Visible-Light-Driven Photodegradation of Rhodamine B on Ag-Modified BiOBr
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Visible-Light-Driven Photodegradation of Rhodamine B on Ag-Modified BiOBr Lufeng Lu • Liang Kong • Zheng Jiang • Henry H.-C. Lai • Tiancun Xiao • Peter P. Edwards
Received: 22 February 2012 / Accepted: 8 April 2012 / Published online: 4 May 2012 Ó Springer Science+Business Media, LLC 2012
Abstract Ag-modified BiOBr composite photocatalysts were prepared via a simple phase-transfer methodology and used for cleanup of Rhodamine B (RhB) aqueous solution under visible light irradiation. X-ray diffraction, ultraviolet–visible diffuse reflectance spectra (UV–VisDRS) and high resolution X-ray photoelectron spectra characterizations confirmed the Ag-modification significantly affected the optical property, structures and reactivity of the BiOBr-based photocatalysts. In the Ag-modification process, a large portion of Ag? may extract Br1- from BiOBr and the as-formed AgBr epitaxially located along the {102} crystal surface of BiOBr. The rest Ag? will be either photo-reduced by methanol into Ag0 or form Ag2O. In nature, the Ag-modified BiOBr materials are multi-junction photocatalysts of Ag/Ag2O/AgBr/BiOBr. The Ag-modification can greatly enhance the absorption of visible light but deteriorates the photocatalytic activity in comparison to the primitive BiOBr in visible-light-driven photodegradation of RhB. The activity of RhB photodegradation on such catalysts is inversely proportional to AgBr loading within 0.2–2.0 wt% region. Such unusual
L. Lu L. Kong Z. Jiang (&) H. H.-C. Lai T. Xiao P. P. Edwards (&) Department of Chemistry, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK e-mail: [email protected] P. P. Edwards e-mail: [email protected] Z. Jiang Jesus College, University of Oxford, Oxford OX1 3DW, UK Z. Jiang Environment and Sustainability Institute, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK
photocatalytic performance was tentatively attributed to the special band structure of the materials. Keywords Visible light Photocatalysis BiOBr Ag modification Rhodamine B
1 Introduction The photocatalytic utilization of solar energy on active photocatalysts has drawn considerable interest worldwide because of its great potential for the cleanup environmental contaminations, water splitting, photoreduction of CO2 and photosensitized polymerizations [1, 2]. In comparison to the extensively studied UV-responsive photocatalysts (TiO2, ZnO, etc.) which can only harvest a small portion of sunlight (\5 %) due to their wide band gaps, visible-lightresponsive photocatalysts may harness more solar energy from the solar spectrum [3, 4]. Great efforts have been made for discovery of new catalytic materials for visiblelight-driven photocatalysis [1–8]. Such visible-lightresponsive photocatalysts can be pristine photocatalysts with intrinsic narrow bandgap, such as semiconductor compounds of tungsten, molybdenum, bismuth, and metal sulfides, or realized by doping impurity into the UV-responsive photocatalysts [1, 2]. As one of the simplest V-VI-VII bismuth oxyhalides, bismuth oxybromide, Bi
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