In recent times, nanomaterials have been applied in the construction and maintenance of the worldALs cultural heritage with the aim of improving the consolidation and protection treatments of damaged stone. These nanomaterials include important advantages that could solve many problems found in the traditional interventions. The present paper aims to carry out a review of the state of art on the application of nanotechnology to the conservation and restoration of the stony cultural heritage. We highlight the different types of nanoparticles currently used to produce conservation treatments with enhanced material properties and novel functionalities.

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New nanomaterials for applications in conservation and restoration of stony materials: A review

The present paper reviews the methods and the performance of in situ formation of calcium phosphates (CaP) for the conservation of materials belonging to cultural heritage. The core idea is to form CaP (ideally hydroxyapatite, HAP, the most stable CaP at pH > 4) by reaction between the substrate and an aqueous solution of a phosphate salt. Initially proposed for the conservation of marble and limestone, the treatment has been explored for a variety of different substrates, including sandstones, sulphated stones, gypsum stuccoes, concrete, wall paintings, archaeological bones and paper. First, the studies aimed at identifying the best treatment conditions (e.g., nature and concentration of the phosphate precursor, solution pH, treatment duration, ionic and organic additions to the phosphate solution, mineralogical composition of the new CaP phases) are summarized. Then, the treatment performance on marble and limestone is reviewed, in terms of protective and consolidating effectiveness, compatibility (aesthetic, microstructural and physical) and durability. Some pilot applications in real case studies are also reported. Recent research aimed at extending the phosphate treatment to other substrates is then illustrated. Finally, the strengths of the phosphate treatment are summarized, in comparison with alternative products, and some aspects needing future research are outlined.

Hydroxyapatite and Other Calcium Phosphates for the Conservation of Cultural Heritage: A Review.

Hydroxyapatite coatings for marble protection: Optimization of calcite covering and acid resistance

Iron-based nanoparticles in wastewater treatment: A review on synthesis methods, applications, and removal mechanisms

Discrete α-FeOOH nanoparticles (5–10 nm) were synthesized by a simple electrochemical method using an ionic liquid (IL), dodecyltrimethylammonium bromide (IL − FeOOH). IL that acts as an only electrolyte is capable of producing IL − FeOOH nanoparticles without any agglomeration. Its crystallinity, morphology, functional characteristics, and surface area were analyzed using an X-ray diffractometer, a transmission electron microscope, a Fourier-transform infrared spectrometer, and the Brunnauer–Emmett–Teller (BET) method, respectively. The characterization results verified that reverse micelle formation of IL plays an important role in the stabilization and miniaturization of the α-FeOOH nanoparticles. The activity of IL-FeOOH was tested on a photo-Fenton-like degradation of 2-chlorophenol (2-CP). Results showed that a nearly neutral condition of pH 5 was able to completely degrade 2-CP within 180 min of reaction at 50 °C, using 0.03 g L−1 of catalyst dosage and 50 mg L−1 of 2-CP initial concentration, with only a small amount of H2O2 (0.156 mM). It was found that the reverse micelle formed around the catalyst surface could trap the photogenerated electron to inhibit the recombination of photo-induced electron–hole pairs thus enhancing its catalytic activity. Kinetic studies using the Langmuir–Hinshelwood model illustrated that a surface reaction was the controlling step of the process. A reusability study showed that the catalyst was still stable after four subsequent reactions as shown by infrared spectroscopy. The results provide strong evidence to support the potential use of using IL as an alternative electrolyte to synthesize photo-Fenton-like nanocatalyst that can be used to treat organic pollutants such as 2-CP.

Synthesis of reverse micelle α-FeOOH nanoparticles in ionic liquid as an only electrolyte: Inhibition of electron–hole pair recombination for efficient photoactivity

Antireflective coating based on TiO2 nanoparticles modified with coupling agents via acid-catalyzed sol-gel method

Caoxite-hydroxyapatite composition as consolidating material for the chalk stone from Basarabi–Murfatlar churches ensemble

Surface investigations of old book paper treated with hydroxyapatite nanoparticles

In this research work, silica nanoparticles and silica-gentamicin nanostructured solution were synthesized by using the microwave-assisted synthesis, in basic medium, using two silane precursors (tetraethylorthosilicate and octyltriethoxysilane) and the antibiotic (gentamicin sulfate). The prepared materials were characterized through Fourier transform infrared (FTIR) spectroscopy, TGA analysis, transmission electron microscopy (TEM), and atomic force microscopy (AFM) to investigate the morphology and structure. Antimicrobial studies of the silica-gentamicin nanostructured solution versus silica nanoparticles were performed against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. FTIR spectra showed that the gentamicin has been loaded to the silica nanoparticles. AFM analysis showed that the morphology of the silica-gentamicin nanostructured solution has changed, and agglomerations of particles are present at the surface. Antimicrobial testing, performed using the diffusion method through spot inoculation, indicates that the silica-gentamicin nanostructured solution exhibited activity against the resistant strain. The obtained silica-gentamicin solution can be used as biochemical agent for the prevention and treatment of microorganisms which are deposited on different surfaces (e.g., glass, plastic, ceramic).

https://www.mdpi.com/1996-1944/14/8/2086/pdf

Valentin Rădiţoiu

Papers

Antireflective coating based on TiO2 nanoparticles modified with coupling agents via acid-catalyzed sol-gel method

Caoxite-hydroxyapatite composition as consolidating material for the chalk stone from Basarabi–Murfatlar churches ensemble

Surface investigations of old book paper treated with hydroxyapatite nanoparticles

Preparation and Characterization of Silica Nanoparticles and of Silica-Gentamicin Nanostructured Solution Obtained by Microwave-Assisted Synthesis.

A facile hydrothermal route for the synthesis of α-FeOOH with controlled morphology