Fig. 1. Low motility of the chemically active titania particles.

Top-down view of the motion of TiO₂ particles, sedimented at the bottom of a drop of hydrogen peroxide solution, at low areal number density (<4% of the area is covered by the particles): a standard Brownian motion in the absence of UV illumination; b enhanced diffusion due to self-propulsion upon illumination with UV light; c the mean squared displacement (MSD) determined from the particle trajectories as in a (black, lower part) and b (red, upper part) tracked over 15 s. The images in a, b show an area near the projection of the center of the drop onto the plane of the glass wall. The scale bar corresponds to 5 μm. The black disks correspond to the particles at the end of the tracked trajectories (red lines). In c the MSD(Δt) for each of the tracked trajectory in the absence or presence of UV illumination, respectively, is located within the corresponding black or red shaded region. Therein, the red and black lines indicate the corresponding mean values.