Pb²⁺ adsorption by ethylenediamine-modified pectins and their adsorption mechanisms

Ethylenediamine-modified pectins (EPs) with different degrees of amidation (DA) were prepared and characterized by Fourier Transform Infrared spectra (FTIR), elemental analysis, X-ray photoelectron spectroscopy (XPS). The prepared EPs were then used to remove Pb²⁺ from the aqueous solution. It was found that EPs with the highest DA (EP₄₈) exhibited great removal efficiency of Pb²⁺ (≥94 %) at low concentrations of 40-80 mg/L. The zeta potential analysis showed that EP₄₈ had the fastest increase in zeta potential when Pb²⁺ was continuously added and was the first to be electroneutralized. Particle size analysis further confirmed that EP₄₈ was the first precipitated and formed a larger EP₄₈-Pb²⁺ complex. The FTIR and XPS analyses indicated that Pb²⁺ was adsorbed via the ion exchange of carboxylic groups and chelation with acylamino and amino groups. These results suggested that the EP₄₈ might be a promising adsorbent for the removal of low concentrations of Pb²⁺ in contaminated water.