| Summary: | 碩士 === 國立成功大學 === 化學系碩博士班 === 100 === When selenium dioxide(SeO2) and selenium tetrachloride(SeCl4) dissolved in room temperature ionic liquids (EMIC-BF4), the coordination mode of these two precursor in ionic liquid can be determined by electrochemical (CV) and spectroscopic (UV/VIS,XAS) methods. The electrochemical behavior of [SeO2Cl]- and [SeCl6]2- in EMIC-BF4 were influenced by chloride ion(Cl-) concentration and the nature of selenium . In addition, near the room temperature (40oC), using XRD, SEM technology to comparison the morphology and the nature of selenium at different reduction potential of these two precursors (SeO2, SeCl4).
The electrochemical behavior of SeCl4 in ionic liquids (40-60 mol% of ZnCl2- EMIC) is very sensitive to oxygen confirmed by adding some oxides (Na2CO3, SeO2). Also, we are choosing lower cost of the selenium dioxide(SeO2) as a precursor to elelctrodeposit of Se and ZnSe semiconductor in the 40-60 mol% of ZnCl2- EMIC ionic liquid. The chronoamperometric result indicates that deposition of Se at tungsten substrate under three-dimensional instantaneous nucleation. Initially, the deposition of Se0 proceeds by four electron reduction of Se4+ to Se0, then further reduced to Se2- which chemically react with Zn2+ to produce ZnSe. The deposition parameters like temperature, reduction potential are discussed. The surface morphology, composition and crystal structure are studied with X-ray diffraction(XRD), Energy-dispersive spectroscopy(EDS) and scanning electron microscope(TEM).
UV/VIS absorption spectrum pointed out that the species of K2ReCl6 in the EMI-BF4 is [ReCl6]2-, would not influence by the weak ligand (BF4-) in the ionic liquid. The CV shows that [ReCl6]2- can be oxidized to Re5+ and reduced to Re3+ via quasi reversible one-electron charge transfer process. The standard heterogeneous rate constant(ko), anodic transfer coefficient(σ), were 1.11x10-3 cm/s , 0.45. [ReCl6]2- in the EMI-BF4 is indeed via one electron oxidation to [ReCl6]- obtain from Nernst Plot . On the other hand, calculation the needed coulomb quantity to reduction of [ReCl6]2-, the result shows that nearly two electrons. At the reduction electrolysis process, [ReCl6]3- will release a Cl- ions and occurring the dimmerization reaction forming dimmer, the proof of this phenomenon are Cyclic Voltammetry, Coulometry and Raman spectra. On other hand, when DCA- anion present in the EMI-BF4, the result of reduction electrolysis is totally different from the reduction results without DCA- ion present in the EMI-BF4. Beside to the above reaction (release of Cl- ions and dimmerization), the reduce product will also complex with DCA- ligand, formation of Re dimmer compound that containing DCA- as a ligand.
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