Applied Catalysis B: Environmental 156–157 (2014) 307–313 Contents lists available at ScienceDirect Applied Catalysis B: Environmental j ourna l h om epage: www.elsevier.com/locate/apcatb Composite Bi 2 O 3 –TiO 2 catalysts for toluene photo-degradation: Ultraviolet and visible light performances María Natividad Gómez-Cerezo a,b , Mario J. Mu˜ noz-Batista a , David Tudela b , Marcos Fernández-García a,∗∗ , Anna Kubacka a,∗ a Instituto de Catálisis y Petroleoquímica, CSIC, C/Marie Curie 2, 28049 Madrid, Spain b Departamento de Química Inorgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Campus Cantoblanco, 28049 Madrid, Spain a r t i c l e i n f o Article history: Received 2 January 2014 Received in revised form 6 March 2014 Accepted 11 March 2014 Available online 20 March 2014 Keywords: Photo-catalysis Mineralization Sunlight Titania Bismuth a b s t r a c t A series of Bi 2 O 3 –TiO 2 composite catalysts with variable quantities of bismuth was prepared by a single pot microemulsion procedure, calcined at 450 ◦ C, and evaluated in the gas-phase degradation of toluene. Samples improve the reaction rate and quantum efficiency of the TiO 2 anatase reference material by a maximum factor ca. 2.2 and increase significantly the selectivity to the total oxidation product, CO 2 , upon both UV and sunlight-type excitation. A complete bulk and surface structural and electronic characteri- zation using X-ray diffraction (XRD), X-ray photoelectron (XPS), Raman, and UV–vis spectroscopies was carried out to interpret the catalytic results. The presence of bismuth enhances the optical response of the composite material to the visible region and modifies the morphology of the titania component. The study interprets the enhanced photoactivity of the composite materials with respect to both Ti anatase and the beta Bi 2 O 3 single oxide reference systems as a compromise between two effects: the contact of anatase with a Bi oxide phase as well as the anatase morphology modification along the Bi–Ti series. Both effects influence the photo-chemical activity of the composite materials and provide the basis to explain the optimum performance achieved with a material containing a 5 wt.% of bismuth oxide. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Heterogeneous photocatalysis is an Advanced Oxidation Process using nanocrystalline semiconductors applied to environmental abatement in both liquid and gas phases but also to synthesis of high added value products. The first application is by far the most broadly used and it is essentially based in the excellent perfor- mance and stability of titania, the most prominent photocatalytic material, for the mineralization of typical pollutants, including refractory or non-biodegradable molecules, under mild condi- tions, e.g. room temperature and atmospheric pressure and using oxygen (air) as oxidant agent [1–4]. Anatase is clearly the most active phase among titania polymorphs largely because it shows a correct balance between its surface chemistry-related proper- ties and the adequate physical properties for efficient handling of light-triggered charge carriers, allowing them to be involved in ∗ Corresponding author. Tel.: +34 91 585 4939; fax: +34 91 585 4760. ∗∗ Corresponding author. Tel.: +34 91 5854775. E-mail addresses: mfg@icp.csic.es (M. Fernández-García), ak@icp.csic.es (A. Kubacka). chemical steps at the surface [4]. The quest of improving anatase photo-degradation properties was however pursued almost from the beginning of the photocatalytic field. Several strategies were tested, being most popular those related to the electronic modifi- cation of titania through cationic [1,2,4–8], anionic [1,2,4,9–11], and anionic–cationic [2,4,12–17] (co)-doping, or the use of additional, visible-light-sensitized phases in intimate contact with TiO 2 . Such sensitizing phases may have semiconductor [2,4,18–25] or metallic [2,4,26–30] nature. Bismuth oxide is another semiconductor frequently used in photocatatalysis, particularly from recent times. It has four main crystallographic polymorphs, monoclinic alpha, tetragonal beta, body-centered cubic gamma and face-centered cubic delta Bi 2 O 3 . All of them can present band gap energies in the visible region and thus correspond to materials with potential for profiting from clean energy sources such as the sun [31]. Alpha and gamma polymorphs are reasonably stable phases but beta seems the most active one as a nanostructured material. This appears to result from a com- bination of factors related to the gain in light absorption power produced by a lower band gap energy as well as a more efficient handling of charge carriers after light excitation [31–35]. The sta- bility of the beta phase is however rather limited, particularly in http://dx.doi.org/10.1016/j.apcatb.2014.03.024 0926-3373/© 2014 Elsevier B.V. All rights reserved.