The activities of the round grid, the double grid and the spiral manufactured with filaments with TiO2 loadings of 𝜔 𝑇𝑖𝑂2 = 0.15 (20 h preactivation) were compared for the initial reaction rate 𝑟 0 . The lowest reaction rate was measured for the round grid, followed by the spiral and the double grid with 𝑟 0 = 0.26 nmol s -1 , 𝑟 0 = 0.34 nmol s -1 and 𝑟 0 = 0.53 nmol s -1 , respectively (see Figure and Table ). Compared to the results of the MB decolorization, the order of the different inserts changed, a higher reaction rate was observed for the spiral as for the grid. This might be due to the changed reaction system, in which shading by the reactant is not as dominant as for the MB system. Remarkably, increasing the area containing photoactive material by about 30 % with the double grid design doubled the initial reaction rate.