| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 151679 | Chemical Engineering Journal | 2010 | 6 Pages |
This study evaluated the effectiveness of decolorizing C.I. Reactive Black 5 (RB5) in UV/TiO2, UV/oxidant and UV/TiO2/oxidant systems in the presence of oxidants H2O2, Na2S2O8, NaBrO3, and NaIO4. The effects of pH, oxidant dosage and ethanol addition on decolorization were determined. Decolorization rate constants (k) were of pseudo-first-order in all systems. In UV/TiO2 and UV/oxidant systems, the k values followed the order pH 4 > pH 7 > pH 10. At pH 7 with 1 mM of oxidant added, the k values followed the order UV/NaIO4 (0.377 min−1) > UV/Na2S2O8 (0.156 min−1) > UV/H2O2 (0.105 min−1) > UV/NaBrO3 (0.101 min−1) > UV (0.002 min−1). In UV/oxidant systems, decolorization effectiveness increased with increasing Na2S2O8 and NaBrO3 doses but reached optima with NaIO4 and H2O2 at 1 and 6 mM, respectively. Addition of oxidants to UV/TiO2 resulted in quenching of conduction band electrons and generation of reactive radical intermediates, enhancing decolorization. In UV/TiO2/oxidant systems, decolorization rate constants varied with oxidant following the order NaIO4 (0.558 min−1) > Na2S2O8 (0.044 min−1) > NaBrO3 (0.036 min−1) > H2O2 (0.035 min−1) > absence of oxidant (0.033 min−1). In UV/oxidant systems, addition of ethanol inhibited decolorization, which indicated the involvement of hydroxyl radicals in the decolorization pathway with UV/H2O2 and UV/Na2S2O8 systems, as well as probable involvement of other radicals with UV/NaBrO3 and UV/NaIO4 systems. Direct oxidation by photogenerated holes was likely significant in UV/TiO2 and UV/TiO2/oxidant systems.
