. 2024 Oct 1;14(10):211. doi: 10.3390/membranes14100211

Table 4.

Spectral features and corresponding wavelengths in SPP membranes.

Wavelength (cm⁻¹)	Functional Group/Bond	Observation/Description
1020 cm⁻¹	C-O-C stretching vibration	Attributable to ether groups in the membrane components [32,39,46].
1130 cm⁻¹	C-C bond	Stretching vibration in the membrane constituents [32,39,46].
1416 cm⁻¹	Carboxylate groups	Stretching vibration indicates the presence of carboxylate in the membrane [32,39,46].
1630 cm⁻¹	Carbonyl (C=O) in SPP S-MMT blends	Red shift due to hydrogen bonding between OH groups in PVA and C=O groups in PEBAX. Peak intensity increases with S-MMT content.
1650 cm⁻¹	Carbonyl (C=O) stretching in pure PEBAX	Indicates a minor shift when compared to the spectrum of PEBAX with hydrogen bonding interactions [1].
1657 cm⁻¹	Amide groups of PEBAX	Reference for pure PEBAX. Overlaps in the presence of S-MMT, suggesting interaction with hydroxyl groups in sulfonic acid [1].
1730–1735 cm⁻¹	Ester carbonyl (-COO-) groups	Appearance due to esterification of carboxyl groups in SSA with hydroxyl groups in PVA, indicating the presence of SSA-modified PVA [32,39,46].
2940 cm⁻¹	C-H stretching vibration	Attributed to stretching vibrations of the C-H groups present in the membrane components [32,39,46].
3150 cm⁻¹	O-H stretching vibration	Represents stretching vibrations of O-H groups, which is indicative of hydroxyl content in the membranes [32,39,46].