Photonic crystals in biology

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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
Poster Session, Tuesday, June 15 Theme A1 - B702 Oxidat ive coupling o f methane for ethylene preparat ion: catalys t and nanocatalys t pe rformance Ali Farsi 1 *, Ali Moradi 1 , Sattar Ghader 1 , Seyed Soheil Mansouri 1 and Vahid Shadravan 1 1 Department of Chemical Engineering, Shahid Bahonar University of Kerman, Kerman, Iran Abstract – The main goal of this work is to study the catalysts and nano-catalysts performance in OCM reaction. Also, about 80 various catalysts and nano-catalysts have been collected and their main parameters such as, method of preparation, temperature of reaction, C 2 yield and selectivity and catalyst test reactor and methane conversion has been studied. Experimental results showed that the conversion of methane over the nano-catalysts was higher than that obtained from the catalysts prepared conventionally. A better low-temperature activity has also been achieved with a higher yield of C 2 hydrocarbons. Natural gas is a mixture of predominantly methane combined with other hydrocarbons and non-hydrocarbons such as N2, CO 2 and H 2 O. The geographical distribution of methane (natural gas) is given in Figure 1. In order to make an efficient utilization of natural gas; we must consider transforming it into mo re valuable chemicals. Higher hydrocarbons are more useful for chemical industries. Figure 1. Geographical distribution of proven natural gas reserves Since 1982 there has been much research on the Oxidative coupling of methane (OCM) process. The main obstacle for converting methane directly to more valuable products by heterogeneous catalysis is the low selectivity at high conversions; the products are more reactive than methane. The main goal of this work is to study the catalysts and nanocatalysts performance in OCM reaction. Also, about 80 various catalysts and nano-catalysts have been collected and their main parameters such as, method of preparation, temperature of reaction, C 2 yield and selectivity and catalyst test reactor and methane conversion has been studied. Experimental results showed that the conversion of methane over the nano-catalysts was higher than that obtained from the catalysts prepared conventionally. A better low-temperature activity has also been achieved with a higher yield of C 2 hydrocarbons. *Corresponding author: 0Tali.farsi@gmail.com [1] Goodwin, A.R. H.; Hill, J.A. J. Chem. Eng. Data 2009, 54 , 2758. [2] Graf, P.O.; Ph.D. dissertation, University of Twente, 2008. [3] BP Statistical Review of World Energy 2007 [4] Veser, G.; Frauhammer, J.; Friedle, U. Catal. Today 2000 ,61 , 55. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 315
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