Enhanced degradation of 2,4-dinitrotoluene by ozonation in the presence of manganese(II) and oxalic acid

Manganese catalytic ozonation of 2,4-dinitrotoluene (DNT) in the presence of oxalic acid was studied. The addition of manganese ion (Mn2+) or oxalic acid alone in ozonation process did not enhance DNT degradation, but the addition of Mn2+ coupled with oxalic acid accelerated degradation of DNT. The DNT degradation efficiency was influenced by carbonate in the catalytic ozonation process. Kinetics study showed that Mn2+ catalytic ozonation significantly promoted the decomposition of ozone. Experimental results of electron spin resonance (ESR) demonstrated that addition of Mn2+ and oxalic acid produced much hydroxyl radicals in catalytic ozonation system than that in single ozonation system. These results suggested that catalytic ozonation followed hydroxyl radical-type mechanism. Mn2+ promoted decomposition of ozone to produce hydroxyl radical and it was oxidized into manganese oxide. Manganese oxide was reduced into Mn2+ by oxalic acid, which is the key step of catalytic process. Based on above results, a cycle catalytic mechanism of Mn2+ was proposed. Intermediates were determined by HPLC and GC–MS, and they mainly included aromatic organics and aliphatic carboxylic acids.

In this manuscript, the homogeneous catalyst Mn (II) was investigated, which showed much highly effective for the degradation of DNT by ozone in the presence of oxalic acid. The study revealed a different catalytic mechanism in Mn (II) homogeneous catalytic ozonation of organics through the addition of oxalic acid, which will enrich the research in catalytic ozonation, especially homogeneous catalytic ozonation.