Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Effect of surfactants on the synthesis of Zn-Al layered double hydroxides
Ceren Yılmaz, Uğur Ünal, Funda Yağcı Acar
1 Department of Chemistry, Koç University, Istanbul 34450, Turkey
Abstract— In the current study, the effect of various surfactants on the crystallization of Zn-Al layered double hydroxide was
investigated. Synthesis in the presence of dodecyl sulfate resulted in ring-like and rose-like structures depending on the
concentration. We have also found that replacement of the surfactant with laurate salt resulted in the formation of large ZnO
platelets intercalated with the surfactant formation. The crystallization mechanism was discussed.
Layered double hydroxides (LDHs) are hydrotalcite-like
layered compounds composed of piled-up positively charged
brucite-like layers and charge balancing anions as well as
water molecules in the interlayer domain. The general formula
of layered double hydroxides is represented by [M 2+ 1-x
M 3+ x(OH) 2 ] q+ [A n- x/n·mH 2 O], where M 2+ and M 3+ are divalent
and trivalent metal cations, and A is n-valent interlayer guest
anion, which might be Cl - , CO 2- 3 , NO - 3 , OH - , etc [1].
The synthesis of LDHs can be carried out with various
methods. Coprecipitation in the presence of NaOH or
hydrolysis of ammonia releasing agent result in well
crystallized LDH crystals [2]. In this study, we have
investigated the crystallization and intercalation behavior
LDHs in the presence of surfactants.
LDHs were synthesized in the presence of surfactants at
different concentrations and concentrations below and above
critical micelle concentration. Zn/Al ratio was 2 and the
concentration of ammonia releasing agent was 2.33 times
higher than the total metal cation concentration. Reaction was
carried out at 90 0 C under continuous stirring. Sampling
during the reaction was done at different times in the range 24-
120 h in order to observe the crystallization of LDHs.
Characterization was carried out with X-ray diffraction,
scanning electron microscopy, Fourier Transform infrared
spectrometer, UV-vis absorbance spectroscopy and
Inductively coupled plasma spectroscopy.
For the LDHs, synthesized under critical micelle formation for
dodecyl sulfate we have observed platelet like structures.
When the concentration increased above critical limit, ring
like structure was observed. The ring formation was attributed
to the crystallization of LDH at the anionic end of the
surfactant where metal cations are concentrated in the
beginning of the reaction. According to SEM micrographs we
have speculated that the crystallization starts with the
formation of central metal hydroxide seed and the
crystallization occurs in a circular path around the central seed
[3]. The mechanism is under investigation.
An important observation during the study was the formation
of large ZnO platelets and Al 3+ was not embedded in the
crystal structure when the synthesis was carried out in the
presence of laurate salt. Energy dispersive X-ray spectroscopy
(EDX) study showed that the platelets are mainly formed from
zinc and oxygen. According to XRD data as seen in figure 1,
ZnO was crystallized as a layered structure and laurate
molecules are placed between the layers. The size of ZnO
platelets is in the range 10-50 m in length as seen in figure 2.
Further study about the structure and properties of ZnO
platelets is in progress.
In conclusion, we have presented the crystallization of LDHs
under different surfactant concentrations. The type of the
surfactant has also substantial effect on the crystallization
behavior.
We are grateful to Assoc. Prof. Mehmet Ali Gülgün for doing
the SEM and XRD analysis of the powders. The work was
supported by Koc University.
Figure 1. XRD pattern of the LDH synthesized in the presence
of laurate salt.
Figure 2. SEM micrograph of ZnO structure formed in the
presence of laurate salt.
Corresponding author: fyagci@ku.edu.tr
[1]S. Miyata, Clays Clay Miner. 23 (1975) 369.
[2] A. de Roy, C. Forano, J.P. Besse, in: V. Rives (Ed.),
Layered Double Hydroxides: Present and Future, Nova
Science Publishers, New York, 2001 p. 1
[3] K. Okamoto, N. Iyi, T. Sasaki, Appl. Clay Sci., 37, (2007)
23-31.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 259