Unprecedented strong intrinsic chemiluminescence generation from degradation of halogenated hydroxy-quinoid pollutants by Co(II)-mediated advanced oxidation processes: The critical role of site-specific production of hydroxyl radicals

Abstract We found previously that an unusual two-step hydroxyl radical (•OH)–dependent chemiluminescence (CL) can be produced by the carcinogenic tetrachloro-1,4-benzoquinone (TCBQ, also known as p-chloranil) and H2O2. However, neither •OH generation nor CL emission could be observed between H2O2 and chloranilic acid (CA), the dihydroxylation product of TCBQ. Here we found, unexpectedly, that distinct CL could be produced from CA/H2O2 in the presence of a variety of transition metal ions, among them Co(II) was found to be the most effective. Interestingly, the kinetic profiles of CL production, CA degradation, and reactive oxygen species (ROS) generation were found to be markedly changed with the molar ratios of Co(II):CA. When compared with the classic Fe(II)-mediated Fenton system, we found that the much stronger CL emission and more effective degradation of CA induced by Co(II)-mediated Fenton-like system is mainly due to the highly reactive •OH generated site-specifically by Co(II)/H2O2, although other ROS such as O2•- and 1O2 were also detected. More interestingly, not only CA, other halogenated anilic acids and catechols could also produce significant CL by Co(II)-mediated Fenton-like system. This is the first report on the distinct CL emission from degradation of halogenated hydroxyl-quinones by Co(II)-mediated Fenton-like advanced oxidation process, which is dependent on the site-specifically produced •OH. These findings may have potential applications in measuring halogenated hydroxyl-quinones, and developing more effective techniques to degrade these types of important environmental pollutants.