Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Synthesis of Pyrogallol Stabilized Gold Nanoparticles Emrah Bulut 1 * and Mahmut Özacar 1 1 Sakarya University, Department of Chemistry, 54187 Sakarya, Turkiye Abstract-Stable gold nanop articles have been synthesized by reducing HAuCl4 with pyrogallol as both the reducing and stabilizing agents. Gold nanoparticles prepare through the reduction of trivalent gold ions to metallic gold, which is accompanied by the simultaneous oxidization of the hydroxyl groups of pyrogallol. Then the pyrogallol serves as surfactant to prevent aggregation of gold nanoparticles. A reaction mechanism for the reduction of HAuCl4 by pyrogallol is proposed. The construction of functional noble metal nanocrystals has received increasing interest because their unique optical, magnetic, and catalytic properties can be tuned by controlling the size, shape, chemical composition, surface and interfacial structure, and they have potential applications such as in catalysis, biodiagnostics, plasmonics, and surface-enhanced Raman spectroscopy [1]. Both academia and industry have paid more attention to nano gold catalysts and predicted more extensive and increasing application prospects [2]. Gold particles of nanometer or micrometer size and with unique morphologies are particularly attractive materials because of their outstanding properties. Consequently, many published reports have focused on the preparation of various colloidal goldmorphologies, including cubes, belts, rods and wires, disks and plates, and urchin-like shapes, among others [3]. In recent years, many chemical and physical methods have been used to prepare a variety of gold nanoparticles; these methods include seed-mediated growth use of reverse micelles, phase transfer reactions, thermolysis, radiolysis, photochemistry, and sonochemistry. Among these, chemical methods are still the preferred method for the preparation of gold nanoparticles. The size and shape of gold nanoparticles are controlled by the ratio of HAuCl 4 to the chemical reducing agent in the preparation with examples such as sodium citrate, borohydride, or other organic compounds. In addition, high molecular weight polymers, thiol derivatives and other ligands, used as capping regents, are often used to control the particle size and shape, prevent aggregation, and improve function of the particle surface for application in bio-analytical methods [4, 5]. In the present study, gold nanoparticles are prepared using pyrogallol acting as both the reducing and stabilizing agent. A novel method was applied to synthesize gold nanoparticles by using pyrogallol which have reduction effect with involving -OH groups and keeps the prepared particles stable because of its molecular structure. Pyrogallol is a polyphenolic compound that may be used as a reducing agent, which is obtained from the hydrolysis of natural plant polyphenols. Here, we tried firstly to use it as reducing agent to prepare nano gold, and gold nanoparticles were facilely synthesized by reducing HAuCl4 with pyrogallol at room temperature. Since phenolic compounds are easily oxidized to form quinones, it was speculated that the product of pyrogallol reduction of HAuCl 4 might be a quinoid compound. The quinoid compound with keto-enol system might be produced by pyrogallol reduction of HAuCl 4 and absorbed on the surface of gold nanoparticles. A proposed reaction mechanism for the reduction of HAuCl 4 by pyrogallol can be ezpressed as shown in Fig. 1 [4, 6]. Produced gold nanoparticles were characterized by XRD, SEM and EDS. SEM image, Fig. 2, show that the major morphologies of the particles were polygonal plates, including triangle and hexagonal shapes. HO - 3 + 2AuCl 4 Au 0 + 3 + 6H + + 8Cl - OH OH Figure 1. Reduction mechanism of gold ions to the metallicgold Figure 2. SEM micrograph of the gold nanoparticles Figure 3 shows the XRD pattern of gold nanoparticles., Several peaks are observed at 2 = 38.1, 44.4, 64.6, 77.5, 81.6 and 98.01 o in the diffraction pattern which are in good agreement with metallic gold peaks. All facets of single crystals parallel to the grid are preferentially along {111} planes. Such features indicate the faceted morphology of gold microplates and their inherent anisotropy, which is important since many optical and electronic properties will depend on the orientation of crystal materials [5]. Figure 3. XRD pattern of the gold nanoparticles *Corresponding author: 0Tebulut@sakarya.edu.tr [1] F.-R. Fan, J. Am. Chem. Soc. 130, 6949 (2008). [2] J. Li et al., Environ. Sci. Technol. 42, 8947 (2008). [3] G. Lin et al., Crystal Growth & Design 10, 1118 (2010). [4] W. Wang et al., Colloids and Surfaces A: Physicochem. Eng. Aspects 301, 73 (2007). [5] L. Wang et al., J. Phys. Chem. B 109, 3189 (2005). [6] T. Ogata and Y. Nakano, Water Res. 39, 4281 (2005). O O OH 6th Nanoscience and Nanotechnology Conference, zmir, 2010 240
Poster Session, Tuesday, June 15 Theme A1 - B702 Electron rich surfactant capped CdS nanoparticles for hybrid solar cells Mahmut Kus 1 *, Alessandra Operamolla 2 , Serhad Tilki 1 ,Esma Yenel 3 3 , Omar Hassan Omar 4 , Francesco Babudri 2 , Gian luca M. Farino la 2 1 Selçuk University, Faculty of Engineering and Architecture, Department of Chemical Engineering, Konya, Turkey 2 Dipartimento di Chimica, Università degli Studi di Bari “Aldo Moro”, via Orabona 4, I-70126 Bari, Italy 3 Selçuk University, Department of Chemistry, Konya Turkey 4 CNR-ICCOM, Dipartimento di Chimica, Università degli Studi di Bari “Aldo Moro”, via Orabona 4, I-70126 Bari, Italy Abstract-We prepared some oligoarylenes bearing thiolic groups as novel semiconducting surfactants for CdS nanoparticles. Two phase synthetic route was used for synthesis of CdS nanoparticles. New surfactants were capped during synthesis or after synthesis by ligand exchange. The new nanohybrid structures were characterized by TEM, XRD, optical absorbance and fluorescence emission. Colloidal nanocrystals (NCs) have been attracting much interest thanks to their excellent and tunable optical properties and perspectives of application in fields such as optoelectronic, photocatalysis and biological labeling [1- 5]. Semiconductor quantum dots (QDs) can be fabricated via several techniques [6-9]. Oil soluble surfactants such as trioctylphosphine oxide (TOPO) and oleic acid (OA) are usually adopted in the synthesis for NPs solubilization. TOPO or OA capped quantum dots can find interesting application in polymer-hybrid light emitting diodes (PLEDs). In such devices these electron-inactive surfactant are generally preferred to prevent the quenching of light emitted by the QDs. However, in solar cells this approach is not convenient, because QDs are supposed to take part in electron transfer processes. and surfactants such as TOPO and OA usually behave as insulators causing the drop of the current. In this study, we prepared some oligoarylenes bearing thiolic groups as novel semiconducting surfactants for CdS nanoparticles. We previously reported the synthetic procedure to the new compounds [10]. The molecular structures of oligoarylenes are given in figure 1. R I R=H II R=alkyl chain Figure 1. Molecular structures of oligoarylenes S Two phase method was used to synthesize CdS nanoparticles. New surfactants were capped during synthesis or after synthesis by ligand exchange. The new nanohybrid structures were characterized by TEM, XRD, optical absorbance and fluorescence emission. Figure 2a shows scheme of oligoarylene capped CdS nanoparticles. It is well known, thiol groups can easily anchor to nanoparticles surface. Optical absorption spectra (b) shows crystal growth of CdS by reaction time. SH SH Abs 1.5 1 0.5 a 0 250 400 600 800 Wavelength [nm] b Figure 2. Scheme of oligoarylene capped CdS nanoparticles (a) and optical absorption of CdS nanoparticles synthesized in different reaction time. *Corresponding author: mahmut_kus@yahoo.com [1] Klabunde, K. J. Nanoscale Materials in Chemistry; Wiley- Interscience: New York, 2001. [2] Fendler, J. H. Nanoparticles and Nanostructured Films; Wiley-VCH: Weinheim, Germany, 1998. [3] Weller, H. Angew. Chem., Int. Ed. Engl. 1993, 32, 41. [4] Rogach, A. L.; Talapin, D. V.; Shevchenko, E. V.; Kornowski, A.; Haase, M.; Weller, H. AdV. Funct. Mater. 2002, 12, 653. [5] Alivisatos, A. P. Science 1996, 271, 933. [6] D. Bimberg, M. Grundmann, N.N. Ledentsov, M.H. Mao, Ch. Ribbat, R. Sellin, V.M. Ustinov, A.E. Zhukov, Zh.I. Alferov, J.A. Lottet al, Phys. Status Solidi B 224 (2001) 787. [7] A. Agostiano, M. Catalano, M.L. Curri, L. Chiavarone, M. Della Monica, P.M. Lugara`, L. Manna, V. Spagnolo, J. Phys. Chem. B 104 (2000) 8391. [8] C.B. Murray, D.J. Norris, M.G. Bawendi, J. Am. Chem. Soc. 115 (1993) 8706. [9] Daocheng Pan, Qiang Wang, Shichun Jiang, Xiangling Ji, and Lijia An, J. Phys. Chem. C 2007, 111, 5661-5666 [10] A. Operamolla, O. Hassan Omar, F. Babudri, G. Farinola, F. Naso, J. Org. Chem. 2007, 72, 10272-10275. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 241
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