Search

The potential of silicon-based fluorescent platforms for the detection of trace toxic metal ions was investigated in an aqueous environment. To this aim, silicon chips were first functionalized with amino groups, and fluorescein organic dyes, used as sensing molecules, were then covalently linked to the surface via formation of thiourea groups. The obtained hybrid heterostructures exhibited high sensitivity and selectivity towards copper(II), a limit of detection compatible with the recommended upper limits for copper in drinking water, and good reversibility using a standard metal–chelating agent. The fluorophore–analyte interaction mechanism at the basis of the reported fluorescence quenching, as well as the potential of performance improvement, were also studied. The herein presented sensing architecture allows, in principle, tailoring of the selectivity towards other metal ions by proper fluorophore selection, and provides a favorable outlook for integration of fluorescent chemosensors with silicon photonics technology.

In this work, industrial waste hexafluorosilicic acid (H2SiF6 or FSA) has been proven to be a low-cost alternative to silicate esters for the synthesis of high-quality MCM-41 (high surface area, hi...

Arsenic pollution in ground and drinking water is a major problem worldwide due to the natural abundance of arsenic by dissolution from ground sediment or mining activities from anthropogenic activities. To overcome this issue, iron oxides as low-cost and non-toxic materials, have been widely studied as efficient adsorbents for arsenic removal, including when dispersed within porous silica supports. In this study, two head-to-head comparisons were developed to highlight the As(V)-adsorptive ability of meso- and macrostructured silica-based adsorbents. First, the role of the textural properties of a meso-(SBA15) and macrostructured (MOSF) silica support in affecting the structural-morphological features and the adsorption capacity of the active phase (Fe2O3) have been studied. Secondly, a comparison of the arsenic removal ability of inorganic (Fe2O3) and organic (amino groups) active phases was carried out on SBA15. Finally, since silica supports are commonly proposed for both environmental and biomedical applications as active phase carriers, we have investigated secondary silicon and iron pollution. The batch tests at different pH revealed better performance from both Fe2O3-composites at pH 3. The values of qm of 7.9 mg g−1 (53 mg gact−1) and 5.5 mg g−1 (37 mg gact−1) were obtained for SBA15 and MOSF, respectively (gact stands for mass of the active phase). The results suggest that mesostructured materials are more suitable for dispersing active phases as adsorbents for water treatment, due to the obtainment of very small Fe2O3 NPs (about 5 nm). Besides studying the influence of the pore size of SBA15 and MOSF on the adsorption process, the impact of the functionalization was analyzed on SBA15 as the most promising sample for As(V)-removal. The amino-functionalized SBA15 adsorbent (3-aminopropyltriethoxysilane, APTES) exhibited a qm of 12.4 mg g−1 and faster kinetics. Furthermore, issues associated with the release of iron and silicon during the sorption process, causing secondary pollution, were evaluated and critically discussed.

Nanostructured spinel ferrites with formula M2+Fe2O4 (where M2+ ═ Fe, Co, Mn, Ni, Zn, etc.) represent a class of magnetic materials widely employed in different research fields, due to the possibility of finely tuning the magnetic properties by changing the chemical composition, size, shape, capping agents, etc. Herein, a review of the most common chemical synthesis in liquid media, distinguishing among aqueous and non-aqueous routes, is presented. The experimental procedure together with the mechanism, advantages and disadvantages, and examples are illustrated for each synthetic strategy.

A Raman study on Zinc-substituted Cobalt ferrites, with different Zn(II) contents in each sample of formula: CoFe₂O₄ (1), Zn0.30Co0.70Fe2.00O₄ (2), Zn0.46Co0.54Fe2.02O₄ (3), Zn0.53Co0.47Fe2.02O₄ (4) is reported. These samples show the same crystallite size (∼6 nm), particle size (∼7 nm) and particle size distribution (∼20%) and they have been synthesized through heating up surfactant-assisted thermal decomposition of metalorganic precursors. The effect of Zn(II) substitution in the cationic distribution is investigated by using the known metal-oxygen vibrational modes in tetrahedral and octahedral sites. The presence of Zn(II) metal ion is determined through the band at 150 cm-1 (T2g(1) phonon mode), which is not present in the pure Co-ferrite, a blue-shift of the Eg vibrational mode depending on Zn(II)/Co(II) cationic distribution and a shoulder at ∼250 cm-1, which appears when zinc enters in the structure, and a broadening and a red-shift in the A1g phonon mode is observed in Raman spectra of 2-4 samples. Interestingly the latter represents a potential key probe to monitor the Zn(II) presence in Zn-substituted Co-ferrites.

In this work, highly dispersed maghemite (λ-Fe₂O₃) in form of ultrasmall nanoparticles (about 2 nm) was embedded into a mesostructured silica MCM-41 (about 600 nm) featuring regular submicrometric hexagonal shaped particles via the two-solvent incipient wetness impregnation strategy. The obtained nanocomposite was then tested as H₂S sorbent in the mid-temperature range. When compared with a commercial sorbent (KatalkoJM 32-5), it showed superior performances after the first sulfidation which remained steady over three repeated sulfidation cycles, highlighting the regenerability properties of the composite. In order to evaluate the effect of the length of the pore channels on the accessibility of H₂S to the active phase, an analogous micrometric λ-Fe₂O₃@MCM-41, featuring micrometric channels and particles of irregular shape was used as reference.

Nanostructured spinel cobalt ferrite samples having crystallite size ranging between 5.6 and 14.1 nm were characterized by X-ray photoelectron spectroscopy and X-ray induced Auger electron spectroscopy in order to determine the chemical state of the elements, the iron/cobalt ratio and the cation distribution within tetrahedral and octahedral sites. The presence of size-dependent trends in the binding energy of the main photoelectron peaks and in the kinetic energy of the X-ray induced O KLL signal was also investigated. The results showed that iron is present as FeIII and cobalt is present as CoII. The iron/cobalt ratio determined by XPS ranges between 1.8 and 1.9 and it is in very good agreement, within experimental uncertainty, with the expected 2 : 1 ratio. The percentage of Fe in octahedral sites ranges between 62% and 64% for all samples. The kinetic energy of the O KLL signals increases with crystallite size. These results are explained in terms of changes in the ionicity of the metal–oxygen bonds. The results of this investigation highlight how the XPS technique represents a powerful tool to investigate the composition, the chemical state and inversion degree of cobalt spinel ferrites, contributing to the comprehension of their properties.

Achieving metal-organic frameworks (MOFs) in the form of nanoparticles (NanoMOFs) represents a recent challenge due to the possibility to combine the intrinsic porosity of these materials with the nanometric dimension, a fundamental requirement for strategic biomedical applications. In this outlook we envision the current/future opportunities of the NanoMOFs in the field of biomedicine, with particular emphasis on (i) biocompatible MOFs composition; (ii) MOFs miniaturization and (iii) nanoMOFs applications.

NiO-CeO2 mixed oxides were prepared by the soft-template method with nominal Ni/Ce molar ratios between 0.3 and 4.0. NiO and CeO2 pure oxides were also prepared through the same procedure. A second series of NiO-CeO2 mixed oxides (nominal Ni/Ce values = 0.3–1.5 mol mol−1) was synthesized by using the soft-templated ceria as the support and depositing Ni through incipient wetness impregnation. All samples were characterized by different techniques as to their chemical composition, structure, morphology, texture, and redox features. NiO nanocrystals of about 4 nm in size were obtained in the case of the soft‐templated samples, regardless of the Ni loading. Larger NiO nanocrystals (up to 20 nm in size) were formed by depositing Ni through the impregnation procedure. The catalytic performance was investigated in the CO2 methanation reaction after mild reduction pretreatment (H2 at 400 °C for 1 h). Catalytic testing was performed under atmospheric pressure, 300 °C, 72,000 cm3 h−1 gcat−1, and stoichiometric H2/CO2 molar ratio. Pure NiO as well as the two NiO-CeO2 mixed oxides series showed high CO2 conversions (up to 87 mol%) together with CH4 selectivity values close to 100 mol%. Despite the significantly different size (6–8 and 15–35 nm, respectively) of the Ni0 nanocrystals originated by NiO reduction, comparable CO2 conversion values were observed for the soft-templated and impregnated catalysts. The catalyst stability as well as the effect of reaction temperature, space velocity, and H2/CO2 molar ratio were investigated on selected samples. The catalytic results were explained by taking into account that CO2 and H2 are activated on different phases.

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.

The fluorescence properties of colloidal sealed Rhodamine 6G doped mesostructured silica nanoparticles prepared by a one-pot templated base-catalyzed sol–gel self-assembly method are reported. The hybrid organic–inorganic nanoparticles is tested against water and alcohols dye leaching showing larger resilience to leaching in water, high quantum yield despite the large dye concentration and huge relative brightness up to 1.5 × 10 5 emitting molecules per nanoparticle. This super fluorescence is 3 times larger of comparable systems and 100 times larger than the fluorescence of CdSe/ZnS quantum dots. The surfactant used for the formation of the mesostructure plays a key role both as dye splitting element and as sealing agent against leaching effect. The resilience to dye leaching in water is further justified by the formation of core–shell architectures made up of mesoporous core and homogeneous low-porous silica shell of 5–12 nm in thickness due to long aging condensation reaction of surface silanols in water. In addition, the comparison with a reference no-doped silica sample points out a possible alternative synthetic strategy to tune the structural, morphological and textural properties of silica-based nanosystems: properly engineering can exploit the effect of dye molecules addition on nanoparticles mean size, polydispersity and mean thickness of matrix silica walls.

In this work, silica and alumina pure sources were used to perform the synthesis of zeolite A (LTA) by both conventional and pre-fused hydrothermal processes. Increasing amount of red mud (RM, a waste formed during the caustic leaching of bauxite to produce alumina and rich in Fe) was added during the synthesis processes. We attempted to investigate if the use of pure sources with the addition of different amounts of red mud promotes, or hinder, the crystallization of the zeolite A and if Fe is structurally-incorporated into the newly-formed zeolite structure (i.e., as framework or extra-framework cation) or if it is concentrated in a proper Fe-rich phase. The results carried out using a multi-methodological approach (laboratory X-ray powder diffraction; synchrotron radiation powder X-ray diffraction; scanning electron microscopy and electron transmission microscopy coupled with EDX elemental mapping) show that LTA zeolite crystals (with cubic morphology) can be efficiently formed using pure source combined with variable amount of red mud. The use of complementary analytical techniques indicate that Fe coming from the red mud is not structurally-incorporated into the newly-formed zeolite crystals, but it is mainly concentrated in nano-clusters of Fe-oxides (with spinel-type structure) located on the zeolite crystal surface. The utilization of non-conventional Fe source, here represented by red mud, can be considered as the first step toward a new solidification/stabilization process for this waste, as dictated by the regenerative economy route. These data make an important contribution to understanding the role played by surface phenomena on zeolite crystals when transition elements are used in the synthesis procedure.

Mesostructured titania (Anatase) and silica (MCM-41) were proposed as supports to design highly active, selective, and regenerable FeIII-based nanostructured sorbents for mid-temperature H2S removal in a model sour syngas. The resulting sorbents (Fe–SiO2 and Fe–TiO2) were tested as H2S removers at 300 °C and exhibited high reactivity and regenerability over repeated sulfidation cycles, with the best sorption performances achieved by the silica-based sorbent. Specifically, Fe–SiO2 showed a constant sorption capacity of 19 ± 1 mgS gsorbent−1 after the first sulfidation cycle. Meanwhile, a lower sorption capacity of 10 ± 1 mgS gsorbent−1 was found for the Fe–TiO2 composite. As evidenced by combining 57Fe Mossbauer spectroscopy with DC magnetometry, the nature (amorphous or crystalline) and composition (SiO2 or TiO2) of the inorganic mesostructures played a crucial role in the formation of the ultrasmall FeIII-active phase: maghemite (γ-Fe2O3) and pseudobrookite (Fe2TiO5) in the case of silica and titania, respectively. Therefore, the performance can be mainly justified in the light of the different reactivity of the active phases (Fe2O3 vs Fe2TiO5). FeIII-active phase in the form of ultrasmall Fe2O3 nanoparticles (about 2 nm) homogeneously dispersed in a highly stable mesostructured silica support assured high reactivity (85%–100% of the active phase involvement) and regenerability in the mid-temperature range as for the sulfidation run during the repeated sulfidation cycles (steady performances) avoiding the common drawbacks of unsupported sorbents (unreacted core and sintering phenomena causing loss of activity).

The synthesis, structural characterization, photophysical studies, and exfoliation of two-dimensional (2D) layered coordination polymers, formulated as {[Ln2(ClCNAn)3(DMF)6]·(DCM)x}n (Ln(III) = Yb(...

An ecofriendly, low-cost, one-pot solvothermal approach has been developed to prepare spherical magnetite nanoparticles with sizes in the 7–12 nm range capped with a dialkylamine. Iron isopropoxide, water vapor, absolute ethanol, oleic acid, and oleylamine were used as iron oxide precursor, hydrolysis agent, solvent and surfactants, respectively. The surfactants’ role was investigated and an accurate correlation among the synthetic parameters, the crystallographic phases, and both crystallite and particle size was found. The amounts of oleylamine and oleic acid and the temperature have been revealed to be the key parameters in order to tune particle size and their polydispersity. An in-depth study on the role of each surfactant has pointed out the fundamental role of the amine as a reduction promoter as demonstrated by using different amines and confirmed by Mossbauer measurements. A dual 1H NMR-Fourier transform infrared spectroscopy approach on selected experiments for the investigation of the capping a...

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.

The synthesis of novel nanoarchitectures is an important way to combine several properties into the same nanometric object. Magnetic, catalytic, optical, and electrical properties can be embedded and used for heating, moving, or monitoring the nanocomposite. Following this approach, smart materials exhibiting remarkable properties could be obtained. Several nanocomposites are based on carbon nanotubes (CNTs). Because of the presence of empty cavities and very large surface external area, this allotropic form of carbon is especially suitable for this purpose and particularly for catalytic applications. In this work, a new general strategy to synthesize by a wet method three-block, smart nanocomposites based on MWCNTs is described [1,2]. The new bifunctional material is shortly referred to as FePt@MWCNTs/ Ru(NPs) to point out that nanoparticles (NPs) of a magnetically soft alloy (FePt fcc) fill the MWCNTs cavity, whereas catalytic Ru NPs decorate the external wall. In this way well separated catalytic and magnetic NPs are obtained. All the synthetic steps are described in detail. TEM, HRTEM, XRD, and magnetic measurements by VSM are used to monitor all the steps and to prove the effectiveness of the method. [1]B. Astinchap, R. Moradian, A. Ardu, C. Cannas, G. Varvaro, A. Capobianchi, Chem. Mat. 24 (2012), 3393 [2]A. Capobianchi, M. Colapietro, D. Fiorani, S. Foglia, P. Imperatori, S. Laureti, E. Palange, Chem. Mater 21 (2009), 2007

We have used time resolved small angle X-ray scattering (SAXS) for investigating the early stages of the formation of crystalline colloidal Ag particles by AgNO3 reduction with ascorbic acid in an aqueous acidic solution of a polynaphthalene sulphonate polymer (Daxad). In order to exploit the polymer role in silver crystallization, the measurements have been performed at different polymer concentrations. Data analysis suggests that the nucleation and growth of primary particles of about 20 nm in diameter, occurring in a surface-fractal arrangement of the dynamic polymeric template, is assisted by the development of long range spatial correlations. These correlations could be a sign of polymer-induced liquid fluctuations as intermediate precursors of Ag crystallization.

Spherical nanoparticles of surfactant-coated CoFe2O4 (core) were prepared through thermal decomposition of metal acetylacetonates in the presence of a mixture of oleic acid and oleylamine and uniformly coated with silica shell by using tetraethylorthosilicate (TEOS) and ammonia in a micellar solution (core/shell). Transmission electron microscopy (TEM) analysis of core/shell nanoparticles evidenced the high homogeneity of the coating process in producing single core/shell nanoparticles with a narrow size distribution. The combined use of spectroscopic studies (NMR and FTIR) on core and core/shell nanoparticles pointed out that the surfactants’ layer bound to the surface core nanoparticles is retained also after the silica coating process. This allows to obtaining systems with very similar magnetic behavior but weaker dipolar interparticle interactions and lower values of saturation magnetization. In view of the interest in biomedical field, the effect of the CoFe2O4 nanoparticles silica coating was also s...

ZnO nanoparticles, of average size of 10–15 nm, homogeneously dispersed in a silica matrix were prepared by a two stage citric acid/sol–gel process and thermal treatments up to 700 °C. The precursors formed at the early stages of the synthesis and their thermal evolution were investigated by FTIR, 29Si NMR MAS and CPMAS, 13C CPMAS and T1ρ(1H). A unidentate complex was revealed in the gel, together with other complexes in which citrate carboxylate groups are bound to one Zn2+ ion or act as a bridge between two Zn2+ ions. A comparison of the results from nanocomposite and silica samples prepared by the same method showed that chemical interactions between amorphous silica and zinc ions are not present either in the precursors or in the final materials. As a consequence, ZnO particles do not react with silica matrix when they are heated up to 700 °C. This result is ascribed to a nanophase segregation of zinc citrate complexes from the host matrix.

A very fast self-combustion reaction was applied for the first time to the synthesis of a series of magnetic CoFe2O4−SiO2 nanocomposites in a wide range of compositions (from 5 to 50 wt % CoFe2O4). Combining a gelation method that adopts metal nitrates, citric acid and tetraethoxysilane as precursors with controlled thermal treatments, a wide variety of samples with properties finely modulated were obtained. Particle formation and evolution of the structural and magnetic properties with the temperature were investigated by thermal analysis, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, nitrogen physisorption, IR, and magnetic susceptibility measurements. It was shown that the formation of metal ammonium carboxylate complexes takes place in all the gel precursors, contributing to the control of nucleation and growth of the nanoparticles. Spherical particles with narrow particle size distribution, uniformly dispersed in the matrix, are obtained in the...

Nanocrystalline CoFe2O4 powders were prepared by decomposition of metal ion citrate precursors. Four samples were synthesized from precursor solutions having different pH values in the range

A sol–gel autocombustion method was used to synthesize nanometric metal-oxide powders, and was extended for the first time to prepare ferrite–silica nanocomposites. The gels obtained by mixing suitable amounts of citric acid, metal nitrates, ammonia (pure phases) and tetraethylortosilicate (nanocomposites) were converted directly to ferrite (either γ-Fe2O3 or CoFe2O4) or ferrite–silica composites through a rapid autocombustion reaction. The combustion involves a thermally induced autocatalytic oxidation–reduction reaction between the nitrate and the citrate ions. The sample characterization by X-ray diffraction, transmission electron microscopy and N2 physisorption measurements revealed nanosized pure phase powders and nanocomposites in which small spherical nanoparticles (mean size 3.5 and 5.0nm, respectively for the γ-Fe2O3and CoFe2O4) are homogeneously dispersed over a mesoporous silica matrix.

A sol–gel procedure for the tailoring of maghemite particle size in silica-based nanocomposites is proposed. The preparation method allows control of the gelation time, which is varied from 2 to 16 days in samples having the same concentration of iron oxide (25%). Superparamagnetic particles of γ-Fe2O3 with sizes in the 2.5–5.6 nm range were found in all the samples, as confirmed by TEM, Mossbauer spectroscopy and magnetic measurements. The particle size was independent of the porosity of the silica host matrix, but strongly dependent on the amount of solvent trapped inside the gels. The solvent plays an important role, favouring the formation of Fe3O4 nanoparticles as an intermediate step before the final oxidation to maghemite.

Organic-inorganic perovskites are a class of solution-processed semiconductors holding promise for the realization of low-cost efficient solar cells and on-chip lasers. Despite the recent attention they have attracted, fundamental aspects of the photophysics underlying device operation still remain elusive. Here we use photoluminescence and transmission spectroscopy to show that photoexcitations give rise to a conducting plasma of unbound but Coulomb-correlated electron-hole pairs at all excitations of interest for light-energy conversion and stimulated optical amplification. The conductive nature of the photoexcited plasma has crucial consequences for perovskite-based devices: in solar cells, it ensures efficient charge separation and ambipolar transport while, concerning lasing, it provides a low threshold for light amplification and justifies a favourable outlook for the demonstration of an electrically driven laser. We find a significant trap density, whose cross-section for carrier capture is however low, yielding a minor impact on device performance.

The CoCr2O4 nanoparticles were prepared by hydrothermal treatment of chromium and cobalt oleates in a mixture of solvents (water and ethanol or pentanol) at various temperatures. The samples were further annealed at the temperatures from 300 to 500 °C. The obtained nanoparticles were characterized using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy, thermogravimetric analysis, Raman and infrared spectroscopy, and magnetic measurements. The particle size, ranging from 4.4 to 11.5 nm, was determined from the TEM and PXRD methods. The tendency of particles to form the aggregates with the increasing annealing temperature has been observed. The magnetic measurements revealed that the typical features of the CoCr2O4 long-range magnetic order are suppressed in the nanoparticles.

The properties of aerogel and xerogel iron oxide–silica nanocomposites prepared by the sol–gel method were investigated by thermal analysis, X-ray diffraction, transmission electron microscopy, Mossbauer spectroscopy and susceptibility measurements. Pure maghemite nanoparticles were obtained starting from both xerogel and aerogel samples, with particles of average size around 5 nm which tend to aggregate into the silica matrix. The role of magnetic interparticle interactions, which have a strong influence on the magnetic properties, is discussed.

X-Ray amorphous ZnO nanoparticles homogeneously dispersed in a silica matrix were evidenced in ZnO-SiO 2 nanocomposites obtained by a sol-gel method and heated to 700°C. TEM observations indicated that the particle size slowly increases with temperature and zinc oxide content, reaching an upper limit of 12 nm. Through a comparison of the 29 Si MAS NMR data of the nanocomposites and silica samples, obtained by the same preparation method, it was possible to observe that reaction occurs between ZnO and silica on heating, which causes a depolymerization of the host matrix with the formation of low condensation groups. This result is discussed in terms of interactions between nanoparticles and the silica matrix at the nanoparticle/matrix interface. A further increase in temperature (900°C) results in the formation of the β-Zn 2 SiO 4 crystalline phase.

Molecular coating of nanoparticles represents probably the most important and, at the same time, critical step to design new nanostructured magnetic materials. The interaction between molecules and surface atoms leads to a strong modification of surface magnetic properties, that are one of the key points in the physics of magnetic nanoparticles. In this paper the magnetic properties of CoFe2O4 nanoparticles (< D > congruent to 4-8 nm) coated with oleic acid have been investigated in order to clarify the role of the molecular coating on the interparticle interactions and surface anisotropy. An increase of magnetic anisotropy (i.e., coercive field and anisotropy constant) with particle size is observed in coated nanoparticles, indicating that the magnetic anisotropy is governed mainly by its magnetocrystalline component. The removal of molecular coating induces a strong increase of anisotropy, because of the increase of its surface component, as indicated by the increase of exchange bias field.

The magnetic properties of ultra-small (3 nm) CoFe(2)O(4) nanoparticles have been investigated by DC magnetization measurements as a function of temperature and magnetic field. The main features of the magnetic behaviour are blocking of non-interacting particle moments (zero-field-cooled magnetization T(max) approximately 40 K), a rapid increase of saturation magnetization (up to values higher than for the bulk material) at low T and an increase in anisotropy below 30 K due to the appearance of exchange bias. The low temperature behaviour is determined by a random freezing of surface spins. Localized spin-canting and cation distribution between the two sublattices of the spinel structure account quantitatively for the observed increase in saturation magnetization.

A set of investigations on selected samples of nanosized cobalt ferrite are reviewed, aimed at studying the various factors affecting the magnetic properties of nanoparticles. Specifically, the effects of inter-particle interactions, of structural and magnetic order, both in the core and on the surface of the particle, have been examined. All factors render the control of the magnetic properties of nanosystems quite difficult, but, at the same time, they also offer the opportunity of tuning them properly, so that materials for specific applications may be created.

The sol-gel synthesis of TiO2 from TiCl4 assisted by the triblock copolymer EO20-PO70 -EO20 (EO = -CH2CH2O-, PO = -CH2 (CH3)CHO-) as templating agent was carried out by systematically changing H2O:Ti (rw) and HCl:Ti (ra) molar ratios. Mesoporous and nanocrystalline TiO2 samples with well-defined and controlled phase composition (anatase, rutile, and mixed phase) were obtained after calcination at 400 °C and characterized for the morphology, particle size, and shape using TEM, HRTEM, XRD, and surface area measurements. The role of rw and ra and influence of the copolymer in determining the phase composition was demonstrated. Rutile becomes the main phase by increasing rw. In fact, the decrease of Ti concentration slows down the condensation rate, favoring formation of rutile seeds in the gel. The photocatalytic activity of TiO2 in the UV photomineralization of phenol depends on the phase composition and oxidizing agent, H2O2 or O2. When the oxidation is performed by H2O2, rutile, formed by large crystalline rods with high aspect ratios (size 15-20 × 100-120 nm), shows higher catalytic activity with respect to the small, almost cubic, anatase particles (5-15 nm). If O2 is used, the catalytic activity generally decreases and the behavior of polymorphous species is reverse. EPR investigation of the paramagnetic charge carriers, formed under UV irradiation at 10 K, showed the resonance lines of holes trapped at O- lattice sites and electrons trapped at Ti3+ and O2- sites. The rutile crystalline rods present the largest quantity of O- and Ti3+ centers. The overall results suggest correlation between TiO2 particle size and shape and the photocatalytic activity and indicate that electron-hole recombination is the most probable rate-controlling process. © 2008 American Chemical Society.

Nanoporous spherical assemblies of iso-oriented cobalt ferrite nanoparticles with a high surface area were prepared via a normal micelles process. The spherical magnetic assemblies were coated with a silica layer through an inverse micelles route. The microstructure and morphology were studied by X-ray diffraction, transmission electron microscopy and N2-physisorption techniques. The primary CoFe2O4 nanocrystalline particles (∼7 nm) assemble into spherical nanoporous aggregates with an average size of about 50−60 nm and the coating process leads to core−shell nanostructures with an amorphous 7−8 nm thick silica shell that covers the spherical assemblies homogeneously. The magnetic properties of both uncoated and silica-coated nanostructures were also investigated.

Nanocrystalline TiO2catalysts based on pure rutile (R100) and a 30% of anatase and 70% of rutile (R70) were synthesized by the sol-gel method, using Pluronic PE 6400 as templating agent. Catalysts were characterized in terms of structural and morphological properties; moreover, the formation of paramagnetic charge carriers under UV irradiation was studied and related to the activity of TiO2in the photoinduced degradation of phenol. With respect to Degussa P25, the two sol-gel catalysts show lower surface area and a wider pore size distribution. The EPR spectra recorded under UV irradiation show enhanced charge separation in the sol-gel samples, with the O−species in higher amount than in Degussa P25. This result is in agreement with the high catalytic activity of R100 sample in the photoinduced degradation of phenol, very similar to that displayed by Degussa P25 and higher than that of R70 sample.

A Eu3+-doped-yttria–silica nanocomposite was synthesized through a deposition–precipitation technique. Yttria nanocrystalline particles with a mean size of 12 nm, dispersed in an amorphous silica matrix, were evidenced by XRD and TEM in a sample treated at 900 °C. The nanoparticles are coated with an amorphous layer visible in the HRTEM micrographs; this amorphous layer is likely to interact with the silica matrix through Si–O–Y bonds, which is consistent with 29Si NMR MAS results. The nanocomposite treated at 1000 °C partially evolves to give an α-Y2Si2O7 crystalline phase. The luminescence spectra of the nanocomposites indicate that the sites in which the Eu3+ ions are accommodated are disordered. On the other hand, the decay times of the 5D0 emission are rather long in the present nanocomposites studied herein, indicating that multiphonon relaxation is not effective in quenching the luminescence. The reduced coupling to OH vibrations in the materials under investigation could be ascribed to the presence of the amorphous layer coating the nanoparticles and effectively shielding the Eu3+ ion from the silanol groups.

The optical and structural properties of sol–gel prepared polycrystalline films of Cerium doped Lutetium and Yttrium oxyorthosilicates (Ce:LYSO) are investigated by means of optical spectroscopy, XRD diffraction and Raman spectroscopy. The sol–gel samples are compared to commercially available Ce-doped LYSO single crystals, and a detailed study of the emission properties from the different cerium sites is performed. The main result is that the polycrystalline films do show very good radioluminescence properties for possible applications as X-ray scintillating panels. The structural characterization indicates that the sol–gel polycrystals have similar phase composition to commercial monocrystals; concerning the excitation and emission properties, the same radiative recombination channels are observed in the polycrystals and commercial monocrystals with a slightly faster decay time in the first case. In addition, low temperature measurements (8 K) indicate the presence of a non-radiative cross-relaxation mechanism among cerium ions in the sol–gel grown samples in the two possible crystallographic sites. The results indicate the possibility to develop sol–gel synthesized polycrystalline thin films as scintillating materials in the X-ray energy range.

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.

Bi-magnetic core-shell spinel ferrite-based nanoparticles with different CoFe2O4 core size, chemical nature of the shell (MnFe2O4 and spinel iron oxide), and shell thickness were prepared using an efficient solvothermal approach to exploit the magnetic coupling between a hard and a soft ferrimagnetic phase for magnetic heat induction. The magnetic behavior, together with morphology, stoichiometry, cation distribution, and spin canting, were investigated to identify the key parameters affecting the heat release. General trends in the heating abilities, as a function of the core size, the nature and the thickness of the shell, were hypothesized based on this systematic fundamental study and confirmed by experiments conducted on the water-based ferrofluids.

In this work, the effect of different molecular coatings on the alternate magnetic field-induced heating properties of 15 nm maghemite nanoparticles (NPs) in water dispersions was studied at different frequencies (159-782 kHz) and field amplitudes (100-400 G). The original hydrophobic oleate coating was replaced with dimercaptosuccinic acid (DMSA) or polyethylene glycol trimethoxysilane (PEGTMS), while cetrimonium bromide (CTAB) or stearic acid-Polaxamer 188 (SA-P188) were intercalated or encapsulated, respectively, to transfer the dispersions into water. Surface modification, based on intercalation processes, induced clustering phenomena with the formation of spherical-like assemblies (CTAB and SA-P188), while ligand-exchange strategies kept the particle isolated. The clustering phenomenon has detrimental effects on the heating performances compared with isolated systems, in line with the reduction of the Brown relaxation times. Furthermore, broader comprehension of the heating phenomenon in this dynamic system is obtained by following the evolution of the SPA and ILP with time and temperature beyond the initial stage.