The curve yielded the features of Type 1 isotherm but the adsorption capacity continues to increase with an increase in relative pressure. So is my assumption correct regarding the type of isotherm? The curvature of desorption branch differs from that of adsorption, so can it be assumed as the presence of hysteresis loop. I have read that the closure point of the hysteresis loop is approximately at p/po=0.42 but in the file, it's seen that desorption branch coincides with the adsorption branch at a very low relative pressure. What is the reason behind that?
I have attached the file below.
There is a good discussion of "low pressure hysteresis" similar to what you describe written here. The following is taken from the paper in the link.
"As described above, the explanation for this phenomenon is
very scarce in the literature when using N2 adsorption at 77 K
on carbon materials. Traditionally, these observations have
been attributed to a real physical phenomenon, i.e., irreversible
uptake, due to the presence of pores of the same width of the
adsorbate molecule and/or to swelling of the nonrigid porous
structure of the activated carbon."
Article Low-Pressure Hysteresis in Adsorption: An Artifact?
The observed hysteresis may be due to strong adsorbate-adsorbent interaction and hence all the adsorbed gas is not desorbed and results in hysteresis. If you have calculated the pore size distribution, You may also be getting the pore size in the mesoporous region in addition to the microporous region.
Hello Sir
I have used 28 mg of the sample ( i.e activated carbon) and it was degassed for 5 hrs at 180oC.
That's indeed a strange shape. The hysteresis loops should indeed close at 0.42 with N2. What kind of sample do you measure ? For example MOF can give "unconventional" hysteresis llops because they are modified by the adsorption. See for example http://pubs.rsc.org.accesdistant.upmc.fr/-/content/articlepdf/2014/cc/c4cc00524d.
Hello
My sample is activated carbon.I have taken 28 mg for analysis and degassed it for 5 hrs at 180 o C.
The link is not opening
There is a good discussion of "low pressure hysteresis" similar to what you describe written here. The following is taken from the paper in the link.
"As described above, the explanation for this phenomenon is
very scarce in the literature when using N2 adsorption at 77 K
on carbon materials. Traditionally, these observations have
been attributed to a real physical phenomenon, i.e., irreversible
uptake, due to the presence of pores of the same width of the
adsorbate molecule and/or to swelling of the nonrigid porous
structure of the activated carbon."
Article Low-Pressure Hysteresis in Adsorption: An Artifact?
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