Serena Esposito

Solid state 27Al NMR and FTIR study of lanthanum aluminosilicate glasses

The structure of lanthanum aluminosilicate (LAS) glasses, containing: (15–25) mol% La2O3, (15–35) mol% Al2O3 and (40–70) mol% SiO2, were studied by 27Al nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The effects of La2O3 and Al2O3 content on the properties and structure of the LAS glasses were evaluated. Al3+ ion enters into the glass structure mainly in fourfold co-ordination, forming (AlO4/2)− tetrahedra, and only in small amounts in fivefold and sixfold co-ordination. La3+ acts as network modifier, producing more non-bridging oxygen atoms as its content increases.

Ftir and dta study of lanthanum aluminosilicate glasses

Abstract Structure and glass transition temperature of lanthanum aluminosilicate (LAS) glasses, containing: (15–25) mol% La2O3, (15–35) mol% A12O3 and (40–70) mol% SiO2, were studied by FTIR spectroscopy and differential thermal analysis. The effects of La2O3 and A12O3 on the properties and structures of LAS glasses were evaluated. The Al+3 ion can assume both four-fold co-ordination, forming (AlO4/2)− tetrahedra, and six-fold co-ordination forming (AlO6/2)−3 octahedra. The amount of these depends on La+3 content; acting as network modifier, it can compensate the charge of three neighbouring (AlO4/2)−units or one (AlO6/2)−3 unit.

FTIR study of the thermal transformation of barium-exchanged zeolite A to celsian

In this study room temperature X-ray diffraction patterns and FTIR spectra of zeolite A in its Na form, Ba-exchanged zeolite A, hexacelsian, monoclinic celsian and Ba-exchanged zeolite A samples thermally treated at temperatures ranging from 200 to 1000 °C are reported. The combined inspection of room temperature X-ray diffraction patterns and FTIR spectra reveals the following points. 1) The thermal collapse of the microporous zeolite structure goes to completion upon thermal treatment at 200–300 °C; in the resulting amorphous phase the presence of the secondary building units of the zeolite A structure may be detected. 2) Thermal treatment in the temperature range 200–400 °C results in a middle-range order which favours the crystallisation of small crystallites of monoclinic celsian at 500 °C. 3) The further evolution of the amorphous phase in the 500–800 °C temperature range of thermal treatment instead of promoting the crystalline growth of monoclinic celsian, creates a middle-range order favourable to the crystallisation of hexacelsian which occurs at 1000 °C.

Sol-Gel Synthesis of Humidity-Sensitive P2O5-SiO2 Amorphous Films

The sol-gel synthesis of silicophosphate gels using phosphoryl chloride and tetraethoxysilane as molecular precursors is reported and discussed. Gel-derived glasses and films having the molar compositions 10P2O5 · 90SiO2 and 30P2O5 · 70SiO2 have been obtained. The structure of the dried gels as well as the structural modifications that occurs during the transformations in gel-derived glasses are analyzed by Fourier transform infrared spectroscopy (FTIR). It has been found that the evidence of the P—O—Si linkages begins to appear only on the FTIR spectra of the bulk gels heat treated up to 400°C while they are well resolved on the FTIR spectra of the bulk gel samples heated up to 1000°C indicating that at this temperature the transformation in the corresponding gel-derived glasses occurs. The humidity sensitive properties of the gel-films have been evaluated by electrochemical impedance spectroscopy (EIS). The phosphorous content as well as the temperature of the heat treatments strongly affect the sensitivity to RH of the gel-derived films.

Sorption Capacity of Mesoporous Metal Oxides for the Removal of MCPA from Polluted Waters

A study was performed to assess the sorption capacity of the phenoxy acid herbicide, MCPA, on two mesoporous oxides, Al(2)O(3) and Fe(2)O(3,) by using a batch equilibrium method. Effects of pH, contact time, initial concentration and sorbent dosage on the sorption of the herbicide were investigated. The collected data evidenced the greater sorption efficiency of Al(2)O(3) with respect to Fe(2)O(3). These results can be explained by considering the specific mesoporous structure of Al(2)O(3) together with the greater value of surface area. MCPA is assumed to be bound to Al(2)O(3) and Fe(2)O(3) by a combination of ionic and ion-dipole bonding. Both oxides present as sorbents for a fast and highly efficient removal of MCPA from contaminated waters. For the first time the possible use of mesoporous metal oxides to remove MCPA from contaminated wastewaters identifies these sorbents as suitable filters for the decontamination of point sources.

29Si and 27Al NMR study of the thermal transformation of barium exchanged zeolite-A to celsian

The thermal transformation of Ba exchanged zeolite A to celsian has been studied by 27Al and 29Si MAS NMR spectroscopy. Evidence for the degradation of the zeolite framework is present in the 29Si NMR spectra after thermal treatment at 200 °C. Confirmation is provided by the 29Si NMR data that synthesis of celsian via the decomposition of Ba exchanged zeolite leads to a single phase. The 27Al NMR data show distorted aluminium co-ordination sites upon the thermal transformation of Ba exchanged zeolite A. The distortions present in the amorphous matrix are greater than those present in the monoclinic and hexagonal crystalline phases of celsian. No evidence could be seen for significant amounts of nanometre scale crystalline domains in the amorphous matrix, prior to the crystallisation of monoclinic celsian.

Imogolite: an aluminosilicate nanotube endowed with low cytotoxicity and genotoxicity.

High-aspect-ratio nanomaterials (HARN) (typically, single-walled carbon nanotubes (SWCNT) or multiwalled carbon nanotubes (MWCNT)) impair airway barrier function and are toxic to macrophages. Here, we assess the biological effects of nanotubes of imogolite (INT), a hydrated alumino-silicate [(OH)3Al2O3SiOH] occurring as single-walled NT, on murine macrophages and human airway epithelial cells. Cell viability was assessed with resazurin. RT-PCR was used to study the expression of Nos2 and Arg1, markers of classical or alternative macrophage activation, respectively, and nitrite concentration in the medium was determined to assess NO production. Epithelial barrier integrity was evaluated from the trans-epithelial electrical resistance (TEER). Potential genotoxicity of INT was assessed with comet and cytokinesis-block micronucleus cytome assays. Compared to MWCNT and SWCNT, INT caused much smaller effects on RAW264.7 and MH-S macrophage viability. The incubation of macrophages with INT at doses as high as 120 μg/cm(2) for 72 h did not alter either Nos2 or Arg1 expression nor did it increase NO production, whereas IL6 was induced in RAW264.7 cells but not in MH-S cells. INT did not show any genotoxic effect in RAW264.7 and A549 cells except for a decrease in DNA integrity observed in epithelial A549 cells after treatment with the highest dose (80 μg/cm(2)). No significant change in permeability was recorded in Calu-3 epithelial cell monolayers exposed to INT, whereas comparable doses of both SWCNT and MWCNT lowered TEER. Thus, in spite of their fibrous nature, INT appear not to be markedly toxic for in vitro models of lung-blood barrier cells.

Cyclic process of simazine removal from waters by adsorption on zeolite H-Y and its regeneration by thermal treatment

Removal of the agrochemical simazine from polluted waters through adsorption by zeolite Y in its protonic form was studied. The investigated parameters were: pH, time, initial simazine concentration and solid/liquid ratio. An iterative process of simazine removal from waters is proposed, featuring: (i) final agrochemical concentration well below 0.05 mg/dm(3), the maximum concentration allowed by Italian laws in wastewaters; (ii) regeneration of the adsorbent by a few minutes thermal treatment in air at about 500°C, which results in the combustion of simazine without damage of the adsorbent; (iii) destruction of the agrochemical compound by combustion.

Decontamination of waters polluted with simazine by sorption on mesoporous metal oxides

Two mesoporous metal oxides, Al(2)O(3) and Fe(2)O(3), were evaluated as regards their ability to remove simazine, a highly persistent herbicide of s-triazines, using a batch equilibrium method. The effect of several experimental parameters such as pH, contact time, initial concentration and sorbent dosage on the sorption of the herbicide was investigated. The maximum sorption of simazine on Al(2)O(3) and Fe(2)O(3) was observed at pH 6.5 and 3.5, respectively. The different sorption capacities of the two oxides were explained considering a set of factors affecting the sorption process such as the surface area and the porosity. The kinetics of sorption on both oxides was described using a pseudo second-order model. The sorption of simazine on Fe(2)O(3) was faster in comparison to that observed on Al(2)O(3). It was shown that aluminum oxide can be regenerated by incineration, and consequently can be considered for industrial treatment systems designed to mitigate the pesticide pollution in the aquatic environments.

Solid state 1H NMR study, humidity sensitivity and protonic conduction of gel derived phosphosilicate glasses

1H Magic Angle Spinning (MAS) NMR and 1H T1 and T1ρ relaxation times measurements were used to investigate structural aspects of gel derived glasses of composition 10P2O5·90SiO2 (10P) and 30P2O5·70SiO2 (30P), with the aim of understanding the different humidity sensitive behaviour observed for films of the same composition. The experimental evidence suggests that 10P and 30P gel samples heat treated at 100 °C have a similar POH environment while further heating causes a different structural evolution of POH units. In particular, the 30P sample heat treated at 400 °C shows a single 1H resonance while a number of resonances are seen in the 1H spectrum of the 10P sample heat treated at 400 °C. Further evidence of the different structure of 10P and 30P samples was given by the NMR relaxation times measurements, the gels were found to be heterogeneous on a nanometric scale. Domains, about 60 nm in size, related to 1H resonance in POH were evenly distributed in the matrix of both gels, only in the 10P gel also larger domains (about 700 nm) were found that can be related to 1H resonance in SiOH groups. Finally, MAS in combination with variable temperature static NMR spectra provided detailed information on the network structural features present in the 30P sample heat treated at 300 °C as well as in the 10P sample heat treated at 400 °C and allowed investigation of the dynamic processes taking place in these samples.