Intrinsic Chemiluminescence Production during Environmentally-friendly Advanced Oxidation of Halogenated Aromatics and Its Applications

Abstract

Haloaromatics (XAr) have been widely used as pesticides, personal care agents, pharmaceuticals and flame retardants, which are now ubiquitously present in our environment. The carcinogenicity coupled with their ubiquitous occurrence have raised public concerns on the potential risks to both human health and the ecosystem posed by XAr. Advanced oxidation processes (AOPs) have been increasingly employed as an environmentally-friendly technology for remediating such highly toxic and recalcitrant XAr. During these AOPs systems, the most reactive radical intermediate formed at near-ambient temperature and pressure is the hydroxyl radical ((OH)-O-center dot). Recently, we found that an intrinsic chemiluminescence can be generated during the advanced oxidation of the priority pollutant pentachlorophenol and all other XAr. Furtherly, by the complementary application of electron spin resonance (ESR) with 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) as the spin-trapping agent, fluorescence method with terephthalic acid (TPA) as the (OH)-O-center dot probe, chemiluminescence analysis in the presence of classic (OH)-O-center dot scavengers and several typical (OH)-O-center dot-generating systems, the chemiluminescence was confirmed to be directly dependent on the production of the extremely reactive (OH)-O-center dot. Further studies showed that halogenated quinoid intermediates were produced during the degradation of XAr by (OH)-O-center dot-generating system, which could produce weak chemiluminescence that was greatly enhanced by addition of extra (OH)-O-center dot. We proposed that this unusual chemiluminescence generation was due to hydroxyl radical-dependent production of halogenated quinoid intermediates and electronically excited carbonyl species. In addition, the time course of chemiluminescence emission correlated well with the degradation of XAr: when the degradation level of XAr reached the maximum, no further chemiluminescence emission could be observed. Based on these findings, we developed a rapid, sensitive, simple, and effective chemiluminescence method to not only measure trace amount of XAr, but also monitor their real-time degradation kinetics. These new findings may have broad chemical, pharmaceutical, toxicological and environmental implications for future studies on remediation of these halogenated persistent organic pollutants by AOPs.