Study On The Electrochemical Reduction Of Eu³⁺ And Electrochemical Preparation Of Eu²⁺

In recent years, the research about rare earth element europium and its complexes has been extremely active. In the development of functional materials of europium, light-emitting materials are particularly important. Europium light-emitting materials have been applicated in daily life, industry and scientific research, etc., because of its high purity of color, high light conversion rate, wide distribution of emission wavelength and stable performance. The related research and applications of Eu³⁺ have received more and more attention. But, because the standard potential of Eu³⁺/Eu²⁺ is very low (-0.35V), and Eu²⁺ is extremely sensitive to water and oxygen. The materials of Eu²⁺ have little been reported. Therefore, the research on the electrochemical reduction of Eu³⁺ is the focus. The electrochemical preparation of Eu²⁺ has meanings of guidance for the synthesis and application of Eu²⁺ complexes. In this paper, the influences of different conditions on the electrochemical reduction of Eu³⁺ have been systematically investigated by cyclic voltammetry and electrochemical impendance spectroscopy, and the process conditions of Eu²⁺ solution preparation have also been discussed. The results can provide a theoretical basis for the electrochemical synthesis of novel materials of Eu²⁺ complexes. The main contents are as followes.The electrochemical reduction of Eu³⁺ on titanium, mercury, multi-walled carbon nanotubes (MWNTs) modified electrodes are studied by linear sweeping voltammetry and cyclic voltammetry. The results indicate that the electrochemical reduction process of Eu³⁺ is diffusion-controlled on the three electrodes. The cathodic peak potentials at mercury, titanium, MWNTs/GC (glassy carbon) electrodes are -1.0 V, -0.75 V, -0.70 V, respectively. The reaction reversibility of Eu³⁺/Eu⁺ is increased in the order of mercury, titanium and MWNTs/GC electrode. The pH value of solution also has influence on the electrochemical reduction behavior of Eu³⁺.The influence of MWNTs/SDS (sodium dodecylsulfate) composition on the electrochemical reduction of Eu³⁺ has been studied by cyclic voltammetry and electrochemical impendance spectroscopy. Kinetic parameters such as D_app,k_s andαhave been calculated. Equivalent circuit has been obtained as R ([CQ] [RW]) by EQU.. Attributed to the different roles of MWNTs and SDS in the composite film, the enhancement effect of the composite film is directly related to the components ratio of the MWNTs-SDS suspension. MWNTs promote the charge transfer process in the whole system, while SDS mainly contributes to the mass transport process from solution into the film. At the same time, experiment on the size effects of MWNTs on the electrochemical reduction of Eu³⁺ have been carried out. The results show that the electrochemical and electrocatalytic activities are mainly depended on the nanotube length. The electrochemical reactivity of S-MWNTs (short MWNTs) is better than that of L-MWNTs (long MWNTs),which may be mainly attributed to the existence of the more open ends of the S-MWNTs compared to L-MWNTs.Study on the Eu²⁺ preparation has been carried out by galvanostatic electrolysis. The influences of the process parameters, such as the current density, electrolysis time, concentration and pH value of cathode solution, on the conversion rate of Eu³⁺ have been discussed. Under the optimal conditions, the conversion rate of Eu³⁺ is higher than 95%. A typical complex of Eu²⁺-salicylic acid europium (â…¡) has been prepared. The result verifies the feasibility of the electrochemical preparation of high-purity Eu²⁺ solution, which can be used for the synthesis of novel Eu²⁺ complexes.