A new catalyst for the activation of peroxydisulfate: Carbonized manganese oxides nanoparticles derived from green tea extracts

A green tea extract was used as a natural reducing agent to prepare three different manganese oxides (Mn 3 O 4 , Mn 2 O 3 and MnO) which after carbonization in different atmospheres, were evaluated for their ability to degrade estriol (E3). Catalytic ability of the three manganese oxides varied in the order Mn 2 O 3  > Mn 3 O 4  > MnO; corresponding to E3 degradation efficiencies of 100, 100 and 92.5 % after 180 min. After calcination, no new functional groups were observed on the surface of three manganese oxides, except the corresponding spectra. The morphology of the manganese oxides was primarily olive-shaped, with numerous small cubic particles stacked at the nanoscale, with a uniform distribution of elements. Free radicals and Mn ion leaching was observed from the prepared manganese oxides where leaching of manganese ions was related to the intensity of singlet oxygen. Advanced material characterization showed while green synthesis resulted in materials being doped with a small amounts of elements such as C and S, the broad crystal structure of the three materials was still the main factor affecting the removal efficiency of E3; with Mn(III) playing a major role in the catalytic peroxydisulfate (PDS) process.