I synthesized Pani (Pani was synthesized by in-situ chemical oxidative polymerization of 0.1 M double distillated aniline in 1M
aqueous HCl solution and slowly dropwise adding of APS
solution with an equal molar ratio to aniline. After 3 h, a good degree of polymerization with dark green color was recovered. The solution was filtered, washed repeatedly with 1 M HCl and
dried under the relative vacuum for 24-36 h at 55 C. The
obtained product was a conductive ES form of Pani. The powder was stirred for 12 h in 0.1 M aqueous solution of ammonia, then washed with deionized water several times and finally dried under the) relative vacuum for 24-36 h at 55 C until to obtain Pani
emeraldine base (EB). 0.2 g of pure Pani was separately mixed with CSA by grinding in a smooth agate mortar. After that any mixtures were separately added in 20 ml DMSO to prepare the conducting solution. After the UV analysis, I reached the following results. Graph (a) is belong to doped Pani and graph (b) is belong to undoped (1) and doped(2) Pani with CSA. These two graphs belong to one solution but examined at two different times. According to the graphs and the place of peaks I am not sure that if I really reach emeraldine salt or not. Also, I have an FTIR analysis but it couldn't ensure me that the result of doping is emeraldine salt. I will be glad to receive some guide.
Also is it possible the suspension of PANI becomes undoped during a period of time for example after 4 months?
Naghmeh Hashemi, sorry, can you first send the spectra in jpg or pdf format? I can not open *.OPJ (what format is that?)
Thanks for exchanging *.OPJ by *.pdf, I was able to open. I have several comments:
1) what doped PAni does graph (a) represent? it does not look at all like doped PAni.
(2) to follow
2) As so often, I see people are still using HCl as counterion for synthesis, then try to dedope and redope. My rcommendation is to use exactly that counterion, that doping acid you want to have PAni finally doped with.
Why?
- HCl is not only doping PAni, but also makes side reactions resulting in covalent benzene ring / Cl bonds
- dedoping is incomplete, one ammonia washing step is by far not sufficient, you need several steps ammonia / neutralize with water, followed by ammonia / neutralize with water and so on
- even then, even after "complete" dedoping, elemental analysis will show Cl which is covalently bound.
(3) to follow
3) If your graph b) curve (1) really shows what you call "dedoped", then you can see it is not pure dedoped PAni, that should look as shown here:
Data PAni UV-VIS spectra
on page 3Doping of dedoped PAni (which in your case obviously was not fully dedoped) in powder form by milling it with CSA powder does not work, you can see that your curve (2) in graph b) is not significantly different from curve (1). A doped PAni must look like here
Data PAni UV-VIS spectra
on page 2(4) to follow
4) why don't you synthesize PAni from aniline (no need to distill) in presence of 1 M CSA? why do you want to take CSA? I suggest to use p-toluene sulfonic acid, that results in the most stable doped PAni and will deliver highest conductivity.
For synthesis, it is not sufficient to "slowly add" the oxidant, but to make sure that the temperature does not increase by more than 1 degree, starting at between 3 to 5 °C. You did not report having used a cooled rection mixture so I assume you did not use, but my experience says you should use an ice bath and control temperature very well!
Your welcome dear Prof. Wessling
The graph (a) is the UV analysis of the same solution as graph (b) at the different time.
I want to use the doped form of Pani as a gas sensor and I want to dope it with CSA. I used an ice bath for controlling the reaction temperature. After the dedoping I reach a dark blue suspension and after milling with CSA the suspension become dark green.
Could it be a partial doped Pani?
yes, it will be partially doped PAni; but again, just believe me: don't make the detour by polymerizing with HCl --> dedoping --> redoping with CSA by milling (not good!);
instead of this detour, just run the polymerisation directly with CSA (and also pTs would wonderfully work as dopant in gas sensor, but as you like)
Dear Prof Wessling
Thank you so much for your guidance and complete answer.
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