Photocatalytic Activity of Anatase Fiber-Mats
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Photocatalytic Activity of Anatase Fiber-Mats Annelise K. Alves1, Felipe A. Berutti1 and Carlos P. Bergmann1 1 Federal University of Rio Grande do Sul, Av. Osvaldo Aranha, 99 sl. 705C, Porto Alegre, RS, 90035190, Brazil ABSTRACT Nanostructured fiber-mats have large surface area, high reactivity, low weight and low agglomeration tendency. These are advantages if compared with nanoparticles for photocatalytic application. Fiber-mats can be used not only as a photocatalytic material on their own, but also incorporated in different surfaces or fabrics and as well as a filtration membrane. In this work, high temperature stable anatase titanium dioxide fiber-mats doped with silica (0.5 to 30 %) or doped with tin (0.5 to 15 %) were produced by electrospinning technology. The precursors used were titanium propoxide (TiP), tetrapropoxysilane (TPS) and tin 2-ethylhexanoate. They were hydrolyzed in acetic acid and mixed with an alcoholic solution of 10 wt% polyvinylpirrolidone. The effect of heat treatment on the microstructure characteristics and the photocatalytic activity of the fiber-mats in comparison with a commercial TiO2 powder (Evonik P-25) were studied. After the electrospinning process, a thin, porous fiber-mat was obtained. This material was dried in air at room temperature for 24h. These fibers were then heat treated from 500 to 800°C for 3 hours at a heating rate of 1.4°C/min. The fiber-mats were then characterized using N2 adsorption (BET method) for surface area measurements, X-ray diffraction for phase determination, SEM and TEM analyses for morphological characterization. The photocatalytic activity was studied using as model system the degradation of methyl orange in water (20ppm) under UV-A light. As-obtained fibers are amorphous but become crystalline after heat treatment. As the heat treatment temperature increases the surface area decreases significantly. Quite the opposite happens with the rutile to anatase ratio and the anatase and rutile crystallite sizes, which increase with higher heat treatment temperatures. The photoactivity increases with the increment in heat treatment temperature until 650°C, when the fibers start to become denser and the surface area drops due to sintering. Fibers produced at higher temperatures and with lower amounts of Si and Sn are predominantly anatase and are generally more photoactive under UV-A radiation. INTRODUCTION Electrospinning technology uses high voltages to produce non-tissue materials made of fibers in the micro- and nanometric range. In this process, a jet of fluid is accelerated and stretched through the electric field to produce the fibers [1-2]. According to recent researches, electrospun fibers have large surface area (up to 300m2/g) and high porosity [9-10]. A larger surface area provides more surface active sites for the adsorption of reactants molecules, which thus make the photocatalytic process more efficient [10]. Titanium dioxide is one the most suitable semiconductors for a wide range of environmental applications [3]. The energy of its band gap i
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