Molten Salt Assisted Self-Assembly (MASA) : synthesis of mesoporous silica-ZnO and mesoporous CdO thin films
Author
Karakaya, Cüneyt
Advisor
Dağ, Ömer
Date
2012Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
A series of mesostructured salt-silica-two surfactants (salt is [Zn(H2O)6](NO3)2,
ZnX or [Cd(H2O)4](NO3)2, CdYand surfactants are cetyltrimethylammonium bromide
(CTAB) and 10-lauryl ether, C12H25(OCH2CH2)10OH, C12EO10) thin films were
synthesized by changing the Zn(II) or Cd(II)/SiO2 mole ratios. The films were prepared
through spin coating of a clear solution of all the ingredients (salt, CTAB, C12E10, silica source (tetramethyl orthosilicate,TMOS, and water) and denoted as meso-silica-ZnX-n
and meso-silica-CdY-n, where n is Zn(II) or Cd(II)/SiO2 mole ratios. The synthesis
conditions were optimized by using the meso-silica-ZnX-1.14 and meso-silica-CdY-1.14
films and XRD, FT-IR spectroscopy, POM and SEM techniques. The stability of the
films, especially in the high salt concentrations, was achieved above the melting point of
salts. Slow calcination of the films, starting from the melting point of the salt to 450 oC
has produced the mesoporous silica-metal oxide (ZnO and CdO) thin films, and denoted
as meso-silica-ZnO-n and meso-silica-CdO-n, with n of 0.29, 0.57, 0.86, 1.14, and 1.43.
The calcination process was monitored by measuring the FT-IR spectra and XRD
patterns at different temperatures. Structural properties of the mesoporous films have
been investigated using FT-IR spectroscopy, XRD, N2 sorption measurements, UV-Vis
spectroscopy, SEM, TEM and EDS techniques. It has been found that the meso-silicaZnO-n
and meso-silica-CdO-n films consist of nanocrystalline metal oxide nanoplates
on the silica pore walls of the mesoporous framework. The formation of nanoplates of
metal oxides was confirmed by etching the silica walls using diluted HF solution and by
reacting with H2S and H2Se gases. The etching process produced CdO nanoplates
without silica framework. The H2S and H2Se reactions with the CdO nanoplates or
meso-silica-CdO have converted them to CdS and CdSe nanoplates or meso-silica-CdS
and meso-silica-CdSe, respectively. Finally, a hypothetical surface coverage of metal
oxide nanoplates has been calculated by combining the data of N2 sorption
measurements, UV-Vis spectroscopy and TEM images and found that there is a full
coverage of CdO and partial coverage of ZnO over silica walls in the meso-silica-CdO-n
and meso-silica-ZnO-n thin films, respectively.
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