Efficient photocatalytic reduction of aqueous Cr(VI) over CaSb2O5(OH)2 nanocrystals under UV light illumination

CaSb2O5(OH)(2) nanocrystals were synthesized via traditional and microwave-assisted hydrothermal methods from aqueous solution of CaCl2 and KSb(OH)(6), respectively. The structures, Brunauer-Emmett-Teller (BET) specific surface areas and optical properties of the as-synthesized samples were characterized by X-ray diffraction, transmission electron microscopy. N-2 sorption-desorption isotherms, and UV-vis diffuse reflectance spectra. The results of photocatalytic reduction of aqueous Cr(VI) revealed that CaSb2O5(OH)(2) possessed a superior activity greatly larger than that of commercial P25 (Degussa Co.). It was shown that proton supply played a crucial role in the reduction reaction. The Cr(VI) photo-reduction rates were systematically accelerated as the proton concentration increased in the aqueous suspensions. Formate ions were also shown to exert a dramatic accelerating influence on Cr(VI) reduction in the system. This observation should be rationalized by considering that these species act as hole scavengers in the reduction process. The consequent improvement in quantum yield combines with the protons provided by H2SO4 result in the observed rate enhancement. (C) 2012 Elsevier B.V. All rights reserved.