A simple method for creating Ag/CeO2 composites involves the reaction between components of an aqueous salt solution and ammonia vapor at the gas-solution interface. The concentrations of the reagents and the reaction time determine the structure and composition of the composite films formed on the solution surface. When the concentration ratio AgNO3/Ce(NO3)3 in the solution is 1/1, a composite film is formed consisting of Ag nanowires and Ceria nanoflakes. A model of the interaction at the liquid-gas interface is proposed. Ag/CeO2 composites have dual capabilities, enabling efficient photodegradation of Methylene Blue organic molecules and improved SERS detection of Rhodamine 6 G dye at concentrations as low as 10−9 mol/L. The synergistic effect of composition and morphology on properties was observed for the composites obtained within 7 minutes of interaction.