Effect of chemical modification of carboxyl groups in apple residues on metal ion binding

Abstract

AR (apple residue) was used as an alternative and cheap material for binding metal ions due to the presence of carboxyl and phenolic functional groups. The binding capacity of copper, lead, and cadmium by AR was pH dependent. Carboxyl groups of AR were esterified by acidic methanol to determine the contribution of carboxyl groups to metal ions binding. The extent of esterification was determined by analyzing the amount of methanol released in the sample hydrolysates by gas chromatography. The effect of esterification on binding metal ions was investigated in batch experiments by unmodified and modified AR. All esterified AR showed significant decreases in binding copper, lead and cadmium. The loss in the capacity of metal ion binding was proportional to the extent of esterification. The capacity of metal binding decreased with increase in the concentration of methanol in the respective hydrolysates or the modified AR. The data indicate that carboxyl groups on AR play an important role in the metal ion binding.