dc.contributor.advisor | Dağ, Ömer | |
dc.contributor.author | Türker, Yurdanur | |
dc.date.accessioned | 2016-01-08T18:25:15Z | |
dc.date.available | 2016-01-08T18:25:15Z | |
dc.date.issued | 2012 | |
dc.identifier.uri | http://hdl.handle.net/11693/15833 | |
dc.description | Ankara : The Department of Chemistry, Bilkent University, 2012. | en_US |
dc.description | Thesis (Ph. D.) -- Bilkent University, 2012. | en_US |
dc.description | Includes bibliographical references leaves 141-155. | en_US |
dc.description.abstract | In this thesis, synthesis of the mesoporous CdS and CdSe by using of liquid
crystalline templating (LCT) approach has been investigated. In the first part of
the thesis, the thermal and structural behavior of the [Cd(H2O)4](NO3)2/surfactant
(P85 = ((PEO)26(PPO)40(PEO)26)) binary lyotropic liquid crystalline (LLC)
systems have been investigated towards synthesis of the mesoporous cadmium
sulfide, CdS, or cadmium selenide (CdSe) directly from the mesostructured CdS
(or CdSe) thin films. However, the mesostructured CdS/P85 films (at low salt
concentrations), which were obtained by reacting [Cd(H2O)4](NO3)2/P85 LLC
thin films under H2S atmosphere, are not stable to calcination process and always
produced bulk CdO and CdS domains over the thin films. More metal ion
containing [Cd(H2O)4](NO3)2-C12EO10-CTAB mesostructured films produced vast
amount of HNO3 under the H2S atmosphere and caused decomposition of CdS
back to their nitrates.
To overcome above problems, a polymerizing agent, such as titania or silica
precursors have been added to salt/surfactant LLC mesophase. Both titania and silica overcame the collapse of the mesophase by rigidifying the structure into
mesostructured solid and also by providing stability for a thermal removal of
nitrates from the medium. For this investigation, both [Cd(H2O)4](NO3)2 and
[Zn(H2O)6](NO3)2 salts and P123 ((PEO)20(PPO)70(PEO)20) and C12EO10-CTAB
couple have been used.
Well-ordered mesostructured Cd(II) titania films have been obtained up to
15.0 Cd(II)/P123 mole ratio for a 60 mole ratio of Ti(IV)/P123 by spin or dip
coating of a mixture of 1-butanol-[Cd(H2O)4](NO3)2-P123-HNO3-Ti(OC4H9)4.
Exposing the mesostructured Cd(II)-TiO2 films to H2Se under a N2 atmosphere
gave stable CdSe nanoparticles in the channels of the mesostructured rigid titania
walls up to 25 mole % Cd(II)/Ti(IV). To further increase the metal ion (Cd(II) and
Zn(II)) content in the structure, the C12EO10-CTAB-salt mesophase has been
employed. The two surfactant-salt systems, in the presence of a titania precursor,
produced sponge like mesoporous CdTiO3 and Zn2TiO4 films up to a mole percent
of 57 and 86, respectively, upon calcination. Exposing the mesoporous CdTiO3 to
H2S or H2Se atmosphere at RT produced homogeneously distributed CdS or CdSe
nanocrystallites on the nanocrystalline TiO2 pore walls, respectively. The reaction
of mesoporous Zn2TiO4 with H2Se produced stable ZnSe nanocrystallites on the
nanocrystalline TiO2 pore walls. The conversion of titania from CdTiO3 to an
anatase and brookite phase under H2S and H2Se atmosphere, respectively, and
from Zn2TiO4 to a rutile phase under H2Se were observed for the first time.
Adding a silica precursor to the two surfactants (C12EO10-CTAB)-salt
mesophase produced mesostructured salted-silica, and its calcination produced
sponge-like mesoporous silica-metal oxide (dumped meso-SiO2-CdO and mesoSiO2-ZnO)
thin films. Up to ~100 % and ~50 % surface coverage could be
achieved by CdO and ZnO as nano-islands over the SiO2 pore walls. Exposing the
mesoporous SiO2-CdO and SiO2-ZnO thin film precursors to H2S and H2Se at RT
enabled the synthesis of mesoporous SiO2-CdS, SiO2-CdSe, SiO2-ZnS, and SiO2-
ZnSe thin films. The MS or MSe nanoflakes could homogenously cover the pore
walls of mesoporous silica by retaining the pore morphology of the MO
precursors. The H2S and H2Se reactions are slow and can be monitored using UV-Vis absorption spectroscopy and EDS to elucidate the reaction mechanism and
kinetics. These data showed that the reaction starts from the top surface of the MO
domains and proceeds until Si-O-M bond break. Finally, the SiO2 walls were
removed from the meso-SiO2-CdS and meso-SiO2-CdSe films through etching in
a dilute HF solution to produce mesoporous CdS (meso-CdS) and mesoporous
CdSe (meso-CdSe). Surface of the meso-CdS has been modified using PEI
(polyethyleneimine) and photoluminescent meso-CdS were obtained. | en_US |
dc.description.statementofresponsibility | Türker, Yurdanur | en_US |
dc.format.extent | xix, 155 leaves, illustrations | en_US |
dc.language.iso | English | en_US |
dc.rights | info:eu-repo/semantics/openAccess | en_US |
dc.subject | Mesoporous CdS | en_US |
dc.subject | Mesoporous CdSe | en_US |
dc.subject | Liquid Crystal Templating | en_US |
dc.subject | Evaporation Induced Self-Assembly | en_US |
dc.subject | Mesoporous Titania | en_US |
dc.subject | Mesoporous Silica | en_US |
dc.subject.lcc | TA418.9.T45 T87 2012 | en_US |
dc.subject.lcsh | Thin films. | en_US |
dc.subject.lcsh | Porous materials. | en_US |
dc.subject.lcsh | Liquid crystals. | en_US |
dc.title | Synthesis and characterization of mesoporous metal sulfide and metal selenide thin films using liquid crystalline mesophases | en_US |
dc.type | Thesis | en_US |
dc.department | Department of Chemistry | en_US |
dc.publisher | Bilkent University | en_US |
dc.description.degree | Ph.D. | en_US |
dc.identifier.itemid | B128323 | |