How can I measure BET analysis for TiO2 films? Is there any special preparation for it or not? I measured BET of TiO2 films , but there was no data? what should I do?
Dear Le Phuc Nguyen ,It means I am getting negative "adsorbed quantities" in the BET adsorption isotherm. my sample is TNT composite on Ti substrate.
Assuming that there was no leakage in the system, while working under vacuum, and that temperature was kept constant, and that your solid system was pre-cleaned and pre-dried (all water and other organic stuff were removed),
and to our own experience, even such assumptions are carefully met,
the relative surface area per gram TiO2 powder is not high (not much higher than 100 m2/g. In other highly porous solids, such activated carbon it can reach above 1000m2/g).
Therefore, in TiO2 study any technical, instrumental or human error will show very high error in the results, and you may end up with no results.
BET can be done by home made set-up or by commercial (more accurate) equipment.
Assuming you have degased your sample for sufficient time and no significant weighing error ,
1) check instrument leakage
2) due to very low surface area you may want to analyze sample in high pressure (use for microporous materials)
3) Your may get different value with different analysis gas. Nitrogen is not very much suitable (may give lots of error and have to repeat anaylysis for atleast 5 times in low surface area type materials ) Kr is most suitable .
Hope this may help.
I have experience negative values from commercial instruments when an insufficient mass of the sample was used. BET instruments have a minimum area required for an accurate measurement. When analyzing materials with relatively low surface area more material may be required to meet the minimum instrument sensitivity for surface area.