The photocatalytic activity of the samples was determined by discoloration of methylene blue. In a small test reactor, the COP platelets (1.5 x 1.5 cm 2 ), previously coated on one side, are clamped in the illumination window (1 x 1 cm 2 ) with the coated side facing the solution. The polymer platelet is illuminated from the back side by a high-power UVA-LED (LEDMOD365.1050.V2, Omicron Laserage, Germany), see Fig. . The decolorization of 1.7 mL of 25 µM methylene blue solution in deionized water was monitored online using a UV-Vis spectrometer (PowerWave HT, BioTek). The degradation constants (kD) for the discoloration of methylene blue represent the initial pseudo-first order degradation and were determined using linear regression of the concentration-time profiles.