Study on the Photolytic Mechanisms of Red 141 Dye Wastewaters with an 185nm Vacuum-UV lamp

Abstract

The decomposition of Reactive Red 141 dye wastewaters by photolysis and VUV/H₂O₂ process with a 185nm Vacuum-UV lamp in a batch photoreactor was studied under various initial concentrations of organics, solution pH values, dosages of H₂O₂, and purging gases (N₂, O₂, and air). The photolytic properties of Red 141 were found to be highly dependent on the solution pH. For the VUV/H₂O₂ system, the individual contribution to the decomposition of Red 141 by direct photolysis, and free hydroxyl radicals destruction generated from the excitement of O₂, H₂O, and H₂O₂ by an 185nm VUV lamp, respectively was differentiated by the proposed assumption. Experimental results for the VUV-only system revealed that photolytic rates of organics by purging O₂ were apparently larger than those by purging N₂ and the removal of Red 141 was found to be above 90%. For the VUV/H₂O₂ process, the reaction rates were significantly raised compared with those by direct photolysis. The individual contribution on the decomposition of Red 141 by OH. destruction generated from the excitement of H₂O₂ molecules was found to be higher than 50% at low pH range (pH=3) in VUV/H₂O₂ system, however, only 30% at high pH range (pH=11) probably because of the production of hydroxyl radicals from the H₂O₂ excitement was hampered by the alkaline catalytic reaction between the molecules of H₂O₂ and HO₂^-.