Andrea Ardu

Magnetic interactions in silica coated nanoporous assemblies of CoFe2O4 nanoparticles with cubic magnetic anisotropy.

Magnetic interactions in silica coated spherical nanoporous assemblies of CoFe(2)O(4) nanoparticles have been investigated by low temperature field dependent remanent magnetization (M(DCD) and M(IRM)) and magnetization relaxation measurements. The synthesis procedure leads to the formation of spherical aggregates of about 50-60 nm in diameter composed of hexagonal shaped nanocrystals with shared edges. The negative deviation from the non-interacting case in the Henkel plot indicates the predominance of dipole-dipole interactions favouring the demagnetized state, although the presence of exchange interactions in the porous system cannot be excluded. The activation volume, derived from time dependent magnetization measurements, turns out to be comparable with the particle physical volume, thus indicating, in agreement with static and dynamic irreversible magnetization measurements, that the magnetization reversal actually involves individual crystals.

Surfactant-assisted route to fabricate CoFe2O4 individual nanoparticles and spherical assemblies

A surfactant-assisted route in aqueous media has been shown to be suitable to prepare either individual primary CoFe(2)O(4) nanocrystals or secondary spherical nanoporous assemblies with a high surface area. The formation of primary nanoparticles or of spherical assemblies is found to be dependent on the presence of the surfactant and on the particle size, but is shown that the nanoparticle-surfactant interface plays a dominant role. The size of the primary CoFe(2)O(4) particles is controlled by the type of salt, the synthesis temperature and the concentration of the precursors. A detailed characterization evidences the shape and size of the primary particles, the way in which the primary particles assemble and their features in terms of morphological, textural and magnetic properties.

MeOx/SBA-15 (Me = Zn, Fe): highly efficient nanosorbents for mid-temperature H2S removal

Zinc oxide/ and iron oxide/SBA-15 composites were synthesized using the innovative Two-Solvents procedure and tested as sorbents for the mid-temperature (300 °C) removal of hydrogen sulphide, and then compared with a commercial unsupported ZnO sorbent. The sulphur retention capacity results showed the superior performance of the iron oxide/SBA-15 composite (401 mg S g−1 Fe2O3) in comparison with the zinc oxide/SBA-15 composite (53 mg S g−1 ZnO), both these sorbents being much more efficient than the commercial sorbent (6 mg S g−1 ZnO). The different sorption behaviour was discussed in terms of the nature of the nanocomposites where: (i) the mesostructure of the support was retained with a high surface area and pore volume; (ii) the zinc oxide phase was incorporated inside the SBA-15 channels as a thin amorphous homogeneous layer while the iron oxide was dispersed in form of small maghemite crystallites; and (iii) significant interactions occurred between the silica matrix and the zinc oxide phase. Remarkable differences in the regeneration behaviour of the exhaust sorbents were revealed by temperature-programmed experiments under an oxidizing atmosphere. After regeneration, the sorption properties of the zinc oxide/SBA-15 composite appeared to be enhanced compared to the commercial sorbent. Incomplete recovery of the sorption activity was observed for the regenerated iron oxide/SBA-15 sorbent, whose performance remained far better than that of the ZnO-based one, either fresh or regenerated. In view of its higher sulphur retention capacity and appropriate regeneration temperature (T ≤ 350 °C), the iron oxide/SBA-15 composite is a promising material for the design of advanced sorbents for a thermally efficient H2S removal process from hot gas streams.

SPION@liposomes hybrid nanoarchitectures with high density SPION association

A simple, versatile and reproducible method for the preparation of hybrid inorganic–organic magnetic nanocolloids based on phospholipids and preformed magnetic nanoparticles has been proposed. Superparamagnetic hydrophilic and hydrophobic iron oxide nanoparticles (SPION) of similar size are synthesized as a first step and subsequently hybrid-lipid based assemblies containing SPION has been prepared according to the thin film hydration method (TLE) using soya phosphatidylcholine. The effects of the different nature of the nanoparticles on the features of the assemblies have been observed by TEM: the hydrophilic nanoparticles are found to be located at the external surface of the vesicle, while the hydrophobic ones are in the inner core of the vesicles. In particular, uni/oligolamellar magnetic vesicles have been achieved with hydrophilic nanoparticles and high density multilamellar magnetic vesicles have been obtained with hydrophobic magnetic nanoparticles. “Cationic” nanoparticles interaction with “anionic” phospholipids has been proposed in the case of hydrophilic nanoparticles, while an aggregation phenomenon probably due to the hydration phase during the magnetoliposome preparation and an interaction of the oleic acid coatings with lipid membrane has been suggested in the case of hydrophobic nanoparticles.

Hierarchical Formation Mechanism of CoFe2O4 Mesoporous Assemblies

The development of synthetic hybrid organic-inorganic approaches and the understanding of the chemico-physical mechanisms leading to hierarchical assembly of nanocrystals into superstructures pave the way to the design and fabrication of multifunction microdevices able to simultaneously control processes at the nanoscale. This work deals with the design of spherical mesoporous magnetic assemblies through a surfactant assisted water-based strategy and the study of the formation mechanism by a combined use of transmission electron microscopy, X-ray diffraction, and time-resolved small angle X-ray scattering techniques. We visualize the hierarchical mechanism formation of the magnetic assemblies in the selected sodium dodecylsulfate (SDS)-assisted water-based strategy. At the first stage, an intermediate lamellar phase (L) represented by β-Co(OH)2 and FeOOH hexagonal plates is formed. Then, the nucleation of primary CoFe2O4 (N1) nanocrystals of about 6-7 nm occurs by the dissolution of FeOOH and the reaction of Fe(III) ions coordinated to the SDS micelles, at the reactive sites provided by vertices and edges of the β-Co(OH)2 plates. The intermediate phase consumes as the primary crystalline nanoparticles form, confined by the surfactant molecules around them, and assembly in spherical mesoporous assemblies. The key role of the surfactant in the formation of porous assemblies has been evidenced by an experiment carried out in the absence of SDS and confirmed by the pore size diameter of the assemblies (about 2-3 nm), that can be correlated with the length of the surfactant dodecylsulfate molecule.

Predictive method for correct identification of archaeological charred grape seeds: Support for advances in knowledge of grape domestication process

The identification of archaeological charred grape seeds is a difficult task due to the alteration of the morphological seeds shape. In archaeobotanical studies, for the correct discrimination between Vitis vinifera subsp. sylvestris and Vitis vinifera subsp. vinifera grape seeds it is very important to understand the history and origin of the domesticated grapevine. In this work, different carbonisation experiments were carried out using a hearth to reproduce the same burning conditions that occurred in archaeological contexts. In addition, several carbonisation trials on modern wild and cultivated grape seeds were performed using a muffle furnace. For comparison with archaeological materials, modern grape seed samples were obtained using seven different temperatures of carbonisation ranging between 180 and 340ºC for 120 min. Analysing the grape seed size and shape by computer vision techniques, and applying the stepwise linear discriminant analysis (LDA) method, discrimination of the wild from the cultivated charred grape seeds was possible. An overall correct classification of 93.3% was achieved. Applying the same statistical procedure to compare modern charred with archaeological grape seeds, found in Sardinia and dating back to the Early Bronze Age (2017–1751 2σ cal. BC), allowed 75.0% of the cases to be identified as wild grape. The proposed method proved to be a useful and effective procedure in identifying, with high accuracy, the charred grape seeds found in archaeological sites. Moreover, it may be considered valid support for advances in the knowledge and comprehension of viticulture adoption and the grape domestication process. The same methodology may also be successful when applied to other plant remains, and provide important information about the history of domesticated plants.

MCM-41 support for ultrasmall γ-Fe2O3 nanoparticles for H2S removal

MCM-41 is proposed to build mesostructured Fe2O3-based sorbents as an alternative to other silica or alumina supports for mid-temperature H2S removal. MCM-41 was synthesized as micrometric (MCM41_M) and nanometric (MCM41_N) particles and impregnated through an efficient two-solvent (hexane–water) procedure to obtain the corresponding γ-Fe2O3@MCM-41 composites. The active phase is homogeneously dispersed within the 2 nm channels in the form of ultrasmall maghemite nanoparticles assuring a high active phase reactivity. The final micrometric (Fe_MCM41_M) and nanometric (Fe_MCM41_N) composites were tested as sorbents for hydrogen sulphide removal at 300 °C and the results were compared with a reference sorbent (commercial unsupported ZnO) and an analogous silica-based sorbent (Fe_SBA15). MCM-41 based sorbents, having the highest surface areas, showed superior performances that were retained after the first sulphidation cycle. Specifically, the micrometric sorbent (Fe_MCM41_M) showed a higher SRC value than the nanometric one (Fe_MCM41_N), due to the low stability of the nanosized particles over time caused by their high reactivity. Furthermore, the low regeneration temperature (300–350 °C), besides the high removal capacity, renders MCM41-based systems an alternative class of regenerable sorbents for thermally efficient cleaning up processes in Integrated Gasification Combined Cycles (IGCC) systems.

Luminescence enhancement by energy transfer in melamine-Y2O3:Tb3+ nanohybrids

The phenomenon of luminescence enhancement was studied in melamine-Y2O3:Tb hybrids. Terbium doped Y2O3 mesoporous nanowires were synthesized by hydrothermal method. X-ray diffraction patterns and Raman scattering spectra testified the realization of a cubic crystal phase. Organic-inorganic melamine-Y2O3:Tb3+ hybrid system was successfully obtained by vapour deposition method. Vibration Raman active modes of the organic counterpart were investigated in order to verify the achievement of hybrid system. Photoluminescence excitation and photoluminescence spectra, preformed in the region between 250 and 350 nm, suggest a strong interaction among melamine and Terbium ions. In particular, a remarkable improvement of 5D4→ FJ Rare Earth emission (at about 542 nm) of about 102 fold was observed and attributed to an efficient organic-Tb energy transfer. The energy transfer mechanism was studied by the use of time resolved photoluminescence measurements. The melamine lifetime undergoes to a significant decrease when ...

Combination of grape extract-silver nanoparticles and liposomes: A totally green approach

&NA; In the present work, silver nanoparticles were prepared using a totally green procedure combining silver nitrate and an extract of grape pomace as a green source. Additionally, nanoparticles were stabilized using phospholipid and water and/or a mixture of water and propylene glycol (PG). To the best of our knowledge, grape‐silver nanoparticle stabilized liposomes or PG‐liposomes were formulated, for the first time, combining the residual products of wine‐made industry, silver nitrate and phospholipids, avoiding the addition of hazardous substances to human health and the environment, in an easy, scalable and reproducible method. The structure and morphology of grape‐silver nanoparticle stabilized vesicles were evaluated by transmission electron microscopy (TEM), UV‐vis spectroscopy and photon correlation spectroscopy. Samples were designed as possible carrier for skin protection because of their double function: the grape extract acts as antioxidant and the colloidal silver as antimicrobial agent, which might be helpful in eliminating dangerous free radicals and many pathogenic microorganisms. Obtained nanoparticles were small in size and their combination with phospholipids did not hamper the vesicle formation, which were multilamellar and sized ˜ 100 nm. TEM images shows a heterogeneous distribution of nanoparticles, which were located both in the intervesicular medium and in the vesicular structure. Further, grape‐silver nanoparticles, when stabilized by liposomes, were able to inhibit the proliferation of both Staphylococcus aureus and Pseudomonas aeruginosa and provided a great protection of keratinocytes and fibroblasts against oxidative stress avoiding their damage and death. Graphical abstract Figure. No caption available.

Colloidal synthesis and characterization of Bi2S3 nanoparticles for photovoltaic applications

Bismuth sulfide is a promising n-type semiconductor for solar energy conversion. We have explored the colloidal synthesis of Bi2S3 nanocrystals, with the aim of employing them in the fabrication of solution-processable solar cells and to replace toxic heavy metals chalcogenides like PbS or CdS, that are currently employed in such devices. We compare different methods to obtain Bi2S3 colloidal quantum dots, including the use of environmentally benign reactants, through organometallic synthesis. Different sizes and shapes were obtained according to the synthesis parameters and the growth process has been rationalized by comparing the predicted morphology with systematic physical-chemistry characterization of nanocrystals by X-ray diffraction, FT-IR spectroscopy, Transmission Electron Microscopy (TEM).