Ultrathin TiO2–CeO2 Composite Films for Efficient Photocatalytic Methylene Blue Degradation

Abstract Contamination of natural water resources by industrial organic pollutants poses serious environmental and health risks, creating a need for efficient and sustainable wastewater treatment technologies. TiO2 is widely regarded as an eco-friendly and low-cost photocatalyst, but it is normally used as a dispersed powder, which must be separated from the treated water. Immobilizing it as a thin film removes that step at the cost of a much smaller accessible surface, so the performance of such films depends strongly on their composition. In this study, ultrathin TiO2–CeO2 films containing 1, 2, and 3 wt % of CeO2 were prepared by sol–gel dip coating, and the influence of CeO2 content on their structure and photocatalytic performance was investigated. Electron microscopy and elemental mapping show distributed cerium, consistent with a TiO2–CeO2 nanocomposite. The degradation of methylene blue under UVA irradiation was used as a model reaction. The first-order rate constant passes through a maximum at 2 wt % CeO2, rising from 4.9 × 10–3 min–1 for pristine TiO2 films to 9.1 × 10–3 min–1, so that the ∼30 nm smooth film approaches the performance of Degussa P25 suspended nanopowder at equal catalyst loading. The TiO2–CeO2(2%) film retains its photoactivity over four consecutive cycles. These results show that sol–gel TiO2–CeO2 thin films are efficient and reusable immobilized photocatalysts for water purification.