Characterization of calcium carbonate nanoparticles with architectural application for the consolidation of Pietraforte

Laboratory-synthesized CaCO3 nanoparticles and their nanodispersion in 1,4-butanediol as a working medium have been first characterized and then tested on the surface of Pietraforte stone that forms the cladding of the bell tower of San Lorenzo. Both CaCO3 nanoparticles and their nanodispersion in 1,4-butanediol were characterized in the church in Florence, Italy by X-ray diffraction, thermal analysis, Raman, and Fourier transform infrared spectroscopy, scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) spectroscopy, and transmission electron microscopy/EDX spectroscopy. The Pietraforte sample surface, before and after CaCO3 nanodispersion treatments, was characterized by comparison of the porosity and specific surface area, capillary absorption, and surface hardness. An ultrastructural morphological investigation by SEM was also carried out, confirming and implementing the effective dynamics of the nanodispersion action. Lastly, differences in stone optical appearance before and after treatment were evaluated by colorimetric measurements. Considering the obtained results of the study, we conclude that CaCO3 nanodispersion in 1,4-butanediol is an effective restorative agent that prevents water infiltration in the stone, reduces stone disruption, and promotes its consolidation without altering its appearance. Finally, the long-lasting stability of the CaCO3 nanodispersion at ambient conditions makes it suitable for production and commercialization.