The PHB (poly (3-hydroxybutyrate)) film and nanocomposite act as catalysts in the oxidation of organic compounds, such as methylene blue dye (MB) using UV radiation. The results indicate that the materials produce in situ hydroxyl radicals, which are responsible for the deep oxidation of MB. The results showed for the first time that only the PHB polymer presents good catalytic activity (similar to 80%), indicating the possibility of avoiding the use of semiconducting metals in the processes. The main effect is the cleavage of the polymer chains which modifies the PHB structure. This effect also promotes the mineralization of the PHB polymer during the process. Thus, the polymer degrades organic molecules present in water and is also transformed without generating pollutant molecules, as shown by the ESI-MS analyzes. This new catalyst concept allows its use for up to 7 cycles efficiently without semiconductor metals.