I have FTIR results for two kinds of zeolites and need to calculate Si/Al ratio.
I draw their diagrams and for each of them I calculate range of Si peak range (I chose an approximate peak range from the Transmittance-Wave Number Cm-1 graph for Si and Al (for example, Si peak happened at 550, I got from 530 to 565 and for Al from 420 to 487) and divided the band range of Si by Al)
Is it right? And how can I relate Si/Al area to Si/Al ratio?
Quantifications with spectroscopic methods is rather difficult. In principle you could use Lambert Beer Law to calculate concentrations if the extinction coefficient is known. However if you want to use FTIR results for the quantification of Si/Al ratio you have to measure at least one or better two other zeolites where both the Si and Al content is known to calibrate the peak areas. Furthermore transmittance measurements must be conducted with comparable conditions, elseway you may have to apply the Kubelka Munk function.
It is possible use frequency of skeletal vibration, measured FTIR by the use of KBr technique to determine Si/Al ratio, but ONLY for Faujasite-type zeolites. It was calibrated in the paper:
H. Fichtner-Schmittler and al.:Correlation between unit-cell parameter, skeletal stretching vibration and molar fraction of aluminum in faujasite type zeolites for Si:Al = 1.1 - 1000, Z. Phys. Chemie Leipzig, 271 (1990), 1, 69-79
Once again, only for X and Y type zeolites
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