Colloidal Nanocrystalline Semiconductor Materials as Photocatalysts for Environmental Protection of Architectural Stone

Francesca Petronella,Antonella Pagliarulo,Maria Curri,Mariateresa Lettieri,Angela Calia,Donato Colangiuli,Roberto Comparelli,Marinella Striccoli

doi:10.3390/cryst7010030

Abstract

Rod-shaped TiO2 nanocrystals (TiO2 NRs), capped by oleic acid molecules (OLEA), were synthesized with controlled size, shape and surface chemistry by using colloidal routes. They were investigated for application as coating materials for preserving architectural stone of monumental and archaeological interest, in consideration of their self-cleaning and protection properties. For this purpose, two different deposition techniques, namely casting and dipping, were tested for the application of a nanocrystal dispersion on a defined stone type, as a relevant example of porous calcarenites, namely the Pietra Leccese, a building stone widely used in monuments and buildings of cultural and historic interest of the Apulia region (Italy). The physical properties of the stone surface were investigated before and after the treatment with the prepared nanostructured materials. In particular, colour, wettability, water transfer properties and stability of the coating were monitored as a function of time and of the application method. The self-cleaning properties of the TiO2 NRs coated surfaces were tested under simulated and real solar irradiation. The obtained results were discussed in the light of the specific surface chemistry and morphology of TiO2 NRs, demonstrating the effectiveness of TiO2 NRs as an active component in formulations for stone protection.

Highlights

Preventive conservation of stone buildings and monuments represents a crucial challenge, due to peculiar relevance of the extraordinary cultural heritage in many countries
TiO2NR Characterization synthesized TiO2 NRs were washed five times according to the procedure described in the Experimental
Section to remove the excess with of uncoordinated infrared spectroscopy in attenuated total reflectance mode (FT-IR-Attenuated Total Reflection (ATR)) characterization, the as Figure 1a, reports the typical transmission electron microscopy (TEM) micrograph of the obtained sample, which is found to consist synthesized TiO2 NRs were washed five times according to the procedure described in the of rod-shaped and high aspect ratio nanocrystals of about 3 nm in diameter

Summary

Introduction

Preventive conservation of stone buildings and monuments represents a crucial challenge, due to peculiar relevance of the extraordinary cultural heritage in many countries. The causes of deterioration of historical immovable objects are multifold, innovative treatments, effective in providing multiple answers, would be amenable. In this perspective, the monument surface should be protected by multifunctional coatings, able to comply several fundamental conditions that make such a multidisciplinary task extremely challenging. Chemical aging of acrylic-based polymers due to photo-oxidative reactions leads to the formation of oxidized species such as c-lactones, which cause the polymeric coating to yellow, affecting the aesthetic features of the treated surfaces [5]

Methods

Results

Conclusion