Table 2 FTIR spectra and their corresponding functional group

3000–3600

–OH stretching (Haeldermans et al. 2019)

2800–2960

Asymmetric C–H stretching (Ma et al. 2022)

2200–2300

Triple bonding such as nitriles (C≡N) and alkynes (C≡C) (Larkin 2011)

1550–1650

Aromatic ring C=C; C=O stretching, or amide group (N–H) (Haeldermans et al. 2019; Rodriguez et al. 2020)

1350–1445

CH₂ units in biopolymers (Dong et al. 2016)

1020–1066

Stretching of ring breathing C–O (Liu et al. 2015)