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Research Papers

Mesostructured Anatase TiO2 for Visible Light and UV Photocatalysis With Confinement Effect and Semiconductor Coupling

[+] Author and Article Information
Florence Bosc

Laboratoire des Matériaux, Surfaces et Procédés pour la Catalyse (LMSPC), European Laboratory for Catalysis and Surface Sciences (ELCASS), CNRS, Louis Pasteur University, 25 rue Becquerel, 67087 Strasbourg Cedex, France

André Ayral1

Laboratoire des Matériaux, Surfaces et Procédés pour la Catalyse (LMSPC), European Laboratory for Catalysis and Surface Sciences (ELCASS), CNRS, Louis Pasteur University, 25 rue Becquerel, 67087 Strasbourg Cedex, France

Nicolas Keller2

Laboratoire des Matériaux, Surfaces et Procédés pour la Catalyse (LMSPC), European Laboratory for Catalysis and Surface Sciences (ELCASS), CNRS, Louis Pasteur University, 25 rue Becquerel, 67087 Strasbourg Cedex, Francenkeller@chimie.u-strasbg.fr

Valérie Keller1

Laboratoire des Matériaux, Surfaces et Procédés pour la Catalyse (LMSPC), European Laboratory for Catalysis and Surface Sciences (ELCASS), CNRS, Louis Pasteur University, 25 rue Becquerel, 67087 Strasbourg Cedex, Francevkeller@chimie.u-strasbg.fr

1

Institut Européen des Membranes, UMR 5635 CNRS-ENSCM (Ecole Nationale Supérieure de Chimie de Montpellier), University of Montpellier II, CC047-Place Eugène Bataillon, 34095 Montpellier Cedex 5, France.

2

Corresponding author.

J. Sol. Energy Eng 130(4), 041006 (Sep 05, 2008) (5 pages) doi:10.1115/1.2969803 History: Received November 13, 2007; Revised December 01, 2007; Published September 05, 2008

Hexagonal and cubic mesostructured TiO2 anatase were synthesized by a templating sol-gel method using triblock copolymers as structuring agents, and used as photocatalysts for providing geometrical assistance to a photocatalytic reaction. The visible light and UV photocatalytic removal of gas-phase concentrated toluene (110ppm) within an annular flow-reactor was used as a tool to evidence the benefit to use mesostructured photocatalysts. The coupling of low amounts of WO3 with mesostructured anatase led to high efficiency using visible light and UV activation. The highly positive effect of WO3 on the toluene removal efficiency was attributed to the coupling between TiO2 and WO3 semiconductors, leading to an improved photogenerated charge separation and thus a weaker charge recombination. The hypothesis of a confinement effect of the reactants inside the mesostructured photocatalyst was put forward to explain the photocatalytic performances obtained under visible light and UV activation. This confinement effect would be based on the inner partial pressure concept. It consists of an increase in the partial pressure of the reactants next to the active sites inside the nanometric cavities of the ordered structure, while the apparent macroscopic partial pressures, outside the mesostructure, would remain unchanged. According to a traditional reaction rate law, such an increase results in the increase in the reaction rate. The photon-assisted reaction could be considered as “structure-assisted,” the geometrical assistance being provided by the surrounding ordered TiO2 walls of the mesostructure.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Scheme of a triblock copolymer, (b) spherical micelle, and (c) schematized mechanism for the template synthesis of mesostructured oxides

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Figure 2

One-pass photocatalytic concentric annular reactor

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Figure 3

TEM images of (a) hexagonal HMA-TiO2 and (b) cubic CMA-TiO2 mesostructured anatase, with non-microporous surface areas of 190m2∕g and 180m2∕g, respectively, and a pore diameter of 4–5nm

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Figure 4

Evolution of the toluene removal efficiency (%) as a function of irradiation time (min) (a) under visible-light illumination for WO3-containing TiO2 catalytic systems (4wt% of WO3) and (b) under UV light for WO3-free TiO2 catalytic systems. Inset: zoom for irradiation time before 50min.

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Figure 5

Fourier transform infrared spectra of samples tested under visible-light illumination

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