Synthesis of sol-gel TiO2 nanoparticles and assessment of their antifungal activity for the eventual conservation of historical documents

One of the main causes of deterioration of ancient documents is the presence of microorganisms, especially fungi. In this study, we report on the detection of microbiological contamination in ancient books from the Franciscan Library of San Pedro Cholula, in the state of Puebla, Mexico. The microscopic observation of different organic pigments and in vitro assays indicated the presence of Rhizopus sp., Mucor sp., and Alternaria sp. on the papers. The fungicidal activity of TiO2 nanoparticles (NPs), synthesized by the sol gel process, was then evaluated against these strains by two different methods: i) the agar well diffusion method using Petri dishes and ii) in pieces of old book pages, where the strains had been previously incubated. From TEM measurements, it was determined that the TiO2 NPs had a diameter of 70 nm. Anatase TiO2 NPs were synthesized as indicated by Raman spectroscopy and XRD. From UV–Vis spectroscopy and the Tauc´s method for an indirect band-gap semiconductor, a band-gap energy value of 2.9 eV was obtained. The surface chemistry of the TiO2 NPs/paper substrates was analyzed by XPS. In addition, a core-level XPS analysis of the O 1s and C 1s orbitals was used to identify signals related to cellulose. The antifungal activity of TiO2 NPs was demonstrated for the investigated fungi. A higher inhibition occurred for Rhizopus sp., followed by Mucor sp., and Alternaria sp. with inhibition halos of 26, 24, and 18 % in diameter, respectively. This work used highly sensitive techniques with the aim of proposing methodologies that contribute to the preservation of historical documents.