Disinfection of Microorganisms

When titanium dioxide nanoparticles and nanocrystallines are irradiated with UV-visible light, this semiconductor can exhibit strong bactericidal activity. For instance, Chang et al. showed that the irradiation of suspensions of Escherichia coli and Ti02 (P-25) with of wavelengths longer than 380 nm led to bactericidal action within minutes [26]. Furthermore, the trends in these simulated laboratory experiments were mimicked in outdoor tests conducted under the summer, noonday sun [27]. Elsewhere, Maness et al. presented the first evidence that Hpid peroxida- 

Ti02 nanoparhcles, as-doped, could also be used for the disinfection of waste-water. For example, Yu et al. reported that sulfur-doped titanium dioxide exhibited a strong visible-light-induced anhbacterial effect [29], while Egerton et al. found that the photoelectrocatalytic disinfechon of E. coli by an iron-doped Ti02 sol-gel electrode was more efficient than disinfection by the corresponding electrode when undoped [30]. 

As a typical study, the synthesis of Ti02-based p-n junction nanotubes has been described [42]. The outside of the tubes was comprised of Ti02, and the inside platinum. The nature of the p-n junction allowed the outside of the tube to act as an oxidizing surface, while the inside of the tube acted as a reductive surface. When exposed to UV Ught, these catalysts were able to degrade toluene, with experimental results showing that the photocatalytic destruction rates of these catalysts were higher than those of non-nanotube-structured material and nanotubes without a p-n junction. 

Moreover, titanate nanotubes can adsorb functional cations from aqueous solution, which may in turn provide a strategy for the deposition of active catalysts on the surface of nanotubes [43]. In addition, when nanoparhcles and htanate nanotubes have good electrical contacts, it can provide an efficient interfacial charge-transfer region, which makes this binary system also suitable for photocatalysis. In photocatalyhc processes, the photosensibilizer could be either wide-bandgap titanate nanotubes [44] or narrow-bandgap semiconductor nanoparhcles [45, 46]. At present, these studies are shU in the early stages of research, but will undoubtedly find applicahons in nanofiltrahon membranes for water heatment. 

As in the case of Ti02 nanotubes, Ti02 nanorods-as another one-dimensional (1-D) nanoshucture-have also been developed for water purificahon. By using a nonhydrolytic sol-gel reachon between htanium(IV) isopropoxide and oleic acid. 

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