Decolorization of Reactive Red 2 by advanced oxidation processes: Comparative studies of homogeneous and heterogeneous systems

This study investigated the decolorization of the Reactive Red 2 in water using advanced oxidation processes (AOPs): UV/TiO2, UV/SnO2, UV/TiO2 + SnO2, O3, O3 + MnO2, UV/O3 and UV/O3 + TiO2 + SnO2. Kinetic analyses indicated that the decolorization rates of Reactive Red 2 could be approximated as pseudo-first-order kinetics for both homogeneous and heterogeneous systems. The decolorization rate at pH 7 exceeded pH 4 and 10 in UV/TiO2 and UV/TiO2 + SnO2 systems, respectively. However, the rate constants in the systems (including O3) demonstrated the order of pH 10 > pH 7 > pH 4. The UV/TiO2 + SnO2 and O3 + MnO2 systems exhibited a greater decolorization rate than the UV/TiO2 and O3 systems, respectively. Additionally, the promotion of rate depended on pH. The variation of dye concentration influenced the decolorization efficiency of heterogeneous systems more significant than homogeneous systems. Experimental results verified that decolorization and desulfuration occurred at nearly the same rate. Moreover, the decolorization rate constants at pH 7 in various systems followed the order of UV/O3 ≧ O3 + MnO2 ≧ UV/O3 + TiO2 + SnO2 > O3 > UV/TiO2 + SnO2 ≧ UV/TiO2 > UV/SnO2.