Browsing by Subject "Transition Metal Complexes"

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    The phase behavior and synthesis of mesostructured coupled semiconductor thin films : MESO-CdS-TiO2
    (2009) Okur, Halil İbrahim
    Mesostructured [Cd(H2O)4](NO3)2 - titania - P123 ((PEO)20(PPO)70(PEO)20, PEO = -OCH2CH2-, PPO = -OCH(CH3)CH2-) materials have been investigated by changing the [Cd(H2O)4](NO3)2 and titania content of the structures. This has been achieved by making thick samples by casting and thin film samples by spin coating of a butanol solution of [Cd(H2O)4](NO3)2, P123, nitric acid and Ti(OC4H9)4. The film samples are named as meso-xCd(II)-yTiO2, where x is the Cd(II)/P123 and y is TiO2/P123 mole ratios. Increasing the titania amount in the media has transformed the samples from LC-like to soft and then to rigid mesostructured materials. Changing the amount of [Cd(H2O)4](NO3)2 salt in the media only influenced the mesostructure, such that no change on the mechanical properties is observed. However, the synthesis of rigid mesostructured titania materials required controlled humidity. The rigid film samples were prepared first by spin coating and then by aging under a 50% humidity oven. The mesostructure remains stable upon H2S reaction, in the soft and rigid materials region. However, only rigid samples stand to removal of nitrates from the media that is important to keep the CdS nanoparticles stable in or on the pore walls of mesostructured film samples. The phase behavior of the meso-Cd(II)-TiO2, the structural properties of the meso-xCdS-yTiO2 samples, coordination and elimination of the NO3 - ions and the particle size of the CdS nanocrystallites were investigated using diffraction (XRD), spectroscopy (FT-IR, Raman and UV-Vis absorption, EDS) and microscopy (POM, SEM, and TEM) techniques.
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    Synthesis of mesostructured metal sulfides using transition metal salts : pluronic liquid crystalline mesophases
    (2007) Türker, Yurdanur
    The Liquid Crystalline Templating (LCT) approach has been extensively used to produce mesostructured Metal Sulfides (MS) powders by using nonionic surfactants (CnEOm). The aim in this work is to synthesize larger pore size mesostructured MS at high salt concentrations by mixing Pluronics (PEOxPPOyPEOx, EO = -OCH2CH2-, PO = -OCH(CH3)CH2-) with transition metal salts (TMS) [M(H2O)4](NO3)2 in a dilute media. This enables to synthesize thin films of mesostructured MS. In this thesis, the MS (M= Cd, Zn, Cd1-xZnx, Cd1-xCox and Cd1-xMnx) were synthesized by the LCT approach using Pluronic P85 ((PEO)26(PPO)40(PEO)26) and TMS. The P85 and salts can be dissolved in various solvents to obtain clear solution that enables one to increase the salt to pluronic mole ratio up to 30:1. However, the LC mesophases form in the [Cd(H2O)4](NO3)2:P85 mole ratio range of 3:1 to 11:1 with a 3D hexagonal structure and P63/mmc space group having unit cell parameters of a = 99.5 Å and c = 162.5 Å with a c/a ratio of 1.633. The CdS thin film samples, obtained by exposing the [Cd(H2O)4](NO3)2:P85 LC phase to H2S gas, could retain the mesostructure of the LC mesophase in the mole ratio range of 3:1 to 11:1. The film samples that consist of 50-100 nm mesostructured CdS and free surfactant molecules are uniform and soft in early stages of the H2S reaction. However, in time, the free surfactant molecules diffuse out of the mesostructured CdS and form dendritic structures, producing CdS thin films with huge domains. The CdS thin film samples consist of 4.3 nm CdS nanoparticles that emit orange light under UV irradiation. Well homogenized LC mesophases produce cracked well structured film samples upon H2S reaction. This method can be used to fine tune both the composition (between x=0.0 and 1.0) and the optical band-gap of Cd1-xZnxS nanocrystallites between 2.60 eV and 4.00 eV. The Zn(II) and Cd(II) ions are homogenously doped throughout the mesostructure and nanocrystallites synthesized by this approach are slightly larger in every composition compared to the ones synthesized in the mesostructured silica channels. Also both Co(II) and Mn(II) ions could be incorporated into the CdS lattice with x ≤ 0.15 for stable Cd1-xCoxS and Cd1-xMnxS film samples, respectively. The Co(II) ions occupy the isolated tetrahedral holes in the CdS lattice until x = 0.15 for stable samples. In this thesis, the structure and structural changes in the LC mesophase during the synthesis of MS and particle size analysis of the nanocrystallites were investigated using diffraction (XRD), spectroscopy (FT-IR, micro-Raman and UVVis absorption) and microscopy (OM and SEM) techniques.