Mesoporous ZnFe2O4 (meso-ZnFe2O4) was synthesized by a hydrothermal process in which cetyltrimethylammonium bromide (CTAB) participates in the reaction to produce nanocrystals. Synthesized ZnFe2O4 was characterized by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and diffuse reflectance spectra (DRS). The meso-ZnFe2O4 was resulted from the agglomeration of nanoparticles with size of 5-10 nm. The photocatalytic activity of ZnFe2O4 under visible light (lambda > 400 nm) was evaluated by the degradation of Acid Orange II (AOII) at different sintering temperatures, the amount of ZnFe2O4, and the concentration of H2O2. The photocatalytic degradation of AOII was almost complete within 2 h in H2O2/visible light system. The high efficiency for AOII degradation was attributed to the strong absorption of ZnFe2O4 in visible-light region and the generation of reactive (OH)-O-center dot by H2O2 in the system. The involvement of (OH)-O-center dot in oxidizing AOII was examined by determining the photocurrent of ZnFe2O4, [(OH)-O-center dot] and degradation rates using different scavengers. Organic compounds as intermediates of the degradation process were identified by LC/MS. Moreover, ZnFe2O4 retained their degradation efficiencies for a series of repetitive batch runs, indicating the true photocatalytic process. (c) 2011 Elsevier B.V. All rights reserved.