The Adsorption of Basic α-Amino Acids in an Aqueous Solution by Titanium(IV) Oxide

Abstract

TiO2 showed a pronounced activity in the adsorption of basic α-amino acids, such as l-lysine and l-arginine, in an aqueous solution. The adsorptive activity of TiO2 containing sulfate ions was lower than that of the sulfate ion-free TiO2, and it was suppressed by phosphate ions. The pH of the aqueous solution hardly affected the adsorption, while the heat-treatment of TiO2 above 500 °C noticeably lowered the adsorption. The Langmuir equation was applicable to the adsorption of l-lysine, showing that the amount of saturated adsorption was about 0.7 mmol/g TiO2 heat-treated at 500 °C. The heat of adsorption of l-lysine, as determined from the adsorption isotherms at 10, 30, and 50 °C, was 2257 J/mol. A linear relationship was observed between the amount of l-lysine adsorbed and that of the surface OH groups.