Influence of doping on the antibacterial effect of TiO2 nanoparticles

TiO2 nanoparticles doped with V, Mn or Zn, respectively, were synthesized from pure TiO2 and dopants calcinating at definite temperature. The physical properties of prepared TiO2 nanoparticles were characterized by TEM, XRD and UV-vis spectrum. The TEM images showed that the diameters of the particles were 20 similar to 50 nm. There was no peak of doping elements in the XRD spectrum of nano-sized TiO2 doped, but the peak of a little amount of rutile was observed, which demonstrated that V, Mn and Zn might locate in the TiO2 octahedral lattice, or might be highly dispersed within crystalline of TiO2. In the meanwhile, doping of the TiO2 decreased the temperature for TiO2 transforming from anatase into rutile, and promoted the transforming. It was found that a little amount of V5+ may take the place of Ti4+ in the lattice of TiO2. The red-shift was clearly observed in the UV-vis spectrum of TiO2 nanopowders doped with V. As a result, the band gap was changed and the TiO2 nanopowders doped with V enable to absorb visible light. The red-shift could be assigned to the charge transfer transition between the 3d orbital of V5+ and the TiO2 conduction or valance band. The red-shift was not observed in the UV-vis spectrum of TiO2 nanopowders doped with Mn and with Zn, the shape of which was similar to that of pure TiO2. The results of the minimum inhibition concentration (MIC) for Escherichia coli and Staphylococcus aureus showed that vanadium ions doping intensely improved the antibacterial efficiency of nanocrystallites. This was attributed to the change of surface properties of metal ions doped semiconductor, such as O vacancies, Ti interstitial ions and vanadium ions which took the place of titanium.