Synergism between n-type WO3 and p-type δ-FeOOH semiconductors: High interfacial contacts and enhanced photocatalysis

Solar-activated p-type delta-FeOOH/n-type WO3 center dot H2O photocatalysts with different tungsten contents were prepared by a facile method, even though single delta-FeOOH or WO3 center dot H2O exhibits lower photocatalytic activity. The photocatalysts were extensively characterized by X-ray fluorescence spectroscopy (XRF), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fe-57 Mossbauer spectroscopy, photoluminescence (PL), UV-Vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (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 WO3 center dot H2O or delta-FeOOH. The optimum amount of WO3 center dot H2O in the composite was 60 wt.%. Based on these results, we propose that photoexcited electrons in the conduction band (CB) of WO3 center dot H2O and photogenerated holes in the valence band (VB) of delta-FeOOH quickly combine, which results in the oxidation of the RhB dye by the accumulated holes in the VB of WO3 center dot H2O. The total organic carbon measurements suggest that a high degree of RhB mineralization was achieved under solar light. The delta-FeOOH/WO3 center dot H2O-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 photocatalytic process. The results from kinetic studies using radical scavengers suggest that O-2(center dot-) 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. (C) 2014 Elsevier B.V. All rights reserved.