ABSTRACT
Iodine compounds that may be released in case of severe nuclear accident will have important radiotoxicity if they are disseminated in air. One of the most important iodine species is CsI that is deposited on the surfaces of the reactor coolant system. However, depending on the conditions, CsI can volatilize or react with oxidants to produce I2(g). Theoretical and experimental studies demonstrate that the oxidation of iodide depends on the temperature and in the presence of oxidants in the gas. It is also slightly influenced by the crystallinity of the CsI particles and the nature of the support. In case of a high temperature deposition, the iodine release started at temperature lower than 300 °C. For the CsI vapour and aerosol depositions, the iodine is detected only at temperature above 450 °C and become very important above 550 °C.
ABSTRACT
Oxide diffusion was studied in two innovative SOFC cathode materials, Ba(2)Co(9)O(14) and Ca(3)Co(4)O(9)+δ derivatives. Although oxygen diffusion was confirmed in the promising material Ba(2)Co(9)O(14), it was not possible to derive accurate transport parameters because of an oxidation process at the sample surface which has still to be clarified. In contrast, oxygen diffusion in the well-known Ca(3)Co(4)O(9)+δ thermoelectric material was improved when calcium was partly substituted with strontium, likely due to an increase of the volume of the rock salt layers in which the conduction process takes place. Although the diffusion coefficient remains low, interestingly, fast kinetics towards the oxygen molecule dissociation reaction were shown with surface exchange coefficients higher than those reported for the best cathode materials in the field. They increased with the strontium content; the Sr atoms potentially play a key role in the mechanism of oxygen molecule dissociation at the solid surface.
ABSTRACT
New assemblies constituted by a microporous matrix of mordenite (MOR) zeolite on which TiO2 nanoclusters are deposited were synthesized using ionic oxalate complexes and TiCl3 titanium precursors. The samples were used to investigate the transfer of electrons produced by spontaneous or photo-induced ionization of a guest molecule (t-stilbene, t-St) occluded in the porous volume towards the conduction band of a conductive material placed nearby, in the pores or at least close to their entrance. The reaction mechanisms were compared in these Ti-rich solids and in a Ti-free mordenite sample. The characterization by XRD, N2 physisorption, TEM, XPS and DRIFT spectroscopy of the supramolecular TiO2/MOR systems before t-St adsorption showed the preservation of the crystalline structure after Ti addition and thermal activation treatments. They also revealed that titanium is mainly located at the external surface of the zeolite grains, in the form of highly dispersed and/or aggregated anatase. After incorporation of the guest molecule in the new assemblies, diffuse reflectance UV-visible and EPR spectroscopies indicate that the electron transfer processes are similar with and without TiO2 but strongly stabilized t-StË(+) radicals are detected in the TiO2-MOR samples whereas such species were never detected earlier in TiO2-free mordenite using these techniques. The stabilization process is found to be more efficient in the sample prepared with TiCl3 as the precursor than with titanium oxalates. It is proposed that the proximity of TiO2 with the formed t-StË(+) radicals provokes the stabilization of the radical through capture of the ejected electron by the semi-conductor and that confinement effects can also play a role.
ABSTRACT
This article deals with an alternative method for bio-separation of surfactin produced by Bacillus subtilis using sorption method on nonwoven PET (polyethylene terephthalate) fibrous membranes functionalized with chitosan. In the first part of the study, surface functionalization of the PET nonwoven fibrous membranes is carried out with aqueous 65% deacetylated chitosan solution with or without a prior surface activation using air-atmospheric plasma treatment. Very small modification of the PET fibrous nonwoven air-permeability confirms the functionalization of PET fibre surface with little reduction of membrane porosity. The functionalized membranes are then characterized by physico-chemical methods: X-ray Photoelectron Spectroscopy (XPS), Wettability and zeta potential. Chitosan increases drastically the zeta potential of PET at all pH values though a prior plasma treatment of the PET membrane reduces slightly the increase in zeta potential values. Sorption of surfactin quantified by HPLC shows that the extent of surfactin sorption on PET nonwovens depends on the surface functionalization method. Surface functionalization with chitosan results in immediate sorption of the entire quantity of surfactin. A prior surface activation by air atmospheric plasma treatment of the PET membranes before chitosan application retards the sorption of entire surfactin which takes place after 1.5h, only. Increased zeta potential and increased hydrophobic behavior in the presence of chitosan without plasma activation would explain the interesting surfactin sorption results.
