Italo Odone Mazali

Preparation and characterization of new niobophosphate glasses in the Li2O-Nb2O5-CaO-P2O5 system

In the present work we describe the synthesis, spectroscopy, thermal and chemical durability properties of the vitreous system Li2O-Nb2O5-CaO-P2O5 (LNCP). Investigations of the short-range order by Fourier transform infrared, Raman, UV-VIS and 31P MAS-NMR spectroscopies suggest that the network former glass consists of Nb octahedra linked to pyro/orthophosphate units through Nb—O—P bonds. The presence of modifier cations (Li+ and Ca2+) promotes depolymerization of the P—O—P chains, yielding pyro/orthophosphate units. The presence of this kind of structure accounts for the improvement of the chemical durability at low pH when the Nb content in the LNCP glass composition is high. The density and linear refractive indices of LNCP glasses increased linearly as the Nb2O5/P2O5 molar ratio increased, as a consequence of P2O5 substitution by Nb2O5 as the glassformer. The dependence of the glass transition temperature, the softening temperature and the crystallization temperature on the Nb2O5/P2O5 ratio exhibits the same behavior. On the other hand, the thermal expansion coefficient decreases with the increased Nb2O5/P2O5 ratio.

Morphosynthesis: high fidelity inorganic replica of the fibrous network of loofa sponge (Luffa cylindrica)

High fidelity calcium carbonate and hydroxyapatite (bio) inorganic replicas of the fibrous network of the dried fruit of Luffa cylindrica are described, utilizing a facile synthetic route. The loofa sponge is a highly complex macroscopic architectural template, an inexpensive and sustainable resource. In the context of the morphosynthesis, the capability of replication of the loofa sponge opens the possibility of the use of biodiversity in obtaining new materials. We would like to emphasize that the template proposed in this paper, makes possible the preparation of inorganic replicas with a very desirable size, on the centimeter scale. This fact is innovative with respect to inorganic replicas described in the literature, which predominate at the micrometric scale, limited to the original size of the template.

Ion-Exchange Properties of Imidazolium-Grafted SBA-15 toward AuCl4– Anions and Their Conversion into Supported Gold Nanoparticles

Imidazolium groups were successfully prepared and grafted on the surface of SBA-15 mesoporous silica. The ion-exchange properties of the functionalized porous solid (SBA-15/R(+)Cl(-)) toward AuCl(4)(-) anions were evaluated through an ion-exchange isotherm. The calculated values of the equilibrium constant (log β = 4.47) and the effective ion-exchange capacity (t(Q) = 0.79 mmol g(-1)) indicate that the AuCl(4)(-) species can be loaded and strongly retained on the functionalized surface as counterions of the imidazolium groups. Subsequently, solids containing different amounts of AuCl(4)(-) ions were submitted to a chemical reduction process with NaBH(4), converting the anionic gold species into supported gold nanoparticles. The plasmon resonance bands, the X-ray diffraction patterns, and transmission electron microscopy images of the supported gold nanoparticles before and after thermal treatment at 973 K indicate that the metal nanostructures are highly dispersed and stabilized by the host environment.

Determination of Judd-Ofelt Intensity Parameters of Pure Samarium(III) Complexes

This work reports an alternative aproach to obtain the Judd-Ofelt intensity parameters of Sm(III) complexes with the general formula: [Sm(tta)3(L)n], with L = H2O, triphenylphosphine oxide (tppo), 2,2′-bipyridine (bipy) and 1,10-phenantroline (phen); n = 2 for H2O and tppo and n = 1 for phen and bipy, using the absorption spectra of rare earth complexes where the powders are dispersed in KBr pellets. This approach can be applied to other complexes of rare earth ions that have spin allowed transitions and it is validated by comparing the emission spectra of the complexes with those dispersed in KBr pellets.

γ-Fe2O3 nanoparticles dispersed in porous Vycor glass : A magnetically diluted integrated system

An investigation of the effect of interparticle interaction and particle size distribution has been carried out on iron oxide nanoparticles dispersed into porous Vycor glass. γ-Fe2O3 nanoparticles dispersed into monoliths of Vycor glass were obtained using impregnation-decomposition cycles through the single-source metallo-organic decomposition process. Magnetic properties were investigated by ac magnetic susceptibility measurements, as a function of temperature at different frequencies, by measuring zero-field-cooled and field-cooled magnetization curves and by constructing hysteresis loops at different temperatures. A log-normal size distribution of monodomain nanoparticles has been deduced from the analysis of the magnetization curves. F57e Mossbauer spectroscopy was also employed for investigating the magnetic behavior as a function of nanoparticle size. The systems exhibit typical superparamagnetic behaviors with a wide particle size distribution that can be changed without significantly affecting th...

Fast detection of paracetamol on a gold nanoparticle–chitosan substrate by SERS

A fast method for detecting pharmaceutical drugs, such as paracetamol, by surface-enhanced Raman spectroscopy (SERS) using a gold nanoparticle substrate was studied. Gold nanoparticles were synthesized using chitosan (AuNP–chitosan) as a reductant and capping agent and subsequently deposited on glass slides as a thin film. The SERS performance of AuNP–chitosan films was evaluated using methylene blue (MB, 10−6 mol L−1) as a SERS probe molecule. The method is based on drop-drying an analyte solution (paracetamol, 10−3 mol L−1) onto a substrate surface and subsequently analyzing by Raman spectroscopy. The spectra were obtained in 10 seconds with two accumulations and exhibit a high signal-to-noise ratio. This preliminary study supports the AuNP–chitosan substrate as a SERS sensor, for a convenient analytical method for detection of paracetamol and other pharmaceutical drug molecules.

Preparation of supported AuPd nanoalloys mediated by ionic liquid-like functionalized SBA-15: structural correlations concerning its catalytic activity

Noble metal nanoalloys are very important in catalysis, sensing, electrochemistry, and plasmonics. Based on the importance of these materials and in order to overcome the synthetic limitations for the in situ synthesis of supported nanoalloys in porous supports, we extended a synthetic protocol to achieve supported AuPd nanoalloys within SBA-15 pores modified with an ionic liquid-like alkoxysilane. The synthesized materials form very small nanoparticles with non-passivated surfaces, which are highly active as heterogeneous catalysts for the reduction of 4-nitrophenol. The anion exchange ability of the functionalized SBA-15 was used to adsorb Au and Pd anionic complexes. The adsorbed species were then reduced and converted into supported monometallic nanoparticles or nanoalloys. Nitrogen physisorption isotherms showed that the synthetic process does not damage the mesoporous support nor block the pores. TEM/EDS and UV-vis analyses were used to prove alloy formation in the bimetallic materials through the concomitant presence of Au and Pd in the same particles and through the disappearance of the gold plasmon band as the palladium content increased. Finally, the catalytic activity of the materials increased as the palladium content increased, showing that it is possible to control the catalytic performance by tuning the material composition during the anion exchange step.

Non-stabilized europium-doped lanthanum oxyfluoride and fluoride nanoparticles well dispersed in thin silica films

Well dispersed non-stabilized lanthanum oxyfluoride and fluoride nanoparticles were prepared in situ in thin silica films from rapid thermal decomposition of lanthanum tris-trifluoroacetate under nitrogen atmosphere. The thin silica films were obtained from sol–gel method and spin-coating. The spectroscopic properties of the non-stabilized nanoparticles as well the nanoparticles dispersed into thin silica films were studied in order to apply the system in future photonic applications such as erbium(III)-doped waveguide amplifiers. The non-stabilized nanoparticles were characterized by XRD, FT-IR, Transmission Electron Microscopy, Confocal Raman Spectroscopy and steady-state and time-resolved Luminescence Spectroscopy and these characterizations were used as a starting point to characterize the nanoparticles dispersed into the films. According to the temperature of the thermal treatments, the non-stabilized nanoparticles may present Eu(III)-doped LaOF in tetragonal and rhombohedral phases as well as a mixed phase of Eu(III)-doped LaF3 and LaOF. The tetragonal LaOF phase has C4v La(III) point symmetry and is more symmetric than the rhombohedral LaOF phase, where the La(III) ion has C3v symmetry, consequently tetragonal LaOF presented lower Ω2 values than rhombohedral LaOF. Theoretical calculations of Judd–Ofelt intensity parameters were also performed and were in good agreement with the experimental values. The samples containing the mixed phase of LaF3 and LaOF presented lower values of intensity parameters than pure LaOF phases. The samples containing the mixed phase presented higher values of emission lifetimes and quantum efficiencies. Confocal Raman spectroscopy of these samples complements the luminescence studies and indicates which LaOF phase is present in the mixed phase of LaF3 and LaOF. The rapid thermal decomposition of the precursor tris-trifluoroacetate on thin silica films results in well-dispersed 10 nm nanoparticles. The mixed phase of LaF3 and LaOF phases is also present in thin films. The luminescence of the Eu(III) and Er(III)/Yb(III)-doped LaF3/LaOF nanoparticles containing thin silica films presented broad emission bands suggesting that in the future the systems may be applied as erbium(III)-doped waveguide amplifiers.

Synthesis and structural characterization of nanometric ceria highly dispersed in SBA-15 with oxygen exchange capacity

Nanometric ceria-decorated SBA-15 was prepared using a route involving the impregnation of SBA-15 pores by a solution of cerium(III) 2-ethylhexanoate, followed by its thermal decomposition. According to XRF analysis, the number of successive impregnation–decomposition cycles (IDC) allows control of the CeO2/SiO2 ratio in the final material, and also the tailoring of the nanoparticle size of the fluorite CeO2nanoparticles supported in the SBA-15, as confirmed by XRD, Raman and UV-Vis spectroscopies. The mean pore size of the SBA-15 decreases with successive IDC, as observed by N2 adsorption–desorption, suggesting that CeO2 nanoparticles are located inside the SBA-15 mesopores, as confirmed by TEM and HRTEM analyses. The degree of oxygen storage capacity (OSC) was measured by the number of hydrogen uptake from the temperature programmed reduction (H2-TPR). It was found that the value of hydrogen uptake of SBA-15 submitted to one IDC corresponds to 3344 μmol of O2 per gram of CeO2, whereas those of SBA-15 submitted to five and ten IDC were 1324 and 2769 μmol of O2 per gram of CeO2, respectively.

Fabrication of a new porous glass-ceramic monolith using vanadium(III) calcium phosphate glass as precursor

Preliminary XRD, IR, Raman and SEM data indicate that porous glass-ceramic monoliths (pgc-LVCP) with skeleton of V(PO3)3 and Ca3(VO4)2 with three-dimensional network structure using an original Li2O-V2O3-CaO-P 2O5 glass as precursor was obtained. The pgc-LVCP is a promising porous host for integrated chemical systems because the Ca3(VO4)2 has ferroelectric and luminophor properties while V(PO3)3 exhibits magnetic properties associated with high degree of mechanical, chemical and thermal stability.