Self-assembly of bioinspired catecholic cyclodextrin TiO2 heterosupramolecule with high adsorption capacity and efficient visible-light photoactivity

Abstract

In this work, an efficient and simple supramolecular approach to introduce cyclodextrin on TiO2 was demonstrated using the protocatechuic acid functionalized β-cyclodextrin (PCA-β-CD) that had a bioinspired catecholic structure. Two types of PCA-β-CD/TiO2 heterosupramolecules were obtained through a facile dip coating of TiO2 nanoparticles (Hombikat UV-100 and Fe3O4@SiO2@TiO2) in PCA-β-CD aqueous solution. The high surface coverage of Hombikat UV-100 or Fe3O4@SiO2@TiO2 by the attached PCA-β-CD was calculated to be 49.4% or 74.2% in the PCA-β-CD/TiO2 based on the TGA results, and it was also confirmed by the optical properties study that PCA-β-CD located onto the TiO2 surface mainly through the coordination of the catechol part on the cyclodextrin small ring side and TiO2. Compared with the adsorption amount onto bare UV-100 and Fe3O4@SiO2@TiO2, the adsorption of bisphenol A onto PCA-β-CD/UV-100 and PCA-β-CD/Fe3O4@SiO2@TiO2 was 6.9 and 7.9 times higher, respectively, because of the high inclusion affinity between PCA-β-CD's cavity and bisphenol A. Moreover, the two PCA-β-CD/TiO2 heterosupramolecules showed a high photoactivity to bisphenol A under light irradiation extending to the visible-light range. The cyclic use and X-ray photoelectron spectroscopy analysis results revealed that the PCA-β-CD layer in PCA-β-CD/TiO2 was stable and that the catalyst possessed reusable properties.