MATERIALE PLASTICE ♦ 47♦ Nr. 1 ♦ 2010 42 Platinum Nanoparticles Synthesis by Sonoelectrochemical Methods LAURA OBREJA 1 *, DANIELA PRICOP 1 , NECULAI FOCA 2 , VIOREL MELNIG 1 1 “Al. I. Cuza” University, Faculty of Physics, 11A Carol I Blvd., 700506, Iasi, Romania 2 “Gh. Asachi” University, Faculty of Chemistry, 71A D. Mangeron Blvd., 700050, Iasi, Romania Platinum nanoparticles with sizes between 10 and 42 nm have been obtained by a sonoelectrochemical method in the presence of a water-soluble polymer, poly(amidehydroxyurethane) (PAmHU), which acted as a coating agent. The PAmHU stabilized Pt nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis and FTIR spectroscopy and dimension distribution and Zeta potential analysis. The analyses showed the fact that these nanoparticles are capped by the polymer, which confers them water-solubility and stability. Keywords: platinum nanoparticles, poly(amidehydroxyurethane), sonoelectrochemical synthesis In the last years, an increasing interest has been observed regarding the synthesis and characterization of colloidal noble metal nanoparticles because of their unique properties and promising applications. The nanoparticles have a characteristic large surface-to-volume ratio, and consequently a high fraction of the metal atoms exposed at the surfaces. The applications of noble metals nanoparticles include catalysis [1], data storage systems, new electronic devices [2], electrochemical chemo- and biosensors [3], and refractometric and fluorescent sensors [4]. The preparation of colloidal metals with desirable properties represents a significant challenge. The metal nanoparticles can be obtained by several methods such as chemical reduction [5, 6], UV photolysis [7], thermal decomposition [8], metal vapor deposition [9], reduction by ionizing radiation [10], electrochemical synthesis [11] and sonochemical reduction [12]. Many practical applications require platinum nanoparticles to be dispersible in water and preserve their physicochemical properties over a long time. Platinum nanoparticles have been prepared previously in the presence of different stabilizers including polymers [13, 14] (poly(vinyl alcohol), poly(vinylpyrrolidone), poly(N- isopropylacrylamide)) and surfactants[15] (sodium dodecyl sulfate), which prevent the nanoparticles from aggregation and allow their isolation. In a previous paper [12] we reported the platinum nanoparticles sonochemical synthesis by reduction of chloroplatinic acid with methanol, ethanol and propanol in the presence of different capping polymers: chitosan, polyethylene glycol and poly(amidehydroxyurethane). In this paper it is presented the synthesis and characterization of platinum nanoparticles capped with poly(amidehydroxyurethane) (PAmHU) water-soluble polymer obtained by sonoelectrochemical method. The advantage of this method is that the size control of nanoparticles is tuned by the current monitoring in the galvanostatic process and the restriction reaction room by the polymer microdomain. Experimental part Materials and methods Chloroplatinic acid, sodium carbonate and sodium bicarbonate were purchased from Sigma Aldrich. Details * email: obrejalaura@yahoo.com regarding PAmHU synthesis and characterization are given in [16]. All solutions were prepared with Milli-Q water (18.2 MÙΩ . cm). The electrosynthesis was performed in galvanostatic regime. As working (WE) and counter electrode (CE) were used two coiled platinum wires of 160 mm length and 1 mm diameter and 140 mm length and 1.5 mm diameter, respectively. The distance between electrodes was of 1.5 mm and kept the same for all the experiments. The electrodes were cleaned by immersion in chromic mixture, sonicated in distilled water and dried before every usage. A 10 -3 M solution consisting in chloroplatinic acid and 0.1% w/w PAmHU was used as electrolyte solution. The pH of electrolyte solutions was adjusted to 10 with a sodium carbonate and bicarbonate mixture. The galvanostatic regime current density was preset within 0.6 and 1.2 mA/ cm 2 using an Amel model 459 potentiostat. The current domain was determined from voltammogram characteristic obtained in a three electrode mode (potentiostatic regime). The working and counter electrode were the same as those used in the synthesis process and the reference electrode was a standard calomel electrode (sce), measurements being carried out in the chloroplatinic acid and polymer precursor solution. The optimum time for synthesis was one hour. The synthesis of platinum nanoparticles was performed at room temperature under nitrogen atmosphere and ultrasound stirring (10% amplitude mode at 20 kHz ± 500 Hz standard frequency; Sonoplus- Bandeline set-up). The characterizations of Pt nanoparticles-PAmHU systems were done in solutions, powders and thin films. The powders containing Pt nanoparticles were obtained by solutions lyophilisation after sonoelectrochemical synthesis. The thin film samples were prepared by spin coating method, using a WS-400B-6NPP/LITE spin coater, being deposited on microscope slide glass substrates with 25x25 mm 2 area. The detailed protocol for cleaning glass substrates was presented elsewhere [11]. Characterization methods The sample powder X-ray diffractograms were recorded in θ - 2θ mode, between 35° and 90° in a Shimadzu XRD 6000 diffractometer with a X-ray generator (CuK α radiation, λ= 1.54060 Å) operated at 40 kV and 30 mA.