New method for the protection and restoration of calcareous cultural heritage stones by polyelectrolytes and hydroxyapatite nanocrystals

Adsorption of malachite green using waste marine cuttlefish bone powder: Experimental and theoretical investigations

Adsorption remediation is an energy-efficient water treatment technology that utilizes the adsorption properties of a biosorbent to remove various pollutants. While many articles have explored the high surface area and adsorption capacity of activated carbon for remediating aquatic systems, few have delved into the environmental impact of its synthesis, which often involves H3PO4, a highly toxic activating agent. In this study, we present a groundbreaking alternative to activated carbon for the adsorption and remediation of aquatic waste that doesn't rely on chemical products. Our discovery that cuttlefish bone, typically considered waste, can serve as an effective adsorbent is a significant leap in eco-friendly research and a source of inspiration for future sustainable solutions. We selected Malachite Green (MG) as a cationic toxic dye to evaluate the adsorption capacity of our green adsorbent. The prepared powder underwent characterization using techniques such as FTIR, XRD, SEM, and elemental analysis. Additionally, the determination of the cuttlefish bone's zero-point charge pH revealed a value of 8.4, which influences the material's surface charge and its interaction with ions and molecules in the solution. We conducted a detailed study on the effects of solution pH, adsorbent amount, Malachite Green concentration, temperature, and contact time on the dye adsorption. The results demonstrated that the adsorption of Malachite Green by cuttlefish bone powder is an endothermic process, requiring heat input. This indicates that the adsorption efficiency increases with temperature. The significant enthalpy results obtained confirmed the endothermic nature of the process. In this study, we combined experimental and theoretical approaches to gain a better understanding of the adsorption mechanism. The results showed that Cuttlefish Bone is an environmentally friendly and highly efficient adsorbent.

Carboxymethyl Chitosan as a Reversible Template of Calcium Phosphate for Multifunctional Conservation of Carbonate Stone

The accelerated deterioration of carbonate stone artifacts under climate change has long been an urgent issue. Inspired by biomineralization, we developed carboxymethyl chitosan-diammonium hydrogen phosphate (CD) composite and investigated the conservation effectiveness of the CD composite compared to diammonium hydrogen phosphate (DAP) on limestone. The morphologies and microstructures were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The consolidating effectiveness was investigated through a compressive strength test. The protective ability was assessed by disintegration resistance test, acid attack resistance test, salt attack resistance test, and freeze-thaw aging cycle test. SEM observations revealed that carboxymethyl chitosan (CMCS) served as an effective template, inducing the in situ formation of a uniform and continuous calcium phosphate coating on both the surface and interior of the stone. The tests indicated that the CD composite further enhanced the consolidating effectiveness and improved resistance to disintegration and freeze-thaw cycles. Notably, as an amphiphilic polyelectrolyte, CMCS functioned as a pH buffer and a protective barrier against sodium sulfate salts, which improved the resistance to acid and salt attacks. Additionally, the CD composite did not cause significant variations in the esthetic appearance or water vapor permeability. We then applied the CD composite at an actual carbonate stone cultural heritage site, successfully demonstrating the feasibility of CD application and the reversibility of CMCS in a real-world setting. Based on the study's results, our approach provides a new perspective for developing multifunctional and sustainable conservation materials for carbonate stone artifacts.

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.

Bioinspired nanostructured hydroxyapatite-polyelectrolyte multilayers for stone conservation

Stone-built cultural heritage faces threats from natural forces and anthropogenic pollutants, including local climate, acid rain, and outdoor conditions like temperature fluctuations and wind exposure, all of which impact their structural integrity and lead to their degradation. The development of a water-based, environmentally-friendly protective coatings that meet a combination of requirements posed by the diversity of the substrates, different environmental conditions, and structures with complex geometries remains a formidable challenge, given the numerous obstacles faced by current conservation strategies. Here we report the structural, electrical, and mechanical characterization, along with performance testing, of a nanostructured hydrophilic and self-healing hybrid coating based on hydroxyapatite (HAp) nanocrystals and polyelectrolyte multilayers (PEM), formed in-situ on Greek marble through a simple spray layer-by-layer surface functionalization technique. The polyelectrolyte-hydroxyapatite multilayer (PHM) structure resembled the design of naturally forming trabecular bone, attained at a short procedural time. It exhibited chemical affinity, aesthetical compatibility and resistance to weathering while offering reversibility. The proposed method is able to generate micron-sized coatings with controlled properties, such as adhesion and self-healing, leading to less weathered surfaces. Our results show that the PHM is a highly effective protective material that can be applied for stone protection and other similar applications.

From Nanoparticles to Gels: A Breakthrough in Art Conservation Science

Cultural heritage is a crucial resource to increase our society's resilience. However, degradation processes, enhanced by environmental and anthropic risks, inevitably affect works of art, hindering their accessibility and socioeconomic value. In response, interfacial and colloidal chemistry has proposed valuable solutions over the past decades, overcoming the limitations of traditional restoration materials and granting cost- and time-effective remedial conservation of the endangered artifacts. Ranging from inorganic nanoparticles to hybrid composites and soft condensed matter (gels, microemulsions), a wide palette of colloidal systems has been made available to conservators worldwide, targeting the consolidation, cleaning, and protection of works of art. The effectiveness and versatility of the proposed solutions allow the safe and effective treatment of masterpieces belonging to different cultural and artistic productions, spanning from classic ages to the Renaissance and modern/contemporary art. Despite these advancements, the formulation of materials for the preservation of cultural heritage is still an open, exciting field, where recent requirements include coping with the imperatives of the Green Deal to foster the production of sustainable, low-toxicity, and environmentally friendly systems. This review gives a critical overview starting from pioneering works up to the latest advancements in colloidal systems for art conservation, a challenging topic where effective solutions can be transversal to multiple sectors even beyond cultural heritage preservation, from the pharmaceutical and food industry, to cosmetics, tissue engineering, and detergency.

Polyelectrolyte Coatings-A Viable Approach for Cultural Heritage Protection

The continuous degradation of cultural heritage artifacts (due to different factors, including the rising air pollution, climate change or excessive biological activity, among others) requires the continuous development of protection strategies, technologies and materials. In this regard, polyelectrolytes have offered effective ways to fight against degradation but also to conserve the cultural heritage objects. In this review, we highlight the key developments in the creation and use of polyelectrolytes for the preservation, consolidation and cleaning of the cultural heritage artifacts (with particular focus on stone, metal and artifacts of organic nature, such as paper, leather, wood or textile). The state of the art in this area is presented, as well as future development perspectives.