I need to take some ir spectra of activated carbon samples. I found a problem using KBr/carbon pellets beacuse of a strong water absorption bands present. Drying of the powders (110 oC in air or 80 oC under vacuum overnight) doesn't help....
Is there any other crystal window I could use in the transmission mode? I was thinking about Cd/Se, is it a good choice?
What exactly did you do, dry the carbon powders and then pressed your pellets? I would expect that enough water for a nice fat band will be adsorbed back into the sample, especially if you grind by hand in a mortar.
And if you are sure you kept the water out, might it not be the C-OH bonds you are seeing?
Dear Claudia,my procedure is: 1. Grinding the carbon powders with KBr, and drying the way I wrote previously. 2. Then I press the powders into pellets in the hydraulic press (5 tons, 3 min under vacuum from the vacuum pump connected to my die).3. Then,as quickly as possible I take the IR spectra. The OH water bands are far to high to be related with my carbon sample. So far, my spectrophotometer hasn't been connected to the inert gas. Is it possible that water comes into my sample during the measurement in ambient atmosphere?
Dear Magdalena!!!Your task is very interesting, but I couldn't understand you written OH band or as(H-O-H) band. In last case you should see absorption at 1640 cm-1.For separation of carbon hydroxyl from ( you nothing say what carbon you used) KBrhydroxyl I recomend you to spray carbon emulsion (solution-ether or CCl4) on the fluorite monocrystall window very tin layer and do IR spectra. I hope you understand me.
Or simply Nujol mull on dried carbon powders? It will let you see differences to KBR-related water bands, though it makes the fingerprint region totally useless.
Mrs/Miss Skunik-Nuckowska,
The absorption of H2O occurs when you keep KBr-powder on air at r.t. You should dry KBr at 120oC for 2h and then cooling in inert atmosphere before KBr-pelletts preparation and measurements.
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