I have attached file with 2 sorption isotherms for cobalt ferrites. I want to know how to classify these them among standard IUPAC isotherms (Type I to Type VI). Is it necessary it has to go to one of these? How to exactly go for the analysis?
Dear Disha
I have seen the attached file and i believe that multilayer adsorption is occuring initally, the deviation of the isotherm from Type III might be due to condensation of the gas within the pores of your compound.
Hi Disha,
I suggest you fit your experimental data for the isotherms to the different adsorption models. You can then observe which models produce the best fits.
I hope this helps.
Hi Adib
Can you give me some suggestion how to do it? I don't have any idea about it?
Figure 1 is a Type IV isotherm. A plateau is reached at a relative pressure of about 0.9. After this there is further condensation leading to another upswing in the isotherm. You would be advised to take the pore volumen micro + meso from the amount adsorbed on the desorption branch at a relative pressure of 0.96. The PSD from the desorption branch will probably show a bimodal distribution with a well defined peak at a diameter of about 3.7 nm due to the sudden closure of the hystersis loop. This pore width is an artefact and only points to the presence of narrower mesopores. For this reason some workers prefer to use the adsorption branch.
In Figure 2 the isotherm is also of Type IV due to the mesoporous nature, however, the plateau is not so well defined, leading to a further upswing at high relative pressure due to the presence of wider mesopores and macropores. In this case the peak at 3.7 nm from the PSD curve of the desorption branch will be even more evident since the sudden closure at a relative pressure close to 0.42 is even more pronounced.
Best regards,
Malcolm
Dr. Yates
Thanks for taking some time out to answer. I have attached the corresponding BJH plot also in the file. For Fig 1, the BJH plot shows maxima from 2.5 nm to 3.7 nm.
Dear Disha, first at all, I recommend you make the isotherms with more results at low pressure. And is important to understand the experiment know the nature of samples. You have normal type IV isotherms whit a loop H2b. In this samples BJH applied to the adsorption branch is a correct model to analyses the mesoporosity. But remember the origin of this model. The thermodynamic rules are deduced for macroscopic liquid and solid and you applied in different conditions, whit a small numbers of particles. The model supposes a cylindrical porosity, and your samples have probably irregular porosity. The model and the reality are different. The mathematical equations used in the model is very sensitive to small errors. You have two peack in your pore distributions. Really is only one. And remember, BJH is very approximate.
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