Based on FTIR and XPs analysis, how to confirm that the obtained carbon dots (CDs) has (-COOH). In which form these groups can present in our material where C-C, C-N, O-H, C-H, C=O, C-O and C-O-C were obtained from both analysis mentioned above.
I shall confine my contribution to confirmation of the presence of a carboxylic acid group (-COOH) in an organic compound by FTIR spectrum:
1) Broad band for O–H stretch @ 3300-2500 cm-1
2) Sharp band for C=O stretch @ 1760-1690 cm-1
3) C–O stretch @ 1320-1210 cm-1
4) O–H bend @ 1440-1395 cm-1 and 950-910 cm-1
Note that the 1440-1395 band may coincide with C–H bending bands in the same region but this is not a big problem.
FTIR and XPS. Examples:
10.1039/c6ra22658b
10.1016/j.apsusc.2016.02.166
In XPS when you perform the analysis of the regions you must take into account the correspondence, that is, if in the C 1s the COOH species appears, in the O 1s this must also be present, otherwise the COOH species does not exist, unless there is overlap of species in one of the two peaks.
In any case, the COOH species in C 1s appears around 289eV. In the O1s it appears twice, in 531.8eV (COOH) and 533.4eV (COOH).
This article can help you:
https://doi.org/10.1002/sia.3831
Of course the FTIR Analysis is the actual method of identification of functional group. But additionally, What I did with my Quantum Dots were also interesting. Just add Sodium Carbonate to your test solution and observe the CO2 bubbles. The formation of CO2 confirms the COOH functional group. even small quantity of COOH group will lead to formation of tiny condensed air bubbles on test tube surface.
As Nizar Matar mentioned above Broad band for O–H stretch @ 3300-2500 cm-1
should appear in carboxylic acids, However, I tried several times for stearic acid which should have the C=O and O-H, only C=O appeared and NO O-H band. How can we explain this situation? Any help please!!
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