Synthesis of Various Transition Metal Oxide Materials by Templating and Evaporation Induced Self-Assembly Technique and Its application

Autor: Kuo-Min Lin, 林國閔
Rok vydání: 2007
Druh dokumentu: 學位論文 ; thesis
Popis: 95
In this thesis, we described the templating and evaporation induced self-assembly methods to synthesize the nano-scale phosphor and transition oxide metal mesoporous materials. The thesis was divided into two parts. Part 1 (chapter 1 and 2) is the discussion mainly in the synthesis of phosphor by template/self-assembly method. Part 2 (chapter 3 and 4) is mainly the discussion of evaporation induced self-assembly to synthesis meso-RuO2/TiO2 and meso-RuO2 materials. In addition, in chapter 1, principles and applications of silica base mesoporous material were reviewed and introduced. In chapter 2, the different shapes of SBA-15 mesoporous material (including nanowire, rod and powder) was synthesized by self-assembly method. The Gd2O3: Eu3+ nanowire phosphors embedded in SBA-15 silica templates were synthesized using a combination of the sol-gel method and hydrothermal reactions followed by a sintering process at 1000 oC. The nanowire diameters were very uniform in the 7~9 nm range. The analysis of PL shows that the main nanowire emission peaks were at 585 nm, 597 nm, 613nm and 620 nm. The CIE value (x = 0.62, y = 0.38) indicates that the nanowire emitted a pink color and not red for the bulk material. As we know, the 1-D Gd2O3: Eu3+ nanowire phosphors emitted a pink color and not red for the bulk material. Therefore, we used the core-shell technical to obtain the pure red emission of Gd2O3: Eu3+ phosphors. In chapter 3, Gd2O3: Eu3+ and Gd2Ti2O7: Eu3+ films 10 nm in thickness were individually coated onto silica spheres (particle size of 150 - 170 nm) using the sol-gel method. Uniform cored-shell phosphor particles were observed using FE-SEM. The XRD and HR-TEM results indicated that the coated-shell layer was well crystallized after sintering at 1000 oC. The Gd2O3: Eu3+ @SiO2 PL measurement showed a red-emission at the main 615 nm wavelength. The Gd2Ti2O7: Eu3+@SiO2 phosphor showed an orange-red emission at the 588 nm and 615 nm wavelengths. The core-shell phosphors maintained the same emission ability as the bulk materials and the novel core-shell phosphors possessed great potential in quantum phosphor applications. On the other hand, a red emitting phosphor material, Gd2Ti2O7: Eu3+ V4+, by added vanadium ions is also synthesized using the sol-gel method. While scanning electron microscopy reveals a uniform phosphor particle size in the range of 230 to 270 nm. X-ray photon electron spectrum analysis demonstrates that the V4+ ion promotes an electron dipole transition of Gd2Ti2O7: Eu3+ phosphors, causing a new red-emitting phenomenon and CIE value shifts to x = 0.63, y = 0.34 (a purer red region) from x = 0.57, y = 0.33 (CIE of Gd2Ti2O7: Eu3+). The optimal composition of the novel red-emitting phosphor is about 26 % of V4+ ions while the material is calcinated at an 800 oC. The results of electroluminescent property of the material by field emission experiment by CNT-contained cathode agreed well with that of photoluminescent analysis. In chapter 4, characteristics of mesoporous 5RuO2-95TiO2 thin films were prepared by a combination of sol-gel deposition and evaporation-induced self-assembly (EISA) processes. The films of 390 nm in thickness consisting of a connected network with the pore diameter of 13 nm were examined using FE-SEM and HR-TEM. XRD patterns showed an induced rutile phase in the anatase meso-TiO2 films by dopping RuO2, which plays a very important role. The energy band gap of a 5RuO2- 95TiO2 thin film was shifted from 3.31 to 3.07 eV with the flat band potential at about -0.56 eV determined by the Mott-Schottky plot. The optimal concentration of RuO2 is 5 mol% in these mesoporous TiO2 thin films, which shows a high photocurrent density of 32 mA/cm2 at the potential of -0.3 V vs. a Pt reference electrode In chapter 5, the mesoporous RuO2 thin-film electrodes were successfully prepared by evaporation induced self-assembled method. The textural analysis was carried out by Raman, SEM and BET analyses. Raman spectra identify the rutile crystalline structure of RuO2 thin-film. From the SEM images, mesoporous RuO2 thin film shows very high porosity with 3D-connected hole. The BET surface area and average pore size of RuO2 thin film is 87 m2/g and 18 nm, respectively. Due to its metallic conductivity and 3D-connected meso-hole, crystal RuO2 mesoporous thin-film electrodes exhibit very excellent capacitive performance, i.e. rectangle-like CV behavior and very high power density of 2.6 MW/Kg obtain from the EIS analyses. Finally, the contributions and significance of this dissertation were summarized in chapter 6.
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