Alginate Ion Adsorption on a TiO2 Particle Film and Interactions of Adsorbed Alginate with Calcium Ions Investigated by Attenuated Total Reflection Infrared (ATR-IR) Spectroscopy

Abstract

The adsorption of alginic acid on a TiO2 particle film from aqueous solution was investigated by attenuated total reflection infrared (ATR-IR) spectroscopy. ATR-IR spectra recorded at different pHs confirmed that alginate adsorption to TiO2 is favored at pH 3.0 and no significant adsorption occurs above pH 5.0. Upon adsorption the carboxylic acid groups of alginic acid are converted to the carboxylate form and bind to surface Ti(IV) ions via bridging bidentate structures. Spectral analyses of the carboxylic acid and carboxylate stretching vibrations indicated that about three in four –COOH groups are converted to –COO− groups as they bind coordinately to TiO2. Additionally, the spectral data at pH 8.0 showed specific interactions of Ca2+ ions with the free COO− groups of the polysaccharide backbone of adsorbed alginic acid.