Effects of oxidant concentration and temperature on decolorization of azo dye: comparisons of UV/Fenton and UV/Fenton-like systems

This study applies photo-Fenton and photo-Fenton-like systems to decolorize C.I. Reactive Red 2 (RR2). The oxidants were H₂O₂ and Na₂S₂O₈; Fe²⁺, Fe³⁺, and Co²⁺ were used to activate these two oxidants. The effects of oxidant concentration (0.3–2 mmol/L) and temperature (25–55 °C) on decolorization efficiency of the photo-Fenton and photo-Fenton-like systems were determined. The decolorization rate constants (k) of RR2 in the tested systems are consistent with pseudo-first-order kinetics. The rate constant increased as oxidant concentration and temperature increased. Activation energies of RR2 decolorization in the UV/H₂O₂/Fe²⁺, UV/H₂O₂/Fe³⁺, UV/Na₂S₂O₈/Fe²⁺ and UV/Na₂S₂O₈/Fe³⁺ systems were 32.20, 39.54, 35.54, and 51.75 kJ/mol, respectively.