Nano-Bi₂Ti₂O₇ with high photocatalytic activity was obtained through a solvothermal synthesis in acetic acid, resulting in Bi₂Ti₂O₇-nanoparticles. Equally in the lower nm-scale two different synthesis-routes for Bi₂WO₆ and Bi₂MoO₆, using a dispersion-technique and phase-transfer route from colloidal precursor with subsequent solvothermal crystallization, were established. The bismuth compounds show a high photo-catalytic activity. All three systems were tested in methyl red decomposition-reaction under UV-radiation. The half time decomposition and the reaction rates were determined.  Assuming a pseudo first order kinetic, Bi₂Ti₂O₇ nanoparticles (7.0 nm) showed the highest reaction rate (0.0990 min^-1) as compared to Bi₂WO₆ (0.0343 min^-1) and Bi₂MoO₆ (0.0700 min^-1). Furthermore, the interest of the pH-value in photocatalytic reactions in liquid medium is demonstrated at the example of Bi₂Ti₂O₇.