Enhancement of the photodegradation of N-nitrosodimethylamine in water using amorphous and platinum manganese oxide catalysts

The enhancement of the photodegradation of toxic N-nitrosodimethylamine (NDMA) in water using amorphous manganese oxide (AMO) and platinum manganese oxide (Pt/Mn3O4) catalysts was investigated. Characterization of the catalysts was carried out using XRD, FESEM, TEM, EDXS, BET, XPS, and AOS. Pt/Mn3O4 and its precursor AMO, synthesized by a redox reaction of Mn2+ and Mn7+, showed similar morphologies. High surface area AMO was confirmed to be amorphous, whereas Pt/Mn3O4 was a mixture of two crystalline structures. The optimum catalyst loading was 25 mg per 100 mL NDMA solution for which the photocatalytic activity was maximized. The average hydrodynamic particle size of a given amount of catalyst increased due to aggregation as a result of an increase in temperature during UV illumination (λ = 254 nm). Photocatalytic studies showed that NDMA degraded according to zero-order kinetics under air saturation at pH 7.0. AMO and Pt/Mn3O4 showed photostability and comparable activities with pure TiO2 and platinized TiO2. Mixed valencies of Mn and the presence of O2 on the surface of the catalysts, which reacts with photogenerated electrons to form reactive oxygen species (hydroxyl and superoxide anion radicals), played significant roles in the enhancement of the photodegradation of NDMA in water.