Testing the antibacterial activity of doped TiO2 for preventing biodeterioration of cultural heritage building materials

Application of biocide products, alone or in combination with protective or consolidants, is a common practice to prevent further colonization on monuments surface. TiO2 is as one of the most fascinating materials characterized by chemical stability, non-toxicity, high photo-reactivity, broad-spectrum antibiosis and cheapness, and it has been used extensively as biocide against various microorganisms: bacteria, fungi and viruses. Its problem is that its reactivity is due to a restricted wavelength in the UV region and thus its application can be limited in certain circumstances (e.g. indoors). Recently, alkaline-earth metal ions have been considered as promising, efficient and economic approaches for doping the TiO2 because they have a larger photocatalytic spectrum. M-TiO2 thus may be more effective in the protection and maintenance of stone surfaces than pure TiO2 in reducing the biodeterioration processes. However before any application on monument surfaces, the products must be tested not only for their biocide efficacy but also for being harmless to cultural heritage material. To fulfil this requirement, a set of experiments has been carried out testing M-doped TiO2 compounds for their efficiency as photocatalysts, for the chromatic changes induced by their application on stone surfaces and for their antibacterial activity against selected Gram positive and Gram negative bacteria. Our results showed that TiO2 doped with Ag alone or in combination Fe3+ or with Sr has antibacterial activity and could be successfully applied in field to prevent stone biodeterioration. (C) 2014 Elsevier Ltd. All rights reserved.