Bactericidal effects of titanium dioxide-based photocatalysts

The photocatalytic degradation of E. coli in water by various catalysts was investigated in a batch spiral reactor. Commercial Degussa P25 (P25), as well as novel magnetic and hydrothermally prepared photocatalysts (MPC and HPC) were investigated in a slurry system. P25 was found to be the most effective catalyst, followed by the HPC and the MPC. Cell destructions followed first order kinetics. Non-buffered samples displayed a greater bactericidal efficiency which was attributed to a decrease in electrostatic repulsions between TiO2 and E. coli and also elevated stress on E. coli at acidic pH. Buffered (NaHCO3) samples showed a decrease in bactericidal efficiency due to HCO3− ions competing with oxidising species and blocking (by adsorption) the TiO2 particles. The optimum catalyst loading for P25 and HPC was 1 and 2 g/L for MPC and was attributed to mass transfer effects (bulk diffusion, available active site and shadowing). An immobilised P25 system was found to be more efficient than the MPC and comparable with the HPC in suspension. The addition of silver to the immobilised system was found to enhance the photocatalytic degradation.