Abstract
The adsorption and photodecomposition of seven kinds of amino acids on TiO₂ surface were investigated by zeta potential measurements and ¹H NMR spectroscopy in TiO₂ aqueous suspension systems. The decomposition rates increased in the order of Phe ＜ Ala < Asp < Trp < Asn < His < Ser. On the adsorption on TiO₂, for Phe, Trp, Asn, His, and Ser, the isoelectric point (IEP) of TiO₂ shifted to the lower pH with increasing decomposition rates, suggesting that the effective adsorption and photocatalytic sites for these amino acids should be the basic terminal OH on the solid surface. Since the amino acids which decomposed faster than the others contain -OH (Ser), -NH (Trp, His), or -NH2 (Asn) in their side chain, they are considered to interact with the basic terminal OH groups more preferably by the side chain and vulnerable to photocatalytic oxidation. On the other hand, Ala interacts with the acidic bridged OH on TiO₂ to cause IEP shift to the higher pH. The correlation of the surface hydroxyl groups with the photocatalysis of amino acids were verified by the use of the calcined TiO₂ without surface hydroxyl groups. The correlation of the surface hydroxyl groups with the photocatalysis of amino acids were verified by the use of the calcined TiO₂ without surface hydroxyl groups.

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