In this work Nexar (R)-based nanocomposite membranes, consisting of tert-butyl styrene end blocks, hydrogenated isoprene inner blocks and a middle block that is selectively and randomly sulfonated, were prepared by dispersing bismuth oxide (Bi2O3) nanoparticles inside. The aim was to evaluate their adsorption properties and photocatalytic activity. The chemical, structural and morphological properties of the produced materials were characterized by scanning electron microscopy (SEM), x-ray photoemission spectroscopy (XPS) and thermo-gravimetric analysis (TGA). We found that a partial reduction of Bi2O3 to metallic Bi takes place during the nanocomposite preparation. The presence of the bismuth-based nanomaterials changes the light absorbance of the polymer affecting positively the dye removal ablity of the polymeric nanocomposite. The removal/degradation properties of the membranes were investigated by measuring the degradation of two dyes, methylene blue (MB) and methyl orange (MO), under UV/visible or blue light illumination. The UV-vis light irradiation increases the MB removal for both the membranes, due to an enhanced adsorption effect, while blue light irradiation induces a similar enhancement only for the filler-free membrane. For the nanocomposite membrane containing Bi2O3 (s-PBC-BO) we observe the highest efficiency in the removal of MO under blue light irradiation due to a combined effect of light absorption by both the nanocomposite and the dye.