Two micropore each having radius r will have a surface area of 2pi*r2h (if h is the depth of the pore).Instead of that one mesopore have a radius of 2r. Then its surface area will be pi(2r2)h = 4pir2h. So mesopore should have more surface area and pore volume than micropore.
Please reply.
Since micropores are smaller a particle can have much more micropores then mesopores.
Dear Debarati,
The key part you overlooked is the number of pores you can fit into a certain volume. As you can see in the graph attached the number of pores that fit into a 1m^3 in a dense packing, quickly goes down with increasing radius. The surface area scales down with the number of pores, although the surface area of a single pore goes up with the radius.
I have all pores are in the mesopore region (4-12 nm),with increasing pore diameter pore volume increases and as a result surface area increases.Surface area we report per gm of the sample.
So it is possible due to the presence of larger pore per gm of sample pore volume is more and surface area is more.Please see the attached file.
which probe molecule/method was used to determine pore volume? The data look like the pores are to small for for the probe molecules
I am doing N2 adsorption.
Pore size distribution has been calculated from BJH desorption.
Hi Debarati
Micropores (pore diameter < 2 nm)
Mesopores (pore diameter between 2-50 nm)
Thus, all three of your samples should be classified as mesoporous.
As Breynaert points out, specific surface areas will generally increase with decreasing pore diameters, and indeed microporous materials such as metal organic frameworks can have extremely high specific surface areas (~5000-7000 m2/g in some cases). Surface area per pore times the number of pores per unit volume of sample is the important thing here.
I have looked at the BJH pore size distributions you posted. Your cumulative pore volumes increase quite dramatically as the pore diameter increases. Thus, it would appear in your 3 samples that the number of pores probably increases with increasing pore diameter, which would explain why the specific surface area of your samples also increases with pore diameter.
What are your samples and what is the relationship between the 3 samples? That information might be useful in explaining the trend in your data.
Best
Geoff
As Breynaert Eric and Geoffrey I.N. Waterhouse point out, it should be note that mean pore diameter has no direct relationship with the total surface area, however, for a given porosity or some ordered porous material with same pore volume.
The proposal of Mr. Geoffrey I.N. Waterhouse is very useful to your experiment.
While calculating the surface ares, materials particle/crystalite size is also important. Smaller the particle size, larger the number of particles per gram of sample and so higher external surface are which can be calculated from t-plot method.
Hello!
Hope you are doing well during the pandemic.
I think, you have a misunderstanding of the terms "Specific Surface Area" and "Surface Area".
The "Surface Area" will be always higher for the particles with a higher radius.
On the other hand, the "Specific Surface Area" (SSA) is the total "Surface Area" of a material per unit of mass (with units of m^2/kg or m^2/g) or bulk volume (units of m^2/m^3 or m^−1). That means Specific surface area is (Total Surface Area)/Volume or (Total surface area)/Mass.
Hence, if you have a given fixed volume (or mass) and are making a large particle smaller, the "Specific Surface Area" will be higher compared to the larger particle, becasue your number of particles increases (hence, total surface area also increase).
But if you compare the "Surface Area" of ONE large particle with ONE small particle, it will be always higher for the large one.
Here, you are comparing ONE mesopore with ONE micropore, so definitely ONE mesopore should have more surface area and pore volume than ONE micropore. But if you make ONE mesopore structure to a micropore structure keeping the mass or volume the same, it will have more than one micropore, and (total surface area)/volume will be higher for the micropores.
Hence, your question is wrong. It should be "Why the microporous sample is having more "Specific surface area" (SSA) than mesoporous one?"
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