Applied Catalysis B: Environmental 165 (2015) 579–588 Contents lists available at ScienceDirect Applied Catalysis B: Environmental j ourna l h om epage: www.elsevier.com/locate/apcatb Synergism between n-type WO 3 and p-type -FeOOH semiconductors: High interfacial contacts and enhanced photocatalysis Lucas V.C. Lima a , Mariandry Rodriguez a , Victor A.A. Freitas b , Talita E. Souza b , Antonio E.H. Machado c , Antonio O.T. Patrocínio c , José D. Fabris d , Luiz C.A. Oliveira b , Márcio C. Pereira a,∗ a Instituto de Ciência, Engenharia e Tecnologia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 39803-371 Teófilo Otoni, MG, Brazil b Departamento de Química, ICEx, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, MG, Brazil c Instituto de Química, Universidade Federal de Uberlândia, 38400-902 Uberlândia, MG, Brazil d Universidade Federal dos Vales do Jequitinhonha e Mucuri, 39100-000 Diamantina, MG, Brazil a r t i c l e i n f o Article history: Received 26 June 2014 Received in revised form 15 September 2014 Accepted 24 October 2014 Available online 1 November 2014 Keywords: Photocatalysis Mechanism Heterojunction Semiconductor Oxidation a b s t r a c t Solar-activated p-type -FeOOH/n-type WO 3 ·H 2 O photocatalysts with different tungsten contents were prepared by a facile method, even though single -FeOOH or WO 3 ·H 2 O exhibits lower photocatalytic activity. The photocatalysts were extensively characterized by X-ray fluorescence spectroscopy (XRF), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), 57 Fe Mössbauer spectroscopy, photoluminescence (PL), UV-Vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared spec- troscopy (FTIR), Raman spectroscopy, BET measurements and temperature programmed reduction (TPR). The photocatalytic activity was evaluated for the oxidation of rhodamine B (RhB) at different pH values. The results indicated that the photocatalytic activity of the composite was superior to that of single WO 3 ·H 2 O or -FeOOH. The optimum amount of WO 3 ·H 2 O in the composite was 60 wt.%. Based on these results, we propose that photoexcited electrons in the conduction band (CB) of WO 3 ·H 2 O and photogen- erated holes in the valence band (VB) of -FeOOH quickly combine, which results in the oxidation of the RhB dye by the accumulated holes in the VB of WO 3 ·H 2 O. The total organic carbon measurements suggest that a high degree of RhB mineralization was achieved under solar light. The -FeOOH/WO 3 ·H 2 O-assisted photocatalytic degradation of RhB should occur via two competitive processes (i.e., a photocatalytic and a photosensitized process). The results indicated that RhB oxidation primarily occurs via a photocat- alytic process. The results from kinetic studies using radical scavengers suggest that O •- 2 and h + reactive species play key roles in the degradation of RhB. The results presented in this study provide new insights for the development of novel solar-light-driven photocatalysts and their potential application for harmful pollutant degradation. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The oxidation of harmful organic substances using photocata- lysts under visible light is an interesting approach for the treatment of water and wastewater because most of the widely available solar radiation can be used in the photocatalytic process [1]. However, the choice of the photocatalyst is a crucial step for effi- ciently degrading pollutants in water. The photocatalytic activity ∗ Corresponding author. Tel.: +55 33 3522 6037; fax: +55 33 3522 6037. E-mail address: mcpqui@gmail.com (M.C. Pereira). of semiconductors depends on several factors, such as their pho- toabsorption, energy levels of the conduction and valence bands, crystallinity, particle size, morphology and electron–hole recom- bination rate [2–4]. Among various photocatalysts, the n-type semiconductors of tungsten oxide (WO 3 ) and its hydrates have been extensively studied as promising materials for solar photo- catalysis due to their relatively low cost, small band gap energy (2.4–2.8 eV), high oxidation power of the valence band holes, non- toxicity and stability [5–10]. However, single phase WO 3 and its hydrates typically exhibit very poor photocatalytic activity under visible light irradiation due to the fast recombination of photogen- erated electrons and holes [11]. Therefore, the practical use of bare WO 3 and its hydrates as photocatalysts is limited. http://dx.doi.org/10.1016/j.apcatb.2014.10.066 0926-3373/© 2014 Elsevier B.V. All rights reserved.