Table 2: Main functional groups in the IR spectrum of the biomass before adsorption.

Wavenumber (cm‒1) Intensity Functional Group Group Name
3304.06 Medium ‒OH Hydroxyl/Phenol
2879.72 Strong C‒H Alkane
1737.86 Strong C=O Carboxylic acid
1664.57 Strong N‒C=O Amide
1598.99 Strong C‒N Amide 1° bending vibration
1423.47 Medium C‒O‒H Carboxylic acid bending
1246.02 Medium C‒O‒C Ether
1045.42 Medium CO‒O‒CO Anhydride

Summarizes the changes in wavenumbers (cm‒1) of each functional group after Pb (II) adsorption. The carboxylic group (‒COOH) shifted significantly from 1737.86 to 1762.92, 1751.36, 1734.01, and 1724.36 after treatment with Pb (II). These shifts in wave number correspond to a change the binding energy corresponding to the functional group. This result confirmed the involvement of carboxylic acid groups in the binding of Pb (II) in the case of B. nigra [57, 58].