Indian Journal of Materials Science

Research Article

Dynamics of Kaolinite-Urea Nanocomposites via Coupled DMSO-Hydroxyaluminum Oligomeric Intermediates

Table 4

Band assignments for the ATR-FTIR absorption bands.


Wavenumber (cm⁻¹)	Band assignment	Reference

3683, 3684, and 3693	OH stretch for the Si-O-Si bonds on the lower octahedral surfaces of kaolinite	[23, 24]

3618–3620	Inner hydroxyl groups between tetrahedral and octahedral kaolinite sheets	[24–26]

3650	In-phase symmetrical stretch due to kaolinite sheets	[25, 26]

3426	N-H out-phase stretch due to urea	[27, 28]

3340	In-phase N-H stretch due to urea	[28, 29]

3256	OH stretching for H bonding associated with urea-oligomer substitution within kaolinite interlayer spaces	[30, 31]

2970	CH stretch/dimeric OH stretch associated with DMSO decomposition during calcination to form paraformaldehyde complexes	[32, 33]

1738	C=O stretch due to intercalated urea	[32, 33]

1669	Free C=O stretch and free NH₂ bending	[34, 35]

1587	C-N stretch due to urea	[34, 35]

1461	In-phase CH₃ bending + scissoring C-N vibrations	[34, 35]

1438	S=O sulfate ester stretching	[32, 33]

1365	S=O sulfonyl stretching	[32, 33]

1202–1216	Amorphous SiO₂ associated with calcination	[36, 37]

1113–1149	Apical Si-O stretching	[23, 24, 26, 38]

1047	Si-O & Si-O-Al stretching due to the presence of DMSO in the kaolinite	[37]

1023–1027	In-phase Si-O planar stretching	[23, 24, 26, 39]

1001–997	Out-phase Si-O planar stretching and alternating Si-O & Al-O bonds	[23, 24, 26, 39, 40]

910–900	OH deformation of inner hydroxyl group due to Al-OH bending vibrations	[23, 24, 39, 41]

788–749	Al-O-Si asymmetric bending	[23, 24, 26, 39, 41]

777 and 434	OH stretch associated with a change from octahedral Al³⁺ in kaolinite to tetrahedral coordination in metakaolinite	[23, 24, 26, 39, 41]

525	Si-O-Al bending vibration for the Al³⁺ in the octahedral configuration	[42]