Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Stabilizing Liquid Crystal Mesophases for Rigid Mesostructured Metal Sulfides/Selenides
Yurdanur Türker 1 *, Halil I. Okur 1 , Nazli Böke 1 , Ö 1
Department of Chemistry, Bilkent University, Ankara 06800, Turkey
1
Abstract- LC templating (LCT) can be used to synthesize meostructured/mesoporous metals, metal oxides, and II-VI semiconductors. By
using LCT approach, we have investigated, to the best of our knowledge, the first mesostructured metal sulfide thin films, at 11 Cd(II)/P85
mole ratio upon exposing the LC mesostructure to H 2S (g) reaction. However, since the metal ion content is still low, phase separation occurs
over the films in time and also, at high metal ion contents, formed HNO 3 become problematic. However, stable mesostructured MS/Se can be
-
synthesized upon addition of TiO 2 polymerizing agent to LC system since it can rigidify the mesostructure and allow aging to remove NO 3
ions before H 2 S/Se (g) reactions. In order to perform calcination process to remove surfactants, the LC mesophases are being rigidified further
by increasing metal ion content by use of charged surfactants.
The mesoporous materials were discovered in the early 90s
using surfactant templating approach [1]. This approach has
been used to synthesize many mesostructured metal oxides
[2], metals [3] and II-VI semiconductors [4]. In 2001, Dag et
al. have discovered a new form of LC mesophase of
transition metal aqua complexes (TMS), [M(H 2 O) 4 ](NO 3 ) 2 ,
and non-ionic surfactants or Pluronics at high metal salt
concentrations [5]. The coordinated water molecules of the
TMS mediate the formation of the LC mesophase through
hydrogen bonding (M-OH 2 ---(OCH 2 CH 2 ) x -R) with ethylene
oxide units of the surfactant molecules [4b,5-8]. Controlling
the quantity and the type of counter ion allows one to control
the structure of salt-surfactant LC mesophases [7]. LC
templating (LCT) can be used to synthesize
meostructured/mesoporous metals, metal oxides, and II-VI
semiconductors.
By using the LCT approach, we have synthesized
mesostructured Metal Sulfides (MS) at high salt
concentrations by mixing Pluronics with TMS in a dilute
media. We have investigated that the reaction between the
thin films of TMS – P85 (EO26PO 40 EO 26 ) LC mesophase
with a relatively high metal salt content, 11.0 mole ratio of
Cd(II)/P85, and H 2 S (g) at room temperature enables us to
synthesize, to the best of our knowledge, the first
mesostructured metal sulfide thin films.[9] However, since
the metal ion content of TMS-Pluronic mesophase is still low
to fully mimic the LLCM during the H 2 S/Se reaction to form
the stable mesostructured MS/Se film samples, the inevitable
result is the slow phase separation of the film samples in time
due to release of the excess surfactant molecules out of the
mesostructured films as shown in Figure A.
In order to synthesize stable mesoporous MS/Se film
samples, it is required to increase the metal ion content of the
Pluronic/TMS binary LC system so that it can fully mimic
the LLCM during calcination processes and H2S/H 2 Se (g)
reactions. Besides, at such high metal ion content, high
amount of nitrate ions form HNO 3 during H 2 S/H 2 Se (g)
reactions which causes decomposition of MS/Se back to their
nitrates. Therefore, the LC mesophase must be rigidified
enough to resist further calcinations at high temperatures
before H 2 S/Se (g) reactions. TiO 2 and SiO 2 are the proper
templates since they can form rigid walls upon controlling
their polymerization.
Recently, we have shown by EISA approach, we could
obtain rigid well-ordered mesostructured Cd(II)-TiO 2 films
until 13 Cd(II)/P123 mo le ratio at 60 TiO 2 /P123 mo le ratio.
Here, by the help of TiO 2 also, 90% of nitrate ions could be
removed by aging at relatively low temperatures, at which
mesostructure could still retain, before H 2 S/Se (g) reactions.
Under those conditions, the stable CdS and CdSe
nanoparticles can be synthesized in the channels of
mesostructured titania films in one-pot and no phase
separation occurs since the mesostructure is rigid enough as
shown in Figure B [10]. However, in order to calcine at high
temperatures to remove the surfactant, the mesostructure is
required to be rigidified more.
Figure 1. A) Phase seperation occurs at mesostructured CdS/P85
thin film in time. B) No phase seperation occurs at mesostructured
CdS/TiO 2 /P123 thin film.
The role of the charged surfactants in order to increase the
metal salt contents in LC systems has been recently
investigated [11]. By using charged surfactants in Cd(II)-
TiO 2-P123 system, CTAB (Cetyltrimethylammonium
Bro mide (C 16 H 33 N(CH 3 ) 3 Br)), Cd(II)/P123 mole ratio could
be increased to 20 at 60 TiO 2 /P123. This high metal ion
content films are going to be calcined at 350 ºC and then,
exposed to H 2 S/H 2 Se (g) reactions to synthesize MS/Se films.
They are going to be characterized to clarify if the films are
rigid enough to perform calcination process.
107T837, UNAM-Regpot (203953) and TÜBA for the
financial support.
*Corresponding author: yurdanur@fen.bilkent.edu.tr
[1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J.
S. Beck, Nature 359, 710 (1992).
[2] O. Dag, I. Soten, O. Celik, S. Polarz, N. Coombs and G. A.Ozin,
Adv. Func. Mater. 13, 30 (2003).
[3] a) G. S. Attard, P.N. Barlett, N.R.B. Coleman, J.M. Elliott,
J.R.Owen and J.H.Wong, Science 278, 838 (1997). b) Y. Yamauchi,
T. Momma, T. Yokoshima, K. Kuroda and T. Osaka, J. Mater.
Chem. 15, 1987 (2005).
[4] a) P.U. Braun, P. Osenar and S.I. Stupp, Nature 380, 325 (1996).
b) O. Dag, S. Alayoglu, C. Tura and O. Celik, Chem. Mater. 15,
2711 (2003).
[5] O. Celik and O. Dag, Angew. Chem. Int. Ed. 40, 3800 (2001).
[6] A.F. Demirors, B.E. Eser and O. Dag, Langmuir 17, 4157
(2005).
[7] C. Albayrak, G. Gulten and O. Dag, Langmuir 19, 876 (2007).
[8] O. Dag, S. Alayoglu and I. Uysal, J. Phys. Chem. B. 108, 8439
(2004).
[9] Turker, Y.; Dag, Ö. J. Mater. Chem. 2008, 18, 3467.
[10] Okur, H. I.; Turker, Y.; Dag, Ö. Langmuir 2010, 26, 538.
[11] Albayrak, C.; Soylu, A. M.; Dag, Ö. Langmuir 2008, 24,
10592.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 314