANI gives more than two peaks of absorbance which was not possible with AgNP.
MANAL, I am also suggest you to measure FTIR measurement with Raman Spectroscopy measurement. You will find structural characterization from these two methods as well as cause of absence of peaks of PANI.
Can be obtained by making solution in an acid or any suitable solvent.
Please try first to check the degree of protonation...either direct by spectroscopy or by conductivity measurements.
I agree with Dr. Ghosh,
High molecular weight PANI is not soluble in ethanol and nothing in water. You try with NMP/DMF solvent and check UV.
PAni is insoluble in anything (please check my publications here o RG), you should find an appropriate *dispersion* medium für your Ag-PAni NP, then you will also find some UV-Vis bands for PAni, but anyway, the amount of Ag will be much higher than the PAni, so maybe PAni bads are hidden in the Ag background?
Thank you all for your valued answers, for your time and for transferring your expertise not only to me but also to every one followed the question. It is really a very good discussion. Thanks to: Sunil Dutt, Rinkesh Bhatt, Jiri Vohlidal, Abdussallam Eldewik, Dr. S. Kalidhasan, Uday Chand Ghosh, Mircea Chipara, Asit Baran Samui, Bernhard Wessling, Cun Li, and Daniela Gogova.
If the composite is conducting, the bands suffer from relaxation, and you have them as a wavy baseline
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