Photochemical Behaviour of Diphenolic Acid in beta-Cyclodextrin and TiO2 Suspensions

This paper investigated the photochemical behavior of diphenolic acid (DPA) in the presence of beta-cyclodextrin (CD) and TiO₂ suspensions under a 250 W metal halide lamp (lambdages 365 nm). The interaction of DPA with CD yielded the formation of inclusion complexes at 1:1 stoichiometric ratio in solution. The irradiation of DPA and TiO₂ suspensions in the presence of beta-CD showed that the photodegradation rate of DPA was enhanced. The photodegradation of 10-80 mumol/L DPA in suspended solutions was found to follow the pseudo-first-order law. Obviously, the photocatalytic degradation reaction rate constant of DPA in the system containing beta-CD is higher than that without beta-CD. The adsorption isotherms of DPA could be plotted with the Langmuir isotherm model, and the maximum adsorption capacity increased in presence of beta-CD/TiO₂. The influence factors of beta-CD concentration, DPA initial concentration on photodegradation of DPA were studied in details. This paper also simply explored the mechanism of the photocatalytic degradation effect in the presence of beta-cyclodextrin. 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. This could be a promising method for contaminated water remediation.