Acetaldehyde Photocatalytic Decomposition over Nanostructured TiO 2 Sol-Gel Catalysts
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Acetaldehyde Photocatalytic Decomposition over Nanostructured TiO2 Sol-Gel Catalysts S. Castillo1, 2, R. Camposeco1,2, R. Carrera1,3,M. Mujica1, P. Del Ángel1, J.A. Montoya1, A.L. Vázquez1,3. M. Morán-Pineda1, R. Goméz3. 1,3
Instituto Mexicano del Petróleo, Programa de Ingeniería Molecular, D.F. México. Universidad Autónoma Metropolitana-A, Dept. Quim. México D.F., 02200. 3 Departamento de Ingeniería Química, ESIQIE-IPN, AP. 75-876, D.F. México. 4 Universidad Autónoma Metropolitana-I, Dept. Quim. A.P. 55-534, México, D.F., 09340.
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Abstract TiO2 nanoparticles were synthesized by the Sol-Gel method by using 2-propanol as solvent in acid medium (pH1). The samples were annealed at 200 and 500°C and were characterized by BET, XRD-Rietveld refinements, TEM and FTIR. The activity was evaluated by the acetaldehyde photodecomposition in an isolated chamber with an initial concentration of contaminant of 300 ppmv with oxygen (2%) assisted with a 365-nm UV lamp. The test results were compared with those obtained with a commercial catalyst (P25). Improved photoactivity (≈ 100 % of acetaldehyde in 150 min) was obtained with catalysts annealed at 200°C (TiO2-P200°C), that showed nanoparticles (≈7 nm) and abundant anatase phase (≈ 63 %) coexist with the brookite phase (≈ 37 %), as well as irregular equiaxial morphology. The samples annealed at 500°C (TiO2-P-500°C), showed an increment in nanoparticles (≈22 nm), different ratio and phase composition (anatase-brookite-rutile), and therefore less activity (≈ 80 %). This high activity could be explained by the special ratio of anatase-brookite and the dimension of nanometric crystal size. The aforementioned characteristics could be useful in the degradation of reactive organic gases like acetaldehyde either in confined spaces or in the open air. Keywords: TiO2, Sol-Gel, anatase-brookite phases, nanoparticles, acetaldehyde photodecomposition.
INTRODUCTION Titanium dioxide (TiO2) is the most commonly used material in electronics, ceramics, catalysis and pigment industries because of its optical and catalytic properties originating from the quantum size effect [1]. There are three types of TiO2 crystalline structures: anatase, rutile, and brookite. Rutile presents the highest refractive index and is the most thermodynamically stable structure. The anatase structure is obtained at low temperatures of around 350 °C, which is useful for industrial applications [2]. At temperatures between 400 and 800 °C, the anatase phase is also present, while, at higher temperatures, only the rutile structure is present. Another possible phase present in the TiO2 compounds is the brookite phase, but according to some studies, it is present at high pressure and temperature. TiO2 has become very important material due to its applications in different processes such as water purification, and more recently, the control of air contaminant gases present in indoor and outdoor environments where the UV-light is the energy source necessary in the photocatalytic processes [3-5]. Furthermore nanosized particle
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