Hi
I am studying about porous carbon materials for using Li-S battery.
I'm using teflon to remove silica from porous carbon & SiO2 particles.
I used to teflon instead of NaOH when etching the silica.
But, there are some questions about the materials that comes out of pyrolysis in teflon.
Teflon is pyrolyzed to C4F8 (g) at 350~450 ºC. (in N2 gas)
C4F8 + 2SiO2 --> 2SiF4 (g) + 2CO2 (g) + 2C (major)
C4F8 + SiO2 --> SiF4 (g) + 2COF2 (g) + 2C (minor)
I believe that SiO2 is removed and COF2 is deposited on carbon, resulting in F-doped carbon.
I think that source of F-doping is COF2 (g).
But, I have not found the exact F-doping mechanism.
Help me. thank you
Lee,
The best way to confirm your hypothesis is to run an experiment and check the XPS spectrum of the resultant carbon. If F element is present, you should see a peak at ~689 eV corresponding to F 1s electrons. Further deconvolution of this peak should tell you if the F element is from the doped F atoms or not.
Hello Lee,
Teflon is not carbonizing polymer you are not going to get a lot of carbon out of it, it will be mostly decomposed to volatile organic compounds. Most of the carbon you are going to get from it is carbon from decomposition compounds trapped in the pores of porous carbon and silica. However fluorocontaining compounds formed during pyrloysis can functionalize the existing porous carbon in conditions of high temperature. Exact mechanism is obviously very complicated due to complexity of the system - very high temperature, porous materials, functional groups, mean time of the contact of volatile compounds with carbon. You will have a lot of radicals there which can directly react with functional group on the carbon surface. If you want to have some insights in the process I suggest you to look into the carbonization of PVDF since it s closest polymer to teflon. Carbonization of PVDF was extensively studied.
In my experinece on PVDF carbonization fluorine containing carbon is formed however in case of mix of teflon and porpous carbon the amount of fluorine is not expected to be big since teflon is not carbonizing polymer and decomposes almost completely, especially if carrier gas flow rate will be big enough to flush the system.
Olga
Tianyu Liu
Thank you.
I measured the XPS and found that there was an F peak and I could see the C-F bond in the carbon peak.
I also confirmed C-F bonds in FT-IR..
Olga Naboka
Thank you for your answer.
(My heating temperature of teflon is 900 degrees.)
"However fluorocontaining compounds formed during pyrloysis can functionalize the existing porous carbon in conditions of high temperature."
this sentence you said, I think that fluorine compounds can dope carbon at high temperatures.
How did you think like this???
Roland Pawelke
Hi Roland.
Thank you for your answer.
I confirmed the presence of F atoms through XPS and EDS mapping.
The content of F from 1.29 to 1.81 was confirmed by XPS.
I think that this is obviously an F atoms in the carbon particles...
and I confirmed the presence of C-F bond through FT-IR..
I think the chemical reaction you told me is right.
Let me talk to my professor.
Thanks.
Hi Lee,
The meaning "high temperature" does not mean exactly 900 C, by the way you did not mention that temperature in your question. The functionalization of carbon with fluorine will take place much earlier than 900 C, I logically assume, at the stage of formation of volatile compounds (350-500 C). Unless you are running flash pyrolysis, I doubt that though. Also those small amounts of carbon originating from teflon can be enriched with F due to the nature of precursor. Since they will be coating the surface of primary porous carbon you will not be able to tell whether fluorine doped the carbon or fluorine was originally in carbon structure through the decomposition of fluorine containing organics. XPS will show you just the presence of element and binding energies, pointing to C-F bonds but it will not tell you the history of your material. I doubt that the mechanism of F incorporation in your carbon is simple process, the process is very complex and can not be described with simple reaction from organic chemistry text book.
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