I'm getting a low BET surface area if I'm not degassing my UNadsorbed sample. For the adsorbed sample, I'm getting a more or less same low BET surface area if I skip the degassing step. How will I know if after adsorption BET values are correct or not if I skip the degassing process? since both the adsorbed and unadsorbed samples are giving very low BET values if the degassing step is skipped.
Hi dear,
the desgassing step is very important previous to BET analysis. So, I suggest you
keep this step. Did you verify the calibration curve of the equipment where you are performing the experiment? Please, check it.
On the other hand, what is “low surface area”? I have had values of 34 and 30 m2/g for zeolites. it could be normal for your sample. Please, check the bibliography.
and Finally, you could try in other equipment for comparison. or another program for determination of the surface area.
With kind regards,
Julián.
Your should degas your sample if you want to know the correct 'BET surface area' of your solid.
Saying that, your sample may have a low surface area. It seems that the char is not activated so this is expected.
If you don't degas, there will be more gas adsorbed and blocking the pores that may exist in your sample.
It is always better to check and understand the whole adsorption isotherm and start the comparison from here instead of just focusing all your attention in the BET surface area.
What I would recommend is that you degass (vacuum + temperature) your "clean" (UNadsorbed) sample and then get the BET surface area of the "clean" (UNadsorbed) sample.
Then, previous to adsorbing H2S, you need to degass (vacuum + temperature) your "clean" (UNadsorbed) sample in order to have the sample in the same state as when you determine BET.At this point you perform your adsorption process.
Finally, I would determine BET area of your adsorbed sample straight after the adsorption process without degassing or using a very light degassing procedure (e.g. only vacuum) in order to eliminate weakly adsorbed species ( in the case you are chemisorbing H2S)
Hi there,
I highly suggest you to outgas your sample before BET measurement in order to get the correct number of the surface area. According to your topic, it is "biochar" I guess it consists of a lot of micropores, you probably can try to measure the surface area with CO2 at 273K as well.
Regards
Hey, you have to degass. Try low temperatures, for longer time. I also suggest you to do FTIR of your sample before and after the degassing process, to be sure of what is happening to your sample. Also, be aware of using at least the minimum weight of sample required to reach the minimun sensibility of gas adsorbed by your equipment. And at last, check your isotherm, poor degassing sometimes give you a not closed isotherm for pressures smaller than 0.3, at this point no hysteresis can be observed for samples behaving well.