JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS - SYMPOSIA, Vol. 2, No. 1, 2010, p. 115 - 118 Synthesis and characterisation of tungsten trioxide powders prepared by sol-gel route M. ŞTEFAN a* , E. BICA a,b , L. MURESAN a , R. GRECU a , E. INDREA c , M. TRIF a , E. J. POPOVICI a a “Raluca Ripan“Institute for Research in Chemistry, Babes-Bolyai University, Fantanele 30, 400294 Cluj-Napoca, Romania b Faculty of Chemistry and Chemical Engineering, “Babes-Bolyai” University, Arany Janos 11, 400028 Cluj-Napoca, Romania c National Institute for R &D of Isotopic and Molecular Technology, 400295, Cluj-Napoca, Romania Nano-structured tungsten trioxide (WO 3 ) powders were prepared following an inorganic sol-gel route by reaction between metallic tungsten and hydrogen peroxide in acidic media. WO 3 powders with different morphological characteristics were obtained by thermal treatment of the peroxo-tungstic acid, performed in air, at 550ºC. In order to prepare WO 3 powders with controllable grain dimensions, some particle size regulating agents such as metacrylic acid (MA) and cetyl- trimethylammoniumbromide (CTAB) were introduced into the peroxotungstic acid solution. Thermal analysis and FT-IR spectroscopy were used to characterise the precursor powders. The morpho-structural properties of sol-gel derived WO 3 powders were evaluated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). (Received April 21, 2009; accepted October 1, 2009) Keywords: Tungsten trioxide, Sol-gel synthesis, Nanostructured powders, Particle size 1. Introduction Micro- and nanoparticulate tungsten oxide powders (WO 3 ) have been investigated extensively due to their distinctive properties [1, 2]. During the past few years, there has been much interest in nanostructured materials that offer numerous new opportunities to study fundamental surface processes, to develop, in a controlled manner, new properties that lead to the fabrication of new devices [3, 4]. Many different semiconducting materials have been widely used in optoelectronics, microelectronics, and environmental engineering [5]. Among them, metal oxides have been found to give the best activity and stability in a variety of organic and inorganic photocatalytic reactions and during long–term irradiation both in acidic and basic media. The transition metal oxides such as tungsten trioxide (WO 3 ) constitute a very interesting class of materials because of the various properties exhibited by them [6-8]. Tungsten oxide and its hydrates can be synthesized using various methods, such as wet chemical precipitation, sol-gel synthesis and thermal decomposition of tungsten salts [9-11]. Sol-gel technique offers many advantages over other preparation methods, such as the precise control of reactants concentration, the simplicity as well as the low temperature processing. The present paper reports our results referring to the influence of preparative conditions on the morpho- structural properties of sol-gel derived tungsten oxide powders. The goal is to obtain WO 3 powders with predetermined properties. 2. Experimental part Preparation of nanostructured WO 3 powders has been performed following an inorganic sol-gel route from a solution of peroxo–tungstic acid. In our experiments, 8 g tungsten powder (Merck) was dissolved into 60 ml 30% hydrogen peroxide (Merck) under magnetic stirring giving a transparent yellow solution. Some particle size regulating agents such as metacrylic acid (MA) and cetyl- trimethylammoniumbromide (CTAB) were introduced into the peroxo-tungstic acid solution. The solution pH was then adjusted to ~1 by adding mineral acid (HCl). The composition of the peroxo-tungstic acid solution corresponds to the reagent ratio: W pwd : H 2 O 2 : =1:50. The resulting solution of peroxo-tungstic acid was dried at 70 o C, in air, to form the peroxo–tungstic acid (PTA) precursors. Finally, the as resulted PTA powders were calcined in air at 550 0 C for 30 minutes to form a crystalline WO 3 powders. PTA precursors were characterised by thermal analysis (Mettler Toledo TGA/SDTA851 thermal analyser, heating rate of 5 0 C /min; nitrogen flow) and FT-IR spectroscopy (JASCO 610 Spectrometer, KBr pellets technique).