Synthesis and structural characterisation of CdS nanoparticles prepared in a four-components "water-in-oil" microemulsion

Nanostructured semiconductor particles are currently under intense investigation because of their enhanced photoreactivity and photocatalytic properties due to the quantum-size effect and the dependence of the photophysical and photochemical properties on their size as it approaches the exciton diameter. This increasing interest has led to the development of several synthetic procedures to prepare and stabilise uniform crystallites. In this paper, we report a novel synthetic pathway to obtain cadmium sulphide (CdS) nanoparticles in a quaternary "water-in-oil" microemulsion formed by a cationic surfactant cetyltrimethylammonium bromide (CTAB), pentanol, n-hexane and water. The synthesis of CdS in this system is achieved by mixing two microemulsions containing Cd(NO3)2 and Na2S, respectively. The nanocrystals have been characterised by using UV--visible spectroscopy and Transmission Electron Microscopy to investigate the influence of various parameters of the particles' formation and stability in solution. Capping of nanoparticles with suitable organic molecules has been performed in order to increase their stability and afford solubility in a wide range of solvents.     

Evidence for negative cross correlations in vibrational dephasing in liquids: isotropic raman-line shift and width phenomena in isotopic mixtures of N2 and O2

To experimentally confirm the hypothesis of negative cross terms between different dephasing mechanisms, potentially leading to a broadening of the isotropic Raman line upon isotopic dilution, we present a detailed study on the concentration dependencies of all of the line shifts and widths in the four isotopic mixtures of type (15N14N)(x)-(14N2)(1-x), (15N2)(x)-(14N2)(1-x), (15N2)(x)-(15N14N)(1-x), and (16O2)(x)-(18O2)(1-x) near the normal boiling point of nitrogen at T = 77.35 K. A quite disparate behavior of the nitrogen oscillators compared to the oxygen oscillators was observed in respect to a change of their isotopic baths.     

Purification of carbon nanotubes grown by thermal CVD

We show the results of a set of purifications on carbon nanotubes (CNT) by acid and basic treatments. CNTs were obtained by thermal decomposition of camphor at 850 °C in a CVD growth system, by means of a growth process catalyzed by iron clusters originating from the addition of ferrocene in the precursors mixture. The purification procedures involved HNO₃, H₂SO₄, HSO₃Cl and NaOH for different process temperatures.As-grown CNTs showed a consistent presence of metal catalyst (about 6 wt%), evidenced by TGA. The purification treatments led to a certain amount of opening of the CNT tips, with a consequent loss of metal catalyst encapsulated in tips. This is also confirmed by BET analysis, which showed an increase of the surface area density of CNT after the purification.FT-IR and XPS revealed the presence of carboxylic groups on the CNT surface chemically modified by the harsh environment of the purification process.Among the various treatments that have been tested, the 1:3 solution of nitric and sulphuric acid was the most effective in modifying the CNT surface and inducing the formation of functional groups.     

Particle size effects on the thermal behavior of hematite

Hematite with different particle sizes was obtained through isothermal annealing and mechanochemical ball-milling methods. The hematite phase is very stable under air atmosphere. The thermal stabilities of hematite under argon atmosphere were characterized by thermal analysis studies up to 800 °C using a simultaneous DSC–TG technique. The lattice parameters a and c of hematite with different particle sizes were extracted from the Rietveld structural refinement of powder X-ray diffraction patterns. Decomposition of hematite into a lower oxidation state in inert argon atmosphere was studied by the TG experiments for the first time and the enthalpy associated with the decomposition reaction was determined from the DSC studies. Particle size has a strong effect on the thermal behavior of hematite samples. Ball-milled hematite samples with smaller particle size showed that the phase transformation was extended to higher temperature range with larger enthalpy. Hematite with larger average particle size showed higher stability under argon atmosphere.     

Morphological and chemical characterization of weathering products on buried Sasanian glass from central Iraq

This paper discusses the morphological and chemical features of the weathering products on Sasanian glass finds excavated at the ancient Sasanian town of Veh Arda?īr, some 30 km south of Baghdad (Iraq), and dated from the third to the sixth century. All the considered fragments represent soda-lime glass, with MgO contents between 3% and 8%, resulting from the use of soda-rich plant ash as a flux; within this general frame, two productions can be distinguished due to their MgO to K₂O ratio. Four main alteration typologies were observed by visual examination of the excavated samples; these were studied by scanning electron microscopy, energy dispersive X-ray analysis, inductively coupled plasma-mass spectrometry, X-ray diffraction and thermal analysis. Different alteration features were generally observed for samples belonging to the two compositional groups. In particular, samples with higher MgO to K₂O ratios show definitely thinner crusts, associated with alteration plugs going down into the glass. Moreover, gray or black crusts are related to the presence of manganese at significant levels in the original glass.     

Thermal analysis of some phytotherapeutic products irradiated with electron beam

The purpose of the present work deals with the evaluation of the electron beam irradiation effects on some natural products based on thermal analysis. Some natural products with therapeutic contributions (artichoke, sea buckthorn, common sage, stonebreaker and cloves) were irradiated with doses up to 9 kGy using accelerated electron beam. The thermal profiles lead to identify three phenomena: dehydration — volatilization, irreversible degradation — molecular reorganization and residue decomposition. The radio-induced degradations determine slight shifts of the temperatures where these phenomena occur. The energetic value of the studied products is affected by e-beam treatment depending on irradiation dose.     

State-specific reactions and autoionization dynamics of Ar produced by synchrotron radiation

The long-lived excited states of doubly charged rare gases can markedly affect their reactivity. In this paper we demonstrate the presence of strong state-specific effects in the charge exchange of Ar²⁺ (³P, ¹D and ¹S) with several neutral targets (He, Ne, Kr, Xe, D₂, and CH₄). State sensitive measurements have been performed by producing the different Ar²⁺ electronic states via tunable synchrotron radiation (Elettra-Trieste, Italy and SuperACO-Orsay, France). From the product ion yield data of charge transfer, state-selected total cross-sections have been deduced. Using the state-specific reactivity of Ar²⁺ towards different neutral targets, it has been possible to extract the photon-energy-dependent production branching of the three doubly charged states and to investigate the autoionization dynamics of neutral or singly charged Ar in the vicinity of the double ionization threshold.     

Decomposition of Methylene Blue in Water by Corona Discharges

The decomposition of methylene blue (MB) in aqueous solution was investigated using a pulsed corona discharge. The discharge was ignited in the gas bubbled in the solution through several needle electrodes. The influence of treatment time, volume of the treated solution and initial concentration of the dye in solution on MB degradation was studied. The effect of the nature of the gas introduced was also investigated. For the same energy input, MB conversion increased in the order air < argon < oxygen. When using oxygen, the decomposition of MB exceeded 95% after ~20 min plasma treatment. Higher efficiency was obtained for higher treated volume and higher initial concentration. At 90% conversion the yield obtained with oxygen was ~5 g/kWh for an initial concentration of 150 mg/l and a treated volume of solution of 100 ml.     

On the normality a posteriori for exponential distributions,using the Bayesian estimation

Summary The Bayesian estimation problem for the parameter θ of an exponential probability distribution is considered, when it is assumed that θ has a natural conjugate prior density and a loss-function depending on the squared error is used. It is shown that, with probability one, the posterior density of the Bayesian—centered and scaled parameter converges pointwise to the normal probability density. The weak convergence of the posterior distributions to the normal distribution follows directly. Both correct and incorrect models are studied and the asymptotic normality is stated respectively.