Synthesis of nanometric TiO 2 in aqueous solution by soft chemistry: obtaining of anatase, brookite and rutile with cont
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Synthesis of nanometric TiO2 in aqueous solution by soft chemistry: obtaining of anatase, brookite and rutile with controlled shapes Magali Koelsch, Sophie Cassaignon and Jean-Pierre Jolivet Laboratoire de Chimie de la Matière Condensée, UMR-CNRS 7574 Université Pierre et Marie Curie 4 place Jussieu, 75252 Paris Cédex 05, France ABSTRACT Nanometric particles of titania, exhibiting anatase, brookite or rutile polymorphs, were synthesized by thermohydrolysis of TiCl4 in aqueous medium. The adjustement of physicochemical parameters (acidity, ionic strength, anions, temperature) allows to tune the crystalline structure, the size and the morphology of the particles. Brookite results from the precipitation of titanium in HCl, HBr or HNO3 whereas anatase is formed in H2SO4 medium. Adding salts in HCl medium leads to ionic strength or complexation effect. Varying the temperature of thermohydrolysis implies modification on yield, size and morphology of the particles. INTRODUCTION Titanium dioxide has attracted increasing attention because of its wide applications in many fields such as a main component of white pigments, paintings, inks and fillers [1]. The high absorption of UV-light allows its utilization in cosmetics. TiO2 has also received much attention for applications as a semiconductor in environmental photocatalysis processes such as removal of pollutants from air and water [2-4] and moreover it is also a common material for photovoltaic devices [5,6]. The performances for a given application are strongly influenced by the crystalline structure, the morphology and the size of the particles [7,8]. Particles with a nanometric size have also a particular interest because of their high surface/volume ratio inducing specific surface properties. Because of its three main crystallographic forms, each with their own physical properties, titanium dioxide is a very versatile system to study. This study reports on the role of acidity, anions and temperature on the synthesis of TiO2 polymorphs in aqueous medium by thermohydrolysis of TiCl4. We show that a precise adjustment of experimental conditions allows the control of the crystalline structure and the morphology of particles. EXPERIMENTAL DETAILS Synthesis A known volume of TiCl4 (Fluka 98 %) was cautiously added to mineral acid solutions whith concentrations ranging from 0.5 to 5 mol.L-1. All experiments were performed with [Ti] = 0.15 mol.L-1, the final concentration of Ti(IV) being measured by complexometry [9]. The so obtained solutions were aged at 60, 95 or 120°C for 24 hours or several weeks. Another procedure was to precipitate a solid by addition of a base. The pH of the mixture was automatically maintained at a selected value between 1 and 7 by addition of a NaOH solution (3
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mol.L-1) using a Combi Titreur 3D Metrohm apparatus. The particles were then centrifuged and washed with distilled water, the solid was dried under nitrogen atmosphere for X-ray diffraction characterization. Techniques X-Ray diffraction. XRD patterns were recorded using a pow
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