I determined the surface area of CeO2 modified with MgO as 1 m2/g. The isotherms showed significant hysteresis loop (type IV), indicating mesoporous structure, which is strange to me. Can anyone please explain why I am getting hysteresis at such small BET surface area of 1 m2/g?
Also, the pore size is significantly large, about 15 nm.
Dear Dailami,
It is difficult to discuss about your results in a proper way without having the sorption isotherm. However, as the specific surface area is so small, to get a proper estimation it would be better to use argon or krypton instead of nitrogen.
About the hysteresis loop, it can originate from different considerations, the first one being the limitations of the measurements, due to the very low SSA. If the measurements are ok, the hysteresis loop could be due to some porosity, either in the material particles, or between these particles. Again, to decide between these options, the sorption isotherm would help.
It must be emphasized that, because of the very small SSA, the extent of the porosity should be very limited, and the sorption likely takes place in interparticular voids of your material.
I could tell you more if you could show me the sorption isotherm.
I hope it helps,
Take care,
Philippe
I would say, it is very hard to prepare a material without a loop of some kind. Alumina retains the loop until 1200°C with SA of ~1 m2/g. Second, SA and pore volume are generally independent. For any value of SA you can find a material with any (reliable) pore volume.
Dear all,
Thanks for the good responses. I was off communication due to a fault my device developed during the last week.
Thanks Maxim.
Thank you Dr. Trens. I would share the sorption isotherms to gain more clarification of what actually is happening with my materials
A solid with such low surface area is either non porous (the surface area being derived from merely external area of powder particles), or has nothing more than just a very few huge pores. If it really has any significant volume of 15nm pores, the surface area would be much higher. Non-porous solids give rise to type II isotherms with no hysteresis whatsoever - except that which is associated with interparticle voids.
Dear Dailami,
First of all, check the measurement error of your sorptometer equipment. In the case of N2, this error is generally close to 1 m2/g. In this case, your result is not valid.
Second: What is the need for physical surface data for a material with such a low SSA? The above, assuming you are synthesizing a catalyst or absorbent.
The SSA could be correct, but first explain better why you need to understand in detail the physical properties of this material (for example: used sample vs fresh sample, etc.)
Regards,
Gonzalo Aguila.
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