The acid-activated Fe-SiO₂ composites were synthesized using tetraethyl orthosilicate (TEOS) as the silica source, cetyltrimethylammonium bromide (CTAB) as the template and salts of Fe as the iron sources. After finishing the preparation, these samples were characterized using scanning electron microscopy for the morphology of the catalysts, X-ray diffractometer for the dispersibility of Fe, and Fourier transform infrared spectrometer for the surface groups. To investigate catalytic activities, various photo-Fenton reactions have been conducted to decontaminate the direct red 4BS simulated wastewater under visible light irradiation. The results indicated that the sample possessing its iron source from FeSO₄ had better dispersibility, but lower activities and stability than that from Fe(NO₃)₃. At initial pH of 6.0, both FS/1 and FS/6 not only led to 100% decolorization of a solution containing 100 mg/L direct red, but also about 79% and 99% total organic carbon were removed in respective system after reaction for 120 min. The kinetics study showed that a model in combination of first order and second order reactions was suitable for this acid-catalyzed process. Analyses of solvent-leaching stability and iron leaching demonstrated these catalysts may have long-term stability.

Key words: Fe-SiO₂, visible light, photo-Fenton, direct red 4BS, acid-catalysis