Adsorption and Photodecomposition of Diphenolic Acid in /spl alpha/- or /spl beta/- Cyclodextrins and TiO/sub 2/ Suspensions

The adsorption and photodecomposition of diphenolic acid (DPA) was investigated in the presence of alpha- or beta- cyclodextrins (CDs) and TiO₂ suspensions. The adsorption of DPA on TiO₂ surface and inclusion complex of CDs and DPA were critical factor in the photocatalytic reaction. Results showed that, the adsorption isotherms of DPA could be plotted with the Langmuir isotherm model, and the maximum adsorption capacity increased in the order of alphaC-CD/TiO₂<TiO₂<beta-CD/TiO₂, while the inclusion constant DPA in the solution containing beta-CD was obviously higher than those in the solution containing alpha-CD. The photodecomposition rate of DPA in suspended solutions containing only TiO₂ was lower than that of beta-CD/ TiO₂ systems but higher than that of alpha-CD/ TiO₂ systems (beta-CD/ TiO₂> TiO₂>alpha-CD/ TiO₂). The influence factors of beta-CD concentration, DPA initial concentration on photodegradation of DPA were studied. This paper also simply explored the mechanism of the different degradation effect in the presence of beta- or alpha-CD. With the addition of beta-cyclodextrin, the enhancement of photodegradation of DPA mainly results from the enhancement of adsorption of DPA on TiO₂ surface and the lower bond energy between some atoms in DPA molecule after inclusion interactions with beta-CD. While with the addition of alpha-CD, the photodecomposition inhibition role of alpha-CD to DPA on TiO₂ surface leaded to reducing photodegradation of DPA, because alpha-CD and DPA did not form a stable inclusion compounds and decreased the adsorption amount of DPA on the TiO₂ surface.