Synergetic promoting/inhibiting mechanisms of copper/calcium compounds in the formation of persistent organic pollutants and environmentally persistent free radicals from anthracene

Copper compounds are considered the strongest promotors of unintentional persistent organic pollutants (POPs) formation, while calcium compounds are widely used to inhibit this process. Understanding the mechanisms underlying these processes is important for synergetic control of multiple POPs. Herein, the promoting ability of CuCl2 on the synergetic formation of POPs from anthracene and the underlying mechanisms were clarified. During thermochemical reaction with CuCl2, Cu2+ was first reduced to Cu+, and finally oxidized to CuO. Furthermore, CuCl2 promoted the formation of environmentally persistent free radicals (EPFRs) during thermochemical reaction. The formed EPFRs were identified as anthrone-type and anthraquinone-type radicals using electron paramagnetic resonance spectroscopy and gas chromatography/quadrupole time-of-flight mass spectrometry. Synergetic inhibition of POPs and EPFRs was achieved using CaO. The inhibiting mechanism of CaO was attributed to the absorption of chlorine originating from CuCl2 through the formation of CaClOH and the inhibition of free radical intermediates for POPs formation.