what is the diffrenece between activated carbon prepared under inert gas and under oxygene gas ??
i prepared two activated carbon with the same procedure, i changed just nitrogen gas by oxygen gas. The results, the surface area of AC prepared using O2 is higer compared to AC prepared using N2 and also adsorption test of Methylene Blue conferme the result obtained.
Thanks in Advance
Dear Mohamed,
Activated carbon can be produced by one of the following processes:
Physical activation: The source material is developed into activated carbons using hot gases. Air is then introduced to burn out the gasses, creating a graded, screened and de-dusted form of activated carbon. This is generally done by using one or a combination of the following processes:Carbonization: Material with carbon content is pyrolyzed at temperatures in the range 600–900 °C, usually in inert atmosphere with gases like argon or nitrogen
Activation/Oxidation: Raw material or carbonized material is exposed to oxidizing atmospheres (oxygen or steam) at temperatures above 250 °C, usually in the temperature range of 600–1200 °C.
The above two methods are generally used for the preparation of activated carbon. The procedure you used belongs to the activation/oxidation method which yields the desired activated carbon.
http://sphinxsai.com/ctvol4/ct_pdf_vol_4/ct=10%20%20(859--864).pdf
https://en.wikipedia.org/wiki/Activated_carbon
Hoping this will be helpful,
Rafik
Oxygen oxidized sample must contain noticeable amount of oxygen groups and structure defects on its surface. O2 oxidation also leads to carbon burning and significant weight loss.
The better texture properties obtained for the activated carbon prepared by physical activation with oxygen or air instead of nitrogen are related to the gasification of organic matter and tar, which are blocking the incipient porosity of the carbonized product. In physical activation, the activating agent should be a gas with certain oxidizing capacity in order to remove tar and other organic byproducts generated during the previous carbonization step. By removing these materials, the incipient porosity in the carbonized product can be completely developed, thus obtaining activated carbons with large surface areas and different surface chemistries. The latter strongly depends on the activating agent (carbon dioxide, air or steam). Regarding your preparations, nitrogen as a rule is not able to oxidize the tar and the organic matter blocking the pores, so it is not usually used as activating agent when preparing activated carbons by physical activation. If you need some literature about the preparation of activation carbons by physical activation, do not hesitate to ask me.
I hope this will be helpful for you.
Best regards.
Adrián B. Bogeat