Equilibrium Sorption of Histidine on Clinoptilolite

Abstract

Sorption of histidine in the cationic and zwitterionic forms on a framework aluminosilicate, clinoptilolite, has been investigated. The contributions of the exchange and nonexchange mechanisms of sorption to the sorption capacity have been determined. It has been shown that monolayer histidine sorption on clinoptilolite by the ion-exchange mechanism proceeds due to the electrostatic interaction between $${\text{NH}}_{3}^{ + }$$ groups of the amino acid and electronegative sites of the sorbent matrix. In the region of equivalent exchange, a smaller value of the ion-exchange component of the sorption of histidine zwitterions is due to the Coulomb repulsion between the dissociated carboxyl groups of the amino acid and the negatively charged aluminum–oxygen clinoptilolite matrix. The isotherm of histidine sorption from dilute solutions has been described using the Langmuir theory. The equilibrium sorption parameters have been found. It has been concluded that polymolecular layers of the amino acid are formed as a result of association via hydrogen bonding, as well as dipole–dipole and hydrophobic interactions.