The degradation of 1,2,4-trichlorobenzene using synthesized Co3O4 and the hypothesized mechanism

Highlights: → Co3O4 was synthesized with three morphologies to degrade 1,2,4-trichlorobenzene. → The cabbage-like Co3O4 exhibited the highest reactivity. → Reaction acts competitively via hydrodechlorination and oxygen-attacking pathways. → The likely hydrodechlorination pathway was elucidated by theoretical calculation. → The superoxide anions might cause ring-cracking oxidation of 1,2,4-trichlorobenzene. - Abstract: Co3O4 was synthesized with cabbage-like, plate-like and sphere-like morphologies. The effect of different morphologies on the degradation of 1,2,4-trichlorobenzene (1,2,4-TrCB) was evaluated, and the cabbage-like Co3O4 exhibited the highest reactivity. The degradation of 1,2,4-TrCB on the cabbage-like Co3O4 is hypothesized to act competitively via hydrodechlorination and oxygen-attacking pathways. By the hydrodechlorination pathway, 1,2,4-TrCB is successively dechlorinated into the three dichlorobenzenes (DCBs) and then monochlorobenzene (MCB). The yield of the DCBs was in the order of p-DCB > m-DCB > o-DCB, which can be explained by the calculated C-Cl bond dissociation energies in 1,2,4-TrCB and DCBs. Derivatization and electron spin resonance experiments identified that lattice oxygen and superoxide anions may take part in the oxidation pathway. The lattice oxygen initiated a partial oxidation of 1,2,4-TrCB, leading to the formation of chlorinated phenols. The superoxide anions caused ring-cracking oxidation of 1,2,4-TrCB, possibly producing some low-molecular-weight products, thus explaining a mass imbalance in the chlorine atoms and total organic carbon.