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|All Authors / Contributors:||
Marie-Olga Sornein; Eric Simoni; Université de Paris-Sud. Faculté des Sciences d'Orsay (Essonne).
|Description:||1 vol. (XVII-195 p.) : ill. en noir et en coul. ; 30 cm.|
|Responsibility:||Marie-Olga Sornein ; [sous la direction de] [Eric Simoni].|
The behaviour of uranyl in presence of chloride or bromide ions has been investigated in two room temperature ionic liquids, [BuMeIm][Tf2N] and [MeBu3N][Tf2N] ([BuMeIm]+ : 1-butyl-3-methyl-imidazolium ; [MeBu3N]+ : tributylmetylammonium ; [Tf2N]- : bis(trifluoromethylsulfonyl)-imide). A combined spectroscopic and electrochemical approach has been performed, by means of several techniques (such as UV-visible absorption spectroscopy, Time Resolved Laser Induced Spectrofluorometry, and cyclic and linear voltammetries). Firstly, the formation of various halide complexes of uranyl was demonstrated. The maximum coordination complex formed under those conditions is [UO2X4]2- (X- = Cl- or Br-). This species is dominant in solution as soon as 4 equivalents of halide ions are added to uranyl. Then, the structure and the redox behaviour of those tetrahalocomplexes of uranyl have been investigated. The structural study revealed that the coordination sphere of those centrosymetric complexes is maintained in the ionic liquids as in solid state, without any supplementary ligand included. Moreover, the electrochemical study allowed us to propose two hypothesis of mechanism to account for the reduction of the tetrahalocomplexes of uranyl. The coupling of a chemical reaction to the charge transfer has been evidenced, and the process would correspond either to a catalytic EC type or to an ECE type. Depending on the halide ions concentration, the reduction of uranyl would lead to the formation of a deposit of amorphous UO2 or uranium hydroxide on the working electrode.