Functionalization of ZnO aggregate films via iodine-doping and TiO2 decorating for enhanced visible-light-driven photocatalytic activity and stability

Abstract

A multifunctional visible-light-driven photocatalyst composed of an iodine-doped ZnO aggregate (ZnO:I) film post-decorated by TiO₂ (ZnO:I@TiO₂) on fluorine-doped tin oxide-coated (FTO) glass via a hydrothermal method and subsequent wet-chemical process is demonstrated. A series of ZnO:I with various iodine concentrations was firstly prepared to study iodine dopant amount dependent-photocatalytic activity. The photocatalytic measurement results showed that the ZnO:I film with an optimum I-doping ratio of 5.0 mol% achieved a degradation efficiency of 93.7% toward RhB, which is much higher than that of undoped ZnO (only ∼54.3%). Furthermore, the ZnO:I@TiO₂ exhibited enhanced light absorption and a charge separation efficiency of photogenerated e⁻–h⁺, as characterized by UV-vis absorption spectra and the photoelectrochemical characterization by EIS, which originates from iodine doping and TiO₂ post-modification. Owing to these synergic advantages, the ZnO:I@TiO₂ composite photocatalyst exhibited significantly enhanced decomposition activity for RhB (∼97% after 4 h of irradiation, a 79% increase over pure ZnO) under visible irradiation. Additionally, the ZnO:I@TiO₂ films exhibited enhanced chemical stability in both acidic and alkaline solutions in comparison to ZnO:I, which was further verified by repeated photodegradation experiments under visible light irradiation. These results indicate that the prepared ZnO:I@TiO₂ could serve as an efficient photocatalytic material to degrade organic pollutants in aqueous eco-environments.