Mixed TiO ₂ –SiO ₂ thin coatings for selective adsorption and sunlight‐powered photodegradation of cationic pollutants

Abstract Water pollution and scarcity rank among the most pressing global challenges, underscoring the need for efficient and scalable technologies for tertiary water remediation, particularly against persistent pollutants that withstand conventional treatments. Photocatalysis offers a promising route for degrading such contaminants; however, standard powdered catalysts are difficult to recover after use and, despite their high specific surface area, introduce significant operational limitations in real systems. To address these challenges, we present mixed TiO 2 –SiO 2 photocatalytic coatings that combine the photoactivity of titania with the selectivity and sorption capacity of porous silica. Although thin films intrinsically provide a lower specific surface area than powders, the mixed oxides compensate for this constraint, offering excellent sorption performance and pronounced selectivity toward cationic species. Sorption and degradation capabilities were evaluated using methylene blue ‐ a benchmark probe in water purification ‐ and Diquat, a widely used herbicide and persistent cationic emerging pollutant. Furthermore, repeated photocatalytic cycling demonstrates good operational stability. Although a slight decrease in performance is observed during the initial cycles, the activity subsequently stabilizes, and the coatings retain high photocatalytic activity after repeated use, highlighting their potential for practical tertiary water treatment applications. Compared with pure titania, the mixed‐oxide coating displays markedly enhanced sorption and photocatalytic degradation effects while eliminating the need for catalyst recovery, thereby overcoming key limitations associated with conventional particulate systems.