Suitability of Gadolinium doped TiO2 nanoparticles to protect heritage building materials from biodeterioration

Heritage buildings possess historical values coming from the attractive architecture and important events taking place around the heritage area. However, they are subjected to degradation process and ageing. Particularly, microorganisms are usually related to harmful biodegradation of artistic materials. Water also is an essential factor of deterioration precisely in porous materials. To protect heritage materials, several methods have been developed. Notably, using nanomaterials to preserve valuable heritage surfaces has been considered as an alternative method. In particular, TiO2 nanoparticles (NPs) have been extensively regarded as one of the most interesting materials. Their interesting features make them a good candidate for photocatalytic application. However, the necessity of using only UV light hinders their practical application. For that reason doping with lanthanide ions, precisely, Gadolinium (Gd) could be an effective method to enhance TiO2 NPs photoactivity. In the present study, pure and Gadolinium doped TiO2 NPs were synthesized by sol-gel method. Prepared NPs were dispersed in a binder at different powder/binder ratios: (0.1, 0.2, 0.5 and 1%w/wTiO2). However, before any application on artefacts, the nanomaterials need to be tested for their biocide efficiency and importantly for being harmless to cultural heritage material. X-ray powder diffractometry (XRPD), UV-Visible and Raman spectroscopies, scanning electron microscopy (SEM), and energydispersive X-ray spectroscopy (EDS) were used to characterize the as-prepared nanopowders. A set of experiments has been performed in order to investigate Gd3+-doped TiO2 nanomaterials as effective photocatalysts, for their photokilling activity against selected Gram positive and Gram negative bacteria and for the chromatic changes induced after their application on Lecce stone surfaces by performing colorimetric measurements.