Table 1.

FT-IR band positions (cm⁻¹) and suggested assignments for CPX and CPX-adsorbed samples.

CPX	CPX-adsorbed samples	Band assignment
1621.85	1631.24	υ (pyridine-keto C = O)
1698.69	–	υ (carboxylic acid C = O)
1445.81	1474.64	υ (Stretching of C–N)
1382.75	1384.16	Protonation of amine group in the piperazine moiety

υ, stretching; δ, bending.