Adsorption, Modeling, Thermodynamic, and Kinetic Studies of Methyl Red Removal from Textile-Polluted Water Using Natural and Purified Organic Matter Rich Clays as Low-Cost Adsorbent

Table 5

Group frequencies (cm⁻¹) and functional groups of the methyl red.

Group frequency (cm^−1)	Functional group
3570–3200	Hydroxy group, H-bonded O-H stretch
3400–3200	Normal “polymeric” O-H stretch
3400–3380	Primary amino: aliphatic primary amine N-H stretch
3000–2800	Simple C-H stretching vibrations for saturated aliphatic species
2820–2780	Methyl-amino, N-CH3, C-H stretch
1780–1714	Carboxylic acid (–COOH)
1630–1575	Open-chain azo (-N = N-)
1650–1550	Secondary amine, NH bend (>N-H)
1680–1601	Conjugated C = C, C = C stretch vibration
1360–1280	Aromatic secondary and tertiary amine CN stretch
1210–1150	Tertiary amino compound
1151–1070	C-O-C stretch, alkyl-substituted ether
900–670	Aromatic C-H out of plane bend
680–610	Alkyne C-H bend