The degradation experiments were conducted in absence of H 2 O 2 as photo-oxidation of RhB can take place in presence of UV light and H 2 O 2 . To resume, the photodecomposition of RhB is reflected by a decrease in the residual concentration of the dye in presence of Pac-Man particles, proving the photocatalytic activity (beyond active propulsion) (Figure ). These results demonstrate that the Pac-Man particles display a superior photocatalytic activity compared to TiO 2 Degussa P-25. It has been reported that 30 nm Degussa P-25 photocatalyst degrades around 40 % of RhB in 30 min. Even though the difference in degradation may not seem significant, it is worth noting that a bigger particle size of the photocatalyst can affect negatively its photocatalytic activity. This phenomenon was described by Wilhelm and Stephan, who studied the photocatalytic degradation of RhB using SiO 2 @TiO 2 spheres of different sizes and titania nanosol. They observed that increasing the particle size decreased the RhB degradation as the specific surface area was smaller. Therefore, for a particle with particle size in the range of micrometers, it is needed a far superior photocatalytic activity to eliminate the same amount of pollutant than a 30 nm particle. To investigate the degradation of microplastics we selected spherical, homogeneous polystyrene particles of sizes 2 µm and 5 µm to facilitate quantitative analysis of SEM images. In order to observe significant degradation of microplastics in contact with the catalytic Pac-Man particles, we selected UV irradiation and H 2 O 2 , i.e. the ideal swimming environment for Pac-Men. The extent of degradation is evaluated from the morphological changes in the polystyrene (PS) particles, an approach that has been used by other authors. ). Degradation studies are also carried out with 5 µm PS particles, a similar effect is observed i.e. higher degradation efficiency at higher concentration of H 2 O 2 but at much lower extent compared to 2 µm PS particles (∼ 7 % degradation at 10 % H 2 O 2 ) (Figure & S9). CI of both PS particles after photodegradation is also studied (Figure ).