Laura Bergamonti

Synthesis and characterization of nanocrystalline TiO2 with application as photoactive coating on stones.

Self-cleaning photocatalytic coatings for biocalcarenite stones, based on TiO2 nanoparticles obtained by sol–gel processes at different pH values and also adding gold particles, have been investigated. The selected test material is a biocalcarenite named “pietra di Lecce” (Lecce stone), outcropping in Southern Italy. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and Raman investigations were carried out to characterize the TiO2 nanoparticles and coatings. Nanocrystalline anatase and, to a lesser extent, brookite phases are obtained. Photocatalytic activity of the TiO2 sols and of the coatings on “pietra di Lecce” was assessed under ultraviolet irradiation, monitoring methyl orange (MeO) dye degradation as a function of time. To evaluate the harmlessness of the treatment, colorimetric tests and water absorption by capillarity were performed. The results show good photodegradation rates for titania nanosols, particularly when putting in Au particles, whereas a satisfactory chromatic compatibility between the sol and the surface of the calcarenite is found only without Au addition.HighlightsSols of nanocrystalline titania at different pH values and with Au particles were prepared and characterized.Satisfactory photodegradation of MeO by the sols in solution and on calcarenite-coated surfaces is obtained.The addition of Au particles improves the photodegradation activity but gives poor chromatic results on “pietra di Lecce.”

The Nature of the Pigments in Corals and Pearls: A Contribution from Raman Spectroscopy

ABSTRACT Raman measurements at 473.1 nm on corals, both calcitic and aragonitic, and on pearls (aragonitic) were performed to elucidate the nature of the pigments, with the relative importance of methylated (carotenoids) or nonmethylated polyenes involved in the color associated with marine mineralized organisms still being a debated question. The resonance condition of the laser excitation enables the observation of overtones and combinations of four main vibrational modes of the polyenic or carotenoid pigment up to > 5000 cm−1. Raman spectroscopy proves to be a powerful tool to determine the biomineralized structure, the nature of the pigments, and the presence of artificial dyes.

Micro-Raman investigation of pigments and carbonate phases in corals and molluscan shells

We report the results of a micro-Raman investigation, in resonance conditions, on the pigments and on the nature of the biogenic carbonate in different species of corals and marine shells of a wide variety of colours. Corallium rubrum (Anthozoa) and Stylaster roseus (Hydrozoa) show calcite and aragonite skeletons, respectively. The shells are mostly aragonitic, with the exception of bivalves of Pectinidae family which reveal a calcite/aragonite distribution. The main Raman features of the pigments (carotenoids or polyenes) show Raman dispersion (upshift of the C=C (ν 1 ) and C–C (ν 2 ) stretching vibration frequencies of the polyenic chain with decreasing excitation wavelength). Partially or completely demethylated polyenes with different conjugation lengths may be responsible for the colours of Corallium rubrum and of most of the marine shells. Stylaster roseus and the dark brown colours of Gibbula sp (Gastropod class) show typical bands of carotenoids, similar to those found in canthaxanthin. Overtones and combination bands are described in terms of the four fundamental vibrations of polyenes. A constant ratio between ν 1 and ν 2 frequencies, nearly independent of the Raman excitation wavelength, has been determined from a large set of data for corals and shells. A simple relationship between the main Raman frequencies and the effective conjugation length N of the polyenic chains is suggested.

Nanocrystalline TiO2 coatings by sol–gel: photocatalytic activity on Pietra di Noto biocalcarenite

Self-cleaning photocatalytic coatings based on TiO2 nanoparticles obtained by sol–gel techniques at two different pH values (1.3–10.6) have been investigated on carbonatic stone. The selected material is the yellowish lithofacies of Palazzolo Formation calcarenite, commonly named Pietra di Noto, widely used in the Baroque monuments of the Noto Valley (Sicily, Italy). SEM–EDS, XRD and Raman investigations were carried out to characterize the TiO2 nanoparticles (mainly nanocrystalline anatase) obtained by the acid and basic nanosols and the corresponding coatings on pietra di Noto. To evaluate the effects of the treatments at two different pH values, changes in the stone color appearance, water absorption by capillarity and the behavior for salt crystallization were measured. The photocatalytic activity of the coatings was evaluated under UV irradiation, by monitoring methyl orange and methylene blue dye degradation as a function of time. The results highlight the compatibility of both treatments with respect to the properties of the calcarenite stone, showing no chromatic changes, no alteration of physical properties, an improvement in the resistance to salts crystallization and the good photocatalytic activity on both dyes. The experimental data suggest that the basic coating has to be preferred for carbonatic stones for its harmlessness and better performances in terms of self-cleaning action and protection against water and salts.Graphical AbstractSelf-cleaning photocatalytic coatings based on TiO2, obtained by sol–gel at two different pH values, are applied on Pietra di Noto carbonatic stone. TiO2 nanoparticles and coatings are characterized by SEM, XRD and Raman. The photocatalytic activity of the coatings is evaluated under UV irradiation, by monitoring methyl orange and methylene blue dye degradation as a function of time. The basic coating is suitable for carbonatic stones for its harmlessness and better performances in terms of self-cleaning action and protection against water and salts.

Characterization and photocatalytic activity of TiO2 by sol–gel in acid and basic environments

The sol–gel synthesis of water-based sols of nanocrystalline TiO2 in a large pH range (1.3–10.6) was carried out by acid hydrolysis of titanium(IV) isopropoxide with acetic acid or malonic acid acting also as complexing agents. Subsequent peptization was achieved in acid medium, in the case of acetic acid, and in basic medium (through triethylamine), in the case of malonic acid. The TiO2 particles were characterized using X-ray diffraction, Raman, high-resolution transmission electron microscopy and dynamic light scattering–electrophoretic light scattering. Methyl orange (MeO) and methylene blue (MB) were used as model contaminants to investigate the degradation activity of the different sols under UV irradiation. MB molecules adsorbed on the TiO2 surface of the basic sol were found as trimeric species. The basic TiO2 sol was effective for the degradation of both dyes, whereas the acid sols gave satisfactory results only for MeO.

Polyamidoamines (PAAs) functionalized with siloxanes as wood preservatives against fungi and insects

Abstract A novel treatment based on polyamidoamines (PAAs) for the preservation of wood against fungi and insects with a broad protection functionality, low effective concentration, and low environmental impact has been developed. PAAs were synthesized by nucleophile addition of ethanolamine (EtA) and/or 3-aminopropyltriethoxysilane (APTES) to N,N′-methylene-bisacrylamide (MBA). The molar ratios in the tested formulation were: I) MBA:EtA=1:1; II) MBA:APTES=1:1; III) MBA:EtA:APTES=1:0.5:0.5. These formulations, characterized by ESI-MS, NMR, FT-IR, were tested against: (a) the wood decay fungi (Coniophora puteana, Coriolus versicolor, and Poria placenta); (b) the subterranean termite Reticulitermes lucifugus, and the drywood termite Kalotermes flavicollis; (c) the woodborer Stegobium paniceum. Tests in combination with leaching showed that formulation II and III can be utilized as fungal wood preservatives for use classes 2–3 (EN 335:2013). In addition, all PAAs formulations were equally effective in preserving wood against the subterranean termite, and formulation II was most effective against drywood termite. On the other hand, the formulation I showed good efficacy against S. paniceum.

Structural investigation of N,N′-methylenebisacryl­amide via X-ray diffraction assisted by crystal structure prediction

The crystal structure of N,N′-methylenebisacrylamide was determined through the geometry optimization of the molecular unit with density functional theory and conformational analysis, and then through the calculation of the packing via a crystal structure prediction protocol, based on lattice energy minimization. All the calculated structures were ranked, comparing their powder pattern with the laboratory low-quality X-ray diffraction data. Rietveld refinement of the best three proposed structures allowed the most probable crystal arrangement of the molecules to be obtained. This approach was essential for disentangling the twinning problems affecting the single-crystal X-ray diffraction data, collected on samples obtained via recrystallization of powder, which definitely confirmed the predicted model. It was found that N,N′-methylenebisacrylamide shows a monoclinic structure in the space group C2/c, with lattice parameters a = 17.822 (12), b = 4.850 (3), c = 19.783 (14) A, β = 102.370 (9)°, V = 1670 (2) A3. Two strong interactions between the amide protons and the carbonyl groups of neighbouring molecules were found along the b axis, determining the crystal growth in the form of wires in this direction. This work provides a further example of how computational methods may help to investigate low-quality molecular crystals with standard diffraction techniques.

Measuring weathering and nanoparticle coating impact on surface roughness of natural stones

ABSTRACT The surface texture of a stone represents a sensitive parameter in evaluating its conservation state. In monuments and sculptures, in fact, external agents continuously alter the appearance of stones, determining peculiar weathering patterns and modifying properties such as retention of water and particles, interaction with light, color, and finishing. The application of protective coatings also determines changes in surface appearance of a stone, usually evaluated and monitored by color change tests. Surface metrology methods offer the possibility to quantify these changes, evaluating the impact of external agents (natural, i.e. weathering, and artificially, i.e. protective coatings) on natural stones. In this research, we demonstrate the potential of surface areal measurements in describing the evolution of weathering processes and the effects of protective treatments on porous stone materials. The obtained results suggest that the extent of the modifications is related to the scale of observation (small- vs. large-scale undulations, i.e. roughness and waviness, respectively), with an overall increase of surface roughness as the weathering proceeds. Unexpectedly, coatings based on nanoparticle dispersions increase the topographic height parameters, due to the absence of a homogeneous film.

Multi-scale laboratory routine in the efficacy assessment of conservative products for natural stones

Graphical abstract

Trattamenti sostenibili per la protezione e il consolidamento di legno e carta

LAURA BERGAMONTIA, CLAUDIA GRAIFFA, CLELIA ISCAA, GIOVANNI PREDIERIA*, PIER PAOLO LOTTICIB, ROSA DI MAGGIOC, SABRINA PALANTID, LARA MAISTRELLOE, MATTEO MONTANARIF ADIPARTIMENTO DI SCIENZE CHIMICHE, DELLA VITA E DELLA SOSTENIBILITÀ AMBIENTALE, UNIVERSITÀ DI PARMA BDIPARTIMENTO DI SCIENZE MATEMATICHE, FISICHE E INFORMATICHE, UNIVERSITÀ DI PARMA CDIPARTIMENTO DI INGEGNERIA CIVILE, AMBIENTALE E MECCANICA, UNIVERSITÀ DI TRENTO DISTITUTO PER LA VALORIZZAZIONE DEL LEGNO E DELLE SPECIE ARBOREE, CNR-IVALSA, FIRENZE EDIPARTIMENTO DI SCIENZE DELLA VITA, UNIVERSITÀ DI MODENA E REGGIO EMILIA FBIORES LAB, BOLOGNA GIOVANNI.PREDIERI@UNIPR.IT