Selective Degradation of Orange II with the Cobalt(II)–Bicarbonate–Hydrogen Peroxide System

A simple and efficient approach to orange II (AOII) degradation using Co2+–HCO3 – system as the catalyst and H2O2 as the oxidant under mild reaction conditions was reported. Complete decolorization of 50 μM AOII was observed with 5 μM Co2+ ions and 4 mM H2O2 in 10 mM NaHCO3 aqueous solution after 10 min, which was much faster that that of Fenton reagent with 50 μM Fe2+ ions. Some intermediate products such as carboxylic acids were detected by electrospray ionization-ion trap mass spectrometry and ion chromatography. In the presence of other pollutants such as methylene blue, sulforhodamine B, and a significant amount of anions including Cl–, CO3 2–, SO4 2–, NO3 –, HPO4 2–, and CH3COO–, AOII was still rapidly degraded. The results of photoluminescence probing technology, electron spin resonance spin-trapping technology, and radical trap experiments indicated that the tightly associated hydroxyl radicals with the cobalt complex were the reactive species for AOII degradation.