Degradation of an Azo Dye with Homogeneous and Heterogeneous Catalysts by Sonophotolysis

摘要

This study illustrates the degradation of an azo dye, Reactive Yellow 81 (RY81), by the combined irradiation of UV-C and ultrasound in the presence of homogeneous (Fe~(2+)) and heterogeneous (TiO_2, ZnO) catalysts. The efficiency of homogeneous and heterogeneous oxidation systems was evaluated in regard of the decolorization and mineralization of RY81. Decolorization followed pseudo-first-order kinetics with homogeneous and heterogeneous catalysts. Complete color removal was accomplished by homogeneous sonocatalytic and sonophotocatalytic oxidation processes with apparent rate constants of 0.96 × 10~(-3) and 46.77 × 10~(-3)s~(-1) respectively, in the presence of Fe~(2+). However, partial color removal was obtained by heterogeneous sonocatalytic, photo-catalytic, and sonophotocatalytic oxidation processes with apparent rate constants of 2.32 × 10~(-3), 3.60 × 10~(-3), and 3.67 × 10~(-3) s~(-1), respectively, in the presence of ZnO. TiO_2 had the worst catalytic effect of all of the oxidation processes. The addition of hydrogen peroxide increased the rate constants of the heterogeneous oxidation processes and decreased the rate constants of the homogeneous oxidation processes. RY81 mineralization was 62.8% for the US/UV/Fe~(2+) homogeneous oxidation process, which was the best oxidation process, whereas it was 43.5% for the US/UV/ZnO/H_2O_2 heterogeneous oxidation process within 2 h reaction time.