Ultramicroelectrode study without deliberately added electrolyte: Application to the analysis of liquid-liquid extraction processes in dichloromethane

International audienceA platinum ultramicroelectrode was used for the in situ study of partition reactions of Bu4NI and Et4NPic between phosphate buffer, pH 7.5, and dichloromethane, without adding supporting electrolyte. Extraction and dissociation constants are determined by voltammetry in the organic phase and compared with those determined by UV-visible spectrophotometry. The results show the significance of the migration effect in the determination of the extracted species by electrochemistry

Reduction of acids at a platinum ultramicroelectrode: application to “in situ” acid number control of fluid lubricants (phosphate esters)

International audienceThe strength of acids, their charge and possibly their behaviour as polyacids can be deduced by comparing their limiting currents at a platinum ultramicroelectrode in the absence and presence of an excess of supporting electrolyte. Acid-base reactions in tributyl phosphate can be followed without deliberately added supporting electrolyte even if their dielectric constant is low. The acidity of phosphate esters resulting from their hydrolysis can be monitored by amperometry at a platinum ultramicroelectrode

In situ Raman monitoring of materials under irradiation: study of uranium dioxide alteration by water radiolysis

International audienceIn situ Raman scattering studies allow following real‐time evolutions of volume or surface structures under extreme conditions. In nuclear materials sciences, ion irradiation‐induced atomic organization modification and water radiolysis are of a major interest. In order to better understand these phenomena, we have developed an in situ versatile portable Raman spectroscopy system coupled with a cyclotron accelerator, allowing monitoring of a solid/liquid interface under irradiation and thus giving access to effects of radiolysis. The different parts of the system and their improvements are described in details.The system efficiency is highlighted by a comparative study of the time dependence of UO2 surface modification induced, on one hand by contact with water under irradiation by 5 MeV He2+ particles, and on the other hand by pure chemical alteration, through contact with a hydrogen peroxide solution

Electrochemical analysis of a microbial electrochemical snorkel in laboratory and constructed wetlands

International audienceMicrobial electrochemical snorkel (MES) is a short-circuited microbial fuel cell applicable to water treatment that does not produce energy but requires lower cost for its implementation. Few reports have already described its water treatment capabilities but no deeper electrochemical analysis were yet performed. We tested various materials (iron, stainless steel and porous graphite) and configurations of snorkel in order to better understand the rules that will control in a wetland the mixed potential of this self-powered system. We designed a model snorkel that was studied in laboratory and on the field. We confirmed the development of MES by identifying anodic and cathodic parts, by measuring the current between them and by analyzing microbial ecology in laboratory and field experiments. An important application is denitrification of surface water. Here we discuss the influence of nitrate on its electrochemical response and denitrification performances. Introducing nitrate caused the increase of the mixed potential of MES and of current at a potential value relatively more positive than for nitrate-reducing biocathodes described in the literature. The major criteria for promoting application of MES in artificial wetland dedicated to mitigation of non-point source nitrate pollution from agricultural water are considered