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

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.