<i>In Situ</i> ATR FTIR Study of Dextrin\nAdsorption on Anatase TiO₂

Abstract

The adsorption of two dextrin-based polymers, a regular\nwheat dextrin\n(TY) and a carboxymethyl-substituted (CM) dextrin, onto an anatase\nTiO₂ particle film has been studied using <i>in situ</i> attenuated total reflection (ATR) FTIR spectroscopy. Infrared spectra\nof the polymer solutions and the polymer adsorbed at the anatase surface\nwere acquired for two solution conditions: pH 3 and pH 9; below and\nabove the isoelectric point (IEP) of anatase, respectively. Comparison\nof the polymer solution spectra and the adsorbed layer spectra highlighted\na number of spectral differences that were attributed to involvement\nof the carboxyl group of CM Dextrin interacting with the anatase surface\ndirectly and the adsorption of oxidized dextrin chains in the case\nof regular dextrin (TY) at high pH. The adsorption/desorption kinetics\nwere determined by monitoring spectral peaks of the pyranose ring\nof both polymers. Adsorption equilibrium was not established for Dextrin\nTY for many hours, whereas CM Dextrin reached equilibrium in its adsorption\nwithin 60 min. The extent of desorption of Dextrin TY (observed by\nflowing a background electrolyte dextrin-free solution) was extensive\nat both pH values, which reflects the poor affinity and binding of\nthe polymer on anatase. In contrast, CM Dextrin underwent almost no\ndesorption, indicating a high affinity between the carboxyl groups\nof the polymer and the anatase surface.