Photodynamics and Surface Characterization of TiO₂ and Fe₂O₃ Photocatalysts Immobilized on Modified Polyethylene Films

Abstract

Polyethylene block-copolymer films containing negative anhydride groups were used to immobilize TiO2, Fe2O3, and Fe3+ photocatalysts. The kinetics of the mineralization of azo-dye Orange II and chlorophenols on copolymer−TiO2, copolymer−Fe2O3, and copolymer−Fe3+ have been tested under optimized experimental conditions. In the case of copolymer−TiO2, the degradation kinetics for the model organic compounds were about the same as those observed with TiO2 suspensions containing about a 27 times higher amount of TiO2 per unit volume. The surface of the derivatized copolymer semiconductor catalysts was studied by infrared attenuated total reflection spectroscopy. The spectroscopic data provided evidence for a TiO2 interaction with the negatively charged conjugated carboxylic groups of the copolymer, leading to an asymmetric-stretching band of −COO−Ti4+ at the position expected for metal carboxylates. In the case of Fe2O3 and Fe3+, the asymmetric-stretching carboxylate bands are ascribed to the carboxylate bands of −COO−Fe2O3 and −COOO−Fe3+. Evidence is presented by X-ray photoelectron spectroscopy for the existence of two oxidation states of Ti and Fe after the photocatalytic degradation of Orange II. This observation is consistent with light-induced interfacial charge transfer (redox processes) taking place at the metal−oxide copolymer surface. The nature of the latter processes is presented in detail during this study.