Ilaria Alfieri

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.”

Natamycin based sol-gel antimicrobial coatings on polylactic acid films for food packaging.

In this work a comprehensive study on a new active packaging obtained by a hybrid organic-inorganic coating with antimicrobial properties was carried out. The packaging system based on polylactic acid was realised by sol-gel processing, employing tetraethoxysilane as a precursor of the inorganic phase and polyvinyl alcohol as the organic component, and incorporating natamycin as the active agent. Films with different organic-inorganic ratios (in a range between 1:19 and 1:4) were prepared, and the amount of antimycotic entrapped was found to be modulated by the sol composition, and was between 0.18 and 0.25mg/dm(2). FTIR microspectroscopic measurements were used to characterise the prepared coatings. The antifungal properties of the films were investigated against mould growth on the surface of commercial semi-soft cheese. The release of natamycin from the films to ethanol 50% (v/v) was studied by means of HPLC UV-DAD. The maximal level released was about 0.105 mg/dm(2), which is far below the value allowed by legislation.

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.

Sol-gel silicon alkoxides-polyethylene glycol derived hybrids for drug delivery systems

PURPOSE The potential application of hybrid systems based on silicon alkoxides and polyethylene glycol 400 as drug delivery systems was studied. METHODS They were synthesized using the sol-gel technique, using ketoprofen as a model drug. The preparation of the materials and their characterization by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis are reported. Drug loading was performed during the gelation of the sols. Drug release studies were performed at pH 1.2 and 7.5 mimicking gastrointestinal environments. RESULTS Drug release was affected by the presence of polyethylene glycol in the formulation: a faster release was observed for polyethylene glycol hybrids. CONCLUSIONS The results suggest that these devices should guarantee long durability after implantation and could be suitable for sustained release: after a first period of release by diffusion, complete release will be reached by bioerosion of the matrix.

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