Synthesis of Ni–Ce Thin Films via Ultrasonic Spray Pyrolysis: Composition–Activity Relationship in Catalytic Ozonation for Methylparaben Elimination

Emerging pollutants such as methylparaben (MePB) are increasingly detected in aquatic environments and require effective removal strategies. This study reports the synthesis of Ni–Ce (x: y) composite catalysts as thin films via ultrasonic spray pyrolysis and evaluates their performance in catalytic ozonation. Although conventional ozonation resulted in complete MePB degradation, it exhibited limited mineralization efficiency. In contrast, the integration of Ni–Ce films significantly improved total organic carbon (TOC) removal, with the Ni–Ce (50:50) composition achieving the highest mineralization (52.1%) after 120 min, compared to 35.4% with ozone alone. The TOC removal efficiency followed the trend: Ni–Ce (50:50) > Ni–Ce (25:75) > Ni–Ce (75:25) ≈ Ni–Ce (10:90) > Ni–Ce (5:95). X-ray photoelectron spectroscopy (XPS) revealed that the enhanced catalytic activity was associated with higher Ce³⁺ content and increased oxygen vacancy concentrations, which facilitated the formation of reactive oxygen species (ROS), including hydroxyl radicals (·OH), superoxide anions (·O₂⁻), and singlet oxygen (¹O₂). The Ni–Ce (50:50) film maintained stable performance across five successive reaction cycles, confirming its reusability. Additionally, phytotoxicity assays using Lactuca sativa seeds demonstrated the treated effluents’ non-toxic nature, supporting the process’s environmental safety.

Graphical Abstract