<p>Photocatalytic degradation of organic pollutants is widely applied in water treatment; however, it is commonly performed using dispersed semiconductor catalyst powders, which requires an additional post-process separation step to remove suspended solids from the treated solution. The solution to this problem is the use of photocatalysts deposited on reusable substrates. However, this solution requires the development of mechanically stable, UV-resistant holders that will ensure repeatable positioning of the substrate in relation to the radiation source and ensure free flow of liquid and will not affect the kinetics of the process. Additive Manufacturing (AM), implemented e.g. via Fused Filament Fabrication (FFF; also referred to as Fused Deposition Modeling (FDM)), enables rapid prototyping and fabrication of photocatalytic reactor-specific holders and iterative geometry optimization, while allowing the same CAD design to be reproduced in different materials. The novelty of this research is a comprehensive assessment of the physicochemical properties of different polymers used in FFF technology in terms of their possible use in the production of holders for mounting substrates covered with photocatalysts. On the one hand, such polymer materials should not affect the kinetics of the process, and on the other, their optimal geometric design should enable the simultaneous mounting of many substrates. Among the tested filamets, the designed flower-shaped PETG/GF holder contributed to an increase in photocatalytic efficiency by over 20%. This improvement is attributed to an increased effective catalytic area enabled by the holder arrangement, together with geometry-driven enhancement of light exposure and solution mixing. In addition our solution will avoid the use of powder catalysts and the associated very difficult separation after process.</p>