The photocatalytic activity of Fe/ZnO/SiO 2 catalysts under visible-light irradiation for the degradation of methylene blue was evaluated. The effect of pH, illumination time, amount of catalyst loaded, and initial dye concentration on the degradation efficiency of methylene blue was investigated. The results reveal that the optimum photocatalytic oxidation conditions of methylene blue are as follows: pH = 4 and illumination time is 30 min, the amount of catalyst loading is 0.075 g/L and 50 ppm methylene blue dye concentration. Under these conditions, the removal efficiency of methylene blue was 100%.

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The ZnO-SiO 2 xerogel photocatalyst was prepared via the sol-gel technique and applied for photodegradation of methylene blue (MB) dye. The optimum conditions for preparation of ZnO-SiO 2 gel is 30:70 ZnO:SiO 2 molar ratio and TEOS:C 2 H 5 OH:H 2 O:HNO 3 is 1:16:12:0.04 molar ratios at 30°C for 30 min, at these conditions the photoactivity of ZnO-SiO 2 xerogel was 99% at a surface area of 500 m 2 /g after 60 min. The optimum loading of ZnO-SiO 2 photocatalyst was 0.050 wt% that gives 99% MB dye removal efficiency after 40 min. The overall kinetics of photodegradation of MB dye using ZnO-SiO 2 photocatalyst was found to be of the first order.

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