Synthesis of Gold Nanoparticles and Hollow Gold Nanostructures Chow W.Y.1 and Fan W.Y.2
Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117543 Abstract Mercaptopranoic acid (MPA) capped gold (Au) nanoparticles have been synthesized in aqueous medium using a citrate reduction method. Size dependent properties of the phase transfer agent, tetraoctylammonium cations (TOA+) was investigated. Au hollow structures have been fabricated in aqueous medium by using the Galvanic replacement method in which Ag nanostructures served as the sacrificial templates. Prior to Galvanic replacement of Ag template by HAuCl4, three sets of Ag nanoparticles were synthesized by varying the surfactant and reducing agent used. MPAcapped Ag nanoparticles reduced by different reducing agent resulted in different of sizes and crystal faces. It was found that the corresponded shape and size of the fabricated hollow nanostructures rely closely on the crystal planes and the size of the sacrificial Ag templates. Introduction Modified surface of colloidal gold nanoparticles with thiolates have been extensively studied because of their potential applications in many fields [1-3]. Recently, it has been focused on the control of the size of nanoparticles. In this regard, the use of tetraoctylammonium cations that capable are of transferring carboxylate-ω-functionalized alkanethiolate-modified Au nanoparticles have been studied [5]. The size-dependent properties of transferring processes lead to an alternative methodology for size selective separation of nanoparticles. The tuning of the intrinsic properties of metal nanostructures have been concerned in the past and this could be done by controlling shape as well as structure (hollow vs solid) [6]. Hollow nanostructures could improve performance over filled nanostructures due to their relatively lower densities and higher surface areas. Synthesis of hollow nanostructures via Galvanic Replacement using Ag nanoparticles as sacrificial templates were developed in which the hollow structures is strongly dependent on the morphologies, size and the crystal faces of the sacrificial template. Materials and methods Chemicals and instrumentation. Silver Nitrate (Sigma Aldrich, 99.50%), Hydrogen tetrachloroaurate(III) trihydrate (Sigma Aldrich, 99.90%), Mercaptopropanoic acid (Sigma Aldrich, 99.90%), Tetraoctylammonium bromide (Sigma Aldrich, 99.90%), Tri-sodium citrate (Sigma Aldrich, 99%), and Sodium Hydroxide (Sigma Aldrich, 99.50%). All UV spectra were obtained from UV-2450 spectrometer by using quark cell. The scanning range was set from 800 nm to 300 nm. The TEM images (JEOL-2010 or JEOL-3010) were taken of direct sampling of the solution on carboncoated copper grids. Synthesis of MPA-capped Au NP. Synthesis was carried out as reported [8]. Briefly, 95 mL deionized water containing HAuCl4 (2.94 x 10-4 M) and Na-MPA (1.47 x 10-4 M) in a round-bottomflask, rbf, was stir vigorously and heated at ~80C. 5 mL of 1% aqueous trisodium citrate was added

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