Many works include the use of nylon membranes to separate the solid particles of photocatalysts from the photocatalytic reactors, before using spectrophotometers to evaluate the catalysts' performance in the photocatalytic degradation of many pollutants. This might lead to significant errors due to the adsorption of some pollutants within the structure of the membranes during the filtration process used to separate the solid particles of the photocatalysts to get a clear filtrate. This, consequently, leads to incorrect calculations, which in turn are translated into false high photocatalytic efficiencies of the used catalysts. In this work, the authors study the interaction between nylon membrane filters and five different model compounds-phenol red, methylene blue, rhodamine B, rhodamine 6G, and phenol. The study reveals a significant interaction between the nylon membranes and both rhodamine B and phenol red.During the investigation of the fluorescence signal in the photodegradation of polymers and pollutant degradation, we serendipitously discovered that a simple model compound, such as phenol red and rhodamine B, is removed efficiently through filtration using the commonly used Whatman nylon filter membranes purchased from Sigma Aldrich. This type of filter membrane, with a 0.2 µm pore size, 47 mm diameter, and 0.5 mm thickness, is proposed to be used after the photodegradation process to remove the submicron photocatalysts and obtain the filtrate for spectrophotometric analysis. This observation made us curious and, thus, we decided to investigate more in depth the removal efficiency of these nylon membranes and the removal mechanism beyond this observation. We chose several probes with different chemical characteristics, such as rhodamine B, phenol, rhodamine 6G, phenol red, and methylene blue. Our results indicate that the nature of the chemical structure is responsible for the removal through a chemical mechanism, involving a negatively charged molecule interacting with a positive charge from the terminal part of a polymer backbone in polyamide-based filters.