Table 5. Surface functional groups.

Adsorbents	Spectrum wave number (cm-1)	Functional group	Reference
Raw CAC	≈1230	Carbonyl group (C = O)	[48]
	≈900	Alkene group (C-H bonds)
ZnAc2- CAC	1271–1224	Ether group (R-O-R)	[47]
	3800–3200	Hydroxyl group (O–H)
KI-CAC	≈2180	alkyne group (C≡C)	[48]
	≈1230	Carbonyl Group (C = O)
KOH-CAC	3800–3200	Hydroxyl group (O–H)	[49]
	1550–1200	the carboxylic acid (O–H bonds)
CuSO4-CAC	3800–3200	Hydroxyl group (O–H)	[49]
	≈2633	Sulfonate group (S-H)
Na2CO3- CAC	1271–1224	Ether group (R-O-R)	[53]
	650–600	acetyleric group (C–H bond)