In this research, cetyltrimethylammonium bromide (CTAB) is used
as organic template and hydrous tin chloride (SnCl4) is used as inorganic
precursor to prepare mesostructured SnO2 powder. The synthesis is
carried out in the room temperature using NH3(aq) as pH-modifier. The
changing variables in the synthesis process include: the mixing sequence
of CTAB(aq), SnCl4(aq) and NH3(aq), the molar ratio of CTAB/SnCl4 (R), the
pH value of the mixture and the aging time of the mixture.
The X-ray diffraction (XRD) results show that the pH value of the
mixture is the determining factor for the successful synthesis of
mesoporous powder. On the other hand, the mixing sequence is of no
consequence on the formation of the mesostructure. For solutions of
pH<1 and R=0.2, 0.5 or 1, a crystalline phase of organic-inorganic
complex is found in the final products, which hinders the hydrolysis and
condensation of the inorganic precursor and hence the formation of
mesoporous structure. For powders derived from the solutions of pH=2~5,
the diffraction peak of mesoporous structure appears and becomes more
intense with increasing pH value. For solutions of pH>7, mesoporous
powders are obtained constantly.
As mesoporous powder is also obtained from solution of R=0.01, it
is concluded that the formation of surfactant cylinders and the
subsequently packed hexagonal arrays are not fulfilled during the
cooperation assembly process of organic and inorganic moleculars
because the concentration of CTAB is far below the critical concentration
for rod micelle (~10wt0/0).
On the other hand, surfactant rod micelles instead of mesoporous
structure is found in the powder derived from the basic solution of R=10
(CTAB: 5 g, SnCl4: 0.5 g). This implies that in spite of the formation of
CTAB rod micelles, the mesostructured SnO2 powder can not be obtained
without sufficient amount of Sn-precursor .
According to the model of mesostructure synthesis, in current work,
surfactant ions (S+), inorganic ions (I+) and counter ions (X-) are
connected in the form of S+X-I+ through the electrostatic attraction and
their cooperation assembly results in mesoporous structure. As pH valueincreases instantly as NH3(aq) is added into CTAB(aq), it is concluded that
CTA+OH- does not exist and X- is Br- or Cl- instead of OH-.
Finally, the mesostructure obtained in this work collapse after a
calcination of 5000C for two hours. Therefore, a great deal needs to be
done to improve the thermal stability in the future.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0716103-133547 |
| Date | 16 July 2003 |
| Creators | Su, Ching-Yi |
| Contributors | Bing-Hwait Hwang, Tzu-Chien Hsu, Hong-Yang Lu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0716103-133547 |
| Rights | withheld, Copyright information available at source archive |
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