TiO2-anataseis presently the most used photocatalyst for environmental applications due to its high stability, good location of the band edges, low charge transport resistance, high photocatalytic activity, high chemical and thermal stability, low toxicity and low price. However, to increase the usefulness o titanium dioxide, it is necessary to increase its photoactivity and ability to absorb visible light.
Since TiO2 may contribute to prevent nosocomial infections, its practical application in this field is strongly envisaged. TiO2 photocatalysis, similarly to the phagocytic cells of the human immune system, use the cytotoxic effects of Reactive Oxygen Species (ROS) to inactivate microorganisms. These ROS are known to be highly reactive with biological mol- ecules and thus they are effective for the inactivation various different types of microorganisms.
Photoinactivation of microorganisms under UV radiation using TiO2 has been thoroughly studied with great success; a wide diversity of microorganisms has been studied, Gram-negative and Gram- positive bacteria, including dormant forms (cysts, spores) fungi, algae and protozoa. Targeting future commercial applications, the research was directed to the use of visible light instead of only on UV ra- diation, and of proper immobilization of the photo- catalyst. TiO2 doping and/or decoration with the objective of increasing photoactivity and photoabsorbance were briefly reviewed as well as the use of TiO2 /graphene composite photocatalysts. The use of graphene reduces the risks of health hazards because in TiO2 /graphene composites TiO2 nanoparticles are attached to micro-size graphene platelets that prevent the catalyst to be absorbed by the human body. In the case of TiO2 /graphene composite photocatalyst, the decoration of TiO2 with metals such asAg andAu further decrease charge recombination, show plasmonic effect and reduce the redox overpotentials.
Although promising, photocatalysis still faces some drawbacks when imposing itself as a refer- ence disinfection technique. Besides the mentioned limitations regarding the optimization of photocatalysts to attain visible light activity, the absence of knowledge on the long time effect of photoinactivation on microorganisms should be a matter of concern.
