The origin of luminescence accompanying electrochemical reduction or chemical decomposition of peroxydisulfates

The spectral features of the electrochemiluminescence occurring during the reduction of peroxydisulfate anions at magnesium, silver or platinum electrodes (ecl), the luminescence following their decomposition on a magnesium surface (mcl), and the chemiluminescence accompanying the thermal decomposition of peroxydisulfates in acidic media (tcl), were thoroughly examined in order to discover the origin of the light emission. The intensity of emission followed the order ecl>mcl⪢tcl and depended on the method of its generation and other experimental conditions. Probable pathways of the reactions leading to the formation of light-emitting species were examined at the density functional theory level. The theoretical studies and experimental findings seem to indicate that the luminescence originates from 1O2, 1(O2)2 and 3(O2)2, the precursors of which are SO4•−, HO•, HOO•, HOOH and O3 formed in the primary and secondary processes following electrochemical reduction or thermal decomposition of peroxydisulfates. Supplementary experiments demonstrated the participation of HOOH in the generation of light emitting entities.