Carmen Canevali

Surface reactivity of SnO2 obtained by sol-gel type condensation: Interaction with inert, combustible gases, vapour-phase H2O and air, as revealed by electron paramagnetic resonance spectroscopy

Electron paramagnetic resonance (EPR) studies have been carried out on lattice oxygen vacancies produced by the interaction of carbon monoxide with SnO 2 obtained by sol–gel type condensation. Under a 0.5% CO–argon reducing atmosphere the vacancies can transfer electrons to Sn 4+ producing Sn 2+ centres. In air the lattice defects interact with molecular oxygen in a manner which depends on whether the gas reducing treatment was performed under dry or moist conditions. Defects that undergo oxygen interaction at the SnO 2 surface, reduce O 2 to O 2 - or O 2- , depending on the temperature of the reaction with oxygen.

A multi-analytical approach for the characterization of powders from the Pompeii archaeological site.

AbstractNine black powders found in Pompeii houses in three different types of bronze vessels (cylindrical theca atramentaria, unguentaries, and aryballoi) were characterized in order to assess a correspondence between the composition and the type of vessel and, possibly, to verify if these powders were inks or not. For the compositional characterization, a multi-analytical approach was adopted, which involved the use of scanning electron microscopy–energy dispersive X-ray, Fourier-transformed infrared spectroscopy, Raman, X-ray diffraction, electron paramagnetic resonance spectroscopy, thermogravimetric analysis, gas chromatography coupled with mass spectrometry (GC/MS), and pyrolysis GC/MS. Powders contained in cylindrical theca atramentaria form a homogeneous group, and their organic and inorganic compositions suggest that they were writing inks, while powders contained in unguentaries and aryballoi could have had several different uses, including writing inks and cosmetics. Furthermore, the composition profile of the powders found in cylindrical cases shows that, at 79 ad, in Pompeii, carbon-based inks were still used for writing, and iron gall inks had not been introduced yet. FigurePhotography of the 12724 black powder contained in a cylindrical theca atramentaria.

Laboratory-scale photomineralization of n-alkanes in gaseous phase by photocatalytic membranes immobilizing titanium dioxide

Kinetics of photocatalytic oxidation of methane, ethane, and n-heptane, to yield intermediates, and photomineralization of intermediates, to yield carbon dioxide and water, was studied in the gaseous phase, at 308±2 K, by a laboratory-scale photoreactor and photocatalytic membranes immobilizing 30±3 wt.% of TiO2, in the presence of aerosolized stoichiometric hydrogen peroxide as oxygen donor, and at a relative humidity close to 100%. The whole volume of irradiated solution was 4.000±0.005 L, the ratio between this volume and the geometrical apparent surface of the irradiated side of the photocatalytic membrane was 3.8±0.1 cm, and the absorbed power was 0.30 W/cm (cylindrical geometry). The pinetic parameters of the present work substantially coincide with those of the same molecules previously studied in aqueous solution, within the limits of experimental uncertainty. Photocatalytic processes thus appear to be controlled by interface phenomena, which are ruled kinetically, and apparently also thermodynamically, by concentration gradients, independently on diffusion and other processes in the aqueous or gaseous bulk, if turbulence in these phases is adequately assured.

Determination of platinum in plasma of patients affected by inoperable lung carcinoma treated with radiotherapy and concurrent low-dose continuous infusion ofcis-dichlorodiammine platinum(II)

Platinum microquantities were determined in plasma of patients affected by lung carcinoma during treatment with radiotherapy (RT) and concurrent low-dose continuous infusion ofcis-dichlorodiammineplatinum(II) (CDDP). RT was given at 50 Gy in continuous course; CDDP was continuously infused at 4 mg/m2 daily for 100h/week for 5 weeks, and the infusions were separated by 68h of rest. The percentage of free drug versus total drug in plasma was about 3%. It did not vary with therapy duration and was not significantly different from that found in 5-day continuous infusions at much higher daily doses. Never-theless, maximal values of free Pt in plasma were very low and agreed with the low level of CDDP toxicity encountered on the present administration schedule.

Nanocrystalline TiO2 with enhanced photoinduced charge separation as catalyst for the phenol degradation

Nanocrystalline TiO2 catalysts 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 TiO2 in 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.

Spectroscopic investigation of the molybdenum active sites on MoVI heterogeneous catalysts for alkene epoxidation

Spectroscopic and spectromagnetic investigations on molybdenum centres in MoO3· H2O and its polymer-supported form have been carried out. Both were tested as catalysts for cyclohexene epoxidation in a heterogeneous phase; both needed activating pretreatment before the reaction. XPS and EPR data show that the metal is mainly present as MoVI. The activation process increases the acidic character of MoVI and its efficiency depends both on the oxidizing power of the activating reactant and on the accessibility of the metal to the reactant. The steric hindrance of MoVI lowers the catalytic activity owing to the replacement of H2O by carboxylic groups of the functionalized resin.

Modelling of quantum yields in photocatalytic membrane reactors immobilising titanium dioxide

For some model molecules (methanoic and ethanoic acids, methane, and phenol), systematic investigations of quantum yields were carried out in the present paper, as a function of concentration and of absorbed radiant power. Quantum yields Φ∞, calculated from rates, followed an apparently Langmuirian function of initial concentration C0, by which Φ∞ values at “infinite” concentration could be obtained. By having thus established that quantum yields of photomineralisation Φ∞ are independent of radiation wavelength, within the absorption range of semiconductor, but depend on radiant power, such a dependency was experimentally investigated. For all the investigated molecules, the maximum allowable values reached in the low radiant power range clearly appeared as a plateau. On the contrary, at high radiant power values, another plateau, at a value of about 1/4-1/5 with respect to the maximum value, was evident. This was interpreted on the basis of a competition kinetics of hydroxyl radicals with themselves, leading to hydrogen peroxide formation, other than with substrate or intermediate molecules leading to full mineralisation. Modelling of quantum yields as a function of concentration and radiant power thus allows a fully consistent and trustworthy design of photoreactors.

Electron paramagnetic resonance characterisation of silica-dispersed copper molybdate obtained by sol-gel and impregnation methods

Silica-dispersed copper molybdates having different Cu:Mo and Cu:Si molar ratios were prepared both by a sol-gel route and a conventional impregnation technique. These materials, used as catalysts for the propene oxidation, were studied in order to assess whether the different preparation methods and/or different Cu:Mo and Cu:Si molar ratios affected the copper(II) coordination. Electron paramagnetic resonance spectroscopy showed that oxo/hydroxo-bridged copper(II) dimers were present in xerogel catalyst precursors and on the surface of fresh impregnated precursor materials, their amount increasing with Cu:Si molar ratio and in impregnated samples. The value of the zero field interaction is very low and decreases with increase in temperature. This means that Cu(II) centres in dimers are spaced fairly far apart and lie in a strongly distorted symmetry field which varies because of the flexible host matrix. Thermal treatment of both xerogels and impregnated samples gave silica-dispersed Cu 3 Mo 2 O 9 catalysts from samples with Cu:Mo molar ratio 1:1 and silica-dispersed CuMoO 4 from those with Cu:Mo 1:2. The presence of polynuclear metal compounds in the crystalline phase seems to be connected to the presence of dimeric species in the precursor. The sol-gel method is more efficient than impregnation to produce catalysts with small and homogeneous particle dimensions of the active phase, for a wide range of Cu:Si molar ratios.

Spectromagnetic investigation of the active species in the oxidation of propenoidic phenols catalysed by [N,N′-bis(salicylidene)ethane-1,2-diaminato]cobalt(II)*

The oxidation of propenoidic phenols by molecular oxygen, catalysed by [N,N′-bis(salicylidene)ethane-1,2-diaminato]cobalt(II) [Co(salen)], was studied in different solvents and for variously substituted phenols to find processes alternative to those reported for the removal of polyphenols from waste waters in the paper industry. The reaction of methyl E-4-hydroxy-3-methoxycinnamate (E-methyl ferulate) selectively gave the corresponding 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde; yields are highest in chloroform, good in methanol and very low in pyridine. Conversion was high with E-methyl ferulate, lower with methyl E-4-hydroxycinnamate, while the other phenols, methyl E-3-hydroxy-4-methoxycinnamate (E-methyl isoferulate) and methyl E-3-chloro-4-hydroxycinnamate, did not react. An EPR investigation of the reaction mixtures, performed on samples taken at different reaction times, demonstrated that the most probable mechanism involves reactions (i)–(iii). The superoxocobalt radical, [CoIII(salen)(ROH)(O2)]–, and the phenoxy cobalt radical, [CoIII(salen)(RO–)(RO˙)], are the EPR-active species; RO˙ is suggested easily to dissociate from [CoIII(salen)(RO–)(RO˙)] and, reacting with O2 at the β-carbon of the allyl substituent, probably gives a dioxethane. This decomposes to aldehyde and acid. The phenol electron-donor properties promote the formation of the superoxocobalt derivative and consequently favour the formation of the phenoxy cobalt radical; a too high stability of this radical does not favour its evolution into oxidation products.

Inverted opal luminescent Ce-doped silica glasses

Inverted opal Ce-doped silica glasses (Ce : Si molar ratio 1 ⋅ 10−3 were prepared by a sol-gel method using opals of latex microspheres as templates. The rare earth is homogeneously dispersed in silica host matrix, as evidenced by the absence of segregated CeO2, instead present in monolithic Ce-doped SG with the same cerium content. This suggests that the nanometric dimensions of bridges and junctions of the host matrix in the inverted opal structures favor the RE distribution avoiding the possible segregation of CeO2.