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Lincolnshire limestone before and after the treatment with nanolime. Schematic representation of the application of calcium hydroxide nanoparticles (Transmission Electron Microscopy image), the formation of calcium carbonate after the reaction with carbon dioxide, and Scanning Electron Microscopy image of the consolidated stone.
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The unpredictable effects of climate change impose the safeguarding of Cultural Heritage (CH) with effective and durable materials as a vital solution in the invaluable socioeconomic resource of CH. Conservation products and methodologies are addressed under recent advancements in colloidal science providing multi-functional solutions for cleaning,...
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... treatments for stone materials aim to "reestablish totally or partially the cohesion loss, while keeping the impact of any foreseeable negative side effect at its possible minimum" [27]. In the '90s nanolime was first synthesised and applied in heritage conservation, in order to overcome some of the drawbacks of limewater, which has been used to consolidate limestones and plasters for centuries (Figure 2). Nanolime consists of a water/alcoholic dispersion of calcium hydroxide (Ca(OH) 2 ) nanoparticles in concentrations of 5-50 g/L, with sizes between 50 and 600 nm [28]. ...
Citations
... Sol in liquid can be easily introduced into cultural heritage, where it solidifies via gelation and/ or drying processes [16,17]. It has been widely used to conserve stone [18,19], paper [20] and paintings [21]. In this study, a hybrid sol with very nice compatibility between two components was prepared by mixing homemade alumina sol and silica sol and it was introduced by a Quasi-Dynamic Equilibrium Method for the conservation of ivory in relatively large size. ...
Large amount of ivory was excavated from Sanxingdui site which was waterlogged, severely degraded and in urgent need for conservation. There has been much effort for the conservation of waterlogged ivory by scientists. However, due to a lack of appropriate conservation material and the need to use non-destructive methods, no satisfactory results have been achieved previously. In this work, a novel formulated water-based Al–Si hybrid sol of size about 20 nm was prepared and introduced through a quasi-dynamic equilibrium method to waterlogged ivory tusk for the purpose of conservation. Good conservation performance could be achieved, since Al–Si sol gradually permeates into the interior of the ivory, distributes homogeneously and connects the loose components of ivory. Samples treated with appropriate amount of Al–Si sol displayed satisfactory compressive strength and porous intact structure. It was found that the fluidity of Al–Si sol had a significant influence on the conservation effect. Moreover, Al–Si sol not only consolidated HAP but also worked well on the soil embedded in unearthed ivory, which was beneficial to conserve ivory intactly. Slightly negatively charged Al–Si hybrid gel could interact with ivory matrix through multiple interactions including van der Waals force, electrostatic interaction, chemical and hydrogen bonding.
... This research aims to provide valuable insights into the intricate relationships between material properties and the performance of surface treatments for natural stone. The efficiency of silver nanoparticles in the protection of stone substrates by treating two different porous sedimentary stones with siloxane-based coupling agents and silver nanoparticles obtained in the laboratory was evaluated and was proved to ensure long-term protection against biofilm formation [32][33][34][35]. Silver nanoparticles have high antimicrobial activity (bactericidal, fungicidal activity) [12]. ...
... The combination of covalent and ionic bonding mechanisms contributes to the effectiveness and longevity of the treatment, making it a promising method for enhancing the properties of natural stone surfaces. One important aspect of the stone treatment is the right selection of coupling agent, which ensures the anchoring of most nanoparticles on the mineral substrate [28,33]. ...
The biodeterioration of the natural surface on monuments, historical buildings, and even public claddings brings to the attention of researchers and historians the issues of conservation and protection. Natural stones undergo changes in their appearance, being subjected to deterioration due to climatic variations and the destructive action of biological systems interfering with and living on them, leading to ongoing challenges in the protection of the exposed surfaces. Nanotechnology, through silver nanoparticles with strong antimicrobial effects, can provide solutions for protecting natural surfaces using specific coupling agents tailored to each substrate. In this work, surfaces of two common types of natural stone, frequently encountered in landscaping and finishing works, were modified using siloxane coupling agents with thiol groups. Through these agents, silver nanoparticles (AgNPs) were fixed, exhibiting distinct characteristics, and subjected to antimicrobial analysis. This study presents a comparative analysis of the efficiency of coupling agents that can be applied to a natural surface with porous structures, when combined with laboratory-obtained silver nanoparticles, in reducing the formation of microbial biofilms, which are a main trigger for stone biodeterioration.
... These materials have the ability to act as reinforcing agents improving hydrophobic and thermo-mechanical properties. Additionally, they can incorporate biocidal capabilities, enabling the development of advanced tailor-made products for different stone lithotypes and protection needs [46,47]. Specifically, TiO 2 and lanthanide-TiO 2 NPs have demonstrated their high effectiveness when combined with silane/siloxane and acrylic or epoxy matrices. ...
This study was aimed at developing a sustainable versatile bio-based epoxy-silica material to be potentially employed as hydrophobic and biocidal consolidating product in the field of stone conservation. For this purpose, two hybrid formulations containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol diglycidylether (CBDO-DGE), a cycloaliphatic epoxy precursor derived from the arnica root, together with (3-glycidyloxypropyl)trimethoxysilane (GPTMS) and octyltriethoxysilane (OcTES) as silica-forming additives, were chosen as the basis of the multifunctional material to be finely adjusted and gain biocidal properties. With this goal in mind, different synthetic strategies based on ionic liquids (ILs), essential oils (EOs) and nanoparticles (NPs) doping have been employed. Specifically, dimethyloctadecyl[3(trimethoxysilyl)propyl]ammonium chloride (QAS), tetradecyl phosphonium chloride (QPS) and thymol, as well as cerium-TiO2 NPs and thymol-loaded SiO2 NPs were incorporated into the starting hybrid formulations, during the sol-gel process, to investigate their influence on the network formation. First, distribution studies by scanning electron microscopy/energy-dispersive X-ray (SEM-EDS) analysis were performed, whereas the suitability of each formulation to match the main requirements for a stone conservation material was evaluated in terms of thermostability, hydrophobicity and inhibition of the microbiological growth by a combination of TG-DTA, DSC, dynamic mechanical analysis (DMA), with contact angle and disk-diffusion measurements, respectively. Based on the data analysis, it was observed that the direct incorporation of ILs and EOs had an adverse effect on the ability of GPTMS to act as a coupling agent. This resulted in decreased thermal stability and a 50 % reduction in glass transition temperatures, along with the retention of hydrophilic behavior. In contrast, the inclusion of NPs did not significantly interfere with the hybrid network formation, and effectively maintained the thermo-mechanical and hydrophobic properties of the hybrids within satisfactory parameters. Consequently, both nanocomposite materials were further tested on stone samples by artificial ageing experiments under acidic atmosphere. In view of the results, the hybrid enriched with thymol-loaded SiO2 NPs demonstrate the most suitable thermo-mechanical and hydrophobic properties (Tonset, Tα and CA values of 276 °C, 54 °C and 100°, respectively), as well as a proper biocidal capability against bacteria. Furthermore, the developed material provided effective stone protection, resulting in a 92 % reduction in material loss, while preserving the substrate chromatic characteristics (ΔE 2.23). These findings suggest that the proposed treatment meets the first main requirements for stone conservation.
... (B) shows the following process of soft lithography, as used for the PDMS micromodel, where the result from hard photolithography (3) is used as a template (4) for PDMS imprint manufacture after and additional anti-stick treatment. PDMS is freshly mixed and poured on to the template (5), then baked before peeling (6), activation, functionalization and bonding, yielding a microchannel in PDMS (7). Based on source [57] with permission. ...
Nanolimes have been commercially available for over a decade as a remineralization agent for natural stone to combat deterioration. While they have been applied successfully and studied extensively, their penetration abilities in different materials have not yet been readily quantifiable in situ and in real time. Using two transparent pore-imitating test systems (acrylic glass (PMMA) and polydimethylsiloxane (PDMS)) and light microscopy, the penetration coefficients (PCs) of two nanolimes (CaLoSiL (CLS) and Nanorestore Plus (NRP)), as well as their solvents, were determined experimentally in square channels of about 100 µm diameter. Their PCs and those for a previously published glass-resin-based test system were also predicted based on measurable material parameters or literature values using the Lucas-Washburn equation. Additionally, a liquid mineral precursor (LMP) of calcium carbonate based on complex coacervation (CC) was investigated as an alternative to the solid particle dispersions of nanolime. In general, the dispersions behaved like their pure solvents. Overall, trends could be reasonably well predicted with both literature and experimentally determined properties using the Lucas-Washburn equation. In absolute terms, the prediction of observed infiltration behavior was satisfactory for alcohols and nanolimes but deviated substantially for water and the aqueous LMP. The commercially available PMMA chips and newly designed PDMS devices were mostly superior to the previously published glass-resin-based test system, except for the long-term monitoring of material deposition. Lastly, the transfer of results from these investigated systems to a different, nontransparent mineral, calcite, yielded similar PC values independently of the original data when used as the basis for the conversion (all PC types and all material/liquid combinations except aqueous solutions in PDMS devices). This knowledge can be used to improve the targeted design of tailor-made remineralization treatments for different application cases by guiding solvent choice, and to reduce destructive sampling by providing a micromodel for pretesting, if transferability to real stone samples proves demonstrable in the future.
This research describes the effects of two innovative aqueous polyacrylate polymers on the microstructure of porous stone materials. Such latex nanodispersions have been designed (with and without fluorination) as consolidation agents and tested on two types of sandstone, namely, Prague (Mšené) and Obernkirchen, largely used as building materials for valuable Cultural Heritage objects. Quantitative description of the polymer distribution within the specimens was obtained noninvasively by adopting synchrotron radiation computed microtomography. The propagation-based phase-contrast mode was adopted to test its effectiveness in enabling the recognition of the polymers in the two matrices, which is usually hampered by their low attenuation coefficient for X-rays. Quantitative image analysis revealed significant dissimilarities in total porosity, specific surface area of pores, connectivity density and fractal dimension as a consequence of the consolidation treatments. For instance, about 7% and 3% lower porosity values were found in the consolidated Prague and Obernkirchen sandstones, respectively, with the distribution shifted towards smaller pores. Furthermore, the simulation of water transport, based on the retrieved pore network, evidenced a decrease in water permeability and diffusivity of more than one order of magnitude in the treated samples; the effect was more pronounced along the direction of penetration of the consolidating agent. Overall, both latexes exhibited similar film-forming and pore-filling abilities. In general, the results highlighted the high potential of synchrotron-based 3D X-ray imaging for the quantitative assessments of the porous microstructure of consolidated building materials.
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.
The present study proposes the one‐step synthesis of Zn/Ca hybrid nano‐oxides combining an electrochemical route to ZnO nanostructures (NSs) with the wet chemical production of Ca(OH)2 NSs. ZnO is a known antimicrobial and Ca(OH)2 has consolidating properties, both appealing for stone artwork preservation in the field of cultural heritage. Two concentrations of the electrolytic bath (NaOH 0.1 and 0.4 M) were studied resulting in distinct final nanomaterials (Zn−Ca0.1 and Zn−Ca0.4). Fourier transform infrared, X‐ray photoelectron spectroscopies, and transmission electron microscopy demonstrated that Zn−Ca0.1 consisted of lamellar calcium hydroxyzincate NSs, whereas Zn−Ca0.4 showed hexagonal Ca(OH)2 (∼500 nm) and ZnO (∼50 nm) NSs. Nanocoatings prepared with Zn−Ca0.1 exhibited a Zn2+ release increasing up to 1 μmol cm−2 in 24 h. Instead, Zn−Ca0.4‐based nanocoatings released a constant value of about 0.35 μmol/cm2. Both types of nanocoatings showed good antimicrobial activity against Bacillus subtilis after 48 h and hydrophilic behavior over 28 days. Two is better than one: A new one‐step synthesis method is proposed here combining the electrosynthesis of zinc oxide nanoparticles and the chemical synthesis of calcium hydroxide nanostructures. Hybrid zinc/calcium nano‐oxides are then produced with the aim of creating synergic nanostructures with antimicrobial/consolidating properties, which are ideal for the preservation and conservation of stone artworks.
