Adsorption of Amino Acids on Iron(III) Hydroxide

Abstract

Amino acids are adsorbed on iron(III) hydroxide from aqueous solution. The adsorption behavior was found to depend on the nature of amino acids. Acidic amino acids are adsorbed strongly in the pH range of 5 to 7. Neutral and basic amino acids are adsorbed, but weakly, in the pH range of 8 to 10. In the optimum pH range as described above, acidic amino acids are present as anions, and neutral and basic amino acids as zwitter ions. The zero point of charge of iron(III) hydroxide was determined to be 7.36. From these results the adsorption of amino acids was explained in terms of the electrostatic interaction between adsorbate and adsorbent. Hydroxyl ion or proton was released during the adsorption reaction of amino acids. The adsorption process was exothermic for all amino acids. The Langmuir equation was applicable to the adsorption of acidic and basic amino acids. The area occupied by glutamic acid on iron(lla) hydroxide was calculated to be 195 m2/g from its saturation adsorption.