Enhanced Decolorization of Orange II Solutions by the Fe(II)–Sulfite System under Xenon Lamp Irradiation

Abstract

Decolorization of Orange II by a ferrous sulfite system in aqueous solutions under a xenon lamp (350W) was investigated to determine the enhancement of decolorization efficiency under UV–vis irradiation. Orange II (10 mg L–1) was efficiently decolorized at an initial pH of 6.1 under irradiation (84% efficiency at 60 min), whereas only 15% efficiency was achieved without irradiation. Although 4 was the optimum pH for enhancing the decolorization rate by irradiation, the enhancement was more significant at an initial pH near neutral. Concentration ratios of Fe(II) to sulfite higher than the optimum ratio (about 1:10) could inhibit the decolorization rate via the scavenging effect of sulfate or hydroxyl radicals. Semibatch experiments with multiple additions of Fe(II), sulfite, and Fe(II)–sulfite, respectively, showed that sulfite was more important in improving the decolorization efficiency of Orange II at higher concentration. However, removal of total organic carbon during the semibatch reaction by the Fe(II)–sulfite system under irradiation was as poor (<10%) as that without irradiation. This result implies that the conjugated chromophore in Orange II was partly but easily transformed into achromatic products mainly through electron transfer with sulfate radicals. In conclusion, UV–vis irradiation could greatly accelerate the decolorization of Orange II solutions by Fe(II)–sulfite system, and extend the initial working pH to near-neutral values. These attributes make the light-coupled Fe(II)–sulfite system a more powerful system (i.e., photo-Fe(II)–sulfite system) for the decolorization of Orange II.