Stone/Coating Interaction and Durability of Si-Based Photocatalytic Nanocomposites Applied to Porous Lithotypes

Advancements in Stone Object Restoration Using Polymer-Inorganic Phosphate Composites for Cultural Heritage Preservation

Recent advancements in cultural heritage preservation have increasingly focused on the development and application of new composites, harnessing the diverse properties of their components. This study reviews the current state of research and practical applications of these innovative materials, emphasizing the use of inorganic phosphatic materials (in particular the hydroxyapatite) and various polymers. The compatibility of phosphatic materials with calcareous stones and the protective properties of polymers present a synergistic approach to addressing common deterioration mechanisms, such as salt crystallization, biological colonization, and mechanical weathering. By examining recent case studies and experimental results, this paper highlights the effectiveness, challenges, and future directions for these composites in cultural heritage conservation. The findings underscore the potential of these materials to enhance the durability and aesthetic integrity of heritage stones, promoting sustainable and long-term preservation solutions.

TEOS-Based Superhydrophobic Coating for the Protection of Stone-Built Cultural Heritage

Tetraethyl orthosilicate (TEOS) is extensively used in the conservation of stone-built cultural heritage, which is often subjected to water-induced degradation processes. The goal of this study was to produce and study a TEOS-based material with the ability to repel liquid water. A sol solution of TEOS and 1H,1H,2H,2H-perfluorooctyl triethoxysilane (FAS) was prepared and deposited on marble. The static contact angles (CAs) of water drops on the coated marble surface were >170° and the sliding angles (SA) were <5°, suggesting that superhydrophobicity and water repellency were achieved on the surface of the synthesized TEOS-based coating. FTIR and SEM-EDS were employed to characterize the produced coating. The latter offered good protection against water penetration by capillarity, reducing the breathability of marble only by a small extent and with practically no effect on its aesthetic appearance. The durability of the coating was evaluated through various tests that provided very promising results. Finally, the versatility of the method was demonstrated as the TEOS-based coating was successfully deposited onto glass, brass, wood, silicon, paper and silk, which obtained extreme wetting properties.

Artificial Ageing of Photocatalytic Nanocomposites for the Protection of Natural Stones

During the last ten years, photocatalytic nanocomposites combining titania nanoparticles with silicon-based matrices have received increasing attention in the stone conservation research field, because they offer an effective multifunctional approach to the issue of stone protection. However, much work still has to be done in studying the behaviour of these nanocomposites in real environmental conditions and understanding to what extent they are able to retain their effectiveness and compatibility once applied on outdoor surfaces. The latter is a key information that should lie at the basis of any successful conservation and maintenance campaign. The present study provides insight into this relevant topic trough laboratory testing by assessing the artificial ageing of two silane-based photocatalytic nanocomposites, previously selected through an accurate testing on different natural stones. Three accelerated ageing procedures, based on artificial solar irradiation, heating and rain wash-out, allowed simulating about two years of outdoor exposure to some of the weathering factors to which stones are normally subjected. The results provided quite accurate information about the long-term behaviour of the products and on the role that the stone properties play therein. It was shown that, when the products are able to penetrate deeply enough inside the stone pores, they retain much of their hydrophobising and photocatalytic properties and maintain a good compatibility with the stone substrates, even after partial chemical degradation of the alkyl-silica matrices has occurred on the very stone surface.

Conservation of the Built Heritage: Pilot Site Approach to Design a Sustainable Process

The conservation project of built heritage is a complex process, dealing with an extremely heterogeneous range of elements and different substrates with a large variety of conservation conditions. In recent years, its sustainability has become a relevant issue, due to the general limitation of resources and unique features of cultural heritage assets. The conservation project, therefore, requires a thorough knowledge of the specific characteristics of the site, a reliable evaluation of the treatment’s efficacy and durability, and efficient control of procedures and timing of the site during the conservation activities. A suitable approach to design the intervention is the implementation of a pilot site for the knowledge of surfaces and structures, and for the testing of different operative procedures. This approach needs the collaborative work of a multidisciplinary team coordinated by the project manager. This paper reports on the design of the conservation project of the Renaissance façade of the Monza cathedral, with the development of a pilot site as a relevant example of a complex surface. The three-phase process—preliminary knowledge, testing and implementation of the treatment methodologies, and scale-up to the general conservation project—is described and discussed with significant reference to real data from the case study.

Special Issue: Novel Photoactive Materials

Photoactivity represents the ability of a material to activate when interacting with light. It can be declined in many ways, and several functionalities arising from this behavior of materials can be exploited, all leading to positive repercussions on our environment. There are several classes of effects of photoactivity, all of which have been deeply investigated in the last few decades, allowing researchers to develop more and more efficient materials and devices. The special issue “Novel Photoactive Materials” has been proposed as a means to present recent developments in the field; for this reason the articles included touch different aspects of photoactivity, from photocatalysis to photovoltaics to light emitting materials, as highlighted in this editorial.