Sustainable polyelectrolyte complexes of pectin and chitosan as adsorbents for heavy metal ions from surface water

Abstract

Polysaccharides like starch, chitosan, and pectin are attractive for removing heavy metal ions from water. Chitosan (n+) is mixed with pectin (n−) to enhance ion adsorption from aqueous media. This study involves two parts. First, 1 g/L stock solutions of pectin and chitosan at pH 5 are prepared and used to create polyelectrolyte complexes (PECs) with varying molar charge ratios (n−/n+). Pectin is added to stirred chitosan solutions to form PECs, relying on ionic interactions between chitosan's amino groups and pectin's carboxyl groups. However, the resultant PEC concentration is insufficient for effective heavy metal ion removal. In response, the second part of the study focuses on a specific PEC with n−/n+ of 0.84. The stock solution concentration is increased to 5 and 10 g/L at pH 5, enhancing efficiency and forming a gel. The gel dispersion is freeze-dried, and the resultant PECs are used for adsorption experiments with Cd²⁺, Ni²⁺, Fe^2+/3+, Mn²⁺, and Cu²⁺ sulfate solutions. Adsorption rates are in the order Cu²⁺ > Fe^2+/3+ > Cd²⁺ > Ni²⁺ > Mn²⁺ for a 20 mg/L salt concentration, indicating high PEC affinity for heavy metal ions.