I thought i could investigate the existence of water vapor onto CNT with TPD-MS machine. However, maybe the water vapor is desorbed from the material near 30 Celcius. As a result, before conducting TPD exp, perhaps the water vapor is gone and no peak appear. do you know another way to prove the existence of water vapor?
Well, first of all I would recommend TPD (or TDS) anyway, because if you have adsorbed water you should might have physically sorbed (broad peak at 100C) and chemisorbed peak between 200 and 300C . Also you can do Karl-Fisher analysis.
Why do you think the water will desorb at 30°C? I think TPD will work just fine.
Adsorption of water on CNTs is usually very weak (type III). If you flow a dry gas on your CNT, the moisture adsorbed (probably from environment) should easily desorb.
You can see some example of CNT-water adsorption isotherms in:
Ind. Eng. Chem. Res., 2008, 47 (9), pp 3170–3178
DOI: 10.1021/ie0713240
I attach their figure 4, which is H2O adsorption at 20ºC. Only panels (a-c) are CNTs. In the only one that adsorption occurs at low pressure (c) is because it was treated with nitric acid.
Anton Manakhov : I know TPD is a good apparatus. But as i know physically adsorbed water vapor is desorbed at ambient Temp. You can refer to Fernando reply
Peter Lodewyckx : Our TPD start at 40 Celcius. As Feranado said, experimentally water vapor is desorbed near 30 celcius
Fernando Vallejos-Burgos : Yes I saw several previous researches. What is the solution for detecting water vapor then? Our TPD start at 40 Celcius and also water vapor adsorption experiment is conducted in the other apparatus.
Well, then I guess the best you can do is to heat your sample gently in an air or gas stream with 0% humidity and analyse that gas stream for moisture content.
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