Recent Advances in Protective Coatings for Cultural Heritage–An Overview

Hot spots and trends in microbial disease research on cultural heritage: a bibliometric analysis

This study is to understand and analyze the development history, research hotspots, and research trends in the study of microbial diseases of cultural heritage through bibliometric analyses in order to fill the current gap of no literature review in this research field and to make certain contributions to the research in this field and the protection of cultural heritage. Bibliometric and visual analyses of the literature on cultural heritage microbial diseases in the Web of Science (WoS) core collection were carried out using VOSviewer and R-bibliometrix, choosing the two main literature types of papers and reviews. The emphasis was placed on analyzing and summarizing core research strengths, hotspots, and trends. Six hundred sixty-seven documents (573 articles and 94 reviews) were retrieved. αIn the WoS core collection, the first literature on cultural heritage microbial disease research was published in January 2000, and the annual number of publications from 2000 to 2009 did not exceed one; the annual number of publications from 2010 onwards increased rapidly, and after 2018, the number of publications per year exceeded 60, reaching 94 in 2020, which indicates that cultural heritage microbial disease research is booming. Our research showed that Italy, the USA, and China were the leading research countries, and Univ Milan was the institution with the most publications. International Biodeterioration &Biodegradation was the most published and co-cited journal, and Gu JD was the most prolific author. The research hotspots in the study of microbial diseases of cultural heritage mainly include biological degradation of cultural heritage; identification of diseased microorganisms and disease mechanisms; cultural heritage microbial disease prevention and control methods; monitoring, prevention, and control of diseased microorganisms in indoor air; antibacterial agents, especially essential oils, nanoparticles, and other safe and efficient antibacterial products research and development; and exploration of the mechanisms of biofilm protection of cultural heritage on cultural heritage surfaces. Monitoring and identifying cultural heritage microbial communities, identifying disease mechanisms, and researching safe and efficient bacteriostatic products such as essential oils and nanoparticles will be the main research directions in the field of cultural heritage microbial disease prevention and control in the future.

New sustainable polymers and oligomers for Cultural Heritage conservation

The development of "green" chemistry materials with enhanced properties is a central topic in numerous applicative fields, including the design of polymeric systems for the conservation of works of art. Traditional approaches in art restoration comprise polymer thickeners and viscous dispersions to partially control solvents in the removal of soil or aged varnishes/coatings from artifacts. Alternatively, polymeric gel networks can be specifically designed to grant full control of the cleaning action, yielding safe, time- and cost-effective restorations. The selection of polymers and oligomers in gel design is crucial to tune solvent upload, retention, and controlled release over the sensitive artistic surfaces. Starting from an overview of traditional polymer formulations and state-of-the-art gel systems for cleaning works of art, we provide here the design of a new class of gels, focusing on the selection of oligomers to achieve gels with tailored hydrophilicity/hydrophobicity. We evaluated the oligomers Hydrophilic-Lipophilic Balance (HLB) by developing, for the first time, a novel methodology combining SEC and DOSY NMR analysis, which was tested on a library of "green" oligoesters synthesized by polycondensation and poorly explored in the literature. Oligomers with moderate polydispersity were chosen to validate the new protocol as a robust tool for designing polymeric gels even on industrial scale. The methodology is more time-effective than traditional methods, and gives additional insights on the oligomers physico-chemical nature, evaluating their compatibility with different solvents. Then, we used the selected oligoesters with castor oil to obtain a new class of organogels able to upload solvents with varying polarity, which effectively removed different types of unwanted layers typically found in painting restoration. These results validate the oligomers screening approach and the new class of gels as promising chemical processes/materials in art preservation. The methodology can potentially allow evaluation of HLB also for small molecules (e.g., surfactants), opening for the formulation of polymers solutions/gels beyond Cultural Heritage conservation, as in pharmaceutics, cosmetics, food industry, tissue engineering, agriculture, and others.

Visualization of the Sol-Gel Transition in Porous Networks Using Fluorescent Viscosity-Sensitive Probes

The sol-gel transition involves the transformation of a colloidal suspension into a system-spanning, interconnected gel. This process is widely used to reinforce mechanically weakened porous artifacts, such as sculptures but the impact of the restricted geometry (porous network) on the gelation dynamics of the solution remains unclear. Here, using fluorescent viscosity-sensitive molecular rotors, confocal microscopy, and model pores, we visualize the local viscosity changes at the microscale that accompany the sol-gel transition of a methyltriethoxysilane solution into a gel network. We show that, with evaporation of the solvent, a viscosity gradient develops near the free surface, triggering the sol-gel transition inside small pores near the surface. In homogeneous porous media, this leads to skin formation, which reduces the evaporation rate. In heterogeneous porous media, a gradient in gel density develops toward the heart of the porous material, where the gel formation mainly occurs as capillary bridges within smaller pores.

Application of Inorganic Nanomaterials in Cultural Heritage Conservation, Risk of Toxicity, and Preventive Measures

Nanotechnology has allowed for significant progress in architectural, artistic, archaeological, or museum heritage conservation for repairing and preventing damages produced by deterioration agents (weathering, contaminants, or biological actions). This review analyzes the current treatments using nanomaterials, including consolidants, biocides, hydrophobic protectives, mechanical resistance improvers, flame-retardants, and multifunctional nanocomposites. Unfortunately, nanomaterials can affect human and animal health, altering the environment. Right now, it is a priority to stop to analyze its advantages and disadvantages. Therefore, the aims are to raise awareness about the nanotoxicity risks during handling and the subsequent environmental exposure to all those directly or indirectly involved in conservation processes. It reports the human-body interaction mechanisms and provides guidelines for preventing or controlling its toxicity, mentioning the current toxicity research of main compounds and emphasizing the need to provide more information about morphological, structural, and specific features that ultimately contribute to understanding their toxicity. It provides information about the current documents of international organizations (European Commission, NIOSH, OECD, Countries Normative) about worker protection, isolation, laboratory ventilation control, and debris management. Furthermore, it reports the qualitative risk assessment methods, management strategies, dose control, and focus/receptor relationship, besides the latest trends of using nanomaterials in masks and gas emissions control devices, discussing their risk of toxicity.

Sustainable Secondary-Raw Materials, Natural Substances and Eco-Friendly Nanomaterial-Based Approaches for Improved Surface Performances: An Overview of What They Are and How They Work

To meet modern society’s requirements for sustainability and environmental protection, innovative and smart surface coatings are continually being developed to improve or impart surface functional qualities and protective features. These needs regard numerous different sectors, such as cultural heritage, building, naval, automotive, environmental remediation and textiles. In this regard, researchers and nanotechnology are therefore mostly devoted to the development of new and smart nanostructured finishings and coatings featuring different implemented properties, such as anti-vegetative or antibacterial, hydrophobic, anti-stain, fire retardant, controlled release of drugs, detection of molecules and mechanical resistance. A variety of chemical synthesis techniques are usually employed to obtain novel nanostructured materials based on the use of an appropriate polymeric matrix in combination with either functional doping molecules or blended polymers, as well as multicomponent functional precursors and nanofillers. Further efforts are being made, as described in this review, to carry out green and eco-friendly synthetic protocols, such as sol–gel synthesis, starting from bio-based, natural or waste substances, in order to produce more sustainable (multi)functional hybrid or nanocomposite coatings, with a focus on their life cycle in accordance with the circular economy principles.

Protection of Patinated Bronze with Long-Chain Phosphonic Acid/Organic Coating Combined System

Bronze cultural heritage in urban areas is susceptible to decay due to the significant amount of pollutants present in the air. This causes the dissolution of bronze and the patina on its surface. The efficient protection of outdoor bronze cultural heritage is still an unresolved problem. The aim of this work is to investigate 16-phosphonohexadecanoic acid as an environmentally friendly and non-toxic corrosion inhibitor for patinated bronze. The corrosion protection of sulphide-patinated bronze by phosphonic acid alone and in combination with acrylic coating Paraloid B-72 is examined. In order to achieve efficient corrosion protection, various parameters of the phosphonic acid application were studied. The efficiency of protection is examined by electrochemical impedance spectroscopy (EIS) during the immersion in simulated acid rain solution and after exposure to a corrosion chamber. It was found that the studied phosphonic acid provides corrosion protection to patinated bronze and significantly improves the protective properties of Paraloid B72. This was also confirmed by scanning electron microscopy (SEM) examination of the coating surface after exposure to a corrosive environment.

Rust Conversion of Proanthocyanidins to Archaeological Steel: A Case Study of Lingzhao Xuan in the Forbidden City

This work was focused on the rust conversion of proanthocyanidins (PC) for goethite (α-FeOOH), akaganeite (β-FeOOH) and lepidocrocite (γ-FeOOH), trying to show the potential of PC as an eco-friendly corrosion inhibitor and rust converter for archaeological steel conservation. The experiment used a rusted steel screw from Lingzhao Xuan of the Forbidden City in the Qing Dynasty and three kinds of pure iron oxyhydroxides as research samples. By means of micro-Raman, FTIR, XRD, XPS, SEM and EIS, PC had the ability to chemically react with iron oxyhydroxides in the rust, forming amorphous PC-FeOOH with a marked signal about 1384 cm^-1 as phenolic-Fe in infrared properties. The original relatively stable iron oxides were not induced to phase transformation and still remained. The converted rust layer could be more stable in the corrosive medium and increased the corrosion potential more effectively. Both the rust layer resistance and the charge transfer resistance of the archaeological samples were improved by at least 3 times with 5.0 g/L of PC, which could reasonably stabilize the archaeological rust and hindered external corrosive penetration into the core. It was a mild protection material that showed satisfactory performance for archaeological steel cultural heritage and has a good application prospect.

Non-Invasive Evaluation of Polymeric Protective Coatings for Metal Surfaces of Cultural Heritage Objects: Comparison of Optical and Electromagnetic Methods

The application of protective coatings is an effective preventive strategy to avoid metal corrosion. Constant monitoring of the coating’s quality is fundamental for the successful preservation of the metallic objects by reducing their interaction with corroding agents. Their evaluation over time helps to identify failure at early stages and promote their removal and substitution. Several methods have been employed for coating evaluation (i.e., chemical analysis, thickness and homogeneity investigation). In this paper, we compare three methods—Optical Coherence Tomography (OCT), Confocal Raman Microspectroscopy (CRM), and Eddy Currents (ECs)—to evaluate thickness values and coating integrity. The results from the two optical techniques (CRM and OCT) agree, being able to detect the inhomogeneity of the layer on a micron scale but requiring correction to account for the refraction phenomenon. The Eddy Current is a fast and efficient method for thickness estimation, providing data with millimetric lateral resolution.

The Susceptibility to Biodegradation of Some Consolidants Used in the Restoration of Mural Paintings

This study evaluated both the possible fungal metabolites involved in the degradation of the commercial consolidant known as Paraloid® B72 and the national artisanal consolidant named transparent dispersion of casein and the deteriorative potential of melanised fungi. Fungi were found to have the capacity to produce organic acids, proteases and esterases when they grow on consolidants, which can be used as nutrients. Mycelia produced by melanised fungi affected the appearance, as well as the integrity, of consolidants applied on painted experimental models and fragments of frescoes. In treatment trials with biocides (Biotin R®, Biotin T® and Preventol® RI 80), the morphology of the consolidants, as well as the vitality of the fungi, were assessed 30 days after the inoculation with melanic fungi. Direct observation, optical microscopy, colourimetry and microbiological analysis highlighted the degradation of the consolidants by fungi and their acquired resistance after biocidal treatments. Biotin R® applied by brushing on the surface of the consolidants proved to be the most effective treatment, followed by Biotin T®. Considering the overall results for both Paraloid® B72 and transparent dispersion of casein, use of Biotin R® applied by brushing is recommended for preventive conservation.

Micro and Nanoscale Structures and Corrosion Patterns in Brass: The Case Study of Ancient Roman Orichalcum Coins

This study investigated the micro and nanoscale structure in Cu-Zn alloy, as well as its corrosion patterns. To achieve this goal, a set of Roman orichalcum coins were analysed using Scanning Electron Microscopy (SEM-EDS), X-ray maps, high resolution field emission scanning electron microscopy (HR-FESEM-EDS) and electron microprobe analyser (EMPA) techniques. The samples showed a high degree of corrosion on their external surfaces, which evolved in depth up to ~1 mm. Micro and sub-micro imaging of the inner metal highlighted the presence of “stressed areas” caused by mechanical processing work, representing the trigger zone of corrosion and causing the loss of material. These images also permitted us to follow the grain-grain interface and selective Zn-dealloying in the examined samples. X-ray maps of Cu and Zn helped us to understand the evolution of the dezincification process, from rim to core. HR-FESEM-EDS imaging investigation highlighted a heterogeneous composition within the strain line structures, confirming that the mechanically stressed areas were active zones for corrosion processes. Cracks and voids also characterised the patina. Conversely, the uncorroded cores of the samples were not affected by dealloying.

Material Characteristics and Comparison of Silver Foil Glass Beads Excavated from the Tomb of King Muryeong in Korea

This study investigated the comprehensive characteristics of silver foil beads excavated from the Tomb of King Muryeong, based on composition analysis of the foil and glass and morphological characterization. The major element components of metal foil and glass were investigated using a scanning electron microscope (SEM) equipped with an Energy Dispersive X-ray spectrometer (EDS). Trace elements were determined using LA-ICP-MS to constrain the source of the raw material. The morphological characteristics of the beads were recognized through an optical microscope. As a result of the analysis, the metal foil was detected as pure in both gold- and silver-colored glass beads. The chemical composition of the glass was determined as a soda glass, with Na+ acting as a flux and CaO added as a stabilizer to improve durability. It was confirmed that plant ash was used because MgO and K2O were found to contain more than 1.5%. Through trace element analysis, it was confirmed that the gold and silver-colored silver foil glass beads were made of plant ash glass using different materials. The content of Fe2O3 was significantly higher in the gold-colored silver foil glass beads than in the silver-colored silver foil glass beads. Therefore, it can be interpreted that the gold-colored silver foil glass beads excavated from the tomb of King Muryeong intentionally achieved the appearance of gold foil glass beads by controlling the color of the outer glass. The silver foil glass beads showed morphological differences according to the color of the outer glass. The gold-colored silver foil glass beads were manufactured as single or segment types, but the silver-colored silver foil glass beads were manufactured as segment types.

Calcitic-based stones protection by a low-fluorine modified methacrylic coating

Atmospheric pollutants, such as NO_x, SO₂, and particulate matter, together with water percolation inside the stone pores, represent the main causes of cultural heritage decay. In order to avoid these undesired phenomena, the application of protective coatings represents a reliable solution. In this context, the present study focused on the synthesis of low-fluorine content methacrylic-based (MMA) polymeric resins characterized by seven F atoms (namely F7 monomer) in the lateral chains. Four different percentages (1.0, 2.5, 5.0, and 10.0%) of the present monomer were adopted to obtain a final polymeric structure showing the desired hydrophobicity, processability, and structural and thermal stability (even after accelerated UV aging tests). MMA_F7(1.0) seemed to be the optimal one; therefore, it was further applied onto Candoglia marble. Specifically, the treated substrates showed good surface hydrophobicity, water repellency, and water vapor transpirability. No color variation was observed even after a 1.5-year exposure in a real polluted environment (Monza Cathedral). Interestingly, the application of this coating hindered the atmospheric nitrates penetration inside the stones and, at the same time, it limited the sulfates (gypsum) formation, thus revealing a very promising marbles protection resin.

Novel Hydrophobic Nanostructured Antibacterial Coatings for Metallic Surface Protection

A simple and cost-efficient method to modify different surfaces in order to improve their bioactivity, corrosion and wear resistance proved to be sol-gel coatings. The silane layers have been shown to be effective in the protection of steel, aluminum or magnesium alloys and copper and copper alloys. Moreover, it has been found that the adding of different inorganic nanoparticles into silica films leads to increasing their performance regarding corrosion protection. In this study, we fabricated, a simple sol-gel method, transparent mono- and bi-layered hydrophobic coatings with simultaneous antibacterial, hydrophobic and anti-corrosive properties for the protection of metallic surfaces against the action of air pollutants or from biological attacks of pathogens. The first layer (the base) of the coating contains silver (Ag) or zinc oxide (ZnO) nanoparticles with an antibacterial effect. The second layer includes zinc oxide nanoparticles with flower-like morphology to increase the hydrophobicity of the coating and to improve corrosion-resistant properties. The second layer of the coating contains a fluorinated silica derivative, 1H,1H,2H,2H-perfluorooctyl triethoxysilane (PFOTES), which contributes to the hydrophobic properties of the final coating by means of its hydrophobic groups. The mono- and bi-layered coatings with micro/nano rough structures have been applied by brushing on various substrates, including metallic surfaces (copper, brass and mild steel) and glass (microscope slides). The as-prepared coatings showed improved hydrophobic properties (water CA > 90°) when compared with the untreated substrates while maintaining the transparent aspect. The corrosion resistance tests revealed significantly lower values of the corrosion rates recorded for all the protected metallic surfaces, with the lowest values being measured for the bi-layered coatings containing ZnO particles, both in the first and in the second layers of the coating. Considering the antibacterial activity, the most effective were the AOAg-II and AOZnO-II coatings, which exhibited the highest reduction of microbial growth.

Impact of Environmental Pollution in the Sustainability of Architectural Heritage: Case Study from Cartagena of India, Colombia

Limited studies have been carried out in emerging nations on the correlation among the environmental pollution, economic factors, and architectural heritage. For this reason, this research presents an assessment of environmental parameter values on materials deterioration used in architectural heritage in Cartagena de Indias; furthermore, it depicts the effect of heritage degradation on socioeconomic aspects of people whose livelihood depends on trade, tourism, and service activities. Dose-response functions were used for estimating of deterioration of carbon steel, copper, and zinc caused by relative humidity (RH), temperature (T), sulphur dioxide deposition (DSO2), and chloride deposition (DCl−). In addition, socioeconomic impact on architectural heritage was studied using a Socioeconomic Impact Survey (SEIS), with the sample of 174 individuals who work in areas of great architectural value in the city. The results show a corrosion rate (Vcorr) in the range of 80 < Vcorr < 200, 2.8 < Vcorr < 5.6 and 4.2 < Vcorr < 8.4 μm/year for carbon steel, copper, and zinc, respectively, due to the high level of pollutants. The high deterioration jointly with the lack of citizen culture affect the architectural heritage monuments causing a negative impact in several economic aspects. The establishment of public programs is essential for the conservation of the heritage monuments of the city.

Eco-Friendly Protective Coating to Extend the Life of Art-Works and Structures Made in Porous Stone Materials

The application of hydrophobic treatments to stone surfaces is the most common proven method to prevent, or at least limit, the degradation of stone-made constructions and artworks brought about by the ingress and action of water, in particular in the case of very porous stone materials. To avoid the use of protective products containing harmful solvents, new green products have been proposed. In this paper, an eco-friendly hydrophobic coating, based on a fluorine polymer dispersed in water, was deeply analyzed to evaluate its protective properties, especially for very porous stone substrates. To this aim, a wide characterization of treated and untreated Lecce stone elements, i.e., a stone typical of the Apulia region, was carried out to assess the optimum required amount, the effectiveness and the protective capability, even against graffiti staining, of the green hydrophobic treatment, still allowing the stone to retain adequate vapor permeability. The efficacy of the eco-friendly product was analyzed also after a short time (four weeks) of outdoor exposure. Suitable performance and short-term durability of the green hydrophobic coating were found, comparable or even greater than those reported in the current literature for other widespread commercial products, confirming the capability of the product to preserve porous stone surfaces even in absence of solvents in its formulation. The study also allowed to experiment with the “contact sponge” test as an appropriate method for evaluating the water absorption properties of the stone.

Innovative Silver-Based Capping System for Mesoporous Silica Nanocarriers Able to Exploit a Twofold Anticorrosive Mechanism in Composite Polymer Coatings: Tailoring Benzotriazole Release and Capturing Chloride Ions

In this work, engineered stimuli-responsive mesoporous silica nanoparticles (MSNs) were developed and exploited in polymer coatings as multifunctional carriers of a typical corrosion inhibitor, benzotriazole (BTA). In detail, a new capping system based on a BTA-silver coordination complex, able to dissolve in acid and alkaline conditions and to simultaneously tailor the BTA release and the capture of chloride ions, was properly designed and realized. Acrylic coatings embedding the engineered MSNs were deposited onto iron rebar samples and tested for their protective capability in acid and alkaline environments. Results highlighted the high potential of the proposed system for the protection of metals, due to the synergistic effect of the mesoporous structure and the capping system, which guaranteed both the sequestration of chloride ions and the on-demand release of the effective amount of anticorrosive agents able to ensure the enhanced protection of the substrate.

How Green Possibilities Can Help in a Future Sustainable Conservation of Cultural Heritage in Europe

We are moving towards a future that must be more sustainable in several aspects of society. Culture and cultural heritage have been recognized as indispensable parts of the sustainable growth of society, and the conservation model implemented in Europe has been considered as an example to follow at the economic, environmental, and social levels. The achievement of excellent results and the development of new technologies for the conservation of cultural heritage have highlighted the fundamental need for a method of sustainable conservation. In this commentary paper, we discuss two aspects that can contribute to sustainability in the future of conservation science: the use of innovative chemical products and the monitoring of outdoor sites by means of the forecast of the impact of dangerous factors on artistic surfaces. We are focusing mainly on the material aspect of cultural assets and how hard science can help in sustainable conservation. Even if the concept of sustainability has an ever-growing presence in our society, and different approaches have been given in different fields, it is still difficult to come up with a specific definition that can include the various hues of the world of cultural heritage conservation. The case studies presented in this paper are related to the European area and the advancements made for the sustainable preservation of such heritage. Considering the results obtained from both the chemical and the forecast side, we will try to summarize concisely the tasks that must be achieved in order to indicate as sustainable an approach to diagnostics for cultural heritage, including both the trans-disciplinary features of cultural heritage science and the scientific conservation of materials.

Nondestructive Evaluation of Heritage Object Coatings with Four Hyperspectral Imaging Systems

Advanced imaging techniques can noninvasively characterise, monitor, and evaluate how conservation treatments affect cultural heritage objects. In this specific field, hyperspectral imaging allows nondestructive characterisation of materials by identifying and characterising colouring agents, binders, and protective coatings as components of an object’s original construction or later historic additions. Furthermore, hyperspectral imaging can be used to monitor deterioration or changes caused by environmental conditions. This paper examines the potential of hyperspectral imaging (HSI) for the evaluation of heritage objects. Four cameras operating in different spectral ranges were used to nondestructively scan a beehive panel painting that originated from the Slovene Ethnographic Museum collection. The specific objective of this research was to identify pigments and binders present in the samples and to spatially map the presence of these across the surface of the art piece. Merging the results with databases created in parallel using other reference methods allows for the identification of materials originally used by the artist on the panel. Later interventions to the original paintings can also be traced as part of past conservation campaigns.

Environmental aspects of the depreciation of the culturally significant Wall of Cartagena de Indias - Colombia

Among the diverse archeological relics of the past, the Cartagena de Indias Wall is one of the greatest representations of European cultural architecture in South America. To assess the implication of contamination on the depreciation of the culturally significant Wall of Cartagena de Indias - Colombia, a detailed, multi-analytical approach was conducted on components of the wall. Accumulated ultra-fine particles (UFPs) and superficial nano-particles (NPs) containing hazardous elements (HEs) on the wall were identified in an attempt to understand whether atmospheric pollution is hastening the depreciation of the structure itself. Mortar which at one point held the stones together is now weak and has fallen away in places. Irreparable damage is being done by salt spray, acid rain and the site's tropical humid climate. Several HEs and organic compounds found within the local environment are also contributing to the gradual deterioration of the construction. In this study, advanced microscopy analyses have been applied to understand the properties of UFPs and NPs deposited onto the wall's weathered external walls through exposure to atmospheric pollution. Several materials identified by X-Ray Diffraction (XRD) can be detected using high-resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscope (FE-SEM). The presence of anglesite, gypsum, hematite containing HEs, and several organic compounds modified due to moisture and contamination was found. Black crusts located on the structure could potentially serve as a source of HEs pollution and a probable hazard to not only to the ecosystem but also to human health.

Surface Active Ionic Liquids Based Coatings as Subaerial Anti-Biofilms for Stone Built Cultural Heritage

New surface active ionic liquids (SAILs), based on cholinium cations and dodecylbenzenesulfonate as anion, have been synthesized and their potential application as antimicrobial colonization agents on cultural heritage (CH)stone materials investigated. The biocidal activity and antifouling capabilities were, preliminarily, evaluated by a screening on pure Gram (+) and Gram (−) bacteria strain cultures, yeasts, hyphomycetes and single-celled algae. Tests on stone materials (marble and tufa) vs. a stabilized community, constituted by a mixture of microbial strains, revealed that some SAILs display both antimicrobial and preventive antibiofilm action against new colonization. Analogous tests have been performed on the cholinium@halide precursors.

Testing the Feasibility of Titanium Dioxide Sol-Gel Coatings on Portuguese Glazed Tiles to Prevent Biological Colonization

Historical glazed wall tiles are a unique vehicle of artistic expression that can be found outdoors, integrating the buildings of many countries, therefore they are often subjected to biodeterioration. In this work, the applicability of protective coatings on glazed tiles to prevent biological colonization was evaluated. Thin films of titanium dioxide (TiO2) obtained by sol-gel were applied on glazed tiles to appraise its anti-biofouling properties and to evaluate their suitability for cultural heritage application. The TiO2 coating was tested on four different Portuguese glazed tiles and a modern tile. The chemical and mineralogical characterization of the glaze and ceramic body of the tiles was examined by wavelength dispersive X-ray fluorescence spectroscopy (WDXRF) and X-ray diffraction (XRD). The produced TiO2 coating was chemically and morphologically characterized by micro Raman spectroscopy (µ-Raman) and field emission scanning electron microscopy (FESEM). The anti-biofouling properties of the TiO2 treatment were evaluated by inoculating the fungus Cladosporium sp. on the glazed tiles. Potential chromatic and mineralogical alterations induced by the treatment were assessed by color measurements and XRD. The TiO2 coating did not prevent fungal growth and caused aesthetical alterations on the glazed tiles. A critical analysis evidenced that the tested coating was not suitable for cultural heritage application and highlighted the challenges of developing protective coatings for glazed tiles.

Present and Future Perspectives for Biocides and Antifouling Products for Stone-Built Cultural Heritage: Ionic Liquids as a Challenging Alternative

This review offers an overview of the most recent research activities on counteracting the biodeterioration process of stone monuments, underlining all those aspects regarding eventual procedural drawbacks and compliance with sustainable criteria. For this purpose, the definition of “green conservation of cultural heritage” has been proposed. Its basics have been utilized in the text to highlight the issues arising from the most common conservative procedures as well as guidelines for the development of innovative technologies. The review then deals with the most innovative antimicrobial approaches, among which nano- and bio-technologies play a main role. Ionic liquids are a special class of salts, which can be prepared by applying Safe by Design concepts, to meet the Green Conservation criteria.

Formulation of Mesoporous Silica Nanoparticles for Controlled Release of Antimicrobials for Stone Preventive Conservation

The biotic deterioration of artifacts of archaeological and artistic interest mostly relies on the action of microorganisms capable of thriving under the most disparate environmental conditions. Thus, to attenuate biodeterioration phenomena, biocides can be used by the restorers to prevent or slow down the microbial growth. However, several factors such as biocide half-life, its wash-out because of environmental conditions, and its limited time of action make necessary its application repeatedly, leading to negative economic implications. Sound and successful treatments are represented by controlled release systems (CRSs) based on porous materials. Here, we report on the design and development of a CRS system based on mesoporous silica nanoparticles (MSNs), as a carrier, and loaded with a biocide. MSNs, with a diameter of 55 nm and cylindrical pores of ca. 3-8 nm arranged as parallel arrays concerning the NP diameter, and with 422 m²/g of specific surface area were synthesized by the sol-gel method assisted by oil in water emulsion. Biocide loading and release were carried out in water and monitored by UV-Vis Spectroscopy; in addition, microbiological assay was performed using as control the MCM-41 mesoporous silica loaded with the same biocide. The role of specific supramolecular interaction in regulating the release is discussed. Further, we demonstrated that this innovative formulation was useful in inhibiting the in vitro growth of Kocuria rhizophila, an environmental Gram-positive bacterial strain. Besides, the CRS here prepared reduced the bacterial biomass contaminating a real case study (i.e., stone derived from the Santa Margherita cave located in Sicily, Italy), after several months of treatment thus opening for innovative treatments of deteriorated stone artifacts.

Superhydrophobic Coatings Based on Siloxane Resin and Calcium Hydroxide Nanoparticles for Marble Protection

Calcium hydroxide (Ca(OH2)) nanoparticles are produced following an easy, ion exchange process. The produced nanoparticles are characterized using transmission electron microscopy (TEM) and Fourier- transform infrared spectroscopy (FTIR) and are then dispersed in an aqueous emulsion of silanes/siloxanes. The dispersions are sprayed on marble and the surface structures of the deposited coatings are revealed using scanning electron microscopy (SEM). By adjusting the nanoparticle concentration, the coated marble obtains superhydrophobic and water repellent properties, as evidenced by the high static contact angles of water drops (> 150°) and the low sliding angles (< 10°). Because Ca(OH)2 is chemically compatible with limestone-like rocks, which are the most common stones found in buildings and objects of the cultural heritage, the produced composite coatings have the potential to be used for conservation purposes. For comparison, the wetting properties of another superhydrophobic and water repellent coating composed of the same siloxane material and silica (SiO2) nanoparticles, which were commonly used in several previously published reports, were investigated. The suggested siloxane+Ca(OH)2 composite coating offers good protection against water penetration by capillarity and has a small effect on the aesthetic appearance of marble, according to colorimetric measurements.